This PDF file contains the front matter associated with SPIE Proceedings Volume 9651, including the Title Page, Copyright information, Table of Contents, Authors, and Conference Committee listing.

This study deals with the kinetics of tissue adhesives used for supporting the hemostasis and wound closure during surgical intervention. There are several types of adhesives of different composition which is closely related with their application. The time of curing plays an important role because some applications may require very fast glue for prompt vessel or wound closure; conversely some situations need slower solidification because of longer manipulation with the glue during surgery. Here, the terahertz time-domain spectroscopy is used for studying the kinetics of the glues. To slow the reaction rate, an oily substance is added to the glue samples. The technique of attenuated total reflection is used in this application; the defined amount of glue sample or its mixture is applied on the silicon crystal and the terahertz response is measured in time. This time dependences are analyzed to find time constants for mathematical description of the glue kinetics.

Pharmaceutical trafficking is common issue in countries where they are under stricter dispensing regime with monitoring of users. Most commonly smuggled pharmaceuticals include trade names Paralen Plus, Modafen, Clarinase repetabs, Aspirin complex, etc. These are transported mainly from Eastern Europe (e.g. Poland, Ukraine, Russia) to countries like Czech Republic, which is said to have one of the highest number of methamphetamine producers in Europe. The aim of this paper is to describe the possibility of terahertz spectroscopy utilization as an examining tool to distinguish between pharmaceuticals containing pseudoephedrine compounds and those without it. Selected medicaments for experimental part contain as an active ingredient pseudoephedrine hydrochloride or pseudoephedrine sulphate. Results show a possibility to find a pseudoephedrine compound spectra in samples according to previously computed and experimentally found ones, and point out that spectra of same brand names pills may vary according to their expiration date, batch, and amount of absorbed water vapours from ambience. Mislead spectrum also occurs during experimental work in a sample without chosen active ingredient, which shows persistent minor inconveniences of terahertz spectroscopy. All measurement were done on the TPS Spectra 3000 instrument.

The U.S. Army Research Laboratory (ARL) has continued to develop and enhance a millimeter-wave (MMW) and submillimeter- wave (SMMW)/terahertz (THz)-band imaging system performance prediction and analysis tool for both the detection and identification of concealed weaponry, and for pilotage obstacle avoidance. The details of the MATLAB-based model which accounts for the effects of all critical sensor and display components, for the effects of atmospheric attenuation, concealment material attenuation, and active illumination, were reported on at the 2005 SPIE Europe Security and Defence Symposium (Brugge). An advanced version of the base model that accounts for both the dramatic impact that target and background orientation can have on target observability as related to specular and Lambertian reflections captured by an active-illumination-based imaging system, and for the impact of target and background thermal emission, was reported on at the 2007 SPIE Defense and Security Symposium (Orlando). Further development of this tool that includes a MODTRAN-based atmospheric attenuation calculator and advanced system architecture configuration inputs that allow for straightforward performance analysis of active or passive systems based on scanning (single- or line-array detector element(s)) or staring (focal-plane-array detector elements) imaging architectures was reported on at the 2011 SPIE Europe Security and Defence Symposium (Prague). This paper provides a comprehensive review of a newly enhanced MMW and SMMW/THz imaging system analysis and design tool that now includes an improved noise sub-model for more accurate and reliable performance predictions, the capability to account for postcapture image contrast enhancement, and the capability to account for concealment material backscatter with active-illumination- based systems. Present plans for additional expansion of the model’s predictive capabilities are also outlined.

A passive millimeter-wave imager prototype based on synthetic aperture interferometric radiometer (SAIR) technique is developing at Beihang University. It is designed for concealed contraband detection on human body in indoor environment at video imaging rate. The radiometric sensitivity requirements have been discussed in details, and the performance requirements of the digital processing subsystem have been analytically determined. A novel distributed digital correlator array architecture is proposed by using FPGA array, which results in reduction of hardware complexity and cost of the digital processing subsystem. In the proposed architecture, multistage pipeline technique is introduced for the reuse of logical resource that in turn results in decrease of transmission rate requirements for each FPGA, so that the feasibility of the digital processing subsystem can be greatly enhanced.

This paper investigates by simulation the use of the three-dimensional aperture synthesis imaging technique to image three-dimensional extended sources. Software was written to access the three-dimensional information from computer graphics models in the formats of *.dxf and *.3ds and use these to generate synthetic cross-correlations, as if they would have been generated by an aperture synthesis antenna/receiver array measuring the radiometric emission from the three-dimensional object. A three-dimensional (near-field) aperture synthesis imaging algorithm generates ^[1] a voxel image of the three-dimensional object. Images created from a sphere indicate faithful reproduction about a single phase centre when the radius of the sphere is less than the Fresnel scale. However, for larger spheres, definition in the threedimensional imagery suffers and a phenomenon, referred to in this paper as Fresnel noise, appears in the image. Images of objects larger than the Fresnel scale can be created by having multiple smaller images, each having a size approximately of the Fresnel scale and centred on separate phase centres. Using the software to generate threedimensional imagery of a person, to demonstrate capabilities for portal security screening, indicates the technique works to first order. Improvements are needed in the software to improve the spatial sampling of the radiometric fields from the three-dimensional objects and implement a volumetric image mosaicking technique to remove the Fresnel noise.

This paper presents part of a feasibility study into the use of the aperture synthesis passive imaging technique to screen vehicles for persons. The aperture synthesis technique is introduced and shown how in the near-field regime of a vehicle screening scenario that a three-dimensional imaging capability is possible. A suggested antenna receiver array is presented and the three-dimensional point spread function which this enables is calculated by simulation. This shows that over the majority of the inside of the vehicle the spatial resolution in all three spatial dimensions is of or less than the radiation wavelength, which at the suggested operational radiation frequency of 20 GHz is 1.5 cm. A radiation transport model that estimates the radiation temperatures of persons and backgrounds when viewing the vehicle either from the side or the top is presented, such a model being useful in the design of vehicle screening systems and as a basis for interpretation codes to assist operators in recognising persons in vehicles.

The threat of concealed weapons, explosives and contraband in footwear, bags and suitcases has led to the development of new devices, which can be deployed for security screening. To address known deficiencies of metal detectors and x-rays, an UWB 3D microwave imaging scanning apparatus using FMCW stepped frequency working in the K and Q bands and with a planar scanning geometry based on an x y stage, has been developed to screen suspicious luggage and footwear. To obtain microwave images of the concealed weapons, the targets are placed above the platform and the single transceiver horn antenna attached to the x y stage is moved mechanically to perform a raster scan to create a 2D synthetic aperture array. The S11 reflection signal of the transmitted sweep frequency from the target is acquired by a VNA in synchronism with each position step. To enhance and filter from clutter and noise the raw data and to obtain the 2D and 3D microwave images of the concealed weapons or explosives, data processing techniques are applied to the acquired signals. These techniques include background subtraction, Inverse Fast Fourier Transform (IFFT), thresholding, filtering by gating and windowing and deconvolving with the transfer function of the system using a reference target. To focus the 3D reconstructed microwave image of the target in range and across the x y aperture without using focusing elements, 3D Synthetic Aperture Radar (SAR) techniques are applied to the post-processed data. The K and Q bands, between 15 to 40 GHz, show good transmission through clothing and dielectric materials found in luggage and footwear. A description of the system, algorithms and some results with replica guns and a comparison of microwave images obtained by IFFT, 2D and 3D SAR techniques are presented.

Detection of explosives has always been a priority for homeland security. Jointly, terahertz spectroscopy and imaging are emerging and promising candidates as contactless and safe systems. In this work, we treated data resulting from hyperspectral imaging obtained by THz-time domain spectroscopy, with chemometric tools. We found efficient identification and sorting of targeted explosives in the case of pure and mixture samples. In this aim, we applied to images Principal Component Analysis (PCA) to discriminate between RDX, PETN and mixtures of the two materials, using the absorbance as the key-parameter. Then we applied Partial Least Squares-Discriminant Analysis (PLS-DA) to each pixel of the hyperspectral images to sort the explosives into different classes. The results clearly show successful identification and categorization of the explosives under study.

We developed new real-time algorithm, based on the correlation function, for concealed object detection using computer processing of the passive THz images without their viewing. This algorithm allows us to make a conclusion about presence of forbidden objects on the human body. To increase the THz image quality we propose a new algorithm in comparison with algorithms which have developed by us early. It allows to increase a temperature resolution of the passive THz camera at least 20 times. This approach is based on a correlation function application for computer processing of the raw THz image. The correlation computing occurs between characteristics of the raw THz image, produced by the passive THz camera, and characteristics of a standard image corresponding to one of the detecting objects (knife, gun,…). The standard image moves in two directions along a image under analysis. As a result, 2 D correlation function is obtained. Multiplying this function by color number belonging to a grey scale, we restore the image under the analysis. This allows to suppress a noise on a new image. This algorithm is very convenient for using and has a high performance. Developed approach opens also new type of algorithms for the passive THz image quality enhancing.

Guidance of weapon systems relies on sensors to analyze targets signature. Defense weapon systems also need to detect then identify threats also using sensors. One important class of sensors are millimeter waves radar systems that are very efficient for seeing through atmosphere and/or foliage for example. This type of high frequency radar can produce high quality images with very tricky features such as dihedral and trihedral bright points, shadows and lay over effect. Besides, image quality is very dependent on the carrier velocity and trajectory. Such sensors systems are so complex that they need simulation to be tested.

This paper presents a state of the Art of millimeter waves sensor models. A short presentation of asymptotic methods shows that physical optics support is mandatory to reach realistic results.

SE-Workbench-RF tool is presented and typical examples of results are shown both in the frame of Synthetic Aperture Radar sensors and Real Beam Ground Mapping radars.

Several technical topics are then discussed, such as the rendering technique (ray tracing vs. rasterization), the implementation (CPU vs. GP GPU) and the tradeoff between physical accuracy and performance of computation. Examples of results using SE-Workbench-RF are showed and commented.

New methods are being developed for efficient detection of terahertz waves. While many detection techniques show promise their commercial development is still limited due to the overall complexity and cost of the imaging system. Using commercially available neon indicator lamps the interaction mechanism between the glow plasma and the millimeter / THz wave is investigated in detail as a function of the device speed, sensitivity to frequency and polarization of the light. A lock-in amplifier was used to measure the response up to 90kHz when the GDD was placed at the focus of a 113GHz center frequency reconfigured Dielectric Resonating Oscillator (DRO) driven multiplied Schottky diode source. In addition the polarization sensitivity of the GDD was tested for two different scenarios whereby rotating the GDD the detected signal is observed to agree well with Malus’s Law for one particular orientation. Furthermore, the frequency dependent GDD-THz interactions are investigated using a 240-380 GHz tunable continuous wave radiation source. Employing both systems allow us to understand the response of GDDs with respect to modulation frequency, RF frequency and polarization orientation. Resonance effects, frequency sensitivity and geometrical structures of GDDs are studied for the purpose of obtaining better performance in THz-GDD interaction for applications including general THz wave detection and imaging.

In this paper, a prototype G-band (140 GHz-220 GHz) monolithic microwave integrated circuit (MMIC) resonant tunneling diode (RTD) oscillator is reported. The oscillator employs two In_0.53Ga_0.47As/AlAs RTD devices in the circuit to increase the output power. The measured output power was about 0.34 mW (-4.7 dBm) at 165.7 GHz, which is the highest power reported for RTD oscillator in G-band frequency range. This result demonstrates the validity of the high frequency/high power RTD oscillator design. It indicates that RTD devices, as one of the terahertz (THz) source candidates, have promising future for room-temperature THz applications in such as imaging, wireless communication and spectroscopy analysis, etc. By optimizing RTD oscillator design, it is expected that considerably higher power (>1 mW) at THz frequencies (>300 GHz) will be obtained.

Graphene is proving to be an efficient medium for the control of mm-wave/THz radiation. Its electrical and dielectric properties allows it to be incorporated into various existing device architectures. One such application is in the modulation of the amplitude of the propagating THz radiation. Due to its electrical properties this interaction is typically broadband in nature. To make this frequency selective we propose the use of metamaterials or frequency selective surfaces. Generally, these structures perform the frequency filtering by modifying the propagation of the input wave with respect to changing structural parameters of the device itself. By fabricating a frequency selective surface based on a periodic circular hole array on an aluminum sheet we show that the transmission of a narrow band of THz radiation can be modulated when the sheet is combined with a highly efficient graphene based supercapacitor device. The modulation depth of the device was 15% in the frequency region of interest. The simple structure of the device coupled with the obtained performance shows that graphene based devices have great potential for the development of THz technologies.

Radiometric sub-millimeter imaging is a candidate technology especially in security screening applications utilizing the property of radiation in the band of 0.2 – 1.0 THz to penetrate through dielectric substances such as clothing. The challenge of the passive technology is the fact that the irradiance corresponding to the blackbody radiation is very weak in this spectral band: about two orders of magnitude below that of the infrared band. Therefore the role of the detector technology is of ultimate importance to achieve sufficient sensitivity. In this paper we present results related to our technology relying on superconducting kinetic inductance detectors operating in a thermal (bolometric) mode. The detector technology is motivated by the fact that it is naturally suitable for scalable multiplexed readout systems, and operates with relatively simple cryogenics. We will review the basic concepts of the detectors, and provide experimental figures of merit. Furthermore, we will discuss the issues related to the scale-up of our detector technology into large 2D focal plane arrays.

Multispectral systems for detection of concealed dangerous objects are becoming more popular because of their higher effectiveness compared to mono-spectral systems. So far, the problem of detecting objects hidden under clothing was considered only in the case of airports but it is becoming more important for public places like metro stations, and government buildings.

Exploration of new spectral bands as well as development of technology result in introduction of new solutions – both mono and multispectral. It has been proved that objects hidden under clothing can be detected and visualized using terahertz (THz) cameras. However, passive THz cameras still offer too low image resolution for objects recognition. Limited range is another issue of passive imagers. On the other hand new infrared cameras offer sufficient parameters to detect objects covered with fabrics in some conditions, as well as high image quality and big pixel resolutions.

The purpose of the studies is to investigate and compare the possibilities of using passive cameras operating in long wavelength infrared (LWIR) and THz spectral ranges for detection of concealed objects. For the purpose of investigations, commercial imagers operating in 6.5-11.7 μm and 250GHz (1.25mm) were used. In the article, we present the measurement setup and the results of measurements in various operating conditions. Theoretical studies of both spectral bands focused on detection of objects with passive imagers are also presented.

In this study common clothing and variety of textile materials were used in research on its influence on remote materials identification. Experimental setup was designed for the terahertz reflection spectroscopy of different materials located at a distance up to 5 m. The source of the radiation is a tunable solid-state optical parametric oscillator (OPO), which generates a narrow-band nanosecond pulses in the range of 0.7-2.7 THz. The signal is detected with hot electron bolometer (HEB). Investigations were carried out for 1 m, 3 m and 5 m distance between the examined sample and the system. Experiment was conducted in the 0.7 – 2.5 THz range. Fabrics subjected to testing were varied in terms of the fibers kind which they were made from and weights of test materials ranged from 53 g/m2 up to 420 g/m2. Also textiles with a composition consisting of several fibers with differing percentage of the fibers composition of each sample were measured. Information about textiles transmission was obtained in separate set of experiments. The study fabrics were made of viscose, polyester, cotton, spandex, wool, nylon, leather, flax.

Amplitude-phase errors and mutual coupling errors among multi-channels in digital array radar (DAR) will seriously deteriorate the performance of signal processing such as digital beam-forming (DBF) and high resolution direction finding. In this paper, a combined algorithm for error calibration in DAR has been demonstrated. The algorithm firstly estimates the amplitude-phase errors of each channel using interior calibration sources with the help of the calibration network. Then the signals from far field are received and the amplitude-phase errors are compensated. According to the subspace theories, the relationship between the principle eigenvectors and distorted steering vectors is expressed, and the cost function containing the mutual coupling matrix (MCM) and incident directions is established. Making use of the properties of MCM of uniform linear array, Gauss-Newton method is implied to iteratively compute the MCM and the direction of arrival (DOA). Simulation results have shown the effectiveness and performance of proposed algorithm. Based on an 8-elements DAR test-bed, experiments are carried out in anechoic chamber. The results illustrate that the algorithm is feasible in actual systems.

Spatio-spectral distribution of THz radiation generated by two-color femtosecond laser breakdown in air is investigated theoretically. The theoretical model is based on the fast oscillating light field propagation and self-consistent free electron generation process. We find that the THz emission spectrum has both the low-frequency component related to the transient photocurrent with the maximum spectral intensity at ~1 THz, and the high-frequency component at ~10 THz related to the nonlinear response of bound electrons.

This paper presents the measurement and analysis method for detection of the mm-wave signal at 96 GHz, by using a low-cost microbolometer infrared (IR) camera with 70 μm pixel-pitch optimized for detection in the 8-12 μm (LWIR) range. The mm-wave beam derived from a multiplied Schottky diode based source is detected within ~ 65 % of the whole area of a 160×120 pixel focal plane array microbolometer sensor. Under ~73 mW incident power, responsivity is measured as 7.3 V/W, and the average noise for the measurement is determined as 12 μV, which includes both detector and readout electronics contribution. From the measured parameters, the integrated Noise Equivalent Power (NEP) is calculated as 1.63 μW within the 7.8 kHz readout bandwidth. By using a simple setup, it is shown that a low-cost microbolometer camera which is designed for LWIR range can detect a distinct mm-wave beam at 96 GHz.