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.
KEYWORDS: Antennas, Signal to noise ratio, Land mines, Signal detection, Interference (communication), Signal processing, Explosives, Filtering (signal processing), Atmospheric modeling, Receivers
Nuclear Quadrupole Resonance (NQR) is being researched as a confirmatory sensor for use in mine detection as part of the research carried out by the Defence Science and Technology Laboratory (Dstl) for the UK MOD Applied Research Programme. NQR is a radio frequency (RF) spectroscopy technique used at close range to detect explosives, typically TNT and RDX, found in anti-tank and anti-personnel landmines. Detection is carried out by averaging NQR data until the signal to noise ratio increases enough for the signal to be distinguished from RF noise and interference. Environmental RF noise dominates the received signal because NQR signals are, in comparison, extremely low in magnitude. Therefore, RF interference, which varies depending on the time of day, environment, and frequency of the radiation, directly affects detection times. Methods of reducing RF interference such as antenna design, signal processing and phase cycling are reviewed and discussed. Results are presented from research undertaken to enhance the signal to noise ratio, taken in various environments.
We report on the development of a novel industrial process, embodied in a new robotic polishing machine, for automatically grinding an polishing aspheric optics. The machine is targeted at meeting the growing demand for inexpensive axially symmetric but aspherical lenses and mirrors for industry and science, non-axisymmetric and conformal optics of many kinds, the planarization of silicon wafers and associated devices, and for controlling form and texture in other artifacts including prosthetic joints. We describe both the physics and the implementation of the process. It is based on an innovative pressurized tool of variable effective size, spun to give high removal rate. The tool traverse and orientation are orchestrated in a unique (and patented) way to avoid completely the characteristic fast peripheral-velocity and center-zero left by conventional spinning tools. The pressurized tooling supports loose abrasive grinding and polishing, plus a new bound-abrasive grinding process, providing for a wide range of work from coarse profiling to fine polishing and figuring. Finally we discuss the critical control, data handling and software challenges in the implementation of the process, contrast the approach with alternative technologies, and present preliminary results of polishing trials.
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