On the low-frequency natural response of conducting and permeable targets

The low-frequency natural response of conducting, permeable targets is investigated. The authors demonstrate that the source-free response is characterized by a sum of nearly purely damped exponentials, with the damping constants strongly dependent on the target shape, conductivity, and permeability, thereby representing a potential tool for pulsed electromagnetic induction (EMI) identification (discrimination) of conducting and permeable targets. This general concept is then specialized to the particular case of a body of revolution (BOR), for which the method-of-moments (MoM)-computed natural damping constants from several targets are compared with measurements. Moreover, theoretical natural (equivalent) surface currents and damping coefficients are shown for other targets of interest. Finally, the authors investigate the practical use of such natural signatures in the context of identification, wherein Cramer-Rao bound (CRB) studies address signal-to-noise ratio (SNR) considerations.