High-frequency electromagnetic induction (HFEMI) extends the established EMI frequency range above 100 kHz to perhaps 20 MHz. In this higher frequency range, less-conductive targets display heretofore unseen responses in their inphase and quadrature components. Improvised explosive device constituent parts, such as carbon rods, small pressure plates, conductivity voids, low metal content mines, and short wires respond to HFEMI but not to traditional EMI. Results from recent testing over mock-ups of less conductive IEDs or their components show distinctive HFEMI responses, suggesting that this new sensing realm could augment the detection and discrimination capability of established EMI technology. The electrical conductivity of soil may contribute, in effect, to the imaginary part of the permittivity of soil and may then, in turn, generate perceptible responses in traditional EMI. In HFEMI, both the real and complete imaginary parts of soil permittivity produce notable effects. Pursuing this, lab tests with tap water and variously saturated Ottawa sand were compared with results from time domain reflectometry.
Thin wires are a critical component of many types of improvised explosive devices. Short wires with lengths on the order of 30 cm to a few meters are difficult to detect using electromagnetic induction metal detectors due to the induction currents having only a small cross-section of the wire to circulate on. Longer wires on the order of tens of meters up to a kilometer are often buried at depths which preclude induction detection. We demonstrate short wire detection and identification through acquiring the electromagnetic induction response at frequencies above the traditional EMI range. In addition, long wire detection and identification is shown through electric field coupling between excitation coils and the long wire itself. We present the relevant physics of detecting both types of wires and experimental and modeling results demonstrating the utility of this high-frequency EMI regime. We present a high-frequency electromagnetic induction instrument utilizing frequencies up to 15 MHz which can detect and classify both short and long wires.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.