This PDF file contains the front matter associated with SPIE Proceedings Volume 7485, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Millimeter-wave and terahertz radar systems can play an important role in multimodal layered sensing systems targeted at measuring both physiological and behavioral biometric data for security and medical applications. We will describe a 228 GHz heterodyne radar system that is capable of measuring respiration rates at standoff distances of up to 50 meters and simultaneously measure respiration and heartbeat rates at a distance of 10 meters. We will discuss the latest hardware and signal processing developments and a wide range of studies aimed at optimizing the performance of the system under a variety of potential field applications.

We present a handheld fiber-coupled terahertz spectrometer operating at a center wavelength of 1550 nm. The key elements are a fs-fiber laser, a fiber stretcher delay line and fiber-coupled antennas, which contain novel InAlAs-InGaAs multi layer chips. First experimental data obtained with this system demonstrates its great potential and robustness. In addition, we investigate different hazardous and harmless liquids in reflection geometry. These experiments show that liquids are in principle distinguishable by terahertz spectroscopy. Finally, first steps towards an algorithm that allows for an extraction of the liquids dielectric properties are discussed. The algorithm works for the analysis of reflection data even if the liquid is located inside a container.

A method of detecting concealed handguns and knives, both on and off body, has been developed. The method utilizes aspect-independent natural, complex resonances (poles) excited by illuminating the target with frequency swept, ultrawide band microwaves in the range 0.5 - 18 GHz. These natural resonances manifest as a Late Time Response (LTR) that extends significantly (~ 5 ns) beyond the direct reflections from the human body (the Early Time Response) and are of the form of a superposition of exponentially decaying sinusoidal waveforms. Two handguns are examined, both on the human body and in isolation, by the established methodology of applying the Generalised-Pencil-Of-Function to the late time response data of the target. These poles allow the weapon to be effectively classified. Out of plane polarized (cross-polarized) scattered response is used here as this gives improved discrimination between the early and late time responses. Determination of the presence or absence of particular weapons concealed under clothing, on the human body, is demonstrated. A novel bow-tie slot antenna is described which has good pulse and frequency response over the range 0.3-1 GHz and which is suitable for excitation of the fundamental natural resonances.

This paper reports on a new dielectric liquid sensor that utilizes an RF sparkgap transmitter coupled with an aluminum microwave resonant cavity. The transmitter is a micromilled polymer transmitter housing with patterned copper electrodes that generate micro-arcs. This transmitter which operates outside the measured liquid generates a directed ultrawideband signal which is received by the aluminum waveguide. Absorption resonances in the microwave cavity, measured with a spectrum analyzer are a function of the liquids' dielectric constant at lower frequencies, as well as from molecular vibrations/rotations at higher frequencies. In many chemical manufacturing processes, liquids being manufactured are removed, tested in a lab, and then disposed of, or else they will contaminate the full batch. In beer brewing, for instance, samples are removed, density tested for alcohol content, then disposed of. Using this sensor, the chemical process could be continuously monitored by a computerized system without risk of contamination.

The contactless control of persons and the remote surveillance of sensitive infrastructures are important tasks in order to provide the required security measures to protect the human population against the threads of international terrorism. Passive microwave imaging allows a daytime independent observation and examination of objects and persons under nearly all adverse ambient conditions without artificial exposure, hence fully avoiding health risks. The penetration capability of microwaves provides the detection of objects through atmospheric obstacles like bad weather, fog or dust, vapour and smoke, as well as through thin non-metallic materials and clothing. For the latter the detection of hidden objects like weapons, explosives, and contraband is possible by monitoring dielectric anomalies. The experiment "Common Shield" is part of a perennial investigation series leaded by the "Center for Transformation of the German armed forces (Bundeswehr)". In 2008 the protection of soldiers and facilities was experimentally investigated under the aspect of a networked operational leadership. In this context as well a harbour protection trial was carried out in August/September 2008 at the naval base Eckernfoerde in Germany. This trial was part of the NATO CNADs program of work for "Defence Against Terrorism (DAT)" starting in 2003, and Germany is the lead nation for item 7 on "Technology for Intelligence, Surveillance, Reconnaissance & Target Acquisition of Terrorists (ISRTA)". One main activity in the Eckernfoerde trial was the simulation of a military entrance control facility by a tent including various imaging and a chemical sensor suite in order to provide security for a military camp. Besides commercial optical and infrared cameras various passive millimeter-wave imagers have been used from different German research institutions. The DLR Microwaves and Radar Institute, Department for Reconnaissance and Security (HR-AS), provided an imaging radiometer scanner operating at W band. A multitude of situations have been simulated and many persons carrying hidden objects under their clothing have been scanned. The ongoing evaluation of the radiometer measurements are shown and discussed in the paper.

Millimetre and terahertz radiation penetration into materials enables non-destructive testing capabilities for the aerospace industry, either remotely using imaging technology or locally using microscope type diagnostics. This paper presents measurements made on Norcoat and Prosial, used in the aerospace industry for thermal insulation and on carbon fibre, used for its high strength weight ratio. Michelson interferometer measurements over the band 100 GHz to 1 THz, with a 30 GHz spectral resolution, are presented, together with images of a range of samples taken using a 35 GHz real-time imaging system. The measured optical properties of these materials are examined and used in modelling to predict signatures of failure modes in these materials when they are attached to cryogenic fuel tanks.

The full potential of terahertz imaging systems for nondestructive aerospace imaging applications has not been realized due to the lack of data linking damage and defects to terahertz signatures coupled with the complexity of modeling the signatures. Terahertz systems (0.1 - 2.0 THz) may be ideally suited for NDI applications because of the ability of THz radiation to penetrate through substances commonly found on the surfaces of aircraft structures while maintaining the optical resolution required to detect defects. We will discuss several systems that we have used to study the signatures of a set of target samples with known defects.

Significant efforts are underway to use either passive or active MMW and Sub-MMW imaging systems to detect objects concealed under clothing. Some have reached the point of commercial availability and have proved useful for contraband detection under controlled conditions. Studies have shown that when the conditions are uncontrolled, passive techniques become less desirable for contraband detection at standoff ranges which give the operators a margin of safety. In recent years, several programs have been funded to investigate using active techniques in the range of 100 to 1000 GHz for standoff detection out to ranges of 100m, a range which has been cited by some to be a desirable operating range. This paper will build on previous work to compare the performance of passive and active sub-MMW imagers used for detecting objects concealed under clothing. The analysis is designed to separate the effects of phenomenology and system components so that tradeoffs in transmitter and receiver characteristics can be performed. The derivation of the analysis and various examples of tradeoffs will be presented.

The unique ability of the millimeter-wave portion of the spectrum to penetrate typical visual obscurants has resulted in a wide range of possible applications for imagers in this spectrum. Of particular interest to the military community are imagers that can operate effectively in Degraded Visual Environments (DVE's) experienced by helicopter pilots when landing in dry, dusty environments, otherwise known as "brownout." One of the first steps to developing operational requirements for imagers in this spectrum is to develop a quantitative understanding of the phenomenology that governs imaging in these environments. While preliminary studies have been done in this area, quantitative, calibrated measurements of typical targets and degradation of target contrasts due to brownout conditions are not available. To this end, we will present results from calibrated, empirical measurements of typical targets of interest to helicopter pilots made in a representative desert environment. In addition, real-time measurements of target contrast reduction due to brownout conditions generated by helicopter downwash will be shown. These data were acquired using a W-band, dual-polarization radiometric scanner using optical-upconversion detectors.

Millimeter-wave (mmW) imaging is presently a subject of considerable interest due to the ability of mmW radiation to penetrate obscurants while concurrently exhibiting low atmospheric absorption loss in particular segments of the spectrum, including near 35 and 94 GHz. As a result, mmW imaging affords an opportunity to see through certain levels of fog, rain, cloud cover, dust, and blowing sand, providing for situational awareness where visible and infrared detectors are unable to perform. On the other hand, due to the relatively long wavelength of the radiation, achieving sufficient resolution entails large aperture sizes, which furthermore leads to volumetric scaling of the imaging platform when using conventional refractive optics. Alternatively, distributed aperture imaging can achieve comparable resolution in an essentially two-dimensional form factor by use of a number of smaller subapertures through which the image is interferometrically synthesized. The novelty of our approach lies in the optical upconversion of the mmW radiation as sidebands on carrier laser beams using electro-optic modulators. These sidebands are subsequently stripped from the carrier using narrow passband optical filters and a spatial Fourier transform is performed by means of a simple lens to synthesize the image, which is then viewed using a standard near-infrared focal plane array (FPA). Consequently, the optical configuration of the back-end processor represents a major design concern for the imaging system. As such, in this paper we discuss the optical configuration along with some of the design challenges and present preliminary imaging data validating the system performance.

Passive millimeter wave (mmW) imagers have improved in terms of resolution sensitivity and frame rate. Currently, the Office of Naval Research (ONR), along with the US Army Research, Development and Engineering Command, Communications Electronics Research Development and Engineering Center (RDECOM CERDEC) Night Vision and Electronic Sensor Directorate (NVESD), are investigating the current state-of-the-art of mmW imaging systems. The focus of this study was the performance of mmW imaging systems for the task of small watercraft / boat identification field performance. First mmW signatures were collected. This consisted of a set of eight small watercrafts; at 5 different aspects, during the daylight hours over a 48 hour period in the spring of 2008. Target characteristics were measured and characteristic dimension, signatures, and Root Sum Squared of Target's Temperature (RRSΔT) tabulated. Then an eight-alternative, forced choice (8AFC) human perception experiment was developed and conducted at NVESD. The ability of observers to discriminate between small watercraft was quantified. Next, the task difficulty criterion, V50, was quantified by applying this data to NVESD's target acquisition models using the Targeting Task Performance (TTP) metric. These parameters can be used to evaluate sensor field performance for Anti-Terrorism / Force Protection (AT/FP) and navigation tasks for the U.S. Navy, as well as for design and evaluation of imaging passive mmW sensors for both the U.S. Navy and U.S. Coast Guard.

An advanced step-graded Gunn diode is reported, which has been developed through joint modelling-experimental work. The ~ 200 GHz fundamental frequency devices have been realized to test GaAs based Gunn oscillators at sub-millimetre wave for use as a high power (multi mW) Terahertz source in conjunction with a mm-wave multiplier, with novel Schottky diodes. The epitaxial growth of both the Gunn diode and Schottky diode wafers were performed using an industrial scale Molecular Beam Epitaxy (V100+) reactor. The Gunn diodes were then manufactured and packaged by e2v Technologies (UK) Plc. Physical models of the high power Gunn diode sources, presented here, are developed in SILVACO.

In order to exploit new possibilities of THz sensing and imaging, it is not only necessary to generate and detect THz radiation but also to measure the radiant power of the THz sources and the responsivity of the detecting systems traceable to the international system of units (SI). This has been missing in the THz range up to now. The Physikalisch- Technische Bundesanstalt (PTB) has focused on this challenging task by using two complementary optical approaches: source- and detector-based THz radiometry. Both methods have been successfully prototyped, and a pyroelectric THz detector with known aperture was used to verify the consistency of the two independent calibration methods.

A new kind of 8×8 focal plane array (FPA) based on glow discharge detector (GDD) elements was constructed and tested experimentally. First THz images of this FPA are presented. The data acquisition of this system is performed with a special VLSI board designed for this system. Previously, signal detection of the FPA elements was based upon a lock in amplifier (LIA) which limited the rate of image formation. This was in order to detect weak signals required for stand-off remote detection. Switching mode is necessary in order to save energy but stabilization time of the GDD found to be 0.5 sec. Recent investigations proved that it is possible to overcome the above timing limitations. It was shown that heterodyne detection yielded 40 times more sensitivity than the direct detection, thus in many circumstances obviating the need for a LIA. Moreover, GDD stabilization time of less than 1 msec was achieved. These developments should enable video rate THz imaging using GDD FPAs.

Recent advances in MMIC-based solutions dedicated to imaging and sensing applications in the atmospheric windows located around 140, 200 and 300 GHz are presented. The MMICs comprise the individual components of a typical architecture of heterodyne analog frontends, and their combination into MMICs performing several functionalities or with full receiver capability. We discuss low-noise amplifiers up to 300 GHz, frequency multipliers and mixers operating up to 300 GHz, a power amplifier MMIC achieving more than 11 dBm of output power at 140 GHz, and a 200 GHz multi-functional, heterodyne receiver MMIC driven by a subharmonic local oscillator signal with low power requirements.

Portability, low cost and fast acquisition rates are key features that a THz imaging system should satisfy for extended commercialized applications. With regards to these features, the source - detector association of a THz Quantum Cascade Laser (QCL) with an un-cooled micro-bolometer two-dimensional array looks promising for THz active imaging. QCLs performance is rapidly improving, with higher operating temperatures and output powers recently demonstrated. On the detector side, un-cooled micro-bolometer array opens the way to real-time video rate, with no raster scanning and potential low cost. In parallel to the development of room temperature micro-bolometer sensors specifically designed for the THz range, the authors have characterized experimentally the sensitivity of CEA-LETI standard amorphous Silicon infrared microbolometers illuminated by a 3THz QCL. The sensitivity of these existing sensors is then compared to the expected sensitivity of the CEA-LETI upcoming THz sensors.

In the last decade there has been an increasing interest for terahertz technology. The reasons of this increasing interest is mainly due to its potential use in security applications with particular reference to drug and explosive detection. In this framework, the appropriate integration of metamaterials with nanotechnologies looks very promising for the construction of new compact low cost devices. Following this line of argument, we are exploring the possibility to combine the use of nanocathodes as sources of electron beams with engineered metamaterial layers in order to deliver coherent tunable terahertz radiation. More exactly, starting from a revised design of microwave sources, we discuss the issues related to manufacture miniaturized planar devices taking advantage of some appropriate integration of post silicon technologies.

The method of image reconstruction with sub-diffraction resolution in radio vision devices (RVD) of shortwave millimeter and terahertz frequency range is proposed. The method is based on image scanning using two-dimensional receiving element array of RVD when array and image move circularly in common plane relatively each to other (rotating or not rotating) with small eccentricity between their centers. The results of scanning are signals reading out by detectors of array receiving elements. Each signal is proportional to the integral of two functions product. One function is a perfect image field distribution of the observed object received by RVD without diffraction distortion. Another one is RVD optical (quasioptical) transfer function comprising beams delivering incident radiation to detectors of array. The second function takes into account whole received radiation beam paths from RVD input to each detector including the effect of diffraction and reciprocal circular scanning of array and image. The image of observed object itself can be found solving inverse ill-posed problem determined by mentioned above integral relations. The estimation using computer simulation has shown that proposed method permits to increase resolution up to ten times in comparison with the case of diffraction restriction. The method is aimed at radioastronomy telescopes and RVD's for the security, medical diagnostics and other systems.

Detection and recognition of covered explosive materials in the THz range can be devided into two areas - passive and active systems. Passive systems in the submilimeter (100÷300 GHz) as well as the terahertz (0.3÷3 THz) range base on thermal emissivity of exemined bodies. Such devices are designed to control persons and baggage in airports mainly at the temperature about 300K. Thermal emissivity of real bodies can be obtained from the Planck's formula for perfect black bodies and an emissvity coefficient. The emissivity coefficient of the real bodies can be determined from laboratory measurements of spectral transmission and reflection for the specific materials. However, values of the thermal emissivity detected in real cases depend strongly on surface of the material, direction of detection in relation to normal to the emitting surface, atmosphere and covering materials. These factors introduce attenuation of the emissivity what can cause camouflage of the characteristic features of individual materials and makes them difficult to identify. In this paper we present the value of the emissivity of hexogen (RDX) based on transmission measurements in FTIR spectrometer. The obtained emissivity is used to simulate intensity of radiation on an aperture.