This PDF file contains the front matter associated with SPIE Proceedings Volume 10800, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

An aperture synthesis passive millimeter wave (PMMW) imager using 256 antennas with 1 GHz bandwidth is currently under development in Beihang University. This imager is designed for concealed contraband detection on human body in indoor environment at video imaging rate. Design of the digital cross-correlation subsystem is presented in this paper. High-speed clocked comparators are used to perform 1-bit A/D convention, while FPGAs are used to perform further signal processing. The cross-correlation system is split into three parts: 1-bit A/D conversion, data distribution and signal processing. The analog signals from receivers are sampled and distributed to several cross-correlation processors based on FPGA. A sampling scheme performing per-bit deskew and serial-to-parallel conversion and a correlator performing cross-correlation of 128 channels on a signal FPGA are presented in this paper. Test results from a 64-channel test board are also presented, which prove the design works.

Aperture synthesis for passive millimetre wave imaging provides a means to screen people for concealed threats in the extreme near-field configuration of a walk-through portal; a regime where the imager to subject distance is of the order of both the required depth-of-field and the field-of-view. As shown here, the field-of-view in these scenarios is unlimited and the spatial resolution is slightly better than the half-wavelength Abbe microscope resolution. As in this scenario the subject would be surrounded by receiving antennas, all surfaces of the human body will be in focus with high-resolution, even at the low frequencies. For example at a frequency of 22.51 GHz the spatial resolution is in the region of ~ 7 mm. This capability is ideally suited to the aircraft security screening industry. Furthermore, the aperture synthesis imager is well suited to non-cooperate screening at longer ranges, as the antenna arrays may be deployed on almost any available surface. The field-of-view of these systems is likewise unlimited, extending from the near-field to the far-field. The spatial resolution of these systems, as here shown, is in the region of the half-wavelength resolution close to the imager, and slightly better than the Fraunhofer diffraction resolution limit at longer ranges. Therefore, also for the non-cooperate screening scenarios, the subject will always be in focus with the best possible spatial resolution allowed by the physics of imaging.

The characterization of dielectric materials is of great importance for many applications, being for instance quality control during product fabrication or status control of outside constructions over time. In many outside situations the objects of interest have limited accessibility, and the investigation has to be done without destruction of any part of the object and without any health risks for an operator. Hence remote sensing from stand-off position is desirable, and the use of microwaves, millimeter-waves or THz waves offers some penetration capability into matter, depending on its chemical and physical decomposition and of course frequency. Many objects of interest consist of a dielectric coating or enclosure, which can electromagnetically be treated as a dielectric layered structure or a dielectric slab surrounded by air.

Radar as an active remote sensing technology has great potential with respect to precise range measurements and spatial resolution. However, its mostly mono-static implementation suffers from low or no back reflection of signals in case of plane and tilted surfaces, delivering hence no information. In contrast radiometric imaging as passive remote sensing technology uses naturally generated noise-like radiation of thermal origin, being available everywhere and from all directions. Quite often the sky can be used as large illumination source, providing rather low radiation power compared to objects on Earth, using frequencies up to few hundred GHz. Furthermore, thermal radiation originally is un-polarized, but becomes polarized when reflected partly on a dielectric surface. Hence, the use of polarimetric measurements at various incidence angles can provide information on the type and structure of the reflecting object. The approach and the measurement setup are described. Experimental results of polarimetric measurements are shown and discussed.

According to the data from the World Health Organization, 285 million people are estimated to be visually impaired worldwide, and 39 million are blind. It is very difficult for visually impaired people to perceive and avoid obstacles at a distance during their travelling. To address this problem, we propose a sensor fusion system, which combines the RGBDepth sensor and millimeter wave radar sensor, to detect the surrounding obstacles. The range and velocity of multiple obstacles are acquired by the millimeter wave radar based on the principle of frequency modulated continuous wave. The positions of the obstacles are verified by the RGB-Depth sensor based on the contour extraction and MeanShift algorithm. The data fusion algorithm based on particle filters obtains accurate state estimation by fusing RGB-Depth data with millimeter wave radar data. The experiment results show that multiple obstacles with different ranges and angles are successfully detected by the proposed system. The measurement uncertainties are reduced by the data fusion system, meanwhile the effective detectable range is expanded compared to the detection with only RGB-Depth sensor. Moreover, the measurement results are stable when the illumination varies. As a wearable prototype, the sensor fusion system has the characteristics of versatility, portability and cost-effectiveness, which is very suitable for blind navigation application.

The Huynen polarisation fork as a representation of the full polarimetric radar signature represents a unique and natural description of a target. This paper investigates the use of full polarimetric radar operating over the band 18-26 GHz to measure the Huynen target parameters of size, orientation, helicity, skip angle and fork angle from a range of canonical polarimetric radar targets and classic concealed weapon surrogates. Measurement will determine how accurately the Huynen target parameters represent the geometries of the canonical targets and surrogate weapons such as concealed metal and ceramic guns, shrapnel and plane sheet dielectrics. Target backgrounds will be large area absorbers and the human body to enable assessment of the capability for stand-off concealed weapons detection. The system used for the measurement comprises a dual channel vector network analyser, a Turnstile orthomode transducer (OMT) and a conical horn antenna. The OMT has an isolation better than -35 dB between orthogonal polarisations. This system measures and calibrates the Sinclair matrices of targets, from which the Huynen target parameters are derived. A simple model of targets based on the original work in Huynen thesis back in 1970 will be presented, enabling comparison between measured and simulated Huynen target parameters to be made. Conclusions are that experimental measurements of the Huynen target parameters of canonical and surrogate targets agree well with the basic theory of the technique and simple model simulations.

Conventionally, for the fully polarimetrical calibration of a general non-reciprocal radar system, at least two calibrators such as a dihedral corner reflector plus a sphere are required. A new polarimetric passive radar calibrator for fully polarimetric calibration is proposed in this paper. With the new design, a single calibrator is enough for the same purpose. The electromagnetic scattering characteristic of the new calibrator is calculated by method of moment (MOM), demonstrating that the new calibrator is suitable for fully polarimetric calibration applications.

We report on the development and application of a random forest regressor that not only identifies but also estimates the relative concentrations of substances (one explosive and two simulants), both in one-substance and two-substance samples. Performance of the regressor is quantified using Receiver Operating Characteristics and the performance is contrasted with that of a simple Spectral Angle Mapping technique that worked well on single-substance samples [1-3].

In earlier experiments [1] we found there was significant transmission of THz radiation through carbon-fiber enforced composites, despite that fact that the dc conductivity of the carbon fibers is expected to be good and hence should prevent penetration of electro-magnetic radiation. To study the relationship between absorption of THz radiation and electrical conductivity we performed measurements on samples with different concentrations of graphene in an epoxy matrix. We observed an increased absorption of THz radiation with increased graphene concentration. Our conductivity measurements (simple transverse DC measurements using tin foil as electrodes that cover the two sample surfaces) showed the typical increase of several orders of magnitude with graphene concentration. Although both the conductivity and the THz absorption increase with graphene concentration, there is no direct cause-and-effect relation between the two quantities. Careful analysis shows that even the highest dc conductivity values cannot explain even the lowest observed values for the THz absorption coefficient.

We investigate an influence of sampling order for averaging of the THz images containing in their sequence captured by the THz passive camera developed by ThruVision Inc. We assume that the image noise is governed by Poisson process. Therefore, to suppress a noise it is necessary to choose the images for summing the frames of the passive THz camera in certain order. For example, we choose every second frame during one second for averaging. It allows decreasing a noise influence stronger than at summing all frames. Another improving the image quality may be achieved by adding a noise to an row images captured by the passive THz came with consequent averaging of this image sequence.

We demonstrate also high effectiveness of using IR Camera for the detection of objects hidden under the clothes. With this aim one needs to realize gradient of temperature along a travel line of a person.

Recent security concerns worldwide have made it necessary to put a large number of people through detailed security inspections in critical infrastructure and border entrances. It is desired to implement inspection processes, which will enhance security while providing improvements in several aspects, such as answering the high throughput at crowded places, standardizing control processes, minimizing operator errors and increasing the feel of security, without making individuals uncomfortable as possible. To answer these requirements, Active Terahertz Imaging Autonomous Biometric Security Access Control and Tracking Gate System, or TRay, integrates various security technologies. TRay offers epassport control, biometric identity check (fingerprint, face etc.) and THz imaging for concealed object detection. During the inspection process, the person using the gate is guided through e-passport control and biometric identity check steps by following a set of instructions, without requiring the assistance of an operator. The person will also be scanned for concealed objects by a THz imaging system. Locations of possible threat objects and contraband, made of metal and, in addition, ceramic, plastic, liquids etc. are identified using object detection algorithms. The system is able to generate a warning in case of a detected object, for further inspection of the location of the body part by security personnel. THz imaging system operates at a standoff distance, which allows scanning to be performed at any point during the inspection process, eliminating the need to use confined spaces for body scanning. Less human intervention and misunderstandings, decreased waiting time at passport/identification checkpoints, improved public satisfaction, standardized control duration, optimized use of space, easy tracking of passenger transitions, generating alarms in case of undesired transitions, 24/7 operation, forged document usage prevention and decreased workload on the security personnel are further advantages of the system, which is unique in terms of the features it combines.

We have investigated the influence of indium content (x) increase on spectral characteristics of In_xGa_1-xAs photoconductor. To avoid the mismatch between crystalline parameters of In_xGa_1-xAs and GaAs wafer we proposed to incorporate a step-graded metamorphic buffer layer. We showed that x increase strongly enhances THz emission and broadens THz spectrum of In_xGa_1-xAs. Since no polarity rehearsal of the THz waveform occurs and electron diffusion mobility increases up to 90% with x increase we attribute the increase of THz intensity to photo-Dember effect contribution. The maximum efficiency of optical-to-THz conversion was obtained for In_0.72Ga_0.28 As at optical fluence ~0.01 μJ=cm². The fabricated photoconductors can be used as promising photo-Dember or lateral photo-Dember THz emitters in pulsed THz spectroscopy and imaging, in particular, operating with long wave optical pump.

Sub-mm and mm waves are used in many applications such as spectroscopy and imaging, detection of weapons concealed under clothing, detection of diseases and non-destructive product inspection. By developing the THz detection mechanisms, the quality of this usability can be enhanced considerably. The commercial detectors currently used to detect THz waves range from Shottky diodes to bolometers, Golay cells and pyroelectric detectors. However, many of these detectors have limitations in terms of speed and responsivity. In addition, they have a common disadvantage of being expensive. For these reason, glow discharge detectors (GDDs) can be a good alternative since they are cheap and can detect mm-wave or THz radiations without the aforementioned limitations. To obtain optimal detection parameters, one needs to understand the interaction of the radiation with the plasma particles. In the literature, efforts to explain this interaction has focused on qualitative descriptions with analytical models. However, these theories have not been tested with real discharge parameters. For that reason, in this study, the plasma in the GDD is simulated by using previously developed parallel 1d3v Particle in Cell/Monte Carlo Collision (PIC/MCC) code to obtain the plasma parameters and determine the gas mixture ratios. Initial results show that the discharge current approximates the current measured through the home built glow discharge detector. Using these results an accurate simulation of the GDD discharge parameters has been performed. This platform will allow for understanding the effect of mm sub-mm radiation when added to the simulation which can aid in understanding optimum detection parameters.

Application of terahertz (THz) spectroscopy for biological tissues is strongly limited by the extremely low penetration depth due to THz absorption by tissue water. One of the possible solution of such problem is the usage of THz wave penetration-enhancing agents (PEA) for optical clearing of tissues. In the present paper, the transmission-mode THz spectroscopy of a set of PEAs (polyethylene glycol with different molecular weight, propylene glycol, ethylene glycol, and dimethyl sulfoxide) was performed in order to reconstruct their dielectric properties and compare them with that of water. The obtained results emphasize the feasibility of using PEG to enhance the depth of THz wave penetration into tissues.

The paper presents the results of application of terahertz radiation for detection of traces of explosives on surfaces of objects in reflected light. The process of detection and identification of explosives is based on a recording of interferograms of reflected radiation in spectral range of 0.5 -2.5 THz with help of a Michelson interferometer. The reverse Fourier processing lets to obtain reflection or transmittance spectra and images of objects. Spectral ranges for imaging are chosen by an operator. An installation elaborated for this purpose is described. Specific features of reflection spectra of some organic substances are determined.

A 110-170 GHz transceiver is designed and fabricated in a 130 nm SiGe BiCMOS technology. The transceiver operates as an amplifier for transmitting and simultaneously as a fundamental mixer for receiving. In a measured frequency range of 120-160 GHz, a typical output power of 0 dBm is obtained with an input power of +3 dBm. As a fundamental mixer, a conversion gain of -9 dB is obtained at 130 GHz LO, and a noise figure of 19 dB is achieved. The transceiver is successfully demonstrated as a FMCW radar front-end for distance measurement. With a chirp rate of 1.6×10¹² Hz/s and a bandwidth of 14.4 GHz, a range resolution of 2.8 cm is demonstrated, and transmission test is shown on different objects.

The results of the study saturation magnetization and crystallographic anisotropy doped with diamagnetic ions of hexagonal ferrites are presented. It is shown that the impedance matching properties of ferrimagnetic fillers depend on equality values of magnetic and dielectric permittivity composite material in the working wave band. The contribution of the proposed replacement complexes to the magnetic and dielectric permittivity resulting materials is determined. Magnetostatic and electrodynamic properties of composites based on doped hexaferrites type M and Z are studied. Hexagonal ferrites, which play the role of an impedance matching medium in frequency range 0.1-3 GHz, are obtained. Recommendations are offered on the possibility using impedance matching composite hexagonal ferrites in the development filtering and frequency separation systems.

The results of numerical electrodynamic modeling and experimental research of slotted waveguide radiator is presented. The operational frequency was decreased on 25%. It was found that the differences between the experimental and calculated characteristics are associated with the following factors: the inaccuracy of manufacture of the geometric dimensions of the slotted waveguide radiator, methodical error of the finite element method in calculating the characteristics, inaccuracy of the values of the relative permittivity and magnetic permeability.