A comparison of discrimination capabilities of time- and frequency-domain electromagnetic induction systems

This paper discusses the ability of time and frequency domain electromagnetic induction systems to discriminate unexploded ordnance from clutter. Toward this end, time and frequency domain electromagnetic induction systems were built and the responses of a wide variety of targets including loops, spheres, cylinders and inert UXOs were measured. Also, time and frequency responses of test targets are numerically modeled using finite element methods to validate the experimental work. Target information is more distinct in the frequency domain than time domain. Moreover, discrimination performance of the frequency domain electromagnetic induction system was enhanced by almost a factor of two when the usual the low frequency spectrum (30 Hz to 24 kHz) was extended down to extremely low frequencies (1 Hz to 30 Hz). However, data acquisition at extremely low frequencies is a time consuming process especially if data averaging is required to achieve acceptable SNR. Therefore, in practice, it would be better to have two operating modes when using a frequency domain electromagnetic induction system; one with very few operating frequencies and the other operating in the entire band (1 Hz to 24 kHz). Once a target location is marked using the first mode, the system can be used as a "cued" sensor in the second mode, thus improving the discrimination.