This PDF file contains the front matter associated with SPIE Proceedings Volume 9057, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Inherent nonlinearities of piezoelectric materials are inevitably pronounced in various engineering applications such as sensing, actuation, their combined applications for vibration control, and most recently, energy harvesting from dynamical systems. The existing literature focusing on the dynamics of electroelastic structures made of piezoelectric materials have explored such nonlinearities in a disconnected way for the separate problems of mechanical and electrical excitation such that nonlinear resonance trends have been assumed to be due to different additional terms in constitutive equations by different researchers. Similar manifestations of softening nonlinearities have been attributed to purely elastic nonlinear terms, coupling nonlinearities, hysteresis, or a combination of these effects, by various authors. However, a reliable nonlinear constitutive equation for a given piezoelectric material is expected to be rather unique and valid regardless of the application, e.g. energy harvesting, sensing, or actuation. A systematic approach focusing on the two-way coupling can result in a sound mathematical framework. To this end, the present work investigates the nonlinear dynamic behavior of a bimorph piezoelectric cantilever under low-to-high mechanical and electrical excitation levels in energy harvesting, sensing, and actuation. A physical model is proposed including both ferroelastic hysteresis, stiffness, and electromechanical coupling nonlinearities. A lumped parameter electroelastic model is developed by accounting for these nonlinearities to analyze the primary resonance of a cantilever using the method of harmonic balance. Strong agreement between the model and experimental investigation is found, providing solid evidence that the the dominant source of observed softening nonlinear effects in geometrically linear piezolectric cantilever beams is well represented by a quadratic term resulting from ferroelastic hysteresis. Electromechanical coupling and cubic softening nonlinearities are observed to become effective only near the physical limits of the brittle and stiff bimorph cantilever used in the experiments, revealing that the quadratic nonlinearity associated with hysteresis has the primary role in nonlinear nonconservative dynamic behavior.

Vibration energy harvesting using piezoelectric material is a promising solution for powering small electric devices, which has attracted great research interest in recent years. Numerous efforts have been done by researchers to improve the efficiency of vibration energy harvesters and to broaden their bandwidths. In most reported literature, harvesters are designed to harvest energy from vibration source with a specific excitation direction. However, a practical environmental vibration source may include multiple components from different directions. Thus, it is an important concern to design a vibration energy harvester to be adaptive to multiple excitation directions. In this article, a novel piezoelectric energy harvester with frame configuration is proposed to address this issue. It can work either in its vertical vibration mode or horizontal vibration mode. Therefore, the harvester can capture vibration energy from arbitrary directions in a twodimensional plane. Experimental studies are carried out to prove the feasibility for multiple-direction energy harvesting using such harvester. The development of this two-dimensional energy harvester indicates its promising potential in practical vibration scenarios.

Sufficient power supply to run GPS machinery and transmit data on a long-term basis remains to be the key challenge for wildlife tracking technology. Traditional way of replacing battery periodically is not only time and money consuming but also dangerous to live-trapping wild animals. In this paper, an innovative wildlife tracking device with multi-source energy harvester with advantage of high efficiency and reliability is investigated and developed. This multi-source energy harvester entails a solar energy harvester and an innovative rotational electromagnetic energy harvester is mounted on the “wildlife tracking collar” which will remarkably extend the duration of wild life tracking. A feedforward and feedback control of DC-DC converter circuit is adopted to passively realize the Maximum Power Point Tracking (MPPT) logic for the solar energy harvester. The rotational electromagnetic energy harvester can mechanically rectify the irregular bidirectional motion into unidirectional motion has been modeled and demonstrated.

Recent work has demonstrated efficient transformation of structure-borne propagating waves into low-power electricity using metamaterial-inspired mirror configurations. Elastoacoustic waves (i) originating from a point source and (ii) arriving as plane waves have been successfully focused on a piezoelectric energy harvester using elliptical and parabolic mirror concepts, respectively. Our present work investigates the spatial optimization of a piezoelectric energy harvester domain weakly coupled to a thin plate housing an elastoacoustic mirror (or lens). Mirrors considered include elliptical arrangements of periodic stubs, and an elliptical arrangement of continuous material. Spatial and temporal transformation of the wave propagation field into the frequency- wavenumber domain is performed in order to identify the wavenumber content inside the mirror. A frequency- domain root-mean-square (RMS) evaluation is then applied to the transformed field in order to extract the preferred propagation directions. Computational modeling and experimental testing are employed to quantify performance enhancement of the presented approach. Specifically, dramatic enhancement of the harvested power output is reported by patterned electroding of a rectangular PVDF harvester in the elliptical mirror domain.

For ecologic sustainability and decreasing reserves of fossile energy sources, fuel efficiency is a major concern especially for passenger aircraft. Therefore, lightweight structures made from carbon fiber plastics offer great potential. But when used for panel-like structures, they have the disadvantage of lower damping and coincidence frequencies compared to conventional differential metal constructions. Both aspects lead to an increased vibration level and by this a higher noise radiation. Because of this, special noise and vibration treatment is needed to ensure passenger cabin comfort. Besides passive damping and active structural acoustic control (ASAC), piezoelectric shunt damping is investigated. Due to its broadband performance, the negative capacitance shunt can be used for multimode systems with varying eigenfrequencies. These shunts are usually built with operational amplifiers and passive components as resistors and capacitors. This setup is sufficient for laboratory tests at low excitation levels. In fact, it is not capable of accessing the full voltage amplitude of common piezoelectric transducers, because most operational amplifiers only deliver ±15V maximum output voltage. Therefore an improved setup is presented in this paper, which addresses the specific voltage requirements of a common piezoelectric transducer to achieve best performance. It comprises a tailored power source and an appropriate concept for the negative capacitance shunt hardware. This new hardware only uses standard operational amplifiers together with a high voltage power amplifier to cover the whole operating range of a piezoelectric transducer. A demonstrator board is developed and experimentally investigated at a test structure. Finally, the results are compared to a conventional setup.

The performance of high precision payloads on board a satellite is extremely sensitive to vibration. Although vibration environment of a satellite on orbit is very gentle compared to the launch environment, even a low amplitude vibration disturbances generated by reaction wheel assembly, cryocoolers, etc may cause serious problems in performing tasks such as capturing high resolution images. The most commonly taken approach to protect sensitive payloads from performance degrading vibration is application of vibration isolator. In this paper, development of vibration isolation platform for low amplitude vibration is discussed. Firstly, single axis vibration isolator is developed by adapting three parameter model using bellows and viscous fluid. The isolation performance of the developed single axis isolator is evaluated by measuring force transmissibility. The measured transmissibility shows that both the low Q-factor (about 2) and the high roll-off rate (about -40 dB/dec) are achieved with the developed isolator. Then, six single axis isolators are combined to form Stewart platform in cubic configuration to provide multi-axis vibration isolation. The isolation performance of the developed multi-axis isolator is evaluated using a simple prototype reaction wheel model in which wheel imbalance is the major source of vibration. The transmitted force without vibration isolator is measured and compared with the transmitted force with vibration isolator. More than 20 dB reduction of the X and Y direction (radial direction of flywheel) disturbance is observed for rotating wheel speed of 100 Hz and higher.

This study investigates the optimum design parameters of a superelastic friction base isolator (S-FBI) system through a multi-objective genetic algorithm and performance-based evaluation approach. The S-FBI system consists of a flat steel- PTFE sliding bearing and a superelastic NiTi shape memory alloy (SMA) device. Sliding bearing limits the transfer of shear across the isolation interface and provides damping from sliding friction. SMA device provides restoring force capability to the isolation system together with additional damping characteristics. A three-story building is modeled with S-FBI isolation system. Multiple-objective numerical optimization that simultaneously minimizes isolation-level displacements and superstructure response is carried out with a genetic algorithm (GA) in order to optimize S-FBI system. Nonlinear time history analyses of the building with S-FBI system are performed. A set of 20 near-field ground motion records are used in numerical simulations. Results show that S-FBI system successfully control response of the buildings against near-fault earthquakes without sacrificing in isolation efficacy and producing large isolation-level deformations.

In this paper we present preliminary experimental results relative to the application of open loop monolithic folded pendulum sensors to the control of large band multistage suspensions (seismic attenuators) and inertial platforms in the band 0.01 ± 10Hz. In fact, beyond the obvious compactness and robustness of monolithic implementations of folded pendulum, high sensitivity, large measurement band (10⁻⁷÷ 100Hz), tunability of the resonance frequency (necessary to adapt the sensors to the mechanics), high sensitive integrated laser optical readout (e.g. optical lever, laser interferometer), and very good immunity to environmental noises are some of the main advantages of this class of sensors. The results are presented and discussed in this paper together with the planned further developments and improvements.

The heaving of ocean waves is a largely untapped, renewable kinetic energy resource. Conversion of this energy into electrical power could integrate with solar technologies to provide for round-the-clock, portable, and mobile energy supplies usable in a wide variety of marine environments. However, the direct drive conversion methodology of gridintegrated wave energy converters does not efficiently scale down to smaller, portable architectures. This research develops an alternative power conversion approach to harness the extraordinarily large heaving displacements and long oscillation periods as an excitation source for an extendible vibration energy harvesting chain. Building upon related research findings and engineering insights, the proposed system joins together a series of dynamic cells through bistable interfaces. Individual impulse events are generated as the inertial mass of each cell is pulled across a region of negative stiffness to induce local snap through dynamics; the oscillating magnetic inertial mass then generates current in a coil which is connected to energy harvesting circuitry. It is shown that linking the cells into a chain transmits impulses through the system leading to cascades of vibration and enhancement of electrical energy conversion from each impulse event. This paper describes the development of the multistable chain and ways in which realistic design challenges were addressed. Numerical modeling and corresponding experiments demonstrate the response of the chain due to slow and large amplitude input motion. Lastly, experimental studies give evidence that energy conversion efficiency of the chain for wave energy conversion is much higher than using an equal number of cells without connections.

Low-power electronic systems are used in various underwater applications ranging from naval sensor networks to ecological monitoring for sustainability. In this work, underwater base excitation of cantilevers made of Macro-Fiber Composite (MFC) piezoelectric structures is explored experimentally and theoretically to harvest energy for such wireless electronic components toward enabling self-powered underwater systems. Bimorph cantilevers made of MFCs with different length-to-width ratios and same thickness are tested in air and under water to characterize the change in natural frequency and damping with a focus on the fundamental bending mode. The real and imaginary parts of hydrodynamic frequency response functions are identified and corrected based on this set of experiments. An electrohydroelastic model is developed and experimentally validated for predicting the power delivered to an electrical load as well as the shunted underwater vibration response under base excitation. Variations of the electrical power output with excitation frequency and load resistance are obtained for different length-to-width ratios. Underwater power density results are reported and compared with their in-air counterparts. Specifically a nonlinear dependence of the power density to the cantilever width is reported for energy harvesting from underwater base excitation.

There is a need for a long-life power generation scheme that could be used downhole in an oil well to produce 1 Watt average power. There are a variety of existing or proposed energy harvesting schemes that could be used in this environment but each of these has its own limitations. The vibrating piezoelectric structure is in principle capable of operating for very long lifetimes (decades) thereby possibly overcoming a principle limitation of existing technology based on rotating turbo-machinery. In order to determine the feasibility of using piezoelectrics to produce suitable flow energy harvesting, we surveyed experimentally a variety of nozzle configurations that could be used to excite a vibrating piezoelectric structure in such a way as to enable conversion of flow energy into useful amounts of electrical power. These included reed structures, spring mass-structures, drag and lift bluff bodies and a variety of nozzles with varying flow profiles. Although not an exhaustive survey we identified a spline nozzle/piezoelectric bimorph system that experimentally produced up to 3.4 mW per bimorph. This paper will discuss these results and present our initial analyses of the device using dimensional analysis and constitutive electromechanical modeling. The analysis suggests that an order-of-magnitude improvement in power generation from the current design is possible.

This paper proposes and experimentally investigates applying piezoelectric energy harvesting devices driven by flow induced vibrations to create self-powered actuation of aerostructure surfaces such as tabs, flaps, spoilers, or morphing devices. Recently, we have investigated flow-induced vibrations and limit cycle oscillations due to aeroelastic flutter phenomena in piezoelectric structures as a mechanism to harvest energy from an ambient fluid flow. We will describe how our experimental investigations in a wind tunnel have demonstrated that this harvested energy can be stored and used on-demand to actuate a control surface such as a trailing edge flap in the airflow. This actuated control surface could take the form of a separate and discrete actuated flap, or could constitute rotating or deflecting the oscillating energy harvester itself to produce a non-zero mean angle of attack. Such a rotation of the energy harvester and the associated change in aerodynamic force is shown to influence the operating wind speed range of the device, its limit cycle oscillation (LCO) amplitude, and its harvested power output; hence creating a coupling between the device’s performance as an energy harvester and as a control surface. Finally, the induced changes in the lift, pitching moment, and drag acting on a wing model are quantified and compared for a control surface equipped with an oscillating energy harvester and a traditional, static control surface of the same geometry. The results show that when operated in small amplitude LCO the energy harvester adds negligible aerodynamic drag.

This paper investigates low-power electricity generation from ultrasound acoustic wave energy transfer combined with piezoelectric energy harvesting for wireless applications ranging from medical implants to naval sensor systems. The focus is placed on an underwater system that consists of a pulsating source for spherical wave generation and a harvester connected to an external resistive load for quantifying the electrical power output. An analytical electro-acoustic model is developed to relate the source strength to the electrical power output of the harvester located at a specific distance from the source. The model couples the energy harvester dynamics (piezoelectric device and electrical load) with the source strength through the acoustic-structure interaction at the harvester-fluid interface. Case studies are given for a detailed understanding of the coupled system dynamics under various conditions. Specifically the relationship between the electrical power output and system parameters, such as the distance of the harvester from the source, dimensions of the harvester, level of source strength, and electrical load resistance are explored. Sensitivity of the electrical power output to the excitation frequency in the neighborhood of the harvester’s underwater resonance frequency is also reported.

Results from experiments using a two-degree-of-freedom airfoil system are presented. Air speeds of the airfoil are determined at which dynamic flutter can be initiated and where limit cycle oscillations (LCO) can be excited by initial (pitch or plunge) displacements. LCO’s with large pitch angle displacements attributed to stall flutter behavior are measured. The LCO oscillations are converted into electric power by an electromagnetic-inductor device. The energy harvester consists of three magnets in which one magnet floats between two fixed magnets. The force-displacement relationship of the harvester is best described by a fifth-order polynomial. The integration of the harvester into the airfoil system introduces nonlinear stiffness into the vertical (plunge) direction. When the LCO has been initiated, displacement amplitudes and resulting power generation are measured.

This paper presents the design, construction, experimental characterization, and system testing of a legged, wall-climbing robot actuated by meso-scale hydraulic artificial muscles. While small wall-climbing robots have seen increased research attention in recent years, most authors have primarily focused on designs for the gripping and adhesion of the robot to the wall, while using only standard DC servo-motors for actuation. This project seeks to explore and demonstrate a different actuation mechanism that utilizes hydraulic artificial muscles. A four-limb climbing robot platform that includes a full closed-loop hydraulic power and control system, custom hydraulic artificial muscles for actuation, an on-board microcontroller and RF receiver for control, and compliant claws with integrated sensing for gripping a variety of wall surfaces has been constructed and is currently being tested to investigate this actuation method. On-board power consumption data-logging during climbing operation, analysis of the robot kinematics and climbing behavior, and artificial muscle force-displacement characterization are presented to investigate and this actuation method.

The goal of this study is to investigate dynamic properties and the total energy change of a bio-inspired spider web. To better understand performance, the effects of preload, radial and spiral string stiffness and damping ratio on the natural frequency and total energy of the web are theoretically examined. Different types of web materials and configurations, such as damaged webs are investigated. It is demonstrated that the pretension, stiffness and damping ratio of the web’s strings can significantly affect the natural frequency and total energy of the full and damaged webs. In addition, it is shown that by increasing the pretension in the radial strings one can compensate for the damaged strings and increase the capability of the damaged web to reach that of the full web.

In this paper, we present the ultrasonic wireless power transmission system as part of a brain-machine interface (BMI) system in development to supply the required electric power. Making a small-size implantable BMI, it is essential to design a low power unit with a rechargeable battery. The ultrasonic power transmission system has two piezoelectric transducers, facing each other between skin tissues converting electrical energy to mechanical vibrational energy or vice versa. Ultrasound is free from the electromagnetic coupling effect and medical frequency band limitations which making it a promising candidate for implantable purposes. In this paper, we present the design of piezoelectric composite transducer, the rectifier circuit, and rechargeable battery that all packaged in biocompatible titanium can. An initial prototype device was built for demonstration purpose. The early experimental results demonstrate the prototype device can reach 50% of energy transmission efficiency in a water medium at 20mm distance and 18% in animal skin tissue at 18mm distance, respectively.

Regenerative semi-active suspensions can capture the previously dissipated vibration energy and convert it to usable electrical energy for powering on-board electronic devices, while achieve both the better ride comfort and improved road handling performance at the same time when certain control is applied. To achieve this objective, the power electronics interface circuit connecting the energy harvester and the electrical loads, which can perform simultaneous vibration control and energy harvesting function is in need. This paper utilized a buck-boost converter for simultaneous semi-active vibration control and energy harvesting with electromagnetic regenerative shock absorber, which utilizes a rotational generator to converter the vibration energy to electricity. It has been found that when the circuit works in discontinuous current mode (DCM), the ratio between the input voltage and current is only related to the duty cycle of the switch pulse width modulation signal. Using this property, the buck-boost converter can be used to perform semi-active vibration control by controlling the load connected between the terminals of the generator in the electromagnetic shock absorber. While performing the vibration control, the circuit always draw current from the shock absorber and the suspension remain dissipative, and the shock absorber takes no additional energy to perform the vibration control. The working principle and dynamics of the circuit has been analyzed and simulations were performed to validate the concept.

This manuscript is motivated by research that shows the shear, d₁₅, mode energy harvesters offer significant improvement in power generation over the traditional normal, d₃₁, mode based harvesters. The premise behind this study is to examine the effect of expanding the design domain of PZT based energy harvesters by considering an arbitrary poling angle. In the first part of the manuscript, we derive the equation of motions of a harvester based on Timoshenko beam theory in an unimorph configuration. The resulting equations are solved using a Rayleigh Ritz analysis. The electric displacement depends on both the normal and shear strain. Thus the proposed device operates using a combination of shear and normal modes to extract power. The extent to which each mode is used depends on the polarization orientation. We examine the effect of poling on the fundamental short and open circuit frequencies. Next, the poling angle is examined over a range to determine the effect on the power harvested at the fundamental modal frequencies of the system. The study demonstrates that an arbitrary poled piezoelectric increases the power that the harvester produces over traditionally poled devices; however, the performance is highly dependent on the geometry.

This paper presents a system integration of micro-piezoelectric energy harvester (MPEH) system based on MPEHs fabricated with an aero-deposited PZT technique, including both the device and the interface circuit design. An in depth look at the deposition method known as aerosol deposition is analyzed. Secondly, various structural designs throughout the years will be introduced and discussed. Thirdly, the non-linear synchronized switching technique interfacing circuit was designed to boost the harvested power in comparison to standard rectifying circuits. The boosting effect in comparison to theoretical expectations will also be presented. The power dissipation effects of self-powered SSHI under low current has also been discussed. Experimental results show that the device based on silicon substrate showed a maximum output power of 21 μW with the output voltage of 2.2 Vrms, excited at 215 Hz under a 1.5 g vibrating source. In comparison, the device based on stainless steel substrate, driven under the same acceleration, had a maximum output power of 34 μW with 1.8 Vrms at the resonant frequency of 202 Hz. The power densities were 4.7 μW mm-2 and 7.6 μW mm-2 for the silicon substrate and the stainless steel substrate based devices, each. The cantilever structured MPEG was later improved to the power output of 200.28 μW. To further improve the output characteristic, the device was tested under vacuumed circumstance, which then gave the output power of 241.60μW, with a 6.02 Vrms under 1.5 g, 104.4Hz. The power boosting circuit gave a power gain of 2.03 times, as the overall system outputs 91.4 μW using the self-powered nonlinear technique under 0.75 g with a similar device. The overall system, using only the standard rectifying circuit was able to light a low consumption red- colored SMD-0805 packaged LED in a duty ratio of approximately 25%.

Aeroelastic instabilities have been frequently exploited for energy harvesting purpose to power standalone electronic systems, such as wireless sensors. Meanwhile, various energy harvesting interface circuits, such as synchronized charge extraction (SCE) and synchronized switching harvesting on inductor (SSHI), have been widely pursued in the literature for efficiency enhancement of energy harvesting from existing base vibrations. These interfaces, however, have not been applied for aeroelastic energy harvesting. This paper investigates the feasibility of the SCE interface in galloping-based piezoelectric energy harvesting, with a focus on its benefit for performance improvement and influence on the galloping dynamics in different electromechanical coupling regimes. A galloping-based piezoelectric energy harvester (GPEH) is prototyped with an aluminum cantilever bonded with a piezoelectric sheet. Wind tunnel test is conducted with a simple electrical interface composed of a resistive load. Circuit simulation is performed with equivalent circuit representation of the GPEH system and confirmed by experimental results. Consequently, a self-powered SCE interface is implemented with the capability of self peak-detecting and switching. Circuit simulation for various electromechanical coupling cases shows that the harvested power with SCE interface for GPEH is independent of the electrical load, similar to that for a vibration-based piezoelectric energy harvester (VPEH). The SCE interface outperforms the standard interface if the electromechanical coupling is weak, and requires much less piezoelectric material to achieve the maximum power output. Moreover, influence of electromechanical coupling on the dynamics of GPEH with SCE is found sensitive to the wind speed.

In this paper, a new type of magnetorheological fluid (MRF) mount is proposed. This design is based on the well-known of two modes of MRF such as flow mode and shear mode. These modes are applied in the design which includes two components: MR mount for controlling vertical vibrations, and MR brake for controlling horizontal vibrations. The structure of MR valve is applied in design mount part, while the disk type of structure is employed in design brake part. These structures contribute to the initial requirements such as small structure, high damping force and high braking force. The theoretical analysis for the design is undertaken followed by design optimization using ANSYS ADPL software. The objective functions are concentrated on maximal damping force for MR mount and maximum braking force for MR brake. As traditional design, rubber mount is used in the proposed design for suffering static loads. It has been shown through computer simulation that the initial requirements with high damping force and high braking force have been successfully achieved.

As the vibration of high speed train becomes fierce when the train runs at high speed, it is crucial to develop a novel suspension system to negotiate train’s vibration. This paper presents a novel suspension based on Magnetorheological fluid (MRF) damper and MRF based smart air spring. The MRF damper is used to generate variable damping while the smart air spring is used to generate field-dependent stiffness. In this paper, the two kind smart devices, MRF dampers and smart air spring, are developed firstly. Then the dynamic performances of these two devices are tested by MTS. Based on the testing results, the two devices are equipped to a high speed train which is built in ADAMS. The skyhook control algorithm is employed to control the novel suspension. In order to compare the vibration suppression capability of the novel suspension with other kind suspensions, three other different suspension systems are also considered and simulated in this paper. The other three kind suspensions are variable damping with fixed stiffness suspension, variable stiffness with fixed damping suspension and passive suspension. The simulation results indicate that the variable damping and stiffness suspension suppresses the vibration of high speed train better than the other three suspension systems.

The goal of this study is to demonstrate the feasibility of a fail-safe, bi-linear spring controllable magnetorheological fluid damper (BLS-CMRD). This research introduces a new device with independently pre-set spring forces in compression and rebound combined with a controllable MR fluid damping. In this work, a BLS-CMRD is designed, fabricated, tested and evaluated. Experiments are performed for sinusoidal displacements in the quasistatic and dynamic ranges to evaluate the performance of the BLS-CMRD under different magnetic fields. The experimental results prove that the device reacts with significantly different spring forces from the compression to rebound regions, while providing passive viscous and controllable MR fluid damping. With this first of a kind system it is demonstrated that the utility of a bi-linear liquid spring can be combined with the reliability of passive viscous fluid damping and the capabilities of controllable MR fluid damping into one compact and versatile device.

Semi-active magnetorheological energy absorbers (MREAs) are one type of the most promising actuator for both the vibration and shock control. This paper investigates the frontal crash mitigation performance of semi-active MR impact seat suspensions for ground vehicles. The characteristics of two MREAs, a conventional MREA and an MREA with an internal bypass, with an identical volume, are theoretically evaluated and compared. To explore the control effectiveness of MREAs in the shock control systems, the mechanical model of a 4-degree-of-freedom (4DOF) sliding seat suspension system with MREAs is constructed. An optimal Bingham number control, which is to minimize the crash pulse loads transmitted to occupants by utilizing maximum stroke of the MREAs based on initial velocity of crash pulse, mass, and damping, is proposed and developed to improve the crash mitigation performance of the 4DOF MR sliding seat suspension control systems. The simulated control performances of the mitigation systems based on the MREAs with different functional structures are evaluated, compared, and analyzed. The research results indicate that (1) the constant stroking load velocity range of the MREAs is of significance to evaluate the controllability of the MREAs (i.e., the effectiveness of the semi-active shock control systems), and (2) suboptimal Bingham number control cannot realize “soft landing” (i.e., either an end-stop impact or incomplete utilization of the MREA stroke happens).

The authors recently reported on a hybrid rotary-translational vibration energy harvesting approach using a spherical permanent-magnet and employing cycloidal motion as a mechanical amplifier. The rotary-translational harvesting approach, which is resonant in nature, can yield approximately twice the e.m.f. compared with a similar translationalonly device. This paper explores the analytic and numerical modelling of the rotary-translational harvester with the goal of finding an efficient method for design optimisation.

A review of the vibration energy harvesting literature has been undertaken with the goal of establishing scaling laws for experimentally demonstrated harvesting devices. In particular electromagnetic harvesting devices are investigated. Power density metrics are examined with respect to scaling length, mass, frequency and drive acceleration. Improvements in demonstrated power density of harvesting devices over the past decade are noted. Scaling laws are observed that appear to suggest an upper limit to the power density achievable with current harvesting techniques.

In this study, experimental characterizations of a new hybrid energy harvesting device consisting of piezoelectric and electromagnetic transducers are presented. The generator, to be worn on the legs or arms of a person, harnesses linear motion and impact forces from human motion to generate electrical energy. The device consists of an unbalanced rotor made of three piezoelectric beams which have permanent magnets attached to the ends. Impact forces cause the beams to vibrate, generating a voltage across their electrodes and linear motion causes the rotor to spin. As the rotor spins, the magnets pass over ten electromagnetic coils mounted to the base, inducing a current through the wire. Several design related issues were investigated experimentally in order to optimize the hybrid device for maximum power generation. Further experiments were conducted on the system to characterize the energy harvesting capabilities of the device, all of which are presented in this study.

Regenerative/Energy harvesting shock absorbers have a great potential to increase fuel efficiency and provide suspension damping simultaneously. In recent years there’s intensive work on this topic, but most researches focus on electricity extraction from vibration and harvesting efficiency improvement. The integration of electricity generated from regenerative shock absorbers into vehicle electric system, which is very important to realize the fuel efficiency benefit, has not been investigated. This paper is to study and demonstrate the integration of regenerative shock absorber with vehicle alternator, battery and in-vehicle electrical load together. In the presented system, the shock absorber is excited by a shaker and it converts kinetic energy into electricity. The harvested electricity flows into a DC/DC converter which realizes two functions: controlling the shock absorber’s damping and regulating the output voltage. The damping is tuned by controlling shock absorber’s output current, which is also the input current of DC/DC converter. By adjusting the duty cycles of switches in the converter, its input impedance together with input current can be adjusted according to dynamic damping requirements. An automotive lead-acid battery is charged by the DC/DC converter’s output. To simulate the working condition of combustion engine, an AC motor is used to drive a truck alternator, which also charges the battery. Power resistors are used as battery’s electrical load to simulate in-vehicle electrical devices. Experimental results show that the proposed integration strategy can effectively utilize the harvested electricity and power consumption of the AC motor is decreased accordingly. This proves the combustion engine’s load reduction and fuel efficiency improvement.

We report the investigation of an energy harvesting system composed of coupled resonators with the magnetostrictive material Galfenol (FeGa). A coupled system of meso-scale (1-10 cm) cantilever beams for harvesting vibration energy is described for powering and aiding the performance of low-power wireless sensor nodes. Galfenol is chosen in this work for its durability, compared to the brittleness often encountered with piezoelectric materials, and high magnetomechanical coupling. A lumped model, which captures both the mechanical and electrical behavior of the individual transducers, is first developed. The values of the lumped element parameters are then derived empirically from fabricated beams in order to compare the model to experimental measurements. The governing equations of the coupled system lead to a system of differential equations with all-to-all coupling between transducers. An analysis of the system equations reveals different patterns of collective oscillations. Among the many different patterns, a synchronous state appears to yield the maximum energy that can be harvested by the system. Experiments on coupled system shows that the coupled system exhibits synchronization and an increment in the output power. Discussion of the required power converters is also included.

Nowadays, thermal-energy-harvesting is an important research topic for powering wireless sensors. Among numerous thermal-energy-harvesting approaches, some researchers demonstrated novel thermomagnetic-energy harvesters to convert a thermal-energy from an ambient temperature-difference to an electrical-output to power the sensors. However, the harvesters are too bulky to be integrated with the sensors embedded in tiny mechanical-structures for some structuralhealth- monitoring applications. Therefore, miniaturized harvesters are needed. Hence, we demonstrate a miniature thermomagnetic-energy harvester. The harvester consists of CuBe-beams, PZT-piezoelectric-sheet, Gd-soft-magnet, NdFeB-hard-magnet, and mechanical-frame. The piezoelectric-sheet and soft-magnet is bounded at fixed-end and freeend of the beams, respectively. The mechanical-frame assembles the beams and hard-magnet. The length×width×thickness of the harvester is 2.5cm×1.7cm×1.5cm. According to this, our harvester is 20-times smaller than the other harvesters. In the initial-state of the energy-harvesting, the beams’ free-end is near the cold-side. Thus, the soft-magnet is cooled lower than its curie temperature (Tc) and consequently changed from paramagnetic to ferromagnetic. Therefore, a magnetic-attractive force is produced between the soft-magnet and hard-magnet. Consequently, the beams/soft-magnet are down-pulled toward the hard-magnet fixed on the hot-side. The soft-magnet closing to the hot-side is heated higher than its Tc and subsequently changed to paramagnetic. Consequently, the magnetic-force is eliminated thus the beams are rebounded to the initial-state. Hence, when the harvester is under a temperature-difference, the beams’ pulling-down/back process is cyclic. Due to the piezoelectric effect, the piezoelectric-sheet fixed on the beams continuously produces voltage-response. Under the temperature-difference of 29°C, the voltage-response of the harvester is 30.4 mV with an oscillating-frequency of 0.098 Hz.

As a result of the documented performance limitations of conventional linear piezoelectric energy harvesters, researchers have focused their efforts towards device designs that can better capture broadband energy. The approaches used can be classified into three categories: frequency tuning, multi-modal energy harvesting, and nonlinear energy harvesting¹. Of the nonlinear harvesting approaches studied, bistable energy harvesters have been shown to have the most robust performance when subjected to broadband harmonic & stochastic excitation^2-4. A conventional method for developing a nonlinear bistable restoring force is through use of magnetic repulsion. In these studies, a common theme of high-energy orbit breakdown occurs during a frequency upsweep. The issue at hand is the inability of the device inertial forces to overcome the potential energy barrier (separatrix) inherent to a bistable potential energy. This paper proposes the use of a high-permeability electromagnet for adaptively controlling the bistable magnetic repulsion force to expand the frequency bandwidth for high-energy harmonic oscillations. Numerical simulations of the nonlinear oscillator are used to study the system response under varying parameters of separation distance and electromagnetic coil current. An analytical model of the magnetic moment of an electromagnet is developed for use in studying the force interaction between repulsing magnets and to determine the parametric space that generates buckling loads in a cantilever bimorph energy harvester.

Nonlinear harvesting devices have been shown to maintain large amplitude oscillations over a wider range of frequencies than their linear counter parts. Central to exploiting the dynamic behaviour for harvesting is the understanding of the cross-well oscillations which involve constant snap-through between the stable states of such systems. Yet the phenomena involving the dynamics of snap-through and their impact in the harvesting characteristics have not been studied in detail. In this paper, the relevant response characteristics for dynamically triggered snap-through of bi-stable composite laminates for energy harvesting are investigated. A nonlinear model for the dynamics of the bi-stable composites is used to study the relation between the properties of the laminate and the acceleration level required for causing snap-through. In particular, the effect of varying the induced stress level on the dynamic response is investigated. The obtained relations provide a tool for designing the excitation level for which broad-band response bi-stable systems is obtained, aiding the design of harvesting devices based on such structures.

This paper presents analytical modeling and case studies of broadband and band-limited random vibration energy harvesting using a piezoceramic patch attached on a thin plate. The literature of vibration-based energy harvesting has been mostly focused on resonant cantilevered structures. However, cantilevered beam-type harvesters have limited broadband vibration energy harvesting capabilities unless they are combined with a nonlinear component. Moreover, cantilever arrangements cannot always be mounted on thin structures (which are basic components of marine, aerospace, and ground transportation systems) without significantly affecting the host system’s design and overall dynamics. A patch-based piezoelectric energy harvester structurally integrated to a thin plate can be a proper alternative to using resonant cantilevers for harvesting energy from thin structures. Besides, plate-like structures have more number of vibration modes compared to beam structures, offering better broadband performance characteristics. In this paper, we present analytical modelling of patch-based piezoelectric energy harvester attached on a thin plate for random vibrations. The analytical model is based on electromechanically-coupled distributed-parameter formulation and validated by comparing the electromechanical frequency response functions (FRFs) with experimental results. Example case studies are then presented to investigate the expected power output of a piezoceramic patch attached on an aluminum plate for the case of random force excitations. The effect of bandwidth of random excitation on the mean power and shunted mean-square vibration response are explored with a focus on the number of vibration modes covered in the frequency range of input power spectral density (PSD).

This paper presents performance analysis of semi-active railway vehicle suspension system using MR damper. In order to achieve this goal, a mathematical dynamic model of railway vehicle is derived by integrating car body, bogie frame and wheel-set which can be able to represent lateral, yaw and roll motion. Based on this model, the dynamic range of MR damper at the railway secondary suspension system and design parameters of MR damper are calculated. Subsequently, control performances of railway vehicle including car body lateral motion and acceleration of MR damper are evaluated through computer simulations. Then, the MR damper is manufactured to be retrofitted with the real railway vehicle and its characteristics are experimentally measured. Experimental performance of MR damper is assessed using test rig which is composed of a car body and two bogies.

The general study and applications of Magneto-Rhelogical (MR) dampers have been spread in the lasts years but only some studies have been focusing on the vibration control problems on rotor-bearings systems. Squeeze-Film Dampers (SFD) are now commonly used to passively control the vibration response on rotor-bearing systems because they can provide flexibility, damping and extend the so-called stability thresholds in rotating machinery. More recently, SFD are combined with MR or Electro-Rheological (ER) fluids to introduce a semiactive control mechanism to modify the rotordynamic coefficients and deal with the robust performance of the overall system response for higher operating speeds. There are, however, some theoretical and technological problems that complicate their extensive use, like the relationship between the centering spring flexibility and the rheological behavior of the smart fluid to produce the SFD forces. In this work it is considered a SFD with MR fluid and a set of circular section beams in a squirrel cage arrangement in combination with latex seals as centering springs. The mathematical model analysis includes the controllable viscoelastic properties associated to the MR fluid. The characterization of the SFD is made by the determination of some coefficients associated with a modified Choi-Lee-Park polynomial model. During the analysis is considered a rotor-bearing system modeled using finite element methods. The SFD with MR fluid is connected to an experimental platform to validate and experimentally evaluate the overall system. Finally, to improve the open-loop system performance, a methodology for the use of different control schemes is proposed.

Phononic crystals are periodic structures consist of different materials in an elastic medium designed to interact with elastic waves. These crystals have practical applications, such as, frequency filters, beam splitters, sound or vibration protectors, acoustic lasers, acoustic mirrors and elastic waveguides. In this study, the wave propagation in a tunable phononic crystal is investigated. The magnetically controllable phononic crystal consists of a soft magnetorheological elastic medium undergoing large deformations upon the application of a magnetic field. Finite deformations and induced magnetic fields influence wave propagation characteristics in the periodic structure. The soft matrix is modeled as a hyperelastic elastomer to take into account the material nonlinearity. The integrated effects of material properties, transformation of the geometry of the unit cell, and the induced magnetic field, are used to tune the band structure of the periodic structure. Both analytical and finite element methods are employed to evaluate the dispersion diagrams considering Bloch boundary conditions. Results show that the applied magnetic field significantly affect the width and the position of band-gaps.

The present manuscript is aimed at describing the PEASSS – PiezoElectric Assisted Smart Satellite Structure project, which was initiated at the beginning of 2013 and financed by the Seventh Framework Program (FP7) of the European Commission. The aims of the project were to develop, manufacture, test and qualify “smart structures” which combine composite panels, piezoelectric materials, and next generation sensors, for autonomously improved pointing accuracy and power generation in space. The smart panels will enable fine angle control, and thermal and vibration compensation, improving all types of future Earth observations, such as environmental and planetary mapping, border and regional imaging. This new technology will help keep Europe on the cutting edge of space research, potentially improving the cost and development time for more accurate future sensor platforms including synthetic aperture optics, moving target detection and identification, and compact radars. The system components include new nano-satellite electronics, a piezo power generation system based on the pyroelectric effect, a piezo actuated smart structure, and a fiber-optic sensor and interrogator system. The present paper will deal only with two of the components, namely the piezo power generation system and the piezo actuated smart structure The designs are going to be prototyped into breadboard models for functional development and testing. Following completion of operational breadboards, components will evolve to flight-test ready hardware and related software, ready to be integrated into a working satellite. Once the nanosattelite is assembled, on ground tests will be performed. Finally, the satellite will be launched and tested in space at the end of 2015.

Smart materials offer several potential advantages for UAV flight control applications compared to traditional servo actuators. One important benefit is that smart materials are lightweight and can be embedded directly into the structure of a wing or control surface. Therefore, they can reduce the overall weight of the vehicle and eliminate the need for mechanical appendages that may compromise the form factor of the wing, benefits that become more significant as the size of the vehicle decreases. In addition, smart materials can be used to realize continuous camber change of aerodynamic surfaces. Such designs offer improved aerodynamic efficiency compared to the discontinuous deflections of traditional hinged control surfaces driven by servo actuators. In the research discussed in this paper, macro-fiber composite (MFC) aileron actuators are designed for implementation on a medium-scale, fixed-wing UAV in order to achieve roll control. Macro-fiber composites, which consist of piezoceramic fibers and electrodes embedded in an epoxy matrix, are an attractive choice for UAV actuation because they are manufactured as lightweight, thin sheets and, when implemented as bending actuators, can provide both large structural deflections and high bandwidth. In this study, several MFC aileron actuator designs were evaluated through a combination of theoretical and experimental analysis. The current design consists of glass fiber composite ailerons with two unimorph MFC actuators embedded in each aileron to produce upward deflection. Wind tunnel test results are presented to assess the changes in lift and drag coefficients for different levels of MFC aileron actuation. Preparations for open-loop flight testing using a Skywalker UAV with MFC ailerons are also discussed. In addition, the development of a closed-loop, autonomous flight control system for the Skywalker is overviewed in preparation for conducting simulations and flight testing of an autonomous Skywalker with MFC aileron actuators.

The flexure-box morphing aileron concept utilizes Macro-Fiber Composites (MFCs) and a compliant box to create a conformal morphing aileron. This work evaluates the impact of the number of MFCs on the performance, power and mass of the aileron by experimentally investigating two different actuator configurations: unimorph and bimorph. Implemented in a NACA 0012 airfoil with 304.8 mm chord, the unimorph and bimorph configurations are experimentally tested over a range of flow speeds from 5 to 20 m/s and angles of attack from -20 to 20 degrees under aerodynamic loads in a wind tunnel. An embedded flexible sensor is installed in the aileron to evaluate the effect of aerodynamic loading on tip position. For both design choices, the effect of actuation on lift, drag and pitching moment coefficients are measured. Finally, the impact on aileron mass and average power consumption due to the added MFCs is considered. The results showed the unimorph exhibiting superior ability to influence flow up to 15 m/s, with equivalent power consumption and lower overall mass. At 20 m/s, the bimorph exhibited superior control over aerodynamic forces and the unimorph experienced significant deformation due to aerodynamic loading.

This paper presents a novel variable modulus cellular structure based on a hexagonal unit cell with pneumatic artificial muscle (PAM) inclusions. The cell considered is pin-jointed, loaded in the horizontal direction, with three PAMs (one vertical PAM and two horizontal PAMs) oriented in an “H” configuration between the vertices of the cell. A method for calculation of the hexagonal cell modulus is introduced, as is an expression for the balance of tensile forces between the horizontal and vertical PAMs. An aluminum hexagonal unit cell is fabricated and simulation of the hexagonal cell with PAM inclusions is then compared to experimental measurement of the unit cell modulus in the horizontal direction with all three muscles pressurized to the same value over a pressure range up to 758 kPa. A change in cell modulus by a factor of 1.33 and a corresponding change in cell angle of 0.41° are demonstrated experimentally. A design study via simulation predicts that differential pressurization of the PAMs up to 2068 kPa can change the cell modulus in the horizontal direction by a factor of 6.83 with a change in cell angle of only 2.75°. Both experiment and simulation show that this concept provides a way to decouple the length change of a PAM from the change in modulus to create a structural unit cell whose in-plane modulus in a given direction can be tuned based on the orientation of PAMs within the cell and the pressure supplied to the individual muscles.

Owing to the two-way electro-mechanical coupling characteristics, piezoelectric transducers have been widely used as sensors and actuators in sensing and control applications. In this research, we explore the integration of piezoelectric transducer with the structure, in which the transducer is connected with a Wheatstone bridge based circuitry subjected to chaotic excitation. It is shown that a type of Wheatstone bridge circuit with proper parameters configuration can increase sensitivity in detecting structural anomaly. Such integration has the potential to significantly amplify the response change when the underlying structure is subject to property change. Comprehensive analytical and experimental studies are carried out to demonstrate the concept and validate the performance improvement.

Devices with increased sensitivities are needed for various applications including the detection of chemical and biological agents. This paper presents the design of microelectromechanical systems (MEMS) devices that incorporate lead zirconate titanate (PZT) films in order to realize highly sensitive sensors. In this work, the piezoelectric properties of the PZT are exploited to produce sensors that perform optimally for mass sensing applications. The sensor is designed to operate as a thin-film bulk acoustic resonator (TFBAR) whereas a piezoelectric is sandwiched between electrodes and senses a change in mass by measuring a change in resonance frequency. Modeling of the TFBAR sensor, using finite element analysis software COMSOL, was performed to examine optimal device design parameters and is presented in this paper. The effect of the PZT thickness on device resonance is also presented. The piezoelectric properties of the PZT is based on its crystal structure, therefore, optimization of the PZT film growth parameters is also described in this work. A detailed description of the fabrication process flow developed based on the optimization of the device design and film growth is also given. The TFBAR sensor consists of 150 nm of PZT, 150nm of silicon dioxide, silicon substrate, titanium/platinum bottom electrodes, and aluminum top electrodes. The top electrodes are segmented to increase the sensitivity of the sensor. The resonance frequency of the device is 3.2 GHz.

Torsional vibrations of circular tubes, rods, rings, and disks are widely used as operation modes of acoustic wave transducers in various piezoelectric devices. In this paper, a piezoelectric disk with spiral interdigitated electrodes is proposed to generate in-plane torsion in a simple and effective manner. Design and working principle of the torsional transducer are introduced. Vibration characteristics of the transducer with a constant spiral angle are studied. A simplified model is established to investigate the basic dynamic characteristics of torsional vibration accompanying with radial vibration. Electric admittance, resonant frequencies, and mode shapes with different boundary conditions are calculated. Resonant frequencies as functions of several structural parameters are discussed.

The principle and structural configuration of an active controlled microfluidic valve with annular boundary is presented in this paper. The active controlled flowrate model of the active controlled microfluidic valve with annular boundary is established. The prototypes of the active controlled microfluidic valves with annular boundaries with three different combinations of the inner and outer radii are fabricated and tested on the established experimental setup. The experimental results show that: (1) The active controlled microfluidic valve with annular boundary possesses the on/off switching and the continuous control capability of the fluid with simple structure and easy fabrication processing; (2) When the inner and outer diameters of the annular boundary are 1.5 mm and 3.5 mm, respectively, the maximum flowrate of the valve is 0.14 ml/s when the differential pressure of the inlet and outlet of the valve is 1000 Pa and the voltage applied to circular piezoelectric unimorph actuator is 100 V; (3) The established active controlled flowrate model can accurately predict the controlled flowrate of the active controlled microfluidic valves with the maximum relative error of 6.7%. The results presented in this paper lay the foundation for designing and developing the active controlled microfluidic valves with annular boundary driven by circular piezoelectric unimorph actuators.

Vibration-based energy harvesting has been heavily researched over the last decade to enable self-powered small electronic components for wireless applications in various disciplines ranging from biomedical to civil engineering. The existing research efforts in this interdisciplinary field have mostly focused on the harvesting of deterministic or stochastic vibrational energy available at a fixed position in space. Such an approach is convenient to design and employ linear and nonlinear vibration-based energy harvesters, such as base-excited cantilevers with piezoelectric laminates. However, persistent vibrations at a fixed frequency and spatial point, or standing wave patterns, are rather simplified representations of ambient vibrational energy. As an alternative to energy harvesting from spatially localized vibrations and standing wave patterns, this work presents an investigation into the harvesting of one-dimensional bending waves in infinite beams. The focus is placed on the use of piezoelectric patches bonded to a thin and long beam and employed to transform the incoming wave energy into usable electricity while minimizing the traveling waves reflected and transmitted from the harvester domain. To this end, performance enhancement by wavelength matching, resistiveinductive circuits, and a localized obstacle are explored. Electroelastic model predictions and performance enhancement efforts are validated experimentally for various case studies.

This article reports a novel finite element model of piezoelectric energy harvesters accounting for the effect of nonlinear interface circuits. The idea is to replace the energy harvesting circuit in parallel with the parasitic piezoelectric capacitance by an equivalent load impedance. This approach offers many advantages. First, the model itself can be implemented conveniently in commercial finite element softwares. Second, it directly provides system-level designs on the whole without resorting to circuit solvers. Third, the extensions to complicated structures such as array configurations are straightforward. The proposed finite element model is validated by considering the case of an array system endowed with the standard, parallel-/series-SSHI (synchronized switch harvesting on inductor) interfaces. Good agreement is found between simulation results and analytic estimates.

The need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted interest in recent years for energy harvesting technologies capable of capturing energy from broadband ambient vibrations. Encouraging results have been reported for an arrangement of piezoelectric layers attached to carbon fiber / epoxy laminates which possess bistability by virtue of their specific asymmetric stacking sequence. The inherent bistability of the underlying structure is exploited for energy harvesting since a transition from one stable configuration to another, or ‘snap-through’, is used to repeatedly strain the surface-bonded piezoelectric and generate electrical energy. Existing studies, both experimental and modelling, have been limited to simple geometric laminate shapes, restricting the scope for improved energy harvesting performance by limiting the number of design variables. In this paper we present an analytical model to predict the static shapes of laminates of any desired profile, validated experimentally using a digital image correlation system. Good accuracy in terms of out-of-plane displacements (5-7%) are shown in line with existing square modelling results. The static model is then mapped to a dynamics model and used to compare results against an experimental study of the harvesting performance of an example arbitrary geometry piezoelectric-laminate energy harvester.

Dielectric loss is one of the important parasitic features of piezoelectric materials; nevertheless, its role in practical piezoelectric energy harvesting (PEH) systems has received little attention in previous studies. Based on the integrated equivalent impedance network model, this paper investigates the susceptibility of harvested power in PEH systems under different dielectric leakage conditions when different harvesting interface circuit is adopted. It shows that dielectric loss always counteracts power generation in PEH systems. In particular, harvested power degrades from the ideal lossless case more significantly under large dielectric leakage, or when power boosting interface circuits, e.g., synchronized switch harvesting on inductor (SSHI), are adopted. These results provide useful insight for the selections of piezoelectric material and harvesting interface circuit towards holistic PEH designs.

Origami engineering, a discipline encompassing the creation of practical three-dimensional structures from two- dimensional entities via folding operations, has the potential to impact multiple fields of manufacturing and design. In some circumstances, it may be practical to have self-folding capabilities instead of creating folds by external manipulations (as in morphing structures in outer space or on the ocean floor). This paper considers the use of a self-folding laminate composite consisting of two outer layers of thermally actuated shape memory alloy (SMA) wire meshes separated by an inner compliant insulating layer. Methods for designing folding patterns and determining temperature fields to obtain desired shapes and behaviors are proposed. Sheets composed of the self-folding laminate are modeled via finite element analysis (FEA) and the proposed methods are implemented to test their capabilities. One method uses a previously developed and freely available software called Freeform Origami for folding pattern design. The second method entails the use of optimization to determine the localized activation temperatures required to obtain desired shapes or to perform specific functions. The proposed methods are demonstrated to be applicable for the design of folding patterns and determination of activation temperatures for the self-folding laminate by showing successful examples of their implementation. This exploratory study provides new tools that can be integrated into the design framework of self-folding origami structures.

This paper develops a smart hybrid rotary damper using a re-centering smart shape memory alloy (SMA) material as well as conventional energy-dissipating metallic plates that are easy to be replaced. The ends of the SMA and steel plates are inserted in the hinge. When the damper rotates, all the plates bend, providing energy dissipating and recentering characteristics. Such smart hybrid rotary dampers can be installed in structures to mitigate structural responses and to re-center automatically. The damaged energy-dissipating plates can be easily replaced promptly after an external excitation, reducing repair time and costs. An OpenSEES model of a smart hybrid rotary was established and calibrated to reproduce the realistic behavior measured from a full-scale experimental test. Furthermore, the seismic performance of a 3-story moment resisting model building with smart hybrid rotary dampers designed for downtown Los Angeles was also evaluated in the OpenSEES structural analysis software. Such a smart moment resisting frame exhibits perfect residual roof displacement, 0.006”, extremely smaller than 18.04” for the conventional moment resisting frame subjected to a 2500 year return period ground motion for the downtown LA area (an amplified factor of 1.15 on Kobe earthquake). The smart hybrid rotary dampers are also applied into an eccentric braced steel frame, which combines a moment frame system and a bracing system. The results illustrate that adding smart hybrid rotaries in this braced system not only completely restores the building after an external excitation, but also significantly reduces peak interstory drifts.

In recent years, an increasing number of breakthroughs have been made in the field of small-scale wind energy harvesting, where specialized materials are utilized to convert flow energy into electric power. Several studies on this power extraction rely on a common energy harvester setup in which a stiff cantilever beam is attached to the trailing edge of a miniature bluff body. At these small scales where boundary layer effects are appreciable in the laminar flow regime, periodic vortex shedding can be used to drive transverse vibrations in the beam. Interestingly, the fluid dynamics involved in this unsteady process have been studied for decades not to exploit their characteristics, but instead to eliminate potentially destructive effects. As a result, there is still much room for improvement and expansion on recent design studies. A study of how subtle changes in bluff body trailing edge geometry effect power output of a model will be presented in this paper. The model under consideration consists of a miniature bluff body on the order of tens of millimeters in diameter, to which a piezoelectric cantilever is attached at the trailing edge. This model is specifically designed for laminar to transitional Reynolds Number flows (500−2800) where the periodicity of vortex shedding approaches the natural frequency of the beam. As the flow speed is further increased, the effect of lock-in occurs where the resonant beam motion resists a change in vortex shedding frequency. Vibration amplitudes of the beam reach a maximum under this condition, thus maximizing power generation efficiency of the system and providing an optimal condition to operate the harvester. In an effort to meaningfully compare the results, a number of dimensionless parameters are employed. The influence of parameters such as beam length and natural frequency, fluid flow speed, and trailing edge geometry are studied utilizing COMSOL Multiphysics laminar, fluid-structure interaction simulations in order to create design guidelines for an improved energy harvester.

Recently, light weight structure becomes an object of attention because increase of energy efficiency becomes the most important global hot issue. Then, composite structures, which have inherent high strength and stiffness to weight ratio, are in the limelight for light weight structures. However, complex failure modes of composite structure are still remains unsolved problem and become main obstacle of wide application of composite structures. Delamination is one of frequent damage phenomenon of laminated composite structure. Delamination can cause reduction of structural stiffness and decrement of natural frequencies. This might induce increase of structural vibration and resonant phenomenon of operating structures. Then, delamination should be detected and complemented. In this work, active control scheme and piezoelectric actuators are used to reduce the delamination effect of damaged composite structure. At first, finite element model for delaminated composite structure is constructed based on improved layerwise theory and then state space control model is established. After design and implementation of active controller, dynamic characteristics and structural performances of damaged composite structure are investigated and effectiveness of active healing is evaluated.

This paper introduces the Modified Positive Velocity Feedback (MPVF) controller as an alternative to the conventional Positive Position Feedback (PPF) controller, with the goal of suppressing unwanted resonant vibrations in smart structures. The MPVF controller uses two parallel feedback compensators working on the fundamental modes of the structure. The vibration velocity is measured by a sensor or state estimator and is fed back to the controller as the input. To control n-modes, n sets of parallel compensators are required. MPVF controller gain selection in multimode cases highly affects the control results. This problem is resolved using the Linear Quadratic Regulator (LQR) and the M-norm optimization method, which are selected to form the desired performance of the MPVF controller. First, the controller is simulated for the two optimization approaches, and then, experimental investigation of the vibration suppression is performed. The LQR-optimized MPVF provides a better suppression in terms of vibration displacement. The M-normoptimized MPVF controller focuses on modes with higher magnitudes of velocity and provides a higher level of vibration velocity suppression than LQR-optimized method. Vibration velocity attenuation can be very important in preventing fatigue failures due to the fact that velocity can be directly related to stress.

Transmission of acoustic waves through a periodic array of sub-wavelength slits or holes have been studied in several recent works in relation with physical phenomena such as resonant (extraordinary) transmission, broadband sound shielding or acoustic induced transparency (AIT). In this work, we present for the first time the study of analogous phenomena for Lamb waves propagating in a thin plate. We study the transmission through one or two rows of a periodic array constituted by thin bridges separated by rectangular holes. When two rows of such an array are considered, the choice of the distance between both rows allows the realization of a broadband attenuation up to 99% in the transmission. These investigations should have implications for sound isolation, filtering and sensing applications.

An unsymmetrical switch circuit is designed for semi-active control method based on synchronized switching damping principle of piezoelectric actuators. A bypass capacitor and an additional switch are used to realize unsymmetrical bipolar voltage. The control logic of the switches is introduced in detail and the switched voltages, which directly influence the control performance, are derived as functions of the vibration amplitude and the outputs of the voltage sources. Simulations were carried out to verify the design circuit and the theoretical results of the switched voltage. The voltage ratio increases with increasing bypass capacitance, but its increasing rate decreases. The results show that large bypass capacitor is needed to realize a voltage ratio of 3, which is common in some piezoelectric actuator such as MFC.

Sheeted or fibrous piezoelectric devices have been recently developed as actuators or sensors. These light and flexible devices are expected to create many innovative methods for the vibration control of structures. In this paper, we discuss the active control of vertical and horizontal micro-vibration of an architectural frame structure using Macro Fiber Composites (MFCs). MFCs are sheeted piezoelectric devices constructed with fibrous piezoceramics that can produce relatively higher forces than other sheeted piezoelectric devices. We arranged MFCs at the lower flange of both ends of a beam as actuators. By the expansion and contraction of the MFC actuators, bending moments act at both ends of the beam. The synchronized movements of the MFC actuators control the vertical vibration of the beam or slab. The opposite phase movements control the horizontal vibration of the frame structure. MFCs used as sensors are arranged at arbitrary positions on the lower flange surface. An experiment of vertical and horizontal vibration control on a scaled frame model is conducted and the results show that the control method effectively minimizes the resonant vibration. A vertical vibration control test on a real architectural structure is also conducted. The MFCs are arranged at the ends of two beam-spanning girders. Consequently, the vertical floor vibration of 0.04 m/s² at 8.5 Hz at the center of the grid was reduced to 0.01 m/s² or about −12 dB.

The increasing interest in engineering systems with excellent mitigation of vibration and shock has required novel design approaches which provide systems with passive adaptive performance across the different fields of engineering. In this paper we present a novel modular design concept to synthesize passive adaptive structures upon a varied loading condition. This concept interconnects linear and nonlinear structural elements depending on the scale and performance requested to the final structural system. To realize this concept we developed a structural synthesis tool integrated with the genetic algorithm. The design optimization problem is formulated considering the prescribed design requirement on stiffness and damping performance. This tool optimally synthesizes the structural network by assembling the available constitutive elements in the set and successfully obtains passive adaptive assembly upon a varied loading condition in terms of vibration amplitude and frequency.

Vibration control logics based on the modal approach allow to increase damping on a certain number of modes. The main limit associated with these strategies is represented by spillover on non modeled modes. Negative Derivative Feedback shows to be particularly robust against spillover since modal velocity is fed back through a band-pass filter so that undesired effects can be limited both at high and low frequencies. In this paper a design strategy for NDF controller based on an optimal approach is proposed for single and multi-degrees of freedom systems and tested on a cantilever beam finite element model.

There has been growing interest in enabling wireless health and usage monitoring for rotorcraft applications, such as helicopter rotor systems. Large dynamic loads and acceleration fluctuations available in these environments make the implementation of vibration-based piezoelectric energy harvesters a very promising choice. However, such extreme loads transmitted to the harvester can also be detrimental to piezoelectric laminates and overall system reliability. Particularly flexible resonant cantilever configurations tuned to match the dominant excitation frequency can be subject to very large deformations and failure of brittle piezoelectric laminates due to excessive bending stresses at the root of the harvester. Design of resonant piezoelectric energy harvesters for use in these environments require nonlinear electroelastic dynamic modeling and strength-based analysis to maximize the power output while ensuring that the harvester is still functional. This paper presents a mathematical framework to design and analyze the dynamics of nonlinear flexible piezoelectric energy harvesters under large base acceleration levels. A strength-based limit is imposed to design the piezoelectric energy harvester with a proof mass while accounting for material, geometric, and dissipative nonlinearities, with a focus on two demonstrative case studies having the same linear fundamental resonance frequency but different overhang length and proof mass values. Experiments are conducted at different excitation levels for validation of the nonlinear design approach proposed in this work. The case studies in this work reveal that harvesters exhibiting similar behavior and power generation performance at low excitation levels (e.g. less than 0.1g) can have totally different strength-imposed performance limitations under high excitations (e.g. above 1g). Nonlinear modeling and strength-based design is necessary for such excitation levels especially when using resonant cantilevers with no geometric constraint.

An electrostatic energy harvesting device is presented that is built up like a film capacitor consisting of PVDF films as electret material. By using separated Aluminum foils as electrodes, the distance between PVDF film and Aluminum foil can be changed by compressive forces if the device is just loosely wound. The change of the distance in addition to the polarized PVDF film acts like an electrostatic generator. One challenge in the design of the device is to ensure a controllable change of distance between PVDF film and Aluminum foil if the device is stressed mechanically. One possibility is the change of parameters of the winding process to generate certain pretensions of the films. Main disadvantage of this method is the difficulty to produce devices with constant properties. A potential solution for this problem is to fold the device in a special way. The advantage of the fold is that the distance of the electrodes changes in a more controlled and uniform way, if it is pushed and pulled. The device was modeled analytically to find the optimum configurations for different constrains. The results found in the simulation have been evaluated experimentally, too.

In this paper, a piezoelectric energy harvesting device consisting of a proof mass and a corrugated cantilever beam is proposed in order to enhance its performance (i.e., an increase in output voltage as well as a reduction in resonant frequency). The sinusoidal or trapezoidal shape of a cantilever beam is able to make the bonding area of piezoelectric materials (e.g., polyvinylidene fluoride (PVDF) film) much larger, resulting in higher output voltages. Moreover, the natural frequency of the device can be significantly decreased due to low flexural rigidity of the beam member. This lownatural frequency device would fit well for civil engineering applications because most civil structures such as bridges and buildings have low natural frequencies. In order to examine the geometrical characteristics of the proposed device, an analytical development and a numerical simulation are carried out. Besides, shaking table tests are conducted with a prototype of energy harvesting device. It is demonstrated from numerical and experimental studies that the proposed energy harvester can shift down its resonant frequency considerably and generate much higher output power as compared with a conventional one having a flat (or straight) cantilever beam.

Negative capacitance shunt damping is an effective broadband method for attenuating flexural vibration. However, proper selection of the location of the piezoelectric patches on a structure to maximize reduction has been an ongoing question in the field. Acoustic black holes are a recently developed concept to reduce vibrations on thin vibrating structures. By engineering the geometric or material properties of these thin structures, it is possible to minimize the reflected wave by gradually reducing the wave speed. However, the flexural wave speed cannot be reduced to zero on a realized structure. Therefore, when acoustic black holes are implemented, some of the incident wave energy is reflected because the wave speed must be truncated. Similarly due to the reduction in wave speed, the transverse velocity significantly increases within the acoustic black hole. It is therefore possible to add piezoelectric transducers to acoustic black hole regions on a structure to utilize negative capacitance shunt damping to address both of these issues. Consequently, the transducers are placed in the locations where the greatest control can be made and the reflected waves can be attenuated. The combination of negative capacitance shunt damping with acoustic black holes shows increased suppression of vibration over shunt damping alone.

The present work considers the optimal placement of piezoelectric actuators on a thin plate using integer coded genetic algorithm. The fitness function reflects on the controllability index which is the singular values decomposition of a control matrix. The index measures the input energy required to achieve the desired structural control using piezoelectric actuators. The LQR (Linear Quadratic Regulator) optimal control scheme has been applied to study the control effectiveness. It is observed that the frequency responses of cantilever obtained from finite element code hold good in agreement with the experimental results. Numerical simulations revealed that optimal locations obtained by integer coded GA based on controllability index with LQR controller offers effective control as compared non-optimal locations.

Atomic Force Microscopy (AFM) uses a scanning process performed by a microcantilever beam to create a three dimensional image of a nano-scale physical surface. AFM includes a microcantilever probe with a tip at the end that is controlled in order to keep the force between the tip and the surface constant by changing the distance of the microcantilever from the surface. Some microcantilevers have a layer of piezoelectric material on one side of the microcantilever for actuation purpose. An accurate understanding of the microcantilever motion and tip-sample force is needed to generate accurate imaging. In this paper, the equations of motion for an AFM piezoelectric microcantilever probe are derived for a nonlinear contact force. The analytical expressions for natural frequencies and mode shapes are determined. Then, the analytical frequency response of the piezoelectric probe is found using the method of multiple scales. The effects of nonlinear excitation force on the microcantilever probe’s frequency and amplitude have been analytically studied. The force nonlinearities lead to a frequency shift in the response. Accurately modeling this frequency shift during contact mode of the AFM probe is a significant consideration for the generation of more accurate imaging.

Structural assemblies incorporating negative stiffness elements have been shown to provide both tunable damping properties and simultaneous high stiffness and damping over prescribed displacement regions. In this paper we explore the design space for negative stiffness based assemblies using analytical modeling combined with finite element analysis. A simplified spring model demonstrates the effects of element stiffness, geometry, and preloads on the damping and stiffness performance. Simplified analytical models were validated for realistic structural implementations through finite element analysis. A series of complementary experiments was conducted to compare with modeling and determine the effects of each element on the system response. The measured damping performance follows the theoretical predictions obtained by analytical modeling. We applied these concepts to a novel sandwich core structure that exhibited combined stiffness and damping properties 8 times greater than existing foam core technologies.

This paper presents the design, modeling and experimental analysis of an amplified footstep energy harvester. With the unique design of amplified piezoelectric stack harvester the kinetic energy generated by footsteps can be effectively captured and converted into usable DC power that could potentially be used to power many electric devices, such as smart phones, sensors, monitoring cameras, etc. This doormat-like energy harvester can be used in crowded places such as train stations, malls, concerts, airport escalator/elevator/stairs entrances, or anywhere large group of people walk. The harvested energy provides an alternative renewable green power to replace power requirement from grids, which run on highly polluting and global-warming-inducing fossil fuels. In this paper, two modeling approaches are compared to calculate power output. The first method is derived from the single degree of freedom (SDOF) constitutive equations, and then a correction factor is applied onto the resulting electromechanically coupled equations of motion. The second approach is to derive the coupled equations of motion with Hamilton’s principle and the constitutive equations, and then formulate it with the finite element method (FEM). Experimental testing results are presented to validate modeling approaches. Simulation results from both approaches agree very well with experimental results where percentage errors are 2.09% for FEM and 4.31% for SDOF.

This work focuses on investigating the effects of thermal cycles in the impedance-based damage detection performance of Macro-Fiber Composites (MFC). A host structure with an MFC bonded to its surface is submitted to a 90 minutes temperature cycle that varies from -20°C to 65° C. After each cycle the electrical impedance of the test sample is measured with and without the presence of a representative damage (an added mass). The results indicate that the thermal cycling affects the smart device by changing its impedance profile, a phenomenon that should be taken into account in damage detection algorithms.

In this paper, a damage detection method based on a combination of wavelet analysis and an interval type-2 fuzzy logic system (IT-2FLS) is proposed. Firstly, synthesizing IT-2FLSs as a data-driven model is proposed. The structure is then divided into elements and excited to be vibrated to measure vibration signal. Average quantity signal of wavelet transform coefficient (AQWTC) of vibration signal with a used-scale-sheet is established. The IT-2FLS is utilized to identify the structure at its undamaged time via AQWTC signal. At each surveying time, AQWTC at each element is calculated to estimate difference of corresponding AQWTCs between two cases: undamaged status and the status at the checked time. By applying the AQWTC’s contrast at two these times, a damage coefficient is described which is used to estimate status of the structure. Besides, in order to predict structure’s status, the time-series prediction using the IT-2FLS and the calculated damage coefficient are also presented. The effectiveness of the proposed method is demonstrated by experiment via data sources measured from dynamic response of a real structure.

In this paper we present a prototype using a dry ionic polymer metal composite (IPMC) in interactive personal devices such as bracelet, necklace, pocket key chain or mobile devices for haptic interaction when audio or visual feedback is not possible or practical. This prototype interface is an electro-mechanical system that realizes a shape-changing haptic display for information communication. A dry IPMC will change its dimensions due to the electrostatic effect when an electrical potential is provided to them. The IPMC can operate at a lower voltage (less than 2.5V) which is compatible with requirements for personal electrical devices or mobile devices. The prototype consists of the addressable arrays of the IPMCs with different dimensions which are deformable to different shapes with proper handling or customization. 3D printing technology will be used to form supporting parts. Microcontrollers (about 3cm square) from DigiKey will be imbedded into this personal device. An Android based mobile APP will be developed to talk with microcontrollers to control IPMCs. When personal devices receive information signals, the original shape of the prototype will change to another shape related to the specific sender or types of information sources. This interactive prototype can simultaneously realize multiple methods for conveying haptic information such as dimension, force, and texture due to the flexible array design. We conduct several studies of user experience to explore how users’ respond to shape change information.

The last two decades have seen evolution of smart materials and structures technologies from theoretical concepts to physical realization in many engineering fields. These include smart sensors and actuators, active damping and vibration control, biomimetics, and structural health monitoring. Recently, additive manufacturing technologies such as 3D printing and printed electronics have received attention as methods to produce 3D objects or electronic components for prototyping or distributed manufacturing purposes. In this paper, the viability of manufacturing all-printed smart structures, with embedded sensors and actuators, will be investigated. To this end, the current 3D printing and printed electronics technologies will be reviewed first. Then, the plausibility of combining these two different additive manufacturing technologies to create all-printed smart structures will be discussed. Potential applications for this type of all-printed smart structures include most of the traditional smart structures where sensors and actuators are embedded or bonded to the structures to measure structural response and cause desired static and dynamic changes in the structure.

Magnetostrictive iron-gallium alloys, known as Galfenol, are a recent class of smart materials with potential in energy harvesting applications. Unimorph energy harvesters consisting of a Galfenol beam bonded to a passive substrate are simple and effective, but advanced models are lacking for these smart devices. This study presents a finite element model for Galfenol unimorph harvester systems. Experiments considering various design parameters such as pick up coil size, load resistance, beam thickness ratio, and bias magnetic field strength are conducted to guide and validate the modeling effort. If the free length of the Galfenol unimorph beam is considered as the effective length, the maximum average power density, peak power density, and open-circuit voltage amplitude achieved in experiments are 13.97 mW/cm³, 35.51 mW/cm³, and 0.66 V, respectively. By only considering the length of Galfenol surrounded by the pickup coil, the maximum average power density and peak power density are 23.66 mW/cm³ and 60.14 mW/cm³, respectively.

The use of cantilevered piezoelectric bimorphs under transversal excitations is an area of research well reported in literature. These devices may be tapered into triangular geometries in order to enhance axial strain over the surfaces of the device for more reliable operation. This study reports the comparison of rectangular and triangular cantilevered bimorphs of equal volume and matching resonance frequency, where it is seen that tapering geometry enhances the electromechanical coupling coefficient, which may not necessarily be the only parameter involved in enhancing power output. This is indicated in the case of a triangular cantilevered device without a proof mass, which with increased coupling is unable to outperform a rectangular device. The addition of a nominal proof mass on a rectangular and triangular device increases not only the electromechanical coupling coefficient, but also increases the damping ratio in the devices. This effect is more pronounced in the case of triangular bimorphs, and a 40% improvement in power output is seen. Therefore, these studies provides insights into the changing parameters with changing shapes, which may provide better optimization parameters for improving piezoelectric energy harvesting from cantilevered devices.

In our previous studies, multiple piezoelectric cantilever plates were placed inside a quarter-wavelength straight tube resonator to harvest low frequency acoustic energy. To investigate the modification of eigenmodes in the tube resonator due to the presence of piezoelectric plates, the eigenfrequency shift properties by introducing single and multiple rectangular blockages in open-closed ducts are studied by using 1D segmented Helmholtz equations, Webster horn equation, and finite element simulations. The first-mode eigenfrequency of the duct is reduced when the blockage is placed near the open inlet. The decrease of eigenfrequency leads to the enhancement of absorbed acoustic power in the duct. Furthermore, the first half of the tube resonator possesses high pressure gradient resulting in larger driving forces for the vibration motion of piezoelectric plates. Therefore, in our harvesters, it is better to place the piezoelectric plates in the first half of the tube resonator to obtain high output voltage and power.

A two-dimensional array of piezoelectric transducer (PZT) shunted on negative capacitance circuit is designed and applied to achieve broadband vibration reduction of a flexible plate over tunable frequency bands. Each surface-bonded patch is connected to a single independent negative capacitance synthetic circuit. A finite element-based design methodology is used to predict and optimize the attenuation properties of the smart structure. The predictions are then experimentally validated by measuring the harmonic response of the plate and evaluating some derived quantity such as the loss factor and the kinetic energy ratio. The validated model is finally used to explore different configurations with the aim of defining some useful design criteria.

An experimental investigation is carried out on a system consisting of a primary structure coupled with a passive/active autoparametric vibration absorber. The primary structure consists of a building-like mechanical structure, it has three rigid floors connected by flexible columns made from aluminium strips, while the absorber consists of a cantilever beam with a PZT patch actuator actively controlled through an acquisition card. The whole system, which is a coupled non-linear oscillator, is subjected to sinusoidal excitation obtained from an electromechanical shaker in the neighborhood of internal resonances. The natural frequency of the absorber is tuned to be one-half of any of the natural frequencies of the main system. With the addition of a PZT actuator, the autoparametric vibration absorber is made active, thus enabling the possibility to control the effective stiffness associated to the passive absorber and, as a consequence, the implementation of an active vibration control scheme able to preserve, as possible, the autoparametric interaction as well as to compensate varying excitation frequencies. This active vibration absorber employs feedback information from an accelerometer on the primary structure, an accelerometer on the tip of the beam absorber and a strain gage on the base of the beam, feedforward information from the excitation force and on-line computations from the nonlinear approximate frequency response, parameterized in terms of a proportional gain provided by a voltage input to the PZT actuator, thus providing a mechanism to asymptotically track an optimal, robust and stable attenuation solution on the primary system.

Buckling of axially loaded beam-columns represents a critical design constraint for light-weight structures. Besides passive solutions to increase the critical buckling load, active buckling control provides a possibility to stabilize slender elements in structures. So far, buckling control by active forces or bending moments has been mostly investigated for beam-columns with rectangular cross-section and with a preferred direction of buckling. The proposed approach investigates active buckling control of a beam-column with circular solid cross-section which is fixed at its base and pinned at its upper end. Three controlled active lateral forces are applied near the fixed base with angles of 120° to each other to stabilize the beam-column and allow higher critical axial loads. The beam-column is subject to supercritical static axial loads and lateral disturbance forces with varying directions and offsets. Two independent modal state space systems are derived for the bending planes in the lateral y- and z-directions of the circular cross-section. These are used to design two linear-quadratic regulators (LQR) that determine the necessary control forces which are transformed into the directions of the active lateral forces. The system behavior is simulated with a finite element model using one-dimensional beam elements with six degrees of freedom at each node. With the implemented control, it is possible to actively stabilize a beam-column with circular cross-section in arbitrary buckling direction for axial loads significantly above the critical axial buckling load.

Any piezoelectric generator structure can be modeled close to its resonance by an equivalent circuit derived from the well known Mason equivalent circuit. This equivalent circuit can therefore be used in order to optimize the harvested power using usual electrical impedance matching. The objective of this paper is to illustrate the full process leading to the definition of the proper passive load allowing the optimization of the harvested energy of any harvesting device. First, the electric equivalent circuit of the generator is derived from the Mason equivalent circuit of a seismic harvester. Theoretical ideal impedance matching and optimal load analyze is then given emphasizing the fact that for a given acceleration a constant optimal output power is achievable for any frequency as long as the optimal load is feasible. Identification of the equivalent circuit of an experimental seismic harvester is then derived and matched impedance is defined both theoretically and experimentally. Results demonstrate that an optimal load can always be obtained and that the corresponding output power is constant. However, it is very sensitive to this impedance, and that even if impedance matching is a longtime well known technique, it is not really experimentally and practically achievable.

Non-linear behavior is present in many mechanical systems operating conditions. In these cases, to improve the vibration control performances achievable with the linearization of the equations of motion, it is possible to design the control system on a set of linearized models (operating conditions) and to apply the gain-scheduling, increasing the system stability too. More recently new control logics are applied to the systems in non-linear form. This paper presents a nonlinear sliding-mode control and compares it to the linearized approaches. A boom formed by three flexible segments and actuated by three electrical motors is chosen to numerically test the proposed logics..

Concentrating solar energy and transforming it into electricity is clean, economical and renewable. One design of solar power plants consists of an array of heliostats which redirects sunlight to a fixed receiver tower and the generated heat is converted into electricity. Currently, the angles of elevation of heliostats are controlled by motors and drives that are costly and require diverting power that can otherwise be used for producing electricity. We consider replacing the motor and drive system of the heliostat with a photosensitive polymer design that can tilt the mirror using the ability of the polymer to deform when subjected to light. The light causes the underlying molecular structure to change and subsequently, the polymer deforms. The deformation of the polymer is quantified in terms of photostrictive constitutive relations. A mathematical model is derived governing the behaviour of the angle of elevation as the photostrain varies. Photostrain depends on the composition of the polymer, intensity and temperature of light and angle of light polarization. Preliminary findings show a photomechanical rod structural design can provide 60° elevation for temperatures of about 40°C. A photomechanical beam structural design can generate more tilt at lower temperatures. The mathematical analysis illustrates that photostrains on the order of 1% to 10% are desired for both rod and beam designs to produce sufficient tilt under most heliostat field conditions.

A novel flow-mode magneto-rheological (MR) engine mount integrated a diaphragm de-coupler and the spoiler plate is designed and developed to isolate engine and the transmission from the chassis in a wide frequency range and overcome the stiffness in high frequency. A lumped parameter model of the MR engine mount in single degree of freedom system is further developed based on bond graph method to predict the performance of the MR engine mount accurately. The optimization mathematical model is established to minimize the total of force transmissibility over several frequency ranges addressed. In this mathematical model, the lumped parameters are considered as design variables. The maximum of force transmissibility and the corresponding frequency in low frequency range as well as individual lumped parameter are limited as constraints. The multiple interval sensitivity analysis method is developed to select the optimized variables and improve the efficiency of optimization process. An improved non-dominated sorting genetic algorithm (NSGA-II) is used to solve the multi-objective optimization problem. The synthesized distance between the individual in Pareto set and the individual in possible set in engineering is defined and calculated. A set of real design parameters is thus obtained by the internal relationship between the optimal lumped parameters and practical design parameters for the MR engine mount. The program flowchart for the improved non-dominated sorting genetic algorithm (NSGA-II) is given. The obtained results demonstrate the effectiveness of the proposed optimization approach in minimizing the total of force transmissibility over several frequency ranges addressed.

In this work, magnetorheological (MR) based haptic master for robot-assisted minimally invasive surgery (RMIS) is proposed and analyzed. Using a controllable MR fluid, the masters can generate a reflection force with the 4-DOF motion. The proposed master consists of two actuators: MR clutch featuring gimbal mechanism for 2-DOF rotational motion (X and Y axes) and MR clutch attached at gripper of gimbal structures for 1-DOF rotational motion (Z axis) and 1-DOF translational motion. After analyzing the dynamic motion by integrating mechanical and physical properties of the actuators, torque model of the proposed haptic master is derived. For realization of master-slave system, an encoder which can measure position information is integrated with the MR haptic master. In the RMIS system, the measured position is converted as a command signal and sent to the slave robot. In this work, slave and organ of patient are modeled in virtual space. In order to embody a human organ into virtual space, a volumetric deformable object is mathematically formulated by a shape retaining chain linked (S-chain) model. Accordingly, the haptic architecture is established by incorporating the virtual slave with the master device in which the reflection force and desired position originated from the object of the virtual slave and operator of the master, respectively, are transferred to each other. In order to achieve the desired force trajectories, a proportional-integral-derivative (PID) controller is designed and implemented. It has been demonstrated that the effective tracking control performance for the desired motion of reflection force is well presented in time domain.

High rotational speeds for brakes and clutches based on magnetorheological fluids represent a remaining challenge for the industrial or automotive application. Beside particle centrifugation effects and rotational speed-depending no-load losses, the torque characteristic is an important property that needs to considered in the design process of actuators. Due to missing experimental data for these operating conditions, in this paper the shear rate and flux depending yield stress behavior of magnetorheological uids is experimentally investigated for high rotational speeds or respectively high shear rates. Therefore a brake actuator with variable shear gap heights up to 4 mm is designed, realized and used for the experimental investigation, which are performed for a maximum shear rate of ƴ= 34; 000 s^-1 under large magnetic elds. The measurement results point out a strong dependency between shear rate, magnetic ux density and resulting yield stress. For low shear gap heights, a significant reduction in the yield stress up to 10 % can be determined. Additionally the development of Taylor vortices is determined, which will not only occur in viscous case without an applied magnetic field. The measurement results are important for a reliable actuator design which should be used in application with high rotational speeds.

The goal of this study is to understand the mechanics of a flexible magnetically-controllable fluid transport system. A two-dimensional time-dependent model using a coupled fluid-solid and magnetic model is developed. The flow of fluids through sinusoidal wall is modeled, numerically analyzed and compared with an analytical solution, for the passive case (i.e., zero applied magnetic field). The modeling and analysis are extended to include a magnetic field that is applied to the wall of the flexible tube in order to produce the one-way forward movement of the fluid. Results demonstrate the fluid transportation capabilities of the one-way transport system.

Current knee designs for prosthetic legs rely on electric motors for both moving and stationary states. The electric motors draw an especially high level of current to sustain a fixed position. The advantage of using magnetorheological (MR) fluid is that it requires less current and can have a variable braking torque. Besides, the proposed prosthetic leg is actuated by NiTinol wire, a popular shape memory alloy (SMA). The incorporation of NiTinol gives the leg more realistic weight distribution with appropriate arrangement of the batteries and wires. The prosthesis in this research was designed with MR brake as stopping component and SMA wire network as actuating component at the knee. The MR brake was designed with novel non-circular shape for the rotor that improved the braking torque while minimizing the power consumption. The design also helped simplify the control of braking process. The SMA wire network was design so that the knee motion was actively rotated in both directions. The SMA wires were arranged and played very similar role as the leg’s muscles. The study started with the overall solid design of the knee including both MR and SMA parts. Theoretical models were derived and programmed in Simulink for both components. The simulation was capable of predicting the power required for moving the leg or hold it in a fixed position for a certain amount of time. Subsequently, the design was prototyped and tested to validate the theoretical prediction. The theoretical models were updated accordingly to correlate with the experimental data.

In this research, a new method to control speed of DC motor using magnetorheological (MR) clutch is proposed and realized. Firstly, the strategy of a DC motor speed control using MR clutch is proposed. The MR clutch configuration is then proposed and analyzed based on Bingham-plastic rheological model of MR fluid. An optimal designed of the MR clutch is then studied to find out the optimal geometric dimensions of the clutch that can transform a required torque with minimum mass. A prototype of the optimized MR clutch is then manufactured and its performance characteristics are experimentally investigated. A DC motor speed control system featuring the optimized MR clutch is designed and manufactured. A PID controller is then designed to control the output speed of the system. In order to evaluate the effectiveness of the proposed DC motor speed control system, experimental results of the system such as speed tracking performance are obtained and presented with discussions.

This research work focuses on optimal design of a high frequency jetting dispenser actuated by two piezoactuators. Firstly, a new configuration of the high frequency jetting dispenser for integrated circuits (ICs) fabricating is proposed. The optimal design of the jetting dispenser is then considered. In the optimal design, significant parts of the jetting dispenser such as the needle, the nozzle, the piezoactuators, the displacement amplification lever and return spring are considered. Firstly, the geometry of the nozzle and needle is optimally designed considering the maximum velocity of dispensed adhesive. The other significant parts of the jetting dispenser such as the piezoactuators, return springs and the amplifying lever are designed so that the jetting dispenser has a compact size and can work well at 1000Hz. In addition, the amplitude of needle motion can reach up to 0.3mm.

In torsionally coupled buildings, the total response of the structure is the result of the translational displacement of the story's center of stiffness and the displacement due to the roof's rotation. In structures with high eccentricity, the effect of the floor’s rotation in the total response is considerable. The order of vibration modes is another important parameter that changes the contribution of the different translational and rotational modes in the total response. To explore the effects of eccentricity and the order of vibration modes on the total response, a number of 3-D steel moment-resistant frames with 4, 8, and 12 stories, with different eccentricities and plans, were considered. The structures were subjected to bidirectional seismic inputs so that their peak ground accelerations were scaled to 0.4g, 0.6g, and 0.8g. Increasing the eccentricity of the structure increases the participation of rotation in the total response. Furthermore, in torsionally flexible structures, where the first or second mode of vibration is a torsional mode, the contribution of the floor’s rotation can be even greater. In some cases, the displacement of exterior columns is primarily the result of the floor's rotation. This suggests that to efficiently dampen the seismic displacement of such structures, the rotational mode of the building should be controlled.

This paper is concerned with a six-degree-of-freedom active vibration isolation system using voice coil actuators with absolute velocity feedback control for highly sensitive measurement equipment, e.g. atomic force microscopes, suffering from building vibration. The main differences between this type of system and traditional isolator, is that there are no isolator resonance. The absolute vibration velocity signal acquired from an accelerator and being processed through an integrator is input to the controller as a feedback signal, and the controller output signal drives the voice coil actuator to produce a sky-hook damper force. In practice, the phase response of integrator at low frequency such as 2~6 Hz deviate from the 90 degree which is the exact phase difference between the vibration velocity and acceleration. Therefore, an adaptive filter is used to compensate the phase error in this paper. An analysis of this active vibration isolation system is presented, and model predictions are compared to experimental results. The results show that the proposed method significantly reduces transmissibility at resonance without the penalty of increased transmissibility at higher frequencies.

An alternative switching technique for piezoelectric energy harvesting is presented. The energy harvester based on piezoelectric elements is a promising method to scavenge ambient energy. Several non-linear techniques such as SSHI have been implemented to improve the global harvested energy. However, these techniques are sensitive to load and should be tuned to obtain optimal power output. This technique, called Series Synchronized Switch Harvesting (S3H), has both the advantage of easy implementation and independence of the harvested power with the load impedance. The harvesting circuit simply consists of a switch in series with the piezoelement and the load. The switch is nearly always open and is triggered-on each time the piezoelectric voltage reaches an extremum. It is opened back after an arbitrary on-time t₀. The energy scavenging process happens when switch is closed. Based on linear motion assumption, the harvester structure is modeled as a “Mass-Spring-Damper” system. The analysis of S3H technique is considered with harmonic excitation. An analytical model of S3H is presented and discussed. The main advantage of this approach compared with the usual standard technique is that the extracted power is independent of the load within a wide range of load impedance, and that the useful impedance range is simply related to the defined switch on-time. For constant displacement excitation condition, the optimal power output is more than twice the power extracted by the standard technique as long as the on-time interval is small comparatively with the vibration period. For constant force excitation, an optimal on-time can be defined resulting in an optimally wide load bandwidth. Keywords: piezoelectric; energy harvesting; non-linear harvesting techniques; switching techniques.

The paper discusses the opportunity to use piezoelectric actuators (PZT) and Fiber Bragg Grating sensors (FBGs) to realize a smart structure including in itself both the sensing and the actuating devices. Different control strategies have been implemented on a test rig consisting on a plate made of carbon fiber using two chains with 15 FBG sensors each and 6 PZT actuators. Control forces are designed to increase the damping of the structures, allowing to increase of damping of the first modes of vibration of about 10 times.

This study proposes a passive control device based on superelastic behavior of shape memory alloys (SMAs) and investigates the device performance for improving response of steel frame structures subjected to multi-level seismic hazards. The device, named as Superelastic Viscous Damper (SVD), exhibits both re-centering and energy-dissipating capabilities and consists of SMA elements and a viscoelastic (VE) damper. SMA elements are mainly used as recentering unit and the viscoelastic damper is employed as energy dissipation unit. The VE damper consists of two layers of VE material bonded with three steel plates. Energy is dissipated through the shear deformation of VE material. Each SMA element forms a continuous loop; wrapping the loops around the outer two plates improves compactness and efficiency. An analytical model of a three-story benchmark steel building with the installed SVDs is developed to determine the response of the structure under a ground motion input. A neuro-fuzzy model is used to capture nonlinear behavior of the SMA elements of the SVD. Nonlinear response history analyses are conducted at MCE level seismic hazard. A suite of 22 ground motion records is employed in dynamic analysis. Peak interstory drift, peak absolute floor acceleration, and residual story drift are selected as the primary demand parameters. Results shows that SVDs can effectively mitigate dynamic response of steel frame structures under strong ground motions and enhance their post-earthquake functionality.

The vibration control plays an important role in energy harvesting systems. Compared to the active control, semi-active control is a more preferred alternative for practical use. Many different semi-active control strategies have been developed, among which LQ-clip, Skyhook and model predictive control are the most popular strategies in literatures. In this paper, a different control strategy that designs semi-active controller via LMI approach is proposed. Different from clipping the control input after controller construction like most existing control methods, the proposed method fulfills the semi-active control input feasibility constraints before the controller construction. The methodology is developed through LMI approach which leads to a stabilizing linear controller to ensure semi-active constraint and the pre-designed performance. An illustrative example, vibration control system of a tall building, is presented to show the efficiency of the method and validate the new approach.

The theoretical analysis and the prototype testing of the integrated relative displacement self-sensing magnetorheological damper (IRDSMRD) indicate that the controllable damping force performance and the relative displacement sensing performance influence each other for varying applied currents. Aiming at verifying the feasibility and capability of the IRDSMRD to constitute semi-active shock and vibration control systems, this study presents a single-degree-of-freedom (SDOF) shock and vibration control system based on the IRDSMRD. The mathematical model of the IRDSMRD, including the control damping force and the linearity of the integrated relative displacement sensor (IRDS), is established, and the governing equation for the SDOF system based on the IRDSMRD is derived. A skyhook control algorithm is utilized to improve the shock and vibration control performance of the SDOF semi-active control systems. The simulated control performances of the SDOF systems individually using the IRDSMRD without any extra-set dynamic sensor, the conventional MR damper with a linear variable differential transformer (LVDT), and the passive damper, under shock loads due to vertical pulses (the maximum initial velocity is as high as 10 m/s), and sinusoidal vibrations with a frequency range of 0-25 Hz, are evaluated, compared, and analyzed.

A new method for the real-time identification of mechanical system modal parameters is used in order to design different adaptive control logics aiming to reduce the vibrations in a carbon fiber plate smart structure. It is instrumented with three piezoelectric actuators, three accelerometers and three strain gauges. The real-time identification is based on a recursive subspace tracking algorithm whose outputs are elaborated by an ARMA model. A statistical approach is finally applied to choose the modal parameter correct values. These are given in input to model-based control logics such as a gain scheduling and an adaptive LQR control.

The phenomenon of fluid-induced instability existing in fluid-film bearing systems has been coped with for long time. The study aims to soothe and even eliminate the occurrence of whirl in rotary machinery by increasing the threshold of instability through the anti-swirl injection using an optimal control based linear quadratic regulator. An acceptance region was established in order to decide starting up the control process. Some case studies were carried out to illustrate the effectiveness of the control scheme. The research results present that a simple control method incorporating with an acceptance region enables to avoid the fluid induced instability flexibly in rotary machinery. Moreover, the developed techniques can also be applied in other fluid-induced instability problems such as whip and rub, etc.

The traditional envelope analysis is an effective method for the fault detection of rolling bearings. However, all the resonant frequency bands must be examined during the bearing-fault detection process. To handle the above deficiency, this paper proposes using the empirical mode decomposition (EMD) to select a proper intrinsic mode function (IMF) for the subsequent detection tools; here both envelope analysis and cepstrum analysis are employed and compared. By virtue of the band-pass filtering nature of EMD, the resonant frequency bands of structure to be measured are captured in the IMFs. As impulses arising from rolling elements striking bearing faults modulate with structure resonance, proper IMFs potentially enable to characterize fault signatures. In the study, faulty ball bearings are used to justify the proposed method, and comparisons with the traditional envelope analysis are made. Post the use of IMFs highlighting faultybearing features, the performance of using envelope analysis and cepstrum analysis to single out bearing faults is objectively compared and addressed; it is noted that generally envelope analysis offers better performance.

This paper studies the stability problem for a piezoelectric shunt damping system with a simple negative capacitor circuit. A key issue is to consider perturbations of parasitic series and parallel-leakage resistances in a piezoelectric element. Then, it is a bit surprising that the perturbed system becomes unstable, in particular, due to the effect of the parasitic leakage resistance. This instability phenomenon is analytically proved based on the Routh-Hurwitz stability criterion and is also demonstrated by numerical simulations. This paper then illustrates robustification of a negative capacitor circuit by inserting a negative resistance in parallel with the negative capacitor in the simple negative capacitor circuit. This robustification is also demonstrated by a numerical simulation.

Wing morphing is one of the emerging methodology towards improving aerodynamic efficiency of flight vehicle structures. In this paper a morphing structural element is designed and studied which has its origin in the well known chiral structures. The new aspect of design and functionality explored in this paper is that the chiral cell is actuated using thermal Shape Memory Alloy (SMA) actuator wires to provide directional motion. Such structure utilizes the potential of different actuations concepts based on actuator embedded in the chiral structure skin. This paper describes a new class of chiral cell structure with integrated SMA wire for actuation. Chiral topological constructs are obtained by considering passive and active load path decoupling and sub-optimal shape changes. Single cell of chiral honeycomb with actuators are analyzed using finite element simulation results and experiments. To this end, a multi-cell plan-form is characterized showing interesting possibilities in structural morphing applications. The applicability of the developed chiral cell to flexible wing skin, variable stiffness based design and controlling longitudinal-to-transverse stiffness ratio are discussed.

It has been hypothesized that Europa, one of the moons of Jupiter, has a large ocean underneath a thick layer of ice. In order to determine whether life exists, it has been proposed that an underwater glider (hydrobot) capable of propulsion could be sent to explore the vast ocean. In this research, we considered various smart materials to create a propulsion device inspired by dolphin tails. Dolphins are highly efficient and excellent gliders, which makes them the ideal candidate for ocean exploration. In order to select the best dolphin species, we began by reviewing literature and then utilized the Analytical Hierarchy Process (AHP) to compare the different species. Lagenorhynchus obliquidens (Pacific White-Sided Dolphin) was found to be the best choice for creating a bioinspired hydrobot. We then conducted literature review of various smart materials and using this knowledge constructed a hydrobot tail prototype. This prototype demonstrates that smart materials can be fashioned into suitable actuators to control a tail fashioned after a dolphin.

Bimolecular unit cells have recently become a focus for biologically-inspired smart materials. This is largely due their ability to exhibit many of the same properties as the natural cell membrane. In this study, two lipid monolayers formed at a water/oil interface are brought together, creating a lipid bilayer at their interface with each droplet containing a different concentration of ions. This ionic concentration gradient leads to the development of a membrane potential across the bilayer as ions begin to passively diffuse across the membrane at varying rates, providing the proof of concept for energy storage through cellular mechanics. The focus of the study is to determine the influence of osmotic pressure on the lifespan of the lipid bilayer. We hypothesize that the greater osmotic pressure that develops from a greater ionic concentration gradient will prove to have a negative impact on the lifespan of the bilayer membrane, causing it to rupture sooner. This is due to the substantial amount of osmotic swelling that will occur to compensate for the ionic concentration gradient. This study will demonstrate how osmotic pressure will continue to be a limiting factor in the effectiveness and stability of cellularly-inspired energy relevant materials.

A novel “dynamic ligament” smart material that exhibits a strongly rate-dependent response in extension is developed and characterized. The devices, based on elastomeric polymers and shear thickening fluids, exhibit low resistance to extension at rates below 10 mm/s, but when stretched at 100 mm/s or higher resist with up to 7 × higher force. A link between the shear thickening fluid’s rheology and the dynamic ligament’s tensile performance is presented to explain the rate-dependent response. Future recommendations for improving device performance are presented, along with a host of different potential application areas including safety equipment, adaptive braces, sporting goods, and military equipment.

This study presents the possibility of dissipating mechanical energy with a proof-of-concept prototype magnetostrictive based shunt circuit using passive electrical components. The device consists of a polycrystalline galfenol (Fe-Ga alloy) strip bonded to a brass cantilever beam. Two brass pieces, each containing a permanent magnet, are used to mass load each end of the beam and to provide a magnetic bias field through the galfenol strip. The voltage induced in an induction coil closely wound around the cantilever beam captures the time rate of change of magnetic flux within the galfenol strip as the beam vibrates. The first bending-mode resonant frequency of the device was 69.42 Hz. To dissipate the electrical voltage from the device, a shunt circuit is attached. The effective mechanical impedance for the magnetostrictive shunt circuit is derived. The shunted model is specialized for two shunt circuits: the case of a resistor and that of a capacitance. The experimental results for both the resistive and capacitance shunt circuits validate the shunted magnetostrictive damping model for couple of cased of resistance and capacitance.