This article presents an implementation of a miniature energy harvester (weighing 0.292 grams) on an insect (hawkmoth Manduca sexta) in un-tethered flight. The harvester utilizes a piezoelectric transducer which converts the vibratory motion induced by the insect's flight into electrical power (generating up to 59 μW_RMS). By attaching a low-power management circuit (weighing 0.200 grams) to the energy harvester and accumulating the converted energy onboard the flying insect, we are able to visually demonstrate pulsed power delivery (averaging 196 mW) by intermittently flashing a light emitting diode. This self-recharging system offers biologists a new means for powering onboard electronics used to study small flying animals. Using this approach, the lifetime of the electronics would be limited only by the lifetime of the individuals, a vast improvement over current methods.

Linear and nonlinear piezoelectric devices are introduced to continuously recharge the batteries of the pacemakers by converting the vibrations from the heartbeats to electrical energy. The power requirement of the pacemakers is very low. At the same time, after about 10 years from the original implantation of the pacemakers, patients have to go through another surgical operation just to replace the batteries of their pacemakers. We investigate using vibration energy harvesters to significantly increase the battery life of the pace makers. The major source of vibrations in chest area is due to heartbeats. Linear low frequency and nonlinear mono-stable and bi-stable energy harvesters are designed according to especial signature of heart vibrations. The proposed energy harvesters are robust to variations of heart beat frequency and can meet the power requirement of the pacemakers.

A novel energy harvester based around capturing the motion of trees has been built and tested. The device consists of an electromagnetic generator located close to ground level, attached via an inelastic cord to a point on the trunk of a 5-6 meter tall eucalypt tree. The device uses the movement of the tree to drive the generator in one direction, rotationally, and a mass to keep the cord taught when the tree returns to its resting position. The electrical output is sent to electrical circuitry that rectifies, stores and switches the electrical power to supply a wireless sensor node. The initial configuration stored energy in a super-capacitor, the voltage of which indicates storage charge level. Once there was sufficient power to operate the sensor node it transmits local information such as temperature, and energy state, in terms of capacitor voltage, to a base node located approximately 80m away. Results show that there is sufficient energy in this method to power a wireless sensor node continuously in wind as low as 3-4m/s. In order to allow continuous operation in lower wind speeds a number of alterations have been investigated. These are reported here and include: operation with a secondary battery in place of the storage capacitor, increasing the electrical storage capacity and varying the connection point on the tree and the electronic duty cycle.

A system has been designed that will allow a network of sensor nodes to request power from a base node and receive it wirelessly. The system consists of a central transmitting node which can be powered from an indefinite power source or from a reliable source of energy harvesting such as solar. This energy is converted into UHF radio waves and transmitted to individual stationary or mobile nodes making up the remainder of the network. When a sensor node detects that its onboard power supply is at a critical level it will request a top up from the base station. The base station will scan through 360° for the sensor node and once located begins charging. The charging station will remain in this position until the sensor batteries are fully charged. At this point the base station will seek out another sensor node if required, or go into a standby mode. If a mobile node is moved out of the charging position or interference of the beam occurs this is indicated to the charging station and the transmitting node will scan again until another node is relocated. Results indicate that charging can be obtained within a radius of up to 1.5 meters or greater for a higher transmission power. The sensor positioning and power monitoring aspects of the system could be retained for a laser based system, which would increase the transmission range. The system has the advantage that if sufficient solar energy can be captured during the day, charging of the sensor nodes can be maintained over night allowing the battery size of each sensor node to be reduced significantly.

A novel idea of combining two kinds of electro-mechanical couplings to build Active Flutter Suppression (AFS) strategy for composite structures is presented. The commercially available MFC and a newly proposed shear actuated fiber composite (SAFC) are considered. MFC induces normal strains and SAFC can be made to couple the transverse shear strains. A four noded plate element is employed to build the clamped-free active laminated plate with four MFC and SAFC each. The stiffness, mass, actuator and sensor matrices are obtained from the electro-mechanical coupling analysis. The open loop flutter velocity is computed using the linear aerodynamic panel theory (DLM). Further, the structural and unsteady aerodynamic matrices are represented in state-space form to build the aero-servo-elastic plant. Presently, the unsteady aerodynamics is approximated using a rational polynomial approach. A Linear Quadratic Gaussian control is designed to perform the closed loop flutter calculations. The actuation authority is maintained same through applied control voltage, while evaluating the performance of MFC and SAFC. The results have significantly encouraged the concept of simultaneously targeting the normal and shear strains of aeroelastically excited modes through electromechanical couplings to build an efficient active flutter suppression system.

The use of surface bonded (MFC) and embedded (SAFC) piezoelectric composite actuators is examined through a numerical study. Modelling schemes are therefore developed by applying the isoparametric finite element approach to idealize normal strain to electric field and shear strain to electric field relations. A four noded coupled finite element is developed to compute the electro-mechanical responses of the active plate. A linear quadratic regulator is employed to perform the active vibration control studies. The system matrices of the smart plate structure are obtained and used in the state-space control model. Two elastic modes are considered, namely bending and torsion of the active plate. The emphasis is given to evaluate the performance of two different kinds of flexible piezoelectric actuators in vibration control application.

Limited degree-of-freedom (DOF) parallel kinematic mechanisms (PKM) are capable of high bandwidth tracking and disturbance rejection with smaller actuators than are required for serial machines. A high performance Nyquist-stable (NS) controller with nonlinear dynamic compensation (NDC) applied to a new PKM is presented. The Popov criterion is used to show absolute stability (AS) of the closed loop system and experimental evidence of closed loop performance is provided. This novel approach to PKM control provides 38 dB of disturbance rejection below 10 Hz, an order of magnitude more that what is achieved by implementing an absolutely stable fixed gain (ASFG) controller.

Variable stiffness fluidic flexible matrix composites (f²mc) are investigated for vibration isolation through analysis and experiments. The fluidic flexible matrix composites are novel structures that have been shown to achieve significant changes in stiffness through simple valve control. The objective of this research is to develop analysis tools to investigate the f²mc variable modulus system for semi-active vibration isolation and to validate the results through experiment. A nonlinear analytical model of an isolation mount based on the f²mc tube with a proportional valve is developed. Analysis results indicate that the f²mc based isolation mount is effective for reducing the force transmitted to the foundation. Simulation studies demonstrate that the transmissibility ratio can be tuned via a proportional valve, where the resonant frequencies and damping can be regulated. Experimental results agree with analysis results and validate semi-active vibration isolation using a proportional valve.

Piezoelectric membranes connected to negative capacitance circuits (NCC) are studied as a possible solution to damping acoustic loads. Two experiments are performed to test this theory. In the first experiment, a piezoelectric patch is stretched across an acoustic tube's cross section and connected to a NCC tuned to minimize the transmitted sound. Variable position microphones are used to measure sound pressure levels. The second experiment models a launch vehicle. Piezoelectric patches are used to enclose the inner payload chamber and isolate it from acoustic noise. Microphones are positioned both inside and outside the chamber to measure the noise reduction.

High frequency vibration in flexible structures may be represented by travelling waves. Such waves carry energy and may travel large distances before being dissipated. These waves can be suppressed by the attachment of localised supports such as dampers etc. These devices can be designed to absorb the energy of such waves but must be tuned to the frequency of the incident wave in order to perform optimally. The paper concerns an adaptive-passive support for suppressing waves. The properties of the support self-tune so that the device remains optimally tuned. The device consists of an electro-magnetic shunt damper, attached either at and end or at some intermediate point. An adaptive algorithm for tuning the damper based on the minimising the reflection and/or transmission coefficients is proposed, these being estimated from measured vibrations. Numerical results are presented. Experimental results for a tunable damper attached to an end of a beam are reported, with a variable resistor in the shunt damper allowing the support to adapt.

Shunted piezoelectric patches form an effective control mechanism for reducing vibrations of a mechanical system. One type of shunt, a negative capacitance circuit, is capable of suppressing vibration amplitude over a broad frequency range. Most previous work has focused on control of simple test structures such as beams and plates. This work studies the performance of the negative capacitance shunt connected to piezoelectric patches attached to a stiffened aircraft panel. The placement of the piezoelectric transducers is determined using a simplified finite element model of one bay of the panel. The numerical predictions are compared to experimental results for spatial average vibration for a point force input. The amount of control for increasing number of patches is also investigated. These results give a more accurate representation of the achievable performance in real world application.

The performance of piezoelectric-based damping and vibration control techniques has been studied and analyzed extensively under impulse response or harmonic steady state conditions. Considered here is their performance when subjected to an excitation whose frequency is close to a structure's resonance frequency but varies sufficiently quickly to preclude a harmonic analysis. Although a rapidly-varying excitation frequency will reduce the peak response amplitude, additional vibration reduction is often desired. The current research investigates the performance of several common passive and semi-active (state switching) vibration reduction techniques. In many cases, particularly for high electromechanical coupling, a system provides sufficient vibration reduction to approximate a steady state condition. Special attention is paid to turbomachinery bladed disks and the feasibility of implementing a particular vibration reduction approach. Semi-active switching approaches are more robust for vibration reduction of multiple frequencies than passive systems which require optimal tuning to the excitation condition. State switching, synchronized switched damping, and resonance frequency detuning provide the most realistic embedded package. Of these three approaches, synchronized switched damping delivers the greatest performance, although all provide significant vibration reduction. With far fewer and less stringent switching requirements, resonance frequency detuning requires significantly less power than other semi-active approaches.

The modified positive position feedback controller, an active vibration control method that uses collocated piezoelectric actuator actuators and sensors, is developed using an adaptive controller. The adaptive mechanism consists of two main parts: 1) Frequency adaptation mechanism, and 2) Adaptive controller. Frequency adaptation only tracks the frequency of vibrations using Fast Fourier Transforms. The obtained frequency is then fed to MPPF compensators and the adaptive controller. This provides a unique feature for MPPF, by extending its domain of capabilities from controlling tonal vibrations to broad band disturbances. The adaptive controller mechanism consists of a reference model that is of the same order as the MPPF system and its compensators. The adaptive law provides the additional control force that is needed for controlling frequency changes caused by broad band vibrations. The experimental results show that the frequency tracking method that is derived has worked quite well. The results also indicate that the MPPF can provide significant vibration reduction on a cantilever beam that is used throughout the experiments.

This paper discusses a preliminary study on harnessing energy from piezoelectric transducers by using bluff body and vortex-induced vibration phenomena. Structures like bridges and buildings tend to deform and crack due to chaotic fluid-structure interactions. The rapid variation of pressure and velocity can be tapped and used to power structural health monitoring systems. The proposed device is a miniature, scalable wind harvesting device. The configuration consists of a bluff body with a flexible piezoelectric cantilever attached to the trailing edge. Tests are run for different characteristic dimensions or shapes for the bluff body and optimized for maximum power over a wide range of flow velocities. The main motive here is to seek a higher synchronized region of frequencies for the oscillation amplitudes. The multi-physics software package COMSOL is used to vary the design parameters to optimize the configuration and to identify the significant parameters in the design. The simulation results obtained show a wider lock-in bandwidth and higher average power for the cylindrical bluff body compared to the other two bluff body shapes investigated, the greatest average power being 0.35mW at a Reynolds number of 900, beam length of 0.04m, and bluff body diameter of 0.02m.

We introduce a design for a magnetic force exciter that applies vibration to a piezo-composite generating element (PCGE) for a small-scale windmill to convert wind energy into electrical energy. The windmill can be used to harvest wind energy in urban regions. The magnetic force exciter consists of exciting magnets attached to the device's input rotor, and a secondary magnet that is fixed at the tip of the PCGE. Under an applied wind force, the input rotor rotates to create a magnetic force interaction to excite the PCGE. Deformation of the PCGE enables it to generate the electric power. Experiments were performed to test power generation and battery charging capabilities. In a battery charging test, the charging time for a 40 mAh battery is approximately 1.5 hours for a wind speed of 2.5 m/s. Our experimental results show that the prototype can harvest energy in urban areas with low wind speeds, and convert the wasted wind energy into electricity for city use.

Plug-in Hybrid Electric Vehicles (PHEVs) and Extended Range Electric Vehicles (EREVs) currently mainly rely on Internal Combustion Engines (ICE) utilizing conventional fuels to recharge batteries in order to extend their range. Even though Piezo-based power generation devices have surfaced in recent years harvesting vibration energy, their output has only been sufficient to power up sensors and other such smaller devices. The permanent need for a cleaner power generation technique still remains. This paper investigates the possibility of using piezoceramics for power generation within the vehicle's wheel assembly by exploiting the rotational motion of the wheel and the continuously variable contact point between the pneumatic tire and the road.

In the past few years, various circuit techniques have been proposed to improve the efficiency of piezoelectric energy harvesting, among which the synchronized charge extraction (SCE) circuit has been enthusiastically pursued. In the literature, the SCE technique is claimed to increase the power output of a piezoelectric energy harvester (PEH) by four times based on the assumption that the vibration of the harvester is not affected by the energy harvesting process. Under such assumption, the circuit model of a PEH is usually over-simplified as an ideal current or voltage source with the piezoelectric internal capacitance placed in parallel or in series. In this paper, the applicability of the SCE technique is investigated by electrical simulation. First, a more accurate circuit model of a cantilevered PEH is derived, taking into account the backward electromechanical coupling effect on vibration. Subsequently, the designed SCE circuit is connected with the simplified and the accurate circuit models of the PEH for simulation. The applicability of the SCE circuit for different cases are investigated, including the PEH excited at resonance and off-resonance frequencies as well as the PEH with various degree of electromechanical coupling. The results show that when the coupling of PEH is not negligible, the SCE technique cannot improve or even reduces the efficiency of energy harvesting for the PEH vibrating at resonance. The SCE technique is found applicable for efficiency improvement only for the PEH vibrating at offresonance or with a weak coupling coefficient because of the very minimum of electrical damping effect from the energy harvesting process, in which cases, the simplified and accurate circuit models are approximately equivalent.

Much of the work on improving energy harvesting systems currently focuses on tasks beyond geometric optimization and has shifted to using complex feedback control circuitry. While the specific technique and effectiveness of the circuits have varied, an important goal is still out of reach for many desired applications: to produce sufficient and sustained power. This is due in part to the power requirements of the control circuits themselves. One method for increasing the robustness and versatility of energy harvesting systems which has started to receive some attention would be to utilize multiple energy sources simultaneously. If some or all of the present energy sources were harvested, the amount of constant power which could be provided to the system electronics would increase dramatically. This work examines two passive circuit topologies, parallel and series, for combining multiple piezoelectric energy harvesters onto a single storage capacitor using an LTspice simulation. The issue of the relative phase between the two piezoelectric signals is explored to show that the advantages of both configurations are significantly affected by increased relative phase values.

This article analyzes the electrical behavior of an array of piezoelectric energy harvesters endowed with several interfacing circuits, including the standard AC/DC circuit and parallel/series SSHI (synchronized switch harvesting on inductor) circuits. The harvesters are classified according to the connection to a single or multiple rectifiers. The analytic estimates of harvested power are derived explicitly for different cases. The results show that DC power output changes from the power-boosting mode to the wideband mode according to various degrees of differences in the parameters of harvesters. In particular, the system with multiple rectifiers exhibits more bandwidth improvement than that with a single rectifier. Finally, it is shown that the electrical performance of an SSHI array system enjoys both power boosting and bandwidth improvement.

The design, fabrication and testing of piezoelectric energy harvesting modules for floors is described. These modules are used beneath a parquet floor to harvest the energy of people walking over it. The harvesting modules consist of monoaxial stretched PVDF-foils. Multilayer modules are built up as roller-type capacitors. The fabrication process of the harvesting modules is simple and very suitable for mass production. Due to the use of organic polymers, the modules are characterized by a great flexibility and the possibility to create them in almost any geometrical size. The energy yield was determined depending on the dynamic loading force, the thickness of piezoelectric active material, the size of the piezoelectric modules, their alignment in the walking direction and their position on the floor. An increase of the energy yield at higher loading forces and higher thicknesses of the modules was observed. It was possible to generate up to 2.1mWs of electric energy with dynamic loads of 70kg using a specific module design. Furthermore a test floor was assembled to determine the influence of the size, alignment and position of the modules on the energy yield.

This paper develops an equivalent linear model for piezomagnetoelastic energy harvesters under broadband random ambient excitations. Piezomagnetoelastic harvesters are used for powering low power electronic sensor systems. Nonlinear behaviour arising due to the vibration in a magnetic field makes piezomagnetoelastic energy harvesters different from the more classical piezoelastic energy harvesters. First numerical simulation of the nonlinear model is presented and then an equivalent linearization based analytical approach is developed for the analysis of harvested power. A cosed-form approximate expression for the ensemble average of the harvested power is derived. The equivalent model is seen to capture the details of the nonlinear model and also provides more details to the behaviour of the harvester to random excitation. Our results show that it is possible to optimally design the system such that the mean harvested power is maximized for a given strength of the input broadband random ambient excitation.

This paper presents the design and optimization of tubular Linear Electromagnetic Transducers (LETs) with applications to large-scale vibration energy harvesting, such as from vehicle suspensions, tall buildings or long bridges. Four types of LETs are considered and compared, namely, single-layer configuration using axial magnets, double-layer configuration using axial magnets, single-layer configuration using both axial and radial magnets, double-layer configuration using both axial and radial magnets. In order to optimize the LETs, the parameters investigated in this paper include the thickness of the magnets in axial direction and the thickness of the coils in the radial direction. Finite element method is used to analyze the axisymmetric two-dimensional magnetic fields. Both magnetic flux densities B_r [T] in the radial direction and power density [W/m³] are calculated. It is found that the parameter optimization can increase the power density of LETs to 2.7 times compared with the initial design [Zuo et al, Smart Materials and Structures, v19 n4, 2010], and the double-layer configuration with both radial and axial magnets can improve the power density to 4.7 times, approaching to the energy dissipation rate of traditional oil dampers. As a case study, we investigate its application to energy-harvesting shock absorbers. For a reasonable retrofit size, the LETs with double-layer configuration and both axial and radial NdFeB magnets can provide a damping coefficient of 1138 N·s/m while harvesting 35.5 W power on the external electric load at 0.25 m/s suspension velocity. If the LET is shorten circuit, it can dissipate energy at the rate of 142.0 W, providing of a damping coefficient of 2276 N·s/m. Practical consideration of number of coil phases is also discussed.

This paper reports on the design and experimental validation of transducers for energy harvesting from largescale civil structures, for which the power levels can be above 100W, and disturbance frequencies below 1Hz. The transducer consists of a back-driven ballscrew, coupled to a permanent-magnet synchronous machine, and power harvesting is regulated via control of a four-quadrant power electronic drive. Design tradeoffs between the various subsystems (including the controller, electronics, machine, mechanical conversion, and structural system) are illustrated, and an approach to device optimization is presented. Additionally, it is shown that nonlinear dissipative behavior of the electromechanical system must be properly characterized in order to assess the viability of the technology, and also to correctly design the matched impedance to maximize harvested power. An analytical expression for the average power generated across a resistive load is presented, which takes the nonlinear dissipative behavior of the device into account. From this expression the optimal resistance is determined to maximize power for an example in which the transducer is coupled to base excited tuned mass damper (TMD). Finally, the results from the analytical model are compared to an experimental system that uses hybrid testing to simulated the dynamics of the TMD.

Conventional energy harvester consists of a cantilevered composite piezoelectric beam which has a proof mass at its free end while its fixed end is mounted on a vibrating base structure. The resulting relative motion between the proof mass and the base structure produces a mechanical strain in the piezoelectric elements which is converted into electrical power by virtue of the direct piezoelectric effect. In this paper, the harvester is provided with a dynamic magnifier consisting of a spring-mass system which is placed between the fixed end of the piezoelectric beam and the vibrating base structure. The main function of the dynamic magnifier, as the name implies, is to magnify the strain experienced by the piezoelectric elements in order to amplify the electrical power output of the harvester. With proper selection of the design parameters of the magnifier, the harvested power can be significantly enhanced and the effective bandwidth of the harvester can be improved. The theoretical performance of this class of Cantilevered Piezoelectric Energy Harvesters with Dynamic Magnifier (CPEHDM) is developed using ANSYS finite element analysis. The predictions of the model are validated experimentally and comparisons are presented to illustrate the merits of the CPEHDM in comparison with the conventional piezoelectric energy harvesters (CPEH). The obtained results demonstrate the feasibility of the CPEHDM as a simple and effective means for enhancing the magnitude and spectral characteristics of CPEH.

Novel designs are presented for piezoelectric-based energy-harvesting power sources that are attached to mortar tubes to harvest energy from the firing impulse. The power sources generate electrical energy by storing mechanical potential energy in spring elements during the firing. The mass-spring unit of the power source begins to vibrate after firing, thereby applying a cyclic force to a set of piezoelectric elements to which it is attached. The mechanical energy of vibration is thereby converted to electrical energy over a relatively long period of time and stored in electrical energy storage elements such as capacitors. The power sources are shown to provide a significant portion of the required electrical energy of the fire control system.

This paper investigates a novel mechanism for powering wireless sensors or low power electronics by extracting energy from an ambient fluid flow using a piezoelectric energy harvester driven by aeroelastic flutter vibrations. The energy harvester makes use of a modal convergence flutter instability to generate limit cycle bending oscillations of a cantilevered piezoelectric beam with a small flap connected to its free end by a revolute joint. The critical flow speed at which destabilizing aerodynamic effects cause self-excited vibrations of the structure to emerge is essential to the design of the energy harvester. This value sets the lower bound on the operating wind speed and frequency range of the system. A system of coupled equations that describe the structural, aerodynamic, and electromechanical aspects of the system are used to model the system dynamics. The model uses unsteady aerodynamic modeling to predict the aerodynamic forces and moments acting on the structure and to account for the effects of vortices shed by the flapping wing, while a modal summation technique is used to model the flexible piezoelectric structure. This model is applied to examine the effects on the cut-in wind speed of the system when several design parameters are tuned and the size and mass of the system is held fixed. The effects on the aeroelastic system dynamics and relative sensitivity of the flutter stability boundary are presented and discussed. Experimental wind tunnel results are included to validate the model predictions.

Harvesting wasted energy and converting it into electrical energy to use as needed is an emerging technology area. In this work, a new design of a cymbal energy harvester is developed and tested to validate analytical energy generating performance. Cymbal transducers have been demonstrated to be beneficial as energy harvesters for vibrating systems under modest load and frequency. In this paper a new design is adopted using a unimorph circular piezoelectric disc between the metal end caps to deal with higher loads. Simple analysis for the new cymbal design to predict voltage output was first conducted. The new cymbal design, 25.4 mm diameter and 8.2 mm thickness, was then fabricated and tested on the load frame with up to 324 lb load and 1 Hz frequency to measure output voltages. This device could be used in numerous applications for potentially self sustaining sensors or other electronic devices. By changing the structure between the metal end caps of cymbal harvesters the new design could be extended in higher load applications.

Due to hundreds of fatalities annually at unprotected railroad crossings (mostly because of collisions with passenger vehicles and derailments resulting from improperly maintained tracks and mechanical failures), supplying a reliable source of electrical energy to power crossing lights and distributed sensor networks is essential to improve safety. With regard to the high cost of electrical infrastructure for railroad crossings in remote areas and the lack of reliability and robustness of solar and wind energy solutions, development of alternative energy harvesting devices is of interest. In this paper, improvements to a mechanical energy harvesting device are presented. The device scavenges electrical energy from deflection of railroad track due to passing railcar traffic. It is mounted to and spans two rail ties and converts and magnifies the track's entire upward and downward displacement into rotational motion of a PMDC generator. The major improvements to the new prototype include: harvesting power from upward displacement in addition to downward, changing the gearing and generator in order to maximize power production capacity for the same shaft speed, and improving the way the system is stabilized for minimizing lost motion. The improved prototype was built, and simulations and tests were conducted to quantify the effects of the improvements.

This study concerns a vibration energy harvester of resonance-type with a nonlinear oscillator which can convert the kinetic energy of the vibration source to electric energy effectively in a wide frequency range. The conventional linear harvesters are designed so as to generate larger power by matching the natural frequency of the oscillator to the frequency of the source vibration. The problem is, however, that if the input frequency changes even in a slight amount, the performance of the harvester can become extremely worse because the effective bandwidth of the resonance is quite narrow. In this study, the resonance frequency band of the oscillator is expanded by using a nonlinear oscillator with a nonlinear spring to allow the harvester to generate larger electric power in wider frequency range. However, the nonlinear oscillator can have multiple stable steady-state responses in the resonance band, and it depends on the initial conditions which solution emerges. In this paper, the mechanism of self-excitation is utilized to unstabilize the solutions except for the largest amplitude solution. A charging circuit with a variable resistance which is controlled from negative to positive as a function of the response amplitude is introduced in order to enable the oscillator entrained by the excitation only in the large amplitude solution. Theoretical and numerical analyses are conducted to show that the nonlinear energy harvester with resistance control can respond in large amplitude in wide frequency range, and a significant improvement is achieved in the regenerated power compared with the one without control.

A piezoelectric based energy harvesting scheme is proposed here which places a capacitor before the load in the conditioning circuit. It is well known that the impedance between the load and source contributes heavily to the performance of the energy harvesting system. The additional capacitor provides flexibility in meeting the optimal impedance value and can be used to expand the bandwidth of the system. A theoretical model of the system is derived and the response of the system as a function of both resistance and capacitance is studied. The analysis shows that the energy harvesting performance is dominated by a bifurcation occurring as the electromechanical coupling increases above a certain value, below this point the addition of an additional capacitor does not increase the performance of the systems and above the maximum power can be achieved at all point between these two bifurcation frequencies. Additionally, it has been found that the optimal capacitance is independent of the optimal resistance. Therefore, the necessary capacitance can be chosen and then the resistance determined to provide optimal energy harvesting at the desired frequencies. For systems with low coupling the optimal added capacitance is negative (additional power to the circuit) indicating that a second capacitor should not be used for. For systems with high coupling the optimal capacitance becomes positive for a range of values inside the bifurcation frequencies and can be used to extend the bandwidth of the harvesting system. The analysis also demonstrates that the same maximum energy can be harvested at any frequency; however, outside the two bifurcation frequencies the capacitor must be negative.

This paper presents the feasibility of semi-active magnetorheological (MR) refueling probe systems for the aerial refueling events through theoretical work. The semi-active smart refueling probe system consists of probe, a coil spring, and an MR damper. The dynamics of the smart refueling probe system using an MR damper was derived and incorporated with the hose-drogue dynamics so as to theoretically evaluate the overload reduction of the refueling hose at the drogue position. The simulated responses of the smart refueling probe system using an MR damper were conducted at different peak closure velocities of 1.56 and 5 ft/s and different tanker flight speeds of 185 and 220 knots.

A novel magnetorheological elastomer (MRE) mount is designed, fabricated, and tested to provide a wide controllable compression static stiffness range for protecting a system with variable payload from external shock and vibration. The shear static stiffness and compression dynamic stiffness were also studied. MRE is a field-controllable material in which the stiffness properties can be altered by changing the applied magnetic field. A MRE mount is developed by using 0.5-inch thick MRE layers and built-in electromagnets. The performance of the 2-layer MRE mount is characterized by compression, shear, vibration, and shock tests. The tests demonstrate that the variable-stiffness MRE mount can be used for shock and vibration isolation applications.

This study presents the feasibility of a new variable stiffness and damping isolator (VSDI) in an integrated vibratory system. The integrated system comprised of two VSDIs, a connecting plate and a mass. The proposed VSDI consists of a traditional steel-rubber vibration absorber, as the passive element, and a magneto-rheological elastomer (MRE), with a controllable (or variable) stiffness and damping, as the semi-active element. MREs' stiffness and damping properties can be altered by a magnetic field. Dynamic testing on this integrated system has been performed to investigate the effectiveness of the VSDIs for vibration control. Experimental results show significant shift in natural frequency, when activating the VSDIs. Transmissibility and natural frequency of the integrated system are obtained from properties of single device. The experimental and predicted results show good agreement between the values of the natural frequency of the system at both off and on states. However, system damping predictions are different from experimental results. This might be due to unforeseen effects of pre-stressed MREs and nonlinear material properties.

In this study, the electrical conductivity and magnetoresistance of magnetorheological elastomers (MREs) are experimentally investigated. The electrical resistivity of MREs is measured as a function of particle volume fraction, under different applied magnetic fields. In addition, the strain of the samples is measured simultaneously in order to evaluate the magnetoresistance and piezoresistance of MREs. It is observed that both magnetoresistance and piezoresistance in MREs are independent of the applied magnetic field and pre-compression force; and only depend on the particle concentration and mechanical strain.

In the present study, two types of MRE with different concentrations, and circular and rectangular shapes having thicknesses from 6.35mm to a maximum of 25.4mm are prepared. These samples are tested under quasi-static compression and quasi-static double lap shear. It is observed that the measured off-state shear modulus has large variations with increase in the thickness of the sample. The measured shear modulus from the double lap shear test results, as well as the Young's modulus from the compression tests at zero-field, follows a logarithmic trend. With the increase in applied magnetic field, it is observed that the change in modulus shifted from a linear at lower field to a nonlinear trend at higher fields. In addition it is observed that the controllability of MRE is more in the compression mode than in the shear mode.

A compact compressible magnetorheological (MR) fluid damper-liquid spring (CMRFD-LS) suspension system is designed, developed and tested. The performances of the CMRFD-LS are investigated under room temperature. However, MR fluids are temperature dependent. The effect of temperature is observed in both the viscosity and the compressibility of the MR fluid. This study is to experimentally determine how temperature affects the performance of a CMRFD-LS device. A test setup is developed to measure the stiffness and energy dissipated by the system under various frequency loadings, magnetic fields and temperatures. The experimental results demonstrate that both the stiffness and the energy dissipated by the CMRFD-LS are inversely related to the temperature of the MR fluid. These changes in damper characteristics show that the compressibility of MR fluid is proportional to the fluid temperature, while the viscosity of the MR fluid is inversely related to the fluid temperature.

Actuators based on magnetorheological fluids, like brakes and clutches, offer a high dynamical and almost linear force generation combined with fast response times and a high force density. In this paper concepts of MRF based actuators with radial and axial shear gaps for realizing braking and coupling functions in HMI devices and industrial applications are presented. Designing well defined shear gaps and appropriate electromagnetically driven excitation systems, combined brake and clutch functionalities can be realized even by providing current less bias torques. While actuators using radial shear gaps meet often the requirements for applications with low rotational speeds, e.g. HMI applications, designs with axial shear gaps are predestinated for applications for higher rotational speeds due to their robustness against centrifugation impacts. Experimental results of realized actuators underlining the potential for HMI and industrial applications and reveal the advantages of MRF as the smooth adjustable torque, fast response time and noiseless operation.

Tracked military vehicles were the choice of fighting vehicles due to their heavy fire power, better armor package distribution, better traction, and ability to fire on the move without spades. Many armies are converting to all wheeled vehicles, but one of the drawbacks is the inability to fire on the move without spades. A 2D heave pitch vehicle model for HMMWV has been developed. Simulation results indicate that by the use of MR-fluid dampers with the skyhook controls, it is possible to remove the spades, control chassis vibration, and prevent vehicle lift off during mortar firing, without bursting the tires.

In this paper, we proposed and investigated a self-powered, self-sensing magnetorheological (MR) damper, which integrates energy harvesting, sensing and MR damping capabilities into one device. This multifunctional integration would bring great benefits such as energy saving, high reliability, size and weight reduction, lower cost, and less maintenance for the use of MR damper systems. A prototype of the self-powered, self-sensing MR damper was designed, fabricated and tested. The power generator hardware could serve as the power generation and velocity sensing simultaneously. Analyses on the generated electrical voltages and power were performed and validated experimentally. A combined magnetic-field isolation method was developed and analyzed. A novel velocity-sensing method was proposed and experimentally validated to extract the velocity information from the signals of the power generator. This method requires real-time signal processing while extra mechanical mechanism is not needed. The damping force characteristic of the separate MR damper was also investigated.

This research work focuses on optimal design of a disc-type magneto-rheological (MR) brake that can replace a conventional hydraulic brake (CHB) of middle-sized motorcycles. Firstly, a MR brake configuration is proposed considering the available space and the simplicity to replace a CHB by the proposed MR brake. An optimal design of the proposed MR brake is then performed considering the required braking torque, operating temperature, mass and size of the brake. In order to perform the optimization of the brake, the braking torque of the brake is analyzed based on Herschel-Bulkley rheological model of MR fluid. The constrain on operating temperature of the MR brake is determined by considering the steady temperature of the brake when the motorcycle is cruising and the temperature increase during a braking process. An optimization procedure based on finite element analysis integrated with an optimization tool is employed to obtain optimal geometric dimensions of the MR brake. Optimal solution of the MR brake is then presented and simulated performance of the optimized brake is shown with remarkable discussions.

In this work, a new configuration of a magnetorheological (MR) brake is proposed and an optimal design of the proposed MR brake for haptic wrist application is performed considering the required braking torque, the zero-field friction torque, the size and mass of the brake. The proposed MR brake configuration is a combination of disc-type and drum-type which is referred as a hybrid configuration in this study. After the MR brake with the hybrid configuration is proposed, braking torque of the brake is analyzed based on Bingham rheological model of the MR fluid. The zero-field friction torque of the MR brake is also obtained. An optimization procedure based on finite element analysis integrated with an optimization tool is developed for the MR brake. The purpose of the optimal design is to find the optimal geometric dimensions of the MR brake structure that can produce the required braking torque and minimize the uncontrollable torque (passive torque) of the haptic wrist. Based on developed optimization procedure, optimal solution of the proposed MR brake is achieved. The proposed optimized hybrid brake is then compared with conventional types of MR brake and discussions on working performance of the proposed MR brake are described.

Machine tools for small work pieces are characterized by an extensive disproportion between workspace and cross section. This is mainly caused by limitations in the miniaturization of drives and guidance elements. Due to their high specific workloads and relatively small spatial requirements, Shape-Memory-Alloys (SMA) possess an outstanding potential to serve as miniaturized positioning devices in small machines. However, a disadvantage of known actuator configurations, such as SMA wire working against a mechanical spring, is that energy is steadily consumed to hold defined positions. In this paper we present a novel SMA actuator design, which, due to an antagonistic arrangement of two SMA elements does only require a minimum amount of energy whilst holding position. The SMA actuators were designed regarding material, geometrical parameters, applied load, and control aspects. Furthermore, closed loop control concepts for positioning applications are implemented. These not only cover approaches using sensors, but also sensorless concepts which utilize the distinctive length - resistance - correlation of SMAs for position controlling. Furthermore, an actuator demonstrator has been used to demonstrate the designs capabilities to serve as miniaturized positioning device in small machines. In addition the novel design concept of the SMA actuator will be compared with commonly used approaches.

This paper deals with the flap control of unmanned aerial vehicles (UAVs) using shape memory alloy (SMA) actuators in an antagonistic configuration. The use of SMA actuators has the advantage of significant weight and cost reduction over the conventional actuation of the UAV flaps by electric motors or hydraulic actuators. In antagonistic configuration, two SMA actuators are used: one to rotate the flap clockwise and the other to rotate the flap counterclockwise. In this content, mathematical modeling of strain and power dissipation of SMA wire is obtained through characterization tests. Afterwards, the model of the antagonistic flap mechanism is derived. Later, based on these models both flap angle and power dissipation of the SMA wire are controlled in two different loops employing proportional-integral type and neural network based control schemes. The angle commands are converted to power commands through the outer loop controller later, which are updated using the error in the flap angle induced because of the indirect control and external effects. In this study, power consumption of the wire is introduced as a new internal feedback variable. Constructed simulation models are run and performance specifications of the proposed control systems are investigated. Consequently, it is shown that proposed controllers perform well in terms of achieving small tracking errors.

Hierarchical carbon fibers show potential as a bio-inspired fluid flow sensor. The sensor is inspired from bat wings, which have thousands of micro-scale hairs that are deflected due to the flow and are believed to feedback flow information through force sensitive cells. Radially aligned carbon nanotube arrays on carbon fiber could function as the transducer in a similar device by decreasing resistance with the application of compressive strain. The bio-inspired flow sensor is first modeled to determine the compliance of the fiber and strains applied to the carbon nanotube arrays. Vertically aligned carbon nanotube arrays are then prepared on planar conductive substrates through transfer from insulating Si wafers; which simplifies the analysis of the mechanical properties of the material. The electromechanical material properties are measured by a modified dynamic mechanical analyzer. Results are presented along with recommendations for the next phase of electromechanical property evaluation.

Current acoustic metamaterials are developed only with controllable directivity characteristics of wave propagation. The wave speed usually remains unaffected. This limits considerably the potential use of acoustic metamaterials in many critical military and civilian applications. In the present work, an attempt is presented for developing a class of acoustic metamaterials that have controllable directivity and dispersion characteristics. Such metamaterials are developed using a linear coordinate transformation of the acoustic domain to achieve the directivity control capabilities. The transformation is augmented with an additional degree of freedom to simultaneously control the dispersion characteristics. With such capabilities, the proposed acoustic metamaterials will be capable of controlling the wave propagation both in the spatial and spectral domains. The proposed control approach affects the density tensor of the acoustic metamaterials. The theory governing the design of this class of acoustic metamaterials is introduced and the parameters that control the tuning of the directivity and dispersion characteristics are presented in details. Several numerical examples are presented to illustrate the potential capabilities of this class of metmaterials. The proposed design approach of acoustic metamaterials with tunable wave propagation characteristics can be invaluable means for the design of many critical military and civilian applications.

The paper describes a simple and cost-effective design and fabrication process of a liquid-filled variable-focal lens. The lens was made of soft polymer material, its shape and curvature can be controlled by hydraulic pressure. An electroactive polymer is used as an actuator. A carbon-polymer composite (CPC) was used. The device is composed of elastic membrane upon a circular lens chamber, a reservoir of liquid, and a channel between them. It was made of three layers of polydimethylsiloxane (PDMS), bonded using the partial curing technique. The channels and reservoir were filled with incompressible liquid after curing process. A CPC actuator was mechanically attached to reservoir to compress or decompress the liquid. Squeezing the liquid between the reservoir and the lens chamber will push the membrane inward or outward resulting in the change of the shape of the lens and alteration of its focal length. Depending on the pressure the lens can be plano-convex or plano-concave or even switch between the two configurations. With only a few minor modifications it is possible to fabricate bi-convex and bi-concave lenses. The lens with a 1 mm diameter and the focal length from infinity to 17 mm is reported. The 5x15mm CPC actuator with the working voltage of only up to ±2.5 V was capable to alter the focal length within the full range of the focal length in 10 seconds.

Contact-Aided Compliant Cellular Mechanisms (C³M) are compliant cellular structures with integrated contact mechanisms. The focus of the paper is on the design, fabrication, and testing of C³M with curved walls for high strain applications. It is shown that global strains were increased by replacing straight walls with curved walls in the traditional honeycomb structure, while the addition of contact mechanisms increased cell performance via stress relief in some cases. Furthermore, curved walls are beneficial for fabrication at the meso-scale. The basic curved honeycomb cell geometry is defined by a set of variables. These variables were optimized using Matlab and finite element analysis to find the best non-contact and contact-aided curved cell geometries as well as the cell geometry that provides the greatest stress relief. Currently, the most effective contact-aided curved honeycomb cell can withstand global strains approximately 160% greater than the most effective contact-aided, non-curved cell. Four different designs were fabricated via the Lost Mold-Rapid Infiltration Forming (LM-RIF) process. An array of the contact-aided optimized curved cell was then mechanically tested using a custom designed test rig, and the results were found to have a higher modulus of elasticity and lower global strain than the predictions. Despite these discrepancies, a high-strength highstrain cellular structure was developed, for potential use in morphing aircraft applications.

Polymer composites inserted with high volume fraction (up to 70 Vol%) of NiMnGa powders were fabricated and their damping behavior was investigated by dynamic mechanical analysis. It is found that the polymer matrix has little influence on the transformation temperatures of NiMnGa powders. A damping peak appears for NiMnGa/epoxy resin (EP) composites accompanying with the martensitic transformation or reverse martensitic transformation of NiMnGa powders during cooling or heating. The damping capacity for NiMnGa/EP composites increases linearly with the increase of volume fraction of NiMnGa powders and, decreases dramatically as the test frequency increases. The fracture strain of NiMnGa/EP composites decrease with the increase of NiMnGa powders.

The concept of energy harvesting in unmanned aerial vehicles (UAVs) has received much attention in recent years. Solar powered flight of small aircraft dates back to the 1970s when the first fully solar flight of an unmanned aircraft took place. Currently, research has begun to investigate harvesting ambient vibration energy during the flight of UAVs. The authors have recently developed multifunctional piezoelectric self-charging structures in which piezoelectric devices are combined with thin-film lithium batteries and a substrate layer in order to simultaneously harvest energy, store energy, and carry structural load. When integrated into mass and volume critical applications, such as unmanned aircraft, multifunctional devices can provide great benefit over conventional harvesting systems. A critical aspect of integrating any energy harvesting system into a UAV, however, is the potential effect that the additional system has on the performance of the aircraft. Added mass and increased drag can significantly degrade the flight performance of an aircraft, therefore, it is important to ensure that the addition of an energy harvesting system does not adversely affect the efficiency of a host aircraft. In this work, a system level approach is taken to examine the effects of adding both solar and piezoelectric vibration harvesting to a UAV test platform. A formulation recently presented in the literature is applied to describe the changes to the flight endurance of a UAV based on the power available from added harvesters and the mass of the harvesters. Details of the derivation of the flight endurance model are reviewed and the formulation is applied to an EasyGlider remote control foam hobbyist airplane, which is selected as the test platform for this study. A theoretical study is performed in which the normalized change in flight endurance is calculated based on the addition of flexible thin-film solar panels to the upper surface of the wings, as well as the addition of flexible piezoelectric patches to the root of the wing spar. Experimental testing is also performed in which the wing spar of the EasyGlider aircraft is modified to include both Macro Fiber Composite and Piezoelectric Fiber Composite piezoelectric patches near the root of the wing and two thin-film solar panels are installed onto the upper wing surface to harvest vibration and solar energy during flight. Testing is performed in which the power output of the various harvesters is measured during flight. Results of the flight testing are used to update the model with accurate measures of the power available from the energy harvesting systems. Finally, the model is used to predict the potential benefits of adding multifunctional self-charging structures to the wing spar of the aircraft in order to harvest vibration energy during flight and provide a local power source for low-power sensors.

The design of the skins has been identified as a major issue for morphing aircraft wings. Corrugated laminates provide a good solution due to their extremely anisotropic behavior. However, the optimal design of a morphing aircraft requires simple models of the skins that may be incorporated into multi-disciplinary system models. This requires equivalent material models that retain the dependence on the geometric parameters of the corrugated skins. An analytical homogenization model, which could be used for any corrugation shape, is suggested in this paper. This method is based on a simplified geometry for a unit-cell and the stiffness properties of original sheet. This paper investigates such a modeling strategy and demonstrates its performance and potential.

The paper begins with a brief historical overview of pressure adaptive materials and structures. By examining avian anatomy, it is seen that pressure-adaptive structures have been used successfully in the Natural world to hold structural positions for extended periods of time and yet allow for dynamic shape changes from one flight state to the next. More modern pneumatic actuators, including FAA certified autopilot servoactuators are frequently used by aircraft around the world. Pneumatic artificial muscles (PAM) show good promise as aircraft actuators, but follow the traditional model of load concentration and distribution commonly found in aircraft. A new system is proposed which leaves distributed loads distributed and manipulates structures through a distributed actuator. By using Pressure Adaptive Honeycomb (PAH), it is shown that large structural deformations in excess of 50% strains can be achieved while maintaining full structural integrity and enabling secondary flight control mechanisms like flaps. The successful implementation of pressure-adaptive honeycomb in the trailing edge of a wing section sparked the motivation for subsequent research into the optimal topology of the pressure adaptive honeycomb within the trailing edge of a morphing flap. As an input for the optimization two known shapes are required: a desired shape in cruise configuration and a desired shape in landing configuration. In addition, the boundary conditions and load cases (including aerodynamic loads and internal pressure loads) should be specified for each condition. Finally, a set of six design variables is specified relating to the honeycomb and upper skin topology of the morphing flap. A finite-element model of the pressure-adaptive honeycomb structure is developed specifically tailored to generate fast but reliable results for a given combination of external loading, input variables, and boundary conditions. Based on two bench tests it is shown that this model correlates well to experimental results. The optimization process finds the skin and honeycomb topology that minimizes the error between the acquired shape and the desired shape in each configuration.

At the Institute of Composite Structures and Adaptive Systems (FA, Prof. Wiedemann) of the DLR the structure of a flexible and gapless wing leading edge has been developed for testing in large scale structure-system ground tests. The absence of gaps in a flexible wing leading edge allows for a significant noise reduction and provides an additional key technology for realizing wings with a fully natural laminar flow. In the years 2009 and 2010 the work in the project SmartLED within the 4^th German Aviation Research Program (LuFo) was focused on the preparation and realization of the first ground test of the in the project developed overall system. The overall smart droop nose concept arose from the cooperation of Airbus and EADS, whereas the DLR Institute FA dealt with the structural design, the test of the material systems, the simulation of the overall system, and the development of manufacturing technologies for the composite structures to be employed in the planned tests. The detailed presentation of this work forms the content of this paper which has been made possible through the application of the process chain for composite structures established at the Institute FA of the DLR.

This article compares two feedback compensator strategies for the task of guiding a morphing aircraft along a perching trajectory. The aircraft model includes novel, actuated degrees of freedom that allow for bulk movement of some airframe structures. This morphing ability allows the aircraft to perform maneuvers in a manner similar to some birds. The control methods compared in this article are a multi-stage compensator and a linear quadratic regulator. Simulations test the effectiveness of the compensators for initial state error and a trajectory disturbance. In these simulations the linear quadratic regulator outperforms the multi-stage compensator by repeatedly producing smaller state errors and by having lower error standard deviations.

The method for analyzing the static aeroelastic deformation of flexible skin under the air loads was developed. The effect of static aeroelastic deformation of flexible skin on the aerodynamic characteristics of aerofoil and the design parameters of skin was discussed. Numerical results show that the flexible skin on the upper surface of trailing-edge will bubble under the air loads and the bubble has a powerful effect on the aerodynamic pressure near the surface of local deformation. The static aeroelastic deformation of flexible skin significantly affects the aerodynamic characteristics of aerofoil. At small angle of attack, the drag coefficient increases and the lift coefficient decreases. With the increasing angle of attack, the effect of flexible skin on the aerodynamic characteristics of aerofoil is smaller and smaller. The deformation of flexible skin becomes larger and larger with the free-stream velocity increasing. When the free-stream velocity is greater than a value, both of the deformation of flexible skin and the drag coefficient of aerofoil increase rapidly. The maximum tensile strain of flexible skin is increased with consideration of the static aeroelastic deformation.

Shape memory polymers (SMP) are attracting increasing attention as a class of smart structural materials due to their light weight, ability to exhibit variable stiffness and undergo large deformations without damage, and, of course, their shape memory effect. SMP have the clear potential to be used to develop a variety of structures that are intrinsically morphable. In theory, a structure composed completely of SMP could have limitless shape-changing functionality, provided sufficient activation and mechanical actuation. Towards the utilization of this potential functionality, this work presents a computational framework to design the optimal activation and actuation to morph a structure composed of a smart material into a predefined shape or set of shapes. A numerical study is shown for the example of thermally activated smart materials in which the objective is to identify the applied boundary heat and traction to deform and lock a given structure into a predefined shape with minimal total energy and without damaging the material. The finite element method is used to analyze the response of the structure given a set of design parameters, and a nonlinear optimization algorithm is applied to identify the ideal activation and actuation to achieve the desired deformation. Through an example problem based on thermally activated SMP, the approach is shown to provide a generalized means to optimally design and/or control smart material structures. The key challenges of this approach are addressed, and the foundation is laid for further exploration into computational approaches for the solution of similar coupled multi-physics inverse problems.

The large-scale and light-weight design trend in aircraft and spacecraft results in extremely flexible structures with lowfrequency vibration modes. Suppression of undesired vibrations in such flexible structures with limited energy is becoming an important design problem to develop energy-autonomous controllers powered using the harvested ambient energy. The objective of this paper is to compare different control laws to suppress low-frequency vibrations using the minimum actuation energy for the same system and under the same design constraint (identical settling time for free vibrations). The vibration suppression performance of four active control systems as well as their hybrid versions employing a switching technique are presented and compared. The control systems compared here are a Positive Position Feedback (PPF) controller, a Proportional Integral Derivative (PID) controller, a nonlinear controller (with a second-order nonlinear term multiplying the position and velocity feedback to create variable damping), a Linear Quadratic Regulator (LQR) controller and their hybrid versions integrating a bang-bang control law (on-off control) with each of these controllers. Experimental results are presented for a thin cantilevered beam with a piezoceramic transducer controlled by these eight controllers with a focus on the fundamental vibration mode under transverse free vibrations and the control energy requirements are compared. Experiments results reveal that all the controllers reduce the vibration settling time to 0.85s as a design constraint (which is 92.3% of the open-loop settling time: 10.9s). The average actuation power input provided to the piezoceramic transducer in each case is obtained for the time current and voltage measurements until the settling time. Comparisons show that the switching technology reduces significant actuation power requirement, so that all the hybrid control systems require much less power than their conventional versions. Especially, the hybrid bang-bang-nonlinear controller requires 67% less power than the conventional nonlinear controller. In order to verify this statement, the actuation current is theoretically calculated through piezo-capacitance using voltage measurements to check out the average power estimation. The theoretical checking out provides the same results with slightly error, which can be explained by measurement errors.

This paper studies the formability of functional composite structures, consisting of a metal substrate, insulating plastic foils, flat copper conductors and printable conductive polymers. The aim is the production of smart components in a sheet metal hydroforming process. In addition to their mechanical properties, these components can also transfer energy and data. Conventional boundaries between mechanics and electronics will be relaxed expediently. The challenge of this study is the design of the forming process, so that all elements of the multi-layer composites will withstand the process conditions. In this context, an analytical method for estimating the formability of these smart components is presented. The main objectives are the definition of basic failure modes and the depiction of the process limits.

Structural damage for spacecraft is mainly due to impacts such as collision of meteorites or space debris. We present a structural health monitoring (SHM) system for space applications, named Adverse Event Detection (AED), which integrates an acoustic sensor, an impedance-based SHM system, and a Lamb wave SHM system. With these three health-monitoring methods in place, we can determine the presence, location, and severity of damage. An acoustic sensor continuously monitors acoustic events, while the impedance-based and Lamb wave SHM systems are in sleep mode. If an acoustic sensor detects an impact, it activates the impedance-based SHM. The impedance-based system determines if the impact incurred damage. When damage is detected, it activates the Lamb wave SHM system to determine the severity and location of the damage. Further, since an acoustic sensor dissipates much less power than the two SHM systems and the two systems are activated only when there is an acoustic event, our system reduces overall power dissipation significantly. Our prototype system demonstrates the feasibility of the proposed concept.

This paper is concerned with measuring experimentally the stroke, generated mechanical power and efficiency of a flapping wing micro air vehicle's piezoelectric actuators when the forces transmitted to the actuator by a thorax are modeled with a nonlinear damping component. The objective is to test, simulate and model the actuators' behavior in conditions as close as possible to what would happen on a flapping wing MAV, without having to build the entire MAV which is still in its design stage. The loading applied to the actuator is created using an electromagnetic actuator to simulate a load varying with the actuator's tip displacement (hence simulating a stiffness) and with the actuator's tip velocity (hence simulating viscous damping). Measurements of velocities, forces and current absorbed are used to calculate the electric power consumed and the mechanical power generated by the actuator in steady state regime. For comparison, the experimental procedure is reproduced with a finite element code and an analytical model is derived.

Thermoacoustic refrigeration is an emerging refrigeration technology which does not rely for in its operation on the use of any moving parts or harmful refrigerants. This technology uses acoustic waves to pump heat across a temperature gradient. The vast majority of thermoacoustic refrigerators to date have used electromagnetic loudspeakers to generate the acoustic input. In this paper, the design, construction, operation, and modeling of a piezoelectric-driven thermoacoustic refrigerator are detailed. This refrigerator demonstrates the effectiveness of piezoelectric actuation in moving 0.3 W of heat across an 18 degree C temperature difference with an input power of 7.6 W. The performance characteristics of this class of thermoacoustic-piezoelectric refrigerator are modeled using DeltaEC software and the predictions are validated experimentally. The obtained results confirm the validity of the developed model. Furthermore, the potential of piezoelectric actuation as effective means for driving thermoacoustic refrigerators is demonstrated as compared to the conventional electromagnetic loudspeakers which are heavy and require high actuation energy. The developed theoretical and experimental tools can serve as invaluable means for the design and testing of other piezoelectric driven thermoacoustic refrigerator configurations.

The present paper summarizes recent results on the study and design of a cellular piezoelectric actuator. A simple analytical model for the static and dynamic behavior of honeycomb-based amplified actuators is presented. Validation of the model is performed with experimental measurements and finite element calculations on off-the-shelf actuators. A parametric study illustrates the effect of the geometric parameters on the optimal mechanical power and corresponding absorbed electrical power. The analytical model is then used to find optimal actuator configurations for a flapping wing entomopter for which we seek to minimize (1) the mass and (2) the absorbed electrical energy, and maximize (3) the generated mechanical power. A multi-objective approach helps select a posteriori the most appropriate configuration for the micro air vehicle as well as compare the proposed active cellular structure to the more commonly used piezoelectric unimorph actuator.

This paper presents a wheel slip control for the ABS(anti-lock brake system) of a passenger vehicle using a controllable piezo valve modulator. The ABS is designed to optimize for braking effectiveness and good steerability. As a first step, the principal design parameters of the piezo valve and pressure modulator are appropriately determined by considering the braking pressure variation during the ABS operation. The proposed piezo valve consists of a flapper, pneumatic circuit and a piezostack actuator. In order to get wide control range of the pressure, the pressure modulator is desired. The modulator consists of a dual-type cylinder filled with different substances (fluid and gas) and a piston rod moving vertical axis to transmit the force. Subsequently, a quarter car wheel slip model is formulated and integrated with the governing equation of the piezo valve modulator. A sliding mode controller to achieve the desired slip rate is then designed and implemented. Braking control performances such as brake pressure and slip rate are evaluated via computer simulations.

This paper proposes a compensator for the dynamic hysteresis of a piezostack actuator. It consists of two components: a rate-independent hysteresis compensator and a nonlinear filter. The compensator is formulated based on a novel rateindependent hysteresis model, whereas the filter is obtained adaptively using the recursive least square algorithm. In order to demonstrate the effectiveness of the proposed model, control performances are experimentally evaluated in time domain with different input voltage waveforms: fixed-frequency and varying-frequency sinusoidal waveforms. Moreover, a comparison between the dynamic model and the rate-independent one is undertaken. It is shown that the proposed dynamic model can provide much better accuracy than the rate-independent one.

This paper presents the effect of equivalent constant and output power on working temperature of concentric disk-type piezoelectric transformer. To analyze the energy loss in the piezoelectric transformer, the equivalent circuit model was built. Losses in the piezoelectric transformer are considered generally having two different parts: dielectric loss and mechanical loss. First of all, a measurement circuit based on an impedance analyzer was built. Then, the circuit simulation software PSIM was employed to verify the experimental results obtained. Secondly, according to the experimental results, temperature and input voltage are the two factors which influenced the energy loss in a piezoelectric transformer. As the input voltage and temperature increased, the energy loss rises, as well. In addition, when the input voltage is low, the temperature becomes the main influencing factor for energy loss of the piezoelectric transformer. On the other hand, when the input voltage is high, the main factor for energy loss of the piezoelectric transformer is the input voltage other than the temperature. Furthermore, the control loop that dealt with the energy loss of the piezoelectric transformer was proposed. At different temperatures, the variations of losses of the piezoelectric transformer are presented in this paper. Finally, the dielectric loss and mechanical loss are combined to analyze the losses within piezoelectric transformers. Then, the relationship between the output power of the piezoelectric transformer and the temperature was revealed. The result showed that as the temperature increased, the output power decreased.

The combination of Network Methods and Finite Element Methods on user level is a time-efficient method for the simulation of dynamic behavior of electromechanical systems. Combined simulation can be structured into five areas of application: determination of network structures with FE-simulations, determination of network parameters with FEsimulations, inclusion of network elements in FE-models, inclusion of equivalent network structures in FE-models and simulation of models incorporating different model levels. The capabilities of the combined simulation are demonstrated by sample applications. Combined Simulation is suited for a better system insight and fast simulation-based optimization.

To achieve an efficient simulation of the dynamic behavior of electromechanical devices it is often necessary to use more than one simulation method or program. The main reason for this is that electromechanical systems contain different physical domains and transduction principles. In many cases a smart solution is the combination of network methods with finite element methods on user level which is referred to as combined simulation. This paper deals with one area of application of the combined simulation, which is the use of network methods to improve finite element models. After the description of the method the procedure is illustrated by the example of the model of a hearing aid.

The analysis of electromechancial transducers using magnetic drive requires multidomain analysis that includes at least the electrical, magnetic, mechanical domains. Such a system results in a set of differential and algebraic equations (DAE) that can be solved by analogy using modern electrical circuit analysis codes, or with codes written specifically for multidomain DAE modelling. Often, some components in the system require partial differential equations for their analysis, and FEA methods are required. This is especially true in magnetic systems where the flux path including leakage defies simple a priori estimation. The examples of a variable reluctance device is shown.

Model based design optimization leads to robust solutions only if the statistical deviations of design, load and ambient parameters from nominal values are considered. We describe an optimization methodology that involves these deviations as stochastic variables for an exemplary electromagnetic actuator used to drive a Braille printer. A combined model simulates the dynamic behavior of the actuator and its non-linear load. It consists of a dynamic network model and a stationary magnetic finite element (FE) model. The network model utilizes lookup tables of the magnetic force and the flux linkage computed by the FE model. After a sensitivity analysis using design of experiment (DoE) methods and a nominal optimization based on gradient methods, a robust design optimization is performed. Selected design variables are involved in form of their density functions. In order to reduce the computational effort we use response surfaces instead of the combined system model obtained in all stochastic analysis steps. Thus, Monte-Carlo simulations can be applied. As a result we found an optimum system design meeting our requirements with regard to function and reliability.

With the ever increasing complexity of designs, the ability to validate and optimize the overall design while simultaneously considering all of the sub-systems, has become increasingly important. System simulation tools seek to address this need by combining control system models and physical device models with links to detailed physics based tools, thereby enabling more complex designs and encouraging collaboration. In this paper, we describe a new state-ofthe- art approach to link a high level system simulation tool (Simplorer) with a fast and accurate rigid dynamics tool (RBD) and its application to multi-physics system design. This approach allows the designer to combine detailed rigid mechanics models with system models such as complex electronic semiconductor device models used in controls.

This paper presents a preliminary design of a smart composite telescope for space laser communication. The smart composite telescope will be mounted on a smart composite platform with Simultaneous Precision Positioning and Vibration Suppression (SPPVS), and then mounted on a satellite. The laser communication is intended for the Geosynchronous orbit. The high degree of directionality increases the security of the laser communication signal (as opposed to a diffused RF signal), but also requires sophisticated subsystems for transmission and acquisition. The shorter wavelength of the optical spectrum increases the data transmission rates, but laser systems require large amounts of power, which increases the mass and complexity of the supporting systems. In addition, the laser communication on the Geosynchronous orbit requires an accurate platform with SPPVS capabilities. Therefore, this work also addresses the design of an active composite platform to be used to simultaneously point and stabilize an inter-satellite laser communication telescope with micro-radian pointing resolution. The telescope is a Cassegrain receiver that employs two mirrors, one convex (primary) and the other concave (secondary). The distance, as well as the horizontal and axial alignment of the mirrors, must be precisely maintained or else the optical properties of the system will be severely degraded. The alignment will also have to be maintained during thruster firings, which will require vibration suppression capabilities of the system as well. The innovative platform has been designed to have tip-tilt pointing and simultaneous multi-degree-of- freedom vibration isolation capability for pointing stabilization.

An integrated system of structural control and health monitoring can be implemented in modern smart structures with multi-purpose sensor system. The integration system not only promotes the reliability of the smart structure but also provides information on the condition of the smart structure. However, the on-line implementation of structural control and evaluation of a large scale structure are difficult due to the complicated calculation with large mass, damping and stiffness matrices. Moreover, the reliability of the structural control and evaluation results will also reduce in a large scale structural system during severe earthquake with centralized control system. In this paper, a new combined system of adaptive structural control and structural evaluation is proposed. The structural control system is implemented with the LQG control and the pseudo negative stiffness (PNS) control both are effective control methods for the vibration mitigation of structures. The structural control is adaptive with the updating of the structural parameters of the system via the structural evaluation system. A modified adaptive regularization method is used in the solution of the structural evaluation via model updating. The combination of the structural control and evaluation is designed as autonomous and decentralized to guarantee the reliability under the harsh environmental excitation. The autonomous decentralized control system explores a new substructure method which is more efficient in calculation with smaller mass, damping and stiffness matrices for the structural evaluation. The proposed integrated system is implemented and verified through numerical simulation of a 16-storey planar shear frame subject to seismic ground motion.

With the rapid advances in deployable membrane and mesh antenna technologies, the feasibility of developing large, lightweight reflectors has greatly improved. In order to achieve the required accuracy, precision surface control is needed on these lightweight reflectors. While studies have shown that domain control of space reflectors via Polyvinylidene Fluoride (PVDF) actuators is promising, the challenge is to realistically control a large number of distributed actuators with limited number of power supplies. In this research, a new En Mass Elimination method is synthesized to determine the optimal grouping of actuators when the actuator number exceeds the number of power supplies available. An analytical model is developed and the methodology is demonstrated numerically through system simulation on the derived model.

Vibration control based on mechanical energy transfer was recently proposed in a technique called synchronized switch damping with energy transfer (SSDET). In this technique, the mechanical energy, which is extracted from a energy source structure is transfered in order to damp another structure. This paper introduces this technique on a multimode vibrating structure. The energy transfer path is from one mode to another. A threshold is set in the control system for the sake of better damping. Experiments are carried out on an one edge clamped plate and both the harmonic response and the impulse response are considered. Results validate the effectiveness of this technique for multimode vibration control.

Visco-elastic damping material is applied to a novel type of isolator for the whole-spacecraft passive vibration isolation system, which can be used to improve the dynamic environment during the stage of launch. The results of the simulation and the experiment show that the vibration transmissibility of the mass center decreases more than 40%. The experiments of the isolator with different damping area are performed. The issues of natural frequency drifts and the transmissibility decreases as excitation level rising are discussed. It is demonstrated that the nonlinear of visco-elastic damping material and structure in the vibration experiment is the main influence factors.

In severe vibration environment, whole-spacecraft isolation is applied to increase the success probability of launch. For keeping the spacecraft safe, a new structure of whole-spacecraft isolation using viscoelastic damping material (VEM) is presented. First, the models of the VEM are described, and the influencing factors of the damping are analyzed. Then the significant of stiffness, area and geometry for VEM in practical use processing is proved through the simulation experimentation of the VEM we designed. Finally, the performance of new whole-spacecraft isolation structure is evaluated in varying operational modes by simulation experiments. Results show that VEM applied in the new whole-spacecraft isolation is reasonable, and the vibration environment of satellite is improved.

In the modern naval battle, as the anti-detection technique developing fleetly, enhancing submarine's hidden ability is becoming more and more important. However, in view of the worse control effect at low-frequency and weak adjustability to external influence, conventional passive vibration control can't satisfy the modern naval rigorous demands. Fortunately, active vibration control technology not only monitors the structure's real-time vibration, but also has more remarkable control effects and superior suitability. At the present time, it has a primary application in the vibration damping of ship engineering. In addition, due to functional materials rapidly developing, with the coming of piezoelectric composite materials, the advanced active control techniques have more applicability, lager damp amplitude and wider applied field, which basing on the piezoelectric-effect and inverse- piezoelectric-effect of piezoelectric materials. Especially, in the end of nineties, NASA had successfully manufactured the excellent macro fiber composite (MFC), which assembles actuating and sensing abilities. Comparing with the conventional piezoelectric ceramic materials, it provides the required durability, excellent flexibility, higher electromechanical coupling factors and stronger longitudinal actuating force by using interdigital electrodes. On the basis of the application of cantilever beam' active vibration control by using MFC actuators, this paper started with the mechanical characteristics of its actuating and sensing equations, and then investigated its piezoelectric feedback scale factor when equipped on the honeycomb aluminous panel. Finally, in order to validate the theoretical analysis method, the vibration control experiment of cantilever beam and honeycomb aluminous panel are built and tested with different activating force. The experimental results verify that MFC used in submarine structures' active vibration control are feasible and effective.

There are two ideologies about structure design: force-based concept and performance-based concept. Generally, if the structure operates during elastic stage, the two philosophies usually attain the same results. But beyond that stage, the shortage of force-based method is exposed, and the merit of performance-based is displayed. Pros and cons of each strategy are listed herein, and then which structure is best suitable to each method analyzed. At last, a real structure is evaluated by adaptive pushover method to verify that performance-based method is better than force-based method.

As an important method to calculate the dynamic response of structure, random vibration analysis is efficient as other method, like response spectrum method, time history method and so on. In the paper, the procedure for transforming response spectrum to power spectral density function attentively is studied. According to Chinese new bridge seismic code, the research on the parameters of Clough-Penzien power spectral model is carried out. The relations between Clough-Penzien spectral intensity and the mean value of maximum ground accelerations, or the earthquake intensity and maximum earthquake affecting parameter are derived. The parameters given in the paper provide a theoretical base for stochastic response analysis of structure.

If the continuous beam bridge is long enough, it is unwise to evaluate earthquake response without considering the spatial and time effect. In seismic response design method, the time history method can be utilized for purpose of spatial and time effect. If the spatial and time effect is ignored, the result is probably bigger or smaller than the result derived by consistent stimulation. As to how long the bridge be considered the spatial and time effect, it usually is decided by field site style and the importance of bridge.

Considering seismic spatial effect, different bridge support has different stimulation, and the action usually be decided by spatial seismic effect. So far, a variety of coherence functions have been modeled and advised. Through the comparison, QWW model is appropriate to create the external stimulation wave. At last, a usual procedure for seismic wave generation is given considering the coherence effect.

In machine tools several time and position varying heat sources causes complex temperature distributions. The resulting problems are varying thermal deformations which cause a loss of accuracy as well as non optimal drive conditions. An option to deal with that issue is to use structure integrated SM-actuators which use the thermal energy accumulated by machining processes to yield an actuator displacement. That creates a structure inherent control loop. There the shape-memory- elements work as sensing element as well as actuation element. The plant is defined by the thermal and mechanical behaviour of the surrounding structure. Because of the closed loop operation mode, the mechanical design has to deal with questions of stability and parameter adjustment in a control sense. In contrast to common control arrangements this issues can only be influenced by designing the actuator and the structure. To investigate this approach a test bench has been designed. The heat is yielded by a clutch and directed through the structure to the shape memory element. The force and displacement of the actuator are therefore driven directly by process heat. This paper presents a broad mechanical design approach of the test bench as well as the design of the SM-actuator. To investigate the thermo-mechanical behaviour of the structure-integrated actuator, a model of the test bench has been developed. The model covers the thermal behaviour of the test bench as well as the thermo-mechanical couplings of the shape memory actuator. The model has been validated by comprehensive measurements.

Positions of actuators play an important role in active vibration control, which affect not only the performance of vibration control but also the stability of whole system, especially for flexible structures. On optimal placement of actuators, many scholars have proposed a variety of optimization criteria, although some of these criteria have generality, but are complex to implement, and the results obtained by using closed-loop design idea to study the optimal placement of actuators are usually affected by initial conditions, the weight matrix and different control laws; which make the problem complicated, and this couldn't improve the effects of vibration control. In fact, before the system design, the initial conditions are difficult to determine, and the placement of the actuators should not affected by initial conditions and control laws, but should only by the inherent characteristics of the system and the external disturbances. In this paper, for a whole-spacecraft vibration isolator using piezoelectric stack actuators, dynamic sensitivity analysis method was used to derive an optimization criteria for piezoelectric stack actuator's placement, this criteria only related to the dynamic characteristics of the structure and the features of disturbance, but wasn't affected by initial conditions and control methods. By using the criteria, optimal placement of the piezoelectric actuators on the whole-spacecraft vibration isolator was studied; simulation results comparison verified the validity of the criteria, and obtained conclusion that different disturbance characteristics and output performances have great effects on the optimal placement.

Ni-free shape memory alloys are promising functional materials for medical applications. A newly developed Ti-Mo based shape memory alloy shows superelasticity after thermomechanical treatment. However, the microstructure evolution and precipitation during thermomechanical processes are still not well understood. In the present paper, compressive deformation behavior at a series of temperatures of 298K - 973K and tensile deformation behavior of the alloy after aged at 573K - 973K have been investigated systematically. It is found that the compressive yield stress and ultimate compressive strength change with the deformation temperature. The ultimate tensile strength and yield stress of aged specimens also change with the aging temperature following a non-linear relationship. Microstructures of aged specimens as well as effects of lattice softening and aging-induced precipitates on the deformation behavior have been investigated and discussed.

In order to overcome the difficulties of multimodal active vibration damping of the flexible thin structure using simultaneous piezoelectric sensing and actuation, an noncollocated vibration control method, in which piezoelectric film sensors and actuators were shaped using different shaping functions, was proposed in this paper. At first, fundamental equations were summarized and vibration responses of the beam were derived based on the modal coordinate systems. Then, it was shown that by considering phase characteristics of the controller in conjunctions with the polarity of the piezofims in high order modal frequencies, multimodal control will be implemented both theoretically and experimentally.

Piezoelectric energy harvesting has become a feasible method for powering micro portable electronics and wireless sensor networks by converting ambient vibration energy into electrical energy. As a thumb of rule, it is critical to tune the resonant frequency of the generator to the frequency of the environmental vibrations in order to induce the maximum structural deformation and then the maximum converted electrical energy through piezoelectric effect. However, it is well-known that the ambient vibrations are not usually fixed in only one single frequency and could span over a limited frequency band. In this paper, a band-pass design optimization of piezoelectric cantilever bimorph (PCB) energy harvester is presented based on the system transfer function of the PCB generator presented in a previous literature. For such an energy harvester, a group of PCB with dimensions appropriately selected can be integrated into a band-pass energy harvester working over a limited frequency band if the dimensions of piezoelectric bimorphs and proof masses are appropriately chosen. Further, the finite element analysis (FEA) of such a band-pass energy harvester is performed in ANSYS to validate the theoretical proposal. The result shows that the band-pass design optimization leads to a piezoelectric generator working over a certain frequency band while keeping outputting the relatively stable open-circuit voltage.