Richard G. Humphreys

Tuning superconducting microwave filters by laser trimming

At present, superconducting filters are usually tuned using screws, but there are many reasons to seek an alternative. Laser trimming is an attractive choice. A laser trimming system is described that can tune a high temperature superconductor microstrip filter while it is cooled and connected to a network analyser. Software has been written to control the system, fit measured data and modify a filter design to account for unintended couplings. The residual material left after trimming YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// has been shown to have negligible microwave loss. The system has been used to tune a simple three-resonator filter.

Passive mm-wave imager using HTS Josephson junction detectors

Passive mm-wave imaging has great potential for all-weather flying aids and security applications. To achieve useful real time images of an ambient temperature scene, >100 detectors are required, and uptake of the technology has been limited by the high cost of detectors. We propose a novel, cost effective solution using integrated arrays of antenna-coupled HTS Josephson junction video detectors. Arrays of 16 antenna coupled YBa2Cu3O7 interface engineered junctions have been fabricated with a design centre frequency of ~100GHz, optically immersed behind a single lens. Detector characteristics have been compared to stochastic RCSJ model simulations, with the antenna represented by an equivalent circuit. A real time demonstration imager has been built, and the first images obtained.

C-axis microbridges for rapid single flux quantum logic

The c-axis microbridge (CAM) junction technology has an inherently low inductance due to its groundplaned geometry which should be well suited to SFQ logic applications. However, the critical currents of the conventional (2 /spl mu/m diameter) CAM technology are too high. Experiments with optical lithography have shown that junctions of /spl sim/0.5 micron dimension are required. A new process using electron beam lithography has been developed. The junction statistics even at this early stage of development look promising. To confirm the validity of the rest of the design and fabrication technology a CAM based RS Flip-Flop has been fabricated which shows the correct traversal of the state graph at 45 K.

A novel locating and discriminating metal detector

We present the first report of a new experimental metal detector that is able to locate an underground metal object in three dimensions with an accuracy of millimeters and measure a signature to provide discrimination against frag (chaff). The ability to pinpoint the metal means that the physical excavation of the target can be conducted more quickly and safely. This detector consists of a single transmitter coil, an array of 40 receiver coils and a computer to control soil rejection and data inversion. An inversion algorithm returns the 3D location of a target with respect to the sensor head and the signature of the metal object that is largely independent of the geometry of the measurement. Tests were conducted in air, in sand and in soil using various surrogate mines and cartridge cases. Location accuracy was generally found to be very good. Several samples of a range of mine surrogates had their signatures recorded, and all samples of each type were found to have a signature falling in a very narrow band. Most of these bands are well separated, leading us to conclude that there is considerable potential for discrimination against frag. During a blind test 80% of the mines were correctly identified. We conclude that this experimental detector can accurately locate metal objects in three dimensions and provide useful information for discriminating frag from mines. This paper reports on the technology within the new detector and the early results of the performance tests conducted against surrogate mines in test lanes.

Performance of 94GHz receivers for passive imaging

64 MMIC receivers built for mm-wave imaging have been systematically characterized. Each receiver comprises three InP MMIC low noise amplifiers and a biased Schottky diode detector in a compact package with a horn antenna. The characterization includes spectral response, responsivity and noise. The noise has both white and 1/f components. The average (±standard deviation) receiver bandwidth is 23.8±3GHz, and the overall noise equivalent temperature difference (NETD) in an integration time of 0.2ms, as used in the imager, is 0.66±0.1K.