Diffraction pattern due to a trapezoidal air cylinder in a dielectric

Abstract

As a theoretical model of frequency-swept cross-borehole radars for locating deeply buried tunnels with asymmetric cross sections, E-polarized scattering by a trapezoidal air cylinder in a dielectric medium is analyzed. The results of simulations performed by employing the boundary-element method illustrate that the null frequencies corresponding to the upper and lower boundaries of the cylinder are different. Also, the physical mechanism for the occurrences of nulls, which depend on the signal frequency and the observation distance, is presented in detail. (C) 2000 John Wiley & Sons, Inc.