Millimeter wave imaging: a historical review

Abstract

The SPIE Passive and Active Millimeter Wave Imaging conference has provided an annual focus and forum for practitioners in the field of millimeter wave imaging for the past two decades. To celebrate the conference's twentieth anniversary we present a historical review of the evolution of millimeter wave imaging over the past twenty years. Advances in device technology play a fundamental role in imaging capability whilst system architectures have also evolved. Imaging phenomenology continues to be a crucial topic underpinning the deployment of millimeter wave imaging in diverse applications such as security, remote sensing, non-destructive testing and synthetic vision.

Microwave Imaging in Security — Two Decades of Innovation

“…In such, the microwave signals can easily penetrate clothing and reveal concealed items, e.g., explosives and firearms. The limitations of diffraction led to a strong interest in utilizing shorter wavelengths in order to maintain a reasonable image resolution [1]. Frequencies in the millimeter-wave (mmWave) range thus have become the favorite choice for most vendors despite the high cost burden associated.…”

Quality Mapping of Offset Lithographic Printed Antenna Substrates and Electrodes by Millimeter-Wave Imaging

“…mm-wave and THz imaging techniques have been developed for last 20 years [23]. Security check-out imaging systems at airports is the most successful civil application in recent years [24], though the low-throughput imaging rate still impedes its screening efficiency. To achieve quality inspection with a high speed, on a large scale and with a high volume throughput in printing electronic industries, in this work, antenna line scanning and THz time domain spectroscopy (TDS)-based charge-coupled device (CCD) imaging systems are implemented to monitor the surface uniformity of the printed antenna substrate boards and electrodes, as well as to quantify their functionality, particularly the permittivity and loss properties for antenna design.…”

Phase Method for Visualization of Hidden Dielectric Objects in the Millimeter Waveband

“…The ability to visualize metal objects behind a dielectric barrier has been shown by holographic methods [1] and direct radiovision [2,3,4,5]. In microwave, millimeter wave and THz, objects made from low loss dielectric material, including explosives, have a low reflectance, but they change the phase of the transmitted wave.…”

“…We refer such objects as phase objects. Phase objects are also visualized for clearance [2]. However, it has not been possible to obtain dielectric object’s images against the reflecting body behind an obstacle yet.…”