About the Authors... Thorkild B. Hansen has worked for the past 10 years on research problems in electromagnetics and acoustics. Within high-frequency diffraction theory, he has developed methods for calculating scattering from corners, narrow grooves, and shadow boundaries. Dr. Hansen has also formulated planar and spherical near-field scanning techniques in the time domain, and derived exact beam representations that are alternatives to the classical multipole expansions. His recent work includes forward and inverse scattering problems for ground-penetrating and subsurface radars. Art...