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.