This paper describes a prototype electromagnetic induction (EMI) sensor system designed specifically to measure the horizontal component of a metal target's eddy current time decay signature. Instead of creating a vertical magnetic field from a horizontal loop transmitter configuration used by most EMI metal detectors, the prototype transmitter geometry has been designed especially for creating a horizontal magnetic field (HMF). One of the potential advantages of the HMF sensor is the relatively uniform magnetic field that is created over a large volume. A second potential advantage is that, compared to a conventional ioop antenna, the magnetic field intensity falls off slowly with distance from the plane of the sensor. These two advantages potentially make the HMF sensor well suited for detection and classification of metal targets buried deeply in the ground (e. g., unexploded ordnance, UXO) or from a vehicle-mounted mine detector sensor. Preliminary modeling of the antenna and laboratory data from a time-domain version of the HMF sensor are presented.
This paper describes a spatial scanning time-domain electromagnetic induction (EMI) sensor and presents results from recent field experiments with buried metal and low-metal content (LMC) anti-personnel (AP) and anti-tank (AT) plastic-cased land mines. The EMI sensor is an modified version of the Electromagnetic Target Discriminator (ETD) sensor developed for the US Army CECOM/NVSED by the Johns Hopkins University Applied Physics Laboratory. The spatial scanning ETD sensor has demonstrated the ability to measure metal target decay times starting approximately 6 µs after the transmitter current is turned off and with metal target decay time constants as short as 1 µs. The sensor antenna sweeps 80 cm over a target area and makes time-decay measurements at 14.5 mm intervals. In addition to metal target signatures, the paper describes coincident void and metal signatures from LMC land mines. The detection of coincident void and metal signatures is shown to be an important classification technique for LMC land mines.
This paper presents wide bandwidth, time decay responses from low metal content (LMC) mines, LMC mine simulates, and ground voids. Measurements were collected both in the laboratory and in the field. The target time decay responses were measured with the Johns Hopkins University Applied Physics Laboratory developed Electromagnetic Target Discriminator (ETD) sensor developed for the US Army CECOMJNVSED. The ETD sensor has demonstrated the ability to measure metal target decay times starting approximately 3 to 5 jts after the transmitter current is turned off and metal target decay time constants as short as 1 .4 ps.
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