We use anisotropic magneto-resistors (AMRs), coils, and flux-gate magnetometers for a variety of applications in magnetometry, EM induction, and eddy current measurements. AMRs are unique sensors that sense magnetic fields over a large range of frequencies from DC to over 1 MHz. This makes them useful for compass applications, magnetic flux-leakage measurements, and EM induction (a.k.a. eddy current) sensors. In fact, the same sensor can be used for all three types of measurements. We have been working with AMRs to detect and characterize metallic objects in the ground such as unexploded ordnance (UXO) and buried utilities such as water pipes and power lines. Other applications include navigation and non-destructive testing of well casing and pipelines.
ESS has built instruments and analysis algorithms for detecting and classifying UXO. The photos below show an AMR sensor board and one of our test fixtures where the sensor is placed in a Helmholtz coil and lowered into a Russian-doll Mu-metal shield for sensitivity measurements. Next, map-view results from a typical EM induction survey are shown that was conducted to detect UXO. By using fully polarimetric EM induction (a.k.a. eddy current) instruments that make broad spectrum measurements, a rich dataset is obtained. Analysis of the complete dataset allows a full characterization and classification of the target. The last plot shown shows the results of analysis by ESS software that determines the location, orientation, aspect ratio, and characteristic signature for a buried UXO target.