Tutorial on basics of time-varying electromagnetic systems and circuits

TL;DR

This tutorial provides a comprehensive overview of the fundamental concepts, historical development, and modeling techniques for linear time-varying electromagnetic systems and circuits, aiming to assist new researchers in the field.

Contribution

It offers a detailed review of the basic theory, models, and effects of time-varying electromagnetic systems, filling a gap for beginners and newcomers to the field.

Findings

Introduction to the general theory of linear time-varying systems

Discussion of frequency dispersion in nonstationary systems

Models of time-varying electrical circuits and effects of time modulation

Abstract

During the last decade, possibilities to realize new phenomena and create new applications by varying system properties in time have gained increasing attention in many research fields, spanning a wide range from acoustics to optics. While the interest in using time-modulation techniques for engineering electromagnetic response has got revitalized only in recent years, the field originates from the middle of the previous century, and a multitude of works have been published ever since. In this tutorial paper, we provide a historical picture and review the basic concepts in this field. In particular, we introduce the general theory of linear time-varying systems and discuss the means to properly account for frequency dispersion of nonstationary systems. Also, we elucidate models of time-varying electrical circuits and some useful effects that can be achieved by time modulation of circuit parameters. We hope that this paper will particularly help inexperienced researchers who would like to work on new ways of manipulating waves and signals by temporally varying the properties of their systems.