Detecting buried non-metal objects using soil magnetic susceptibility measurements

摘要

Soil magnetic susceptibility is always greater than zero and is detectable using an electromagnetic (EM) induction sensor. When the frequency-domain EM response is affected by magnetic polarization, the in-phase component becomes negative at the low frequency and proportional to the ground magnetic susceptibility. The in-phase measurement can thus be used to compute the apparent magnetic susceptibility. This approach provides a means of detecting a buried object based on its susceptibility contrast to the host medium. For example, an M19 anti-tank mine is physically large (33cmx33cmx9cm) but has so little metal that metal detectors can miss it. When an M19 is buried in soil, it produces a cavity in magnetic susceptibility, which may be detected as a region of low or anomalous apparent susceptibility compared to the surrounding area. We derived a simple formula to compute the apparent magnetic susceptibility from the in-phase data at the resistive limit. The behavior of the apparent susceptibility for layered earth models has been studied using synthetic data. Apparent susceptibility anomalies may be predicted from these studies based on the susceptibility contrast, and geometry of the sensor and target. Finally, we present experimental data obtained using two sensors, a GEM-2 and a GEM-3.