Detection of conductivity voids and landmines using high frequency electromagnetic induction

Electromagnetic induction (EMI) instruments have been traditionally used to detect high electric conductivity discrete targets such as metal unexploded ordnance (UXO). The frequencies used for this EMI regime have typically been less than 100 kHz. To detect intermediate conductivity objects like carbon fiber, even less conductive saturated salts, and even voids embedded in conducting soils, higher frequencies up to the low megahertz range are required in order to capture characteristic relaxation responses. In this context, nonconducting lastic landmines can be considered a void plus small metallic parts such as the firing pin. To predict EMI phenomena at frequencies up to 15MHz, we modeled the response of conducting and nonconducting targets using the the Method of Auxiliary Sources. Our high-frequency electromagnetic induction (HFEMI) instrument is able to acquire EMI data at frequencies up to that same high limit. Modeled and measured characteristic relaxation signatures compare favorably and indicate new sensing possibilities in a variety of scenarios including the detection of voids and landmines.