Scott L. Cassidy

340-GHz 3D radar imaging test bed with 10-Hz frame rate

We present a 340 GHz 3D radar imaging test bed with 10 Hz frame rate which enables the investigation of strategies for the detection of concealed threats in high risk public areas. The radar uses a wideband heterodyne scheme and fast-scanning optics to achieve moderate resolution volumetric data sets, over a limited field of view, of targets at moderate stand-off ranges. The high frame rate is achieved through the use of DDS chirp generation, fast galvanometer scanners and efficient processing which combines CPU multi-threading and GPU-based techniques, and is sufficiently fast to follow smoothly the natural motion of people.

DEER Sensitivity between Iron Centers and Nitroxides in Heme-Containing Proteins Improves Dramatically Using Broadband, High-Field EPR.

This work demonstrates the feasibility of making sensitive nanometer distance measurements between Fe(III) heme centers and nitroxide spin labels in proteins using the double electron–electron resonance (DEER) pulsed EPR technique at 94 GHz. Techniques to measure accurately long distances in many classes of heme proteins using DEER are currently strongly limited by sensitivity. In this paper we demonstrate sensitivity gains of more than 30 times compared with previous lower frequency (X-band) DEER measurements on both human neuroglobin and sperm whale myoglobin. This is achieved by taking advantage of recent instrumental advances, employing wideband excitation techniques based on composite pulses and exploiting more favorable relaxation properties of low-spin Fe(III) in high magnetic fields. This gain in sensitivity potentially allows the DEER technique to be routinely used as a sensitive probe of structure and conformation in the large number of heme and many other metalloproteins.

Concealed threat detection with the IRAD sub-millimeter wave 3D imaging radar

Sub-millimeter wave 3D imaging radar is a promising technology for the stand-off detection of threats concealed on people. The IRAD 340 GHz 3D imaging radar uses polarization intensity information to identify signatures associated with concealed threats. We report on an extensive trials program which has been carried out involving dozens of individual subjects wearing a variety of different clothing to evaluate the detection of a wide range of threat and benign items. We have developed an automatic algorithm to run on the radar which yields a level of anomaly indication in real time. Statistical analysis of the large volume of recorded data has enabled performance metrics for the radar system to be evaluated.

Nonlinearity and phase noise effects in 340 GHz 3D imaging radar

Security scanning using sub-millimeter wave 3D imaging radar maps the subsurface structure of subjects, revealing objects hidden under clothing. This requires a wide dynamic range to detect small targets near large ones and centimeter range resolution to resolve small objects. For radar designers this translates into requiring a very low phase noise source which maintains good chirp linearity over a very wide fractional bandwidth, and other researchers have highlighted these effects. We present an assessment of the phase noise and chirp nonlinearity in our IRAD 340 GHz 3D imaging radar and make comparisons of different source architectures and nonlinearity compensation schemes.

Micro-doppler and vibrometry at millimeter and sub-millimeter wavelengths

Micro-Doppler is an emerging technique for the measurement and analysis of target modulation characteristics, rooted in the analysis of X-band radar measurements of people. Despite the advantage of higher Doppler sensitivity, there appears to be little such work reported at (sub-) millimeter wave frequencies. We have developed fully coherent, solid state, FMCW radar systems operating at 94 and 340 GHz, suitable for micro-Doppler and vibrometry studies (as well as SAR/ISAR), which make use of DDS chirp generation combined with upconversion and MMIC or Schottky diode frequency multiplication. Due to the low phase noise architecture, the phase (i.e. displacement) sensitivity can be below 1 micron in distance.

The use of composite pulses for improving DEER signal at 94 GHz

The sensitivity of pulsed electron paramagnetic resonance (EPR) measurements on broad-line paramagnetic centers is often limited by the available excitation bandwidth. One way to increase excitation bandwidth is through the use of chirp or composite pulses. However, performance can be limited by cavity or detection bandwidth, which in commercial systems is typically 100-200MHz. Here we demonstrate in a 94GHz spectrometer, with >800MHz system bandwidth, an increase in signal and modulation depth in a 4-pulse DEER experiment through use of composite rather than rectangular π pulses. We show that this leads to an increase in sensitivity by a factor of 3, in line with theoretical predictions, although gains are more limited in nitroxide-nitroxide DEER measurements.

Passive and active imaging at 94 GHz for environmental remote sensing

We report on the use of the All-weather Volcano Topography Imaging Sensor (AVTIS) 94 GHz dual mode radar/radiometric imager for environmental monitoring. The FMCW radar yields 3D maps of the terrain whilst the passive radiometer records brightness temperature maps of the scene. AVTIS is a low power portable instrument and has been used operationally to survey terrain at ranges up to 6 km. AVTIS was originally developed for the ground-based measurement of active volcanoes and has been used successfully to measure the Arenal Volcano in Costa Rica and the Soufrière Hills Volcano on Montserrat. However, additional environmental remote sensing applications are emerging for this technology and we will present details of how the instrument is used to perform terrain mapping and thermal surveys of outdoor scenes. The extraction of digital elevation maps is the primary function of the AVTIS radar mode. We review this process covering range drift compensation, radar cross section (RCS) histogram analysis and thresholding, and georeferencing to GPS. Additionally, we will present how careful calibration enables RCS imaging of terrain and the extraction of the intrinsic reflectivity of the terrain material (normalized RCS, or sigma-nought) which can potentially be used to classify terrain types. We have validated the passive mode imagery against infrared thermal imagery and they show good agreement once the differences in spatial resolution are accounted for. This comparison also reveals differences in propagation due to obscurants (steam, gas, ash) in the two wavebands.

High resolution, wide field of view, real time 340GHz 3D imaging radar for security screening

The EU FP7 project CONSORTIS (Concealed Object Stand-Off Real-Time Imaging for Security) is developing a demonstrator system for next generation airport security screening which will combine passive and active submillimeter wave imaging sensors. We report on the development of the 340 GHz 3D imaging radar which achieves high volumetric resolution over a wide field of view with high dynamic range and a high frame rate. A sparse array of 16 radar transceivers is coupled with high speed mechanical beam scanning to achieve a field of view of ~ 1 x 1 x 1 m3 and a 10 Hz frame rate.

A high frame rate, 340 GHz 3D imaging radar for security

The need for improved security at airports with high detection performance, high throughput rates and an improved passenger experience is motivating research into new sensing technologies. The European Union funded CONSORTIS project is addressing these aims by demonstrating a system which combines a submillimeter wave radar, a dual-band passive submillimeter wave camera and automatic anomaly detection software for reliable detection while ensuring passenger privacy. In this paper we describe the 340 GHz 16-channel FMCW radar which produces 3D maps of the subject with ∼1 cm3 voxel resolution over a 1 m3 sense volume at multi-hertz frame rates. The radar combines advanced transceiver electronics with high speed mechanical beam steering and parallelized processing to achieve this level of performance.

The CONSORTIS 16-channel 340 GHz security imaging radar

We have completed a 16-channel 340 GHz 3D imaging radar for next-generation airport security screening under the European Union funded CONSORTIS (Concealed Object Stand-Off Real-Time Imaging for Security) project. The radar maps a 1 x 1 x 1 m3 sense volume with ~1 cm3 voxel resolution at multi-hertz frame rates. The radar has been installed in the CONSORTIS system enclosure and integrated with a passenger control system and command module. The full system will ultimately also incorporate a dual-band passive submillimeter wave imager and automatic anomaly detection software for reliable, ethical detection of concealed objects. A large data collection trial on targets of interest has been conducted to support the development of automatic anomaly detection software. Initial threat detection analysis indicates promising results against aviation-relevant objects including simulant dielectric threat materials.