Christopher A. Martin

Passive millimeter-wave imaging for airborne and security applications

As a result of its relatively short wavelength coupled with relatively high penetration of such things as fog, bad weather and clothing, millimeter-wave imaging provides a powerful tool for both airborne and security type applications. By using a passive approach such as that implemented here, it is possible to image through bad weather or detect concealed weapons and articles all without generating any form of radiation that might either help an enemey or raise health concerns. In this paper we will show imagery from our second generation state-of-the-art unit and discuss the technology involved.

Regularization methods for inverse problems in X-ray tomography

Scintillators, optical systems and CCD cameras used to record projections also blur them. Therefore the recorded projections are smooth functions of spatial variables. This can be used to construct special methods to suppress ring artefacts. Several such algorithms based on ideas of the theory of inverse and ill-posed problems and using various forms of Tikhonov functional are proposed: a fast ring artefact suppression algorithm in a case of homogeneous specimens and its modified versions for anisotropically attenuated samples.

A passive millimeter-wave imaging system for concealed weapons and explosives detection (Invited Paper)

This paper describes a passive millimeter-wave image scanner that leverages technologies previously developed for a video-rate passive millimeter-wave camera (PMC) [1, 2]. The imager has a prime focus elliptical frequency scanned antenna operating in the 75-93 GHz millimeter-wave band, a low noise receiver and a vertical beam former that allows the instantaneous capture of 128 pixel (vertical) column images in 1/30th of a second, with 2-3 K sensitivity. Two dimensional images are created by mechanically rotating the antenna, which produces a 128x60 raster image in 2 seconds. By integrating (averaging) images over a longer time period, we have demonstrated a sub-degree temperature resolution. This sensor has proven itself as a low cost tool for studying the potential of W-band passive imaging for various applications.

Rapid passive MMW security screening portal

Trex Enterprises Corporation has developed a full body passive millimeter-wave security screening imager. The system images naturally occurring W-band blackbody radiation, which penetrates most types of clothing. When operated indoors, the primary mechanism for image formation is the contrast between body heat radiation and the room temperature radiation emitted or reflected by concealed objects that are opaque at millimeter-wave wavelengths. Trex Enterprises has previously demonstrated that an imager noise level of 0.25 to 0.5 K is necessary to detect and image small concealed threats indoors. Achieving this noise level in a head-to-toe image required image collection times of 24 seconds using the previous imager design. This paper first discusses the measurement of the noise temperature of the MMW detectors employed. The paper then explores reducing the image collection times through a new front-end amplifier design and the addition of more imaging units. By changing the orientation and direction of travel of the imaging units, the new design is able to employ more detectors and collect imagery from a subjects front and sides. The combination of lower noise amplifiers and a new scanning architecture results in an imager appropriate for high throughput security screening scenarios. Imagery from the new configuration is also presented.

Concealed weapons detection with an improved passive millimeter-wave imager

Trex Enterprises has developed a second-generation passive millimeter-wave imaging system for detection of concealed weapons and explosives at standoff ranges. Passive millimeter-wave sensors form an image from naturally emitted blackbody radiation in the millimeter-wave portion of the electromagnetic spectrum. Radiation at this wavelength passes through most types of clothing, allowing the user to acquire an image of any articles on a suspect’s person that differ significantly from the human body in their reflectivity or radiometric temperature at millimeter-wave wavelengths. Trex Enterprises previously demonstrated a first-generation concealed weapon detection system with the ability to detect handguns and knives under heavy clothing at a range of 27’. The second-generation imager, while similar in concept, has an improved field-of-view and a much reduced size and weight. The imager is to be put through a battery of tests by both Trex Enterprises and the National Institute Of Justice to determine its ability to detect both metallic and non-metallic knives and handguns as well as various types of explosive devices. The tests will be conducted indoors and outdoors at various ranges.

Real-time wide field of view passive millimeter-wave imaging

Passive millimeter wave imaging has been shown to be a useful for enhanced vision and concealed weapons detection applications. Trex Enterprises is developing a second generation passive millimeter wave imaging system which operates in real time with a 20 X 30 degree field of view and a 2K temperature sensitivity. This system is based on a pupil-plane aperture architecture used in a first generation system, but also includes advances in technology which improve system performance and utility. These include a flat panel dielectric antenna and W-band amplifiers, detectors, and processors. This second generation system will serve as the basis for a production millimeter-wave imager.

Real-time millimeter-wave imaging radiometer for avionic synthetic vision

ThermoTrex Corporation (TTC) has developed an imaging radiometer, the passive microwave camera (PMC), that uses an array of frequency-scanned antennas coupled to a multi-channel acousto-optic (Bragg cell) spectrum analyzer to form visible images of a scene through acquisition of thermal blackbody radiation in the millimeter-wave spectrum. The output of the Bragg cell is imaged by a standard video camera and passed to a computer for normalization and display at real-time frame rates. One application of this system could be its incorporation into an enhanced vision system to provide pilots with a clear view of the runway during fog and other adverse weather conditions. The unique PMC system architecture will allow compact large-aperture implementations because of its flat antenna sensor. Other potential applications include air traffic control, all-weather area surveillance, fire detection, and security. This paper describes the architecture of the TTC PMC and shows examples of images acquired with the system.

High-resolution passive millimeter-wave security screening using few amplifiers

Trex Enterprises has applied the frequency scanned antenna architecture found in the ST-150 stand-off imager to closein personnel screening devices, including a full-body imager and a handheld scanning imager. These devices present the user with an image with 3mm square pixels and 10-18 mm spatial resolution using few amplifiers and a low level of mechanical complexity. The frequency scanned architecture permits the real-time imaging of a linear array of 64 pixels with a single amplifier module. The linear imager or imagers are slowly mechanically scanned to provide a twodimensional image. The imagers were used to capture images of concealed threat items at thermal resolutions from 1 K to 0.2 K, indoor and outdoors. Image quality is generally superior to that of stand-off detectors, detecting items as small as 10 mm.

Real-time passive millimeter-wave imaging from a helicopter platform

Real time passive millimeter-wave imaging systems have a wide variety of uses from aircraft navigation and landing in fog to detection of concealed weapons. A useful imaging system for flight platforms requires a large number of pixels and a high frame rate combined with a small antenna volume and a lost cost. We present a millimeter-wave imaging system which uses 32 MMIC low noise amplifiers to display a 60 X 75 pixel image at a 30 Hz frame rate. The systems pupil-plane phased array architecture allows for a relatively thin large aperture antenna. A remotely located processor utilizes microwave guiding circuit boards to perform phase and frequency discrimination on the radiation received by the antenna array.

Passive millimeter-wave imaging using a sparse phased-array antenna

Passive Millimeter-wave Imaging (PMI) technology provides a powerful sensor capability for military and commercial imaging applications, during day or night, and in adverse weather. Recent advances in high-frequency antennas, MMW electronics, and high-speed signal processing, have brought real-time, high-contrast, high-resolution, wide-field PMI into the realm of technological feasibility. However, the substantial size, weight, and cost of previous PMI architectures have proved impractical for all but a few scientific implementations, creating a barrier to large- volume production. This reality has precluded PMI usage in several applications with demonstrable benefits, such as aircraft navigation and landing, radio-silent airborne surveillance/battle damage assessment, concealed weapons detection (CWD), or through-wall imaging. A new PMI architecture has been demonstrated which allows this wide- area, near-real-time staring capability with significant reductions in size, weight, and cost relative to previous designs. Specifics of this new PMI architecture will be presented along with a host of imaging data representing its current capability for airborne imaging, CWD, and through- wall imaging.