The aim of this book is to familiarize the reader with the concept of electromagnetic time reversal, and introduce up-to-date applications of the concept found in the areas of electromagnetic compatibility and power systems. It is original in its approach to describing propagation and transient issues in power networks and power line communication, and is the result of the three main editors' pioneering research in the area.

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Yes, you can access Electromagnetic Time Reversal by Farhad Rachidi, Marcos Rubinstein, Mario Paolone in PDF and/or ePUB format, as well as other popular books in Physical Sciences & Electromagnetism. We have over one million books available in our catalogue for you to explore.

Information

Publisher

Wiley

Year

2017

ISBN

9781119142102

Edition

Topic

Physical Sciences

Subtopic

Electromagnetism

1
Time Reversal: A Different Perspective

M. Rubinstein,¹ F. Rachidi,² and M. Paolone²

¹University of Applied Sciences of Western Switzerland, Yverdon, Switzerland
²Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland

1.1 Introduction

In this introductory chapter, we will present the theoretical background of the time reversal in electromagnetism. We will start by discussing the notion of time in physics. The time-reversal invariance of physics laws will then be described. Special attention will be devoted to the time-reversal invariance of Maxwell's equations. The concept of time-reversal cavity and the use of time reversal as a means of refocusing electromagnetic waves will be described. Finally, the chapter will end by briefly presenting application areas of electromagnetic time reversal.

1.2 What is Time?

Most of the words that define very complex concepts are rarely used in our daily language and writings.¹ There are, however, exceptions, time being a particularly notable one. Even though time appears to be a quite familiar notion that carries the feeling of an obvious reality to everyone, there is nothing harder than giving a definition that truly captures its essence using concepts other than our intuitive idea of time itself. Let us look at some entries given in dictionaries:

Indefinite, unlimited duration in which things are considered as happening in the past, present, or future; every moment there has ever been or ever will be.

(Webster's New World College Dictionary)

The indefinite continued progress of existence and events in the past, present, and future regarded as a whole.

(Oxford Dictionaries)

Etienne Klein, a French physicist, has also proposed an interesting definition for time [1]: a jail on wheels. Why a jail? Because we are not free to choose our position along the timeline. We are in the present instant and we cannot get away from it. Why on wheels? Because time moves forward. Time takes us from the present to the future.

One can find hundreds of other definitions, proposed by philosophers, physicists, and linguists. Many of them use metaphors to describe this concept, as in the one proposed by Klein. However, none of these tells us about the nature of time since some idea of time is used in the definition itself [1]. This paradox was noticed by Saint Augustine in the fourth century: “If I am not asked, I know what time is; but if I am asked, I do not.”

Physicists have managed to consider time as an operative concept. The first mathematical expression of physical time was enunciated by Galileo and formalized by Newton, assuming that time has one dimension and is expressed by a real number. Furthermore, in that definition, time is absolute in the sense that there is only one time associated with any given moment, and that time is the same everywhere in the universe. In 1905, Einstein's special relativity theory showed that time is not an absolute quantity and should be considered in relation to space. Quantum mechanics changed again the time paradigm [2] with the Heisenberg uncertainty principle, which applies not only to position and momentum, but also to time and energy.

1.3 Time Reversal or Going Back in Time

In this section, using a simple example, we will pr...

Cover
Title page
Copyright
Dedication
List of Contributors
Preface
About the Companion Website
1 Time Reversal: A Different Perspective
2 Time Reversal in Diffusive Media
3 From Electromagnetic Time-Reversal Theoretical Accuracy to Practical Robustness for EMC Applications
4 Amplification of Electromagnetic Waves Using Time Reversal
5 Application of Time Reversal to Power Line Communications for the Mitigation of Electromagnetic Radiation
6 Application of Electromagnetic Time Reversal to Lightning Location
7 Electromagnetic Time Reversal Applied to Fault Location in Power Networks
Index
EULA