Investigation of Special Problems in Electromagnetics with the Finite-Difference Time-Domain Method

Abstract

The Finite-Difference Time-Domain(FDTD) method is a robust numerical time-domain technique capable of handling a broad range of electromagnetic problems. This work explores the application of FDTD method to two special problems in electromagnetics: the modeling of antennas loaded with time-varying components, and the modeling of the human head at microwave frequencies. A recent surge in interest for non-LTI antennas -- driven by a desire to circumvent the performance bounds of their LTI counterparts -- has made apparent the need for modeling techniques capable of handling nonlinear or time-variant behavior on antenna structures. Modeling of time-varying components in FDTD will be demonstrated through direct implantation in the FDTD algorithm with a modified update equation, and through SPICE co-simulation. There is currently a large body of work studying the impact of microwave and radio frequency radiation on human tissue. The effects of prolonged exposure to non-ionizing radiation is typically characterized using specific absorption rate (SAR), and research has often been conducted in the context of wireless communication devices. Many papers in open literature involve simulations with a source antenna in close proximity to the head, excited by a single tone continuous wave or narrow-band gaussian pulses. Using relaxation models to account for the frequency dependent behavior of tissue, this work investigates the interactions of plane waves excited by linear-frequency modulated pulses incident upon the human head in FDTD.