Initial Development of a High-frequency EMI Sensor for Detection of Subsurface Intermediate Electrically Conductive (IEC) Targets

The U.S. military has developed and currently uses composite material munitions. These composite munitions are typically comprised of carbon fiber and, because of their low electrical conductivity, have a much lower electromagnetic induction signature, which makes them difficult to detect using traditional metal detecting methods. The term intermediate electrically conductive (IEC) is used to describe these lower conductivity materials, with conductivity, sigma, typically in the range 10 < sigma < 10(5) S/m. The electromagnetic induction (EMI) relaxation response of carbon fiber munitions peaks in the low megaHertz range (< 15 MHz), but above 100 kHz. Thus, detecting and characterizing these munitions for remediation on military ranges is problematic using available geophysical EMI sensors. This paper describes initial efforts in the development of a prototype frequency-domain EMI sensor with the goal of extending the measurement frequency range to 15 MHz.