Chapter 1 - Introduction

Abstract

Although the Maxwell curl equations are usually first encountered in the time domain (TD), until recently most electromagnetic instruction and research has taken place in the frequency domain (FD) where time-harmonic behavior is assumed. A principal reason for favoring FD over TD in the precomputer era had been that a FD approach was generally more tractable, analytically. Furthermore, the experimental hardware available for making measurements in past years was largely confined to the FD. This chapter summarizes the status of direct TD (as opposed to Fourier-transformed FD results) modeling and highlights some of the current research areas. The chapter discusses some important aspects related to radiation phenomena using TD snapshots. It also describes some general electromagnetic modeling choices, the reasons why TD modeling in particular might be advantageous, and a brief account of the evolution of TDEM modeling. Basic steps in developing a TD model and its subsequent application are also discussed along with some specific issues related to TDIE and TDDE modeling, including spatial meshes, closure conditions, obtaining far fields, and alternate formulations. The chapter additionally summarizes topics common to TD modeling such as increasing late-time stability, extracting resonances, signal processing of TD results, total/scattered field formulations, and handling dispersion, nonlinearities, and time variations.