Active metamaterials have been used to realize terahertz imaging with a single-pixel detector Compressive techniques permit high-fidelity images to be acquired at high frame rates The technique involves no moving parts and yields improved signal-to-noise ratios over standard raster scanning techniques

Terahertz compressive imaging with metamaterial spatial light modulators

A compact and uniplanar antenna with broadband characteristics is presented. The novel Yagi-like printed dipole array antenna is fed by a microstrip-to-coplanar strip transition, and uses the truncated microstrip ground plane as its reflecting element. An X-band prototype measures a bandwidth of 17%. With 6.5 dB gain, 18 dB front-to-back ratio, and lower than -15 dB cross-polarisation level at 10 GHz.

Microstrip-fed quasi-Yagi antenna with broadband characteristics

An overview of recent progress in the research and development of micromachined antennas, transmission lines, waveguides structures, and planar movable components for terahertz frequencies is presented. Micromachining is shown to provide a low-cost alternative to conventional (and very expensive) machined-waveguide technology, resulting in antennas with excellent radiation patterns, low-loss tuners, and three-dimensional (3-D) micromachined structures suitable for terahertz applications. Fabrication procedures for a variety of micromachined waveguide and planar structures are described here, along with measured terahertz performance. Applications of micromachining techniques for terahertz systems include focal-plane imaging arrays requiring a large number of elements and low-cost receivers for commercial and industrial applications such as pollution monitoring.

Micromachining for terahertz applications

In one aspect, the present invention provides an apparatus 10 for imaging. At least one source 12 (or 12/14 ) of composite radiation illuminates a field of view 16 . The radiation includes a set of multiple phase-independent partials that are independently controllable and exhibit distinct physical features. A quasi-optical element 21 is disposed between the field of view 16 and a multi-element receiver 18 . The multi-element receiver 18 is disposed to receive image radiation 28 from the quasi-optical element 21 . Particular ones of the receiver elements transform the image radiation 28 into a set of electrical signals that include information relating to features of the partials.

Systems and methods for millimeter and sub-millimeter wave imaging

Significant advances in the development of millimeter-wave and terahertz (30-10 000 GHz) technologies have been made to cope with the increasing interest in this still not fully explored electromagnetic spectrum. The nature of electromagnetic waves over this frequency range is well suited for the development of high-resolution imaging applications, molecular-sensitive spectroscopic devices, and ultrabroadband wireless communications. In this paper, millimeter-wave and terahertz antenna technologies are overviewed including the conventional and nonconventional planar/nonplanar antenna structures based on different platforms. As a promising technological platform, substrate-integrated circuits (SICs) attract more and more attention. Various substrate-integrated waveguide (SIW) schemes and other synthesized guide techniques have been widely employed in the design of antennas and arrays. Different types of substrate-integrated antennas and beamforming networks are discussed with respect to theoretical and experimental results in connection with electrical and mechanical performances.

Substrate-Integrated Millimeter-Wave and Terahertz Antenna Technology

The authors discuss critical aspects of imaging system design and describe several different imaging systems employing focal plane array receivers operating in the 3-mm-2-mm wavelength range. Recent progress in millimeter-wavelength optics, antennas, receivers and other components permits greatly enhanced system performance in a wide range of applications. A radiometric camera for all-weather autonomous aircraft landing capability and a high sensitivity cryogenically cooled array for use in radio astronomical spectroscopy are presented. A near-focus system for identification of plastic materials concealed underneath clothing employs a two element lens, and has been demonstrated in active (transmitting) and passive (radiometric) modes. A dual-mode imaging system for plasma diagnostics utilizes both active and passive modes at its approximately=140-GHz operating frequency to study small-scale structure. The radiometric imaging systems employ between 15 and 256 Schottky barrier diode mixers, while the imaging receivers for the active systems include 64-element video detector arrays. >

Focal plane imaging systems for millimeter wavelengths

Plastic weapons and explosives concealed under clothing present unique challenges to conventional contraband detection technology. Nonmetallic, nonmagnetic objects cannot be detected by conventional systems that use low-frequency magnetic fields. Common techniques that can reveal these types of contraband involve X-rays or other ionizing radiation, which are inappropriate for use on the human body. We have found that millimeter-wavelength radiation is an excellent means for revealing objects hidden beneath clothing. Naturally occurring thermal radiation from the subject can be used in a process called passive imaging. An alternative process called active imaging uses one or more millimeter-wave sources to illuminate the subject. In this paper we describe the basic theory of millimeter-wave imaging. We present single-channel scanned images of both metal and plastic objects concealed beneath ordinary clothing. The clothing appears substantially transparent and the objects are distinguishable. The paper concludes with a discussion of prospective advances that should make multiple-channel real-time imaging systems practical.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

C. T. Hsieh

Papers

Focal plane imaging systems for millimeter wavelengths

Contraband detection through clothing by means of millimeter-wave imaging