Electromagnetic Wave Absorbers

Detailed Theories and Applications

Youji Kotsuka

• Publisher: Wiley
• Year: 2019
• ISBN:
  9781119564386
• Edition: 1
• Topic: Scienze fisiche
• Subtopic: Elettromagnetismo

Addresses the importance of EM wave absorbers and details pertinent theory, design, and applications

Demands for various EM-wave absorbers are rapidly increasing along with recent trends toward complicated electromagnetic environments and development of higher-frequency communication equipment, including AI technology. This book provides a broad perspective on electromagnetic wave absorbers, as well as discussion of specific types of absorbers, their advantages and disadvantages, their applications, and performance verification.

Electromagnetic Wave Absorbers: Detailed Theories and Applications presents the theory behind wave absorbers and their practical usage in design of EM-wave absorber necessary particularly for EMC environments, and similar applications. The first half of the book contains the foundations of electromagnetic wave engineering, specifically the transmission line theories necessary for EM-wave absorber analysis, the basic knowledge of reflection, transmission, and absorption of electromagnetic waves, derivation of Maxwell's equations and computer analysis. The second half describes special mediums, absorber application examples, simplified methods of absorber design, autonomously controllable EM-wave absorber, and more. This valuable text:

• Provides detailed explanations of basic theory and applied theory for understanding EM-wave absorbers
• Discusses the material constant measurement methods of EM-wave absorption characteristics that are necessary for designing EM-wave absorbers
• Includes examples of novel EM-wave absorber configurations

Electromagnetic Wave Absorbers: Detailed Theories and Applications is an ideal read for researchers and students concerned with electromagnetic wave engineering. It will also appeal to computer software engineers and electromagnetic field theory researchers.

1
Fundamentals of Electromagnetic Wave Absorbers

Needless to say, learning the theory and application of wave absorbers entails learning the fundamentals of electromagnetic (EM)‐wave engineering itself. In short, this means learning about a broad range of basic matters such as the following:

1. (a) Transmission line theory, which will aid in understanding the fundamental phenomena of EM waves;
2. (b) Analytical methods to learn EM‐wave reflection and transmission phenomena;
3. (c) Various behaviors of EM waves;
4. (d) Theory of EM‐wave analysis by computer simulation;
5. (e) Basic knowledge of EM‐wave materials;
6. (f) Measurement of EM‐wave material constants;
7. (g) The EM‐wave environment associated with wave absorbers;
8. (h) Fundamental concepts of artificial materials;
9. (i) Knowledge of EM‐wave absorbers that can be assimilated with artificial intelligence (AI) technology, and other matters.

Even if called just an “EM‐wave absorber,” its application fields are broadly extended. Particularly, in recent years, higher frequency applications in various kinds of communication systems have advanced rapidly. However, as the frequency region becomes higher, measures against EM scattering and diffracted waves are inevitably required.

Also, as is well known, EM waves are widely used in fields ranging from communication technologies to medical applications. Therefore, the existence of a radio wave absorber plays an important role ranging from preservation of such communication environment safety down to human body protection [1].

In this chapter, in order to make it easier to understand the contents of this book, basic matters on EM‐wave absorbers are arranged from various perspectives.

After first defining what an EM‐wave absorber is, Section 1.1 briefly describes the history of EM‐wave absorber development along with the application fields.

In Section 1.2, the quantitative representation method of the EM‐wave absorption characteristic, namely, the reflection coefficient is defined. In Section 1.3, the EM‐wave absorbers are classified and described from the viewpoint of appearance, composition form, material, and frequency characteristics; these are summarized in a table. In Section 1.4, various applications of EM‐wave absorbers are introduced together with the literature. Finally, new wave absorber technologies described in the later chapters are briefly introduced.

1.1 Introduction to Electromagnetic‐Wave Absorbers

As the name of the EM‐wave absorber, “radio wave absorber,” is often interpreted conventionally. However, the expressions “electromagnetic wave absorber” or, more simply, “absorber” are, except for a special case, adopted in this book. The EM‐wave absorber refers to structures that can absorb an incident EM wave based on the principles of transforming the incident EM‐wave energy into Joule heat or canceling mutually the phases between the incident EM wave and the reflected wave.

An object that completely absorbs all light wavelengths is known as a black body, and carbon is considered as nearly a black body. As for sound wave environments, sound‐absorbing materials have been often utilized, and glass fibers, rock wools, etc. have been used as materials that absorb sound waves well. Thus, even before the EM‐wave absorber was developed, objects that can be referred to as “absorbers” have been used in various scenarios in our daily lives.

The study of wave absorbers is said to date back to the study of EM‐wave absorbers for the 2‐GHz band carried out in the mid‐1930s at the Naamlooze Vennootschap Machinerieen in the Netherlands [2].

Ever since the various types of EM‐wave absorbers were developed, mostly for anechoic chamber applications, they basically have been composed of carbon‐based materials.

During World War II, research began to be carried out, associated with the deep interest in wave absorbers for military use. For example, in the German Schornsteinfeger Project, two types of wave absorbers used for radar camouflage by mounting them on the periscope and snorkel of a submarine were developed [3]. One of the wave absorbers was made of a material called “Wesch,” in which a carbonyl iron material is dispersed in a rubber sheet. The other, namely, the Jaumann absorber [3], was one in which a resistance sheet and a dielectric (plastic plate) were alternately superimposed, as shown in Figure 1.1d in Section 1.3. In addition, in the United States, in a project organized by O. Halpern at the MIT Radiation Laboratory, with the aim of realizing a coating‐type wave absorber, theHalpern antiradar paint (HARP) was developed.

This was an EM‐wave absorber using...