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 ... Read moreare alternatives to the classical multipole expansions. His recent work includes forward and inverse scattering problems for ground-penetrating and subsurface radars. Arthur D. Yaghjian s research at the National Institute of Standards and Technology, at the Air Force Research Laboratory, and most recently as an independent consultant in electromagnetics, has led to the development of exact, numerical, and high-frequency methods for predicting and measuring the near and far fields of antennas and scatterers. He has contributed to the determination of electromagnetic fields in continuous media and to the formulation of classical equations of motion of charged particles. Show Less