Microwave/RF Applicators and Probes

for Material Heating, Sensing, and Plasma Generation

Mehrdad Mehdizadeh

• Publisher: William Andrew
• Year: 2015
• Print ISBN: 9780323322560
• eBook ISBN: 9780323328425
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Microwave/RF Applicators and Probes for Material Heating, Sensing, and Plasma Generation, Second Edition, encompasses the area of high-frequency applicators and probes for material interactions as an integrated science. Based on practical experience rather than entirely on theoretical concepts, and emphasizing phenomenological explanations and well-annotated figures, the book represents one of the most important resources on the topics of microwave technologies, applications of RF and microwaves in industry (industrial heating and drying), and microwave engineering. After covering the basics of field-material interactions, the book reviews and categorizes probes and applicators, demonstrates their real-world applications, and offers numerically solved examples. Readers will find valuable design rules and principles of high-frequency applicators and probes for material processing and sensing applications in this expanded edition. - Presents new information on how the interactions of electromagnetic fields with materials at high frequencies have given rise to a vast array of practical applications in industry, science, medicine, and consumer markets - Thoroughly revised and expanded edition, providing an update on the most recent trends and findings - Contains many new sections within existing chapters, along with new chapters on applicators for plasmas at microwave/RF frequencies

Chapter 1

The impact of fields on materials at microwave and radio frequencies

Field interaction with materials is a vast area of science, and a large body of literature is devoted to it. High-frequency applicators and probes operate in a relatively small, but important, part of the electromagnetic spectrum. This chapter serves as a brief background on electromagnetic and material topics related to the scope of this book. Furthermore, a number of definitions, concepts, and equations are reviewed that are referred to in other chapters. For a more extensive treatment of electromagnetic principles and material properties, the interested reader can consult many excellent sources, both in print and online, in this area.

Keywords

Electromagnetic spectrum; high-frequency field; wave equations; dielectric loss effect; lossy dielectrics; dielectric properties; material electric properties

Chapter Outline

Introduction 2

1.1 High-Frequency Fields Imposed on Uniform Materials 2

1.1.1 The Wave Equations and Materials 2

1.1.2 High-Frequency Electric Fields and Materials 4

1.1.3 Joule’s Loss Effect in Conductive Materials with Free Charges 6

1.1.4 Energy Deposition into Materials with the Dielectric Loss Effect 6

1.1.5 High-Frequency Magnetic Fields and Materials 8

1.2 Fields at Material Boundaries in RF/Microwave Frequencies 8

1.2.1 Fields at Boundaries Between Two Real Materials 8

1.2.2 Wave Impedance in Various Environments 9

1.2.3 Lumped Field Approximations in Electrically Small Systems 11

1.2.4 Fields at Conductor Boundaries, Skin Depth, and Surface Resistance 12

1.2.5 Standing Waves in Cavity and Transmission-Line Applicators 13

1.2.6 Penetration and Reflection of Waves into Lossy Dielectrics 14

1.2.7 Wave Reflection and Transmission at Boundaries Between Free Space and Materials 16

1.3 Material/Field Issues of Interest in Applicator/Probe Design 16

1.3.1 Distinction Between Dielectric Loss and Conductivity 16

1.3.2 Temperature Rise and Thermal Issues in Electromagnetic Heating 17

1.3.3 Special and Nonthermal Electromagnetic Effects on Materials 19

1.3.4 Nonlinearity Issues and Thermal Runaway in Electromagnetic Heating 19

1.4 Classification of Materials at High Frequencies 20

1.4.1 Solid Dielectrics: Ceramics and Polymers 20

1.4.2 Conductive Materials: Metals and Carbon-Based Conductors 22

1.4.3 Water and Water-Rich Organic Materials 23

1.4.4 Moisture Measurement and Management Topics in Applicator/Probes 27

1.4.5 Gases or Vapors 28

1.4.6 Plasma 28

1.4.7 Composites Made of Conductive Fillers Added to Dielectrics 29

1.4.8 Metamaterials or Periodic Structures 29

References 30

Introduction

Field interaction with materials is a vast area of science, and a large body of literature is devoted to it. High-frequency applicators and probes operate in a relatively small, but important, part of the electromagnetic spectrum. This chapter serves as a brief background on electromagnetic and material topics related to the scope of this book. Furthermore, a number of definitions, concepts, and equations are reviewed that are referred to in other chapters. For a more extensive treatment of electromagnetic principles and material properties, the interested reader can consult many excellent sources, both in print and online [1–4], in this area.

Knowledge of field–material interactions is critical to the design of high-frequency applicators because the electrical properties of the material of interest will become a part of the device’s functioning. This fact is a unique feature of these devices, which sets them apart. For example, in the design of a conventional furnace, it is of little importance what material is to be heated, but the dielectric properties of a material being processed by a microwave applicator are of great importance in the design of the device.

The electromagnetic spectrum is shown in Figure 1.1, and the frequency bands of interest in this book are highlighted. This is a region in the spectrum covering a frequency range typically known as radio frequency (RF), through microwave and into millimeter wave (a few megahertz [mHz] to tens of gigahertz [GHz]). This general part of...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Preface
• Acknowledgments
• Introduction
• Chapter 1. The impact of fields on materials at microwave and radio frequencies
• Chapter 2. Fundamentals of field applicators and probes at radiofrequencies and microwave frequencies
• Chapter 3. Electric field (capacitive) applicators/probes
• Chapter 4. Single-mode microwave cavities for material processing and sensing
• Chapter 5. Microwave multimode cavities for material heating
• Chapter 6. Applicators and probes based on the open end of microwave transmission lines
• Chapter 7. Magnetic field and inductive applicators and probes at high frequencies
• Chapter 8. RF/microwave applicators and systems for joining and bonding of materials
• Chapter 9. Design considerations for applicators in continuous-flow microwave/radio frequency processing
• Chapter 10. Plasma applicators at RF and microwave frequencies
• Appendix A2.1. Mode chart for cylindrical cavities
• Appendix A2.2. Human safety regulations on maximum exposure to electromagnetic fields at high frequencies
• Appendix A2.3. Frequency allocations for industrial, scientific, and medical (ISM) applications
• Appendix A3.1. Impedance/Admittance and electric field solutions for a parallel-plate applicator with dual layers of real dielectric materials
• Appendix A3.2. Mathematica™ worksheet for derivation of dual-layer parallel plates with real dielectrics
• Appendix A4.1. Field analysis of TM0n0 cylindrical cavities with two concentric layers of real dielectric at the axis
• Appendix A4.2. Mathematica™ Notebook for Computation of Single-mode TM0n0 Cavities for Material Heating and Sensing Applications
• Appendix A5.1. Analysis of an Example of Rectangular Cavity Mode for Power Density
• Appendix A5.2. Mathematica™ Notebook for Computation of Possible Modes Over a Given Bandwidth for a Rectangular Multimode Cavity
• Appendix A6.1. Mathematica Worksheet for Finding the Admittance and Equivalent Circuit Parameters of the Open-ended Coaxial Probe
• Appendix A6.2. Mathematica™ Notebook for Impedance of the Extended Center Conductor Coaxial Line
• Appendix A6.3. Admittance of Open-ended Waveguide with Dielectric Material Loading
• Appendix A7.1. Field Analysis of Circular Loop Applicator
• Appendix A7.2. Mathematica™ Program for Eddy Current Induction Into a Conductive Cylinder
• Index