Microwave/RF Applicators and Probes (eBook)

for Material Heating, Sensing, and Plasma Generation

Mehrdad Mehdizadeh (Autor)

eBook Download: PDF | EPUB

2015 | 2. Auflage
440 Seiten
Elsevier Science (Verlag)
978-0-323-32842-5 (ISBN)

Infos

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

Mehrdad Mehdizadeh earned his PhD in electrical engineering at Marquette University in 1983, with specialty in RF/microwave design. After working as an R&D engineer, first in microwave components industry then in MRI scanner RF design, he then joined DuPont Company Engineering working on RF/microwave processes and sensors for materials, plus high-frequency materials characterization. He is a senior member of IEEE and the IEEE Standards Committee.

Textauszug

Chapter 2

Fundamentals of field applicators and probes at radiofrequencies and microwave frequencies

In Chapter 1, the first principles of field interactions with materials were discussed. Different effects of high-frequency electric fields and magnetic fields in various types of materials were established. The purpose of this chapter is to introduce the applicator and the probe head, which are devices for establishing those fields within the material. While the electromagnetic principles behind the two devices are the same, the functions are different.

Keywords

Field applicators; material load geometry; electric field applicator; field uniformity; material under test; RF probes; microwave probes; microwave heating applicators; RF heating applicators

Chapter Outline

Introduction 35

2.1 Basic Applicator/Probe Definitions 35

2.1.1 Distinctions Between Applicators and Probes 35

2.1.2 Far-Field and Near-Field: Antennas Versus Applicators/Probes 36

2.1.3 Electrically Small and Electrically Large Applicators 37

2.1.4 Applicator/Probe Categorization Based on Applicator/Material Load Geometry 37

2.2 Applicator/Probe Figures of Merit 38

2.2.1 Applicator Coupling, Efficiency, and Power Management 38

2.2.2 Effective Field Volume 40

2.2.3 Fill Factor of Applicators and Probes 40

2.2.4 Field Uniformity: Definition and Contributing Factors 41

2.3 Categorization of Applicators/Probes by Useful Field Type: E or H 42

2.3.1 Rationale for Making a Distinction Between Useful Field Types 42

2.3.2 Electric Field Applicators/Probes 43

2.3.3 Magnetic Field (Inductive Coil) Applicators/Probes 44

2.4 Resonance in Applicators/Probes 45

2.4.1 Lumped Resonance: Fields and Energy Storage 46

2.4.2 Distributed Resonance: Field and Energy Storage 47

2.4.3 Resonant Frequency 47

2.4.4 Quality Factor, Bandwidth, and Efficiency in Resonant Applicators 50

2.4.5 Parasitic Energy Storage in Resonant Applicators and Probes 51

2.4.6 Improving Applicator Efficiency and Probe Sensitivity 52

2.4.7 Self-Resonant and Semi-Lumped Applicator/Probes 54

2.4.8 Cavity Resonators as Applicators or Probes 55

2.5 Common Properties and Applications as Heating Devices and Sensors 57

2.5.1 Nonresonant and Transmission-Line Applicators and Probes 57

2.5.2 Material Loading Effects 59

2.5.3 Reciprocity Between Applicators and Probes: Sensitivity 60

2.5.4 Applicators/Probes for ISM Applications Across the Frequency Spectrum 60

2.6 Common Practical Issues in Applicator and Probe Design 62

2.6.1 Grounding and Shielding Issues 62

2.6.2 Balanced/Unbalanced Devices and Balun circuits 63

2.6.3 Emission Regulations for Safety and Interference in Power Applications 65

References 66

Introduction

In Chapter 1, the first principles of field interactions with materials were discussed. Different effects of high-frequency electric fields and magnetic fields in various types of materials were established. The purpose of this chapter is to introduce the applicator and the probe head, which are devices for establishing those fields within the material. While the electromagnetic principles behind the two devices are the same, the functions are different.

The evolution and development of applicators and probes in radio frequency (RF) or microwave frequency have been fragmented due to their usage by a wide variety of disciplines and industries. Due to this fact, the terminology developed for these devices is often not standardized. We have made an attempt here to use the most frequently used terms, as long as they suggest accuracy and are not too suggestive of specific applications. For example, some industries use the term “material under test” or “sample” to refer to the material that is subjected to electromagnetic fields. Here, we have avoided such terminology because in many cases, testing is not intended, and the idea is to heat or process the material. Instead, we have used the term “material load” to describe the material subjected to the fields.

2.1 Basic Applicator/Probe Definitions

2.1.1 Distinctions between applicators and probes

The term “field applicator” or, simply, “applicator” is used for a device that applies RF/microwave energy into a material volume at a level sufficient to create either a permanent or temporary change in a material parameter or property. The change could be a rise in temperature, driving out moisture, enhancing a chemical reaction, ablation of a biologic tissue, breakdown of gases to form plasmas, and so on. We use the term “energy deposition systems” to refer to this class of industrial, scientific, or medical (ISM) systems.

The term “probe” or “sensor head” is typically used when the purpose of the field interaction is only to obtain information from the material. For example, in an industrial process, a probe system may be used to apply a field into the process material to obtain information about dielectric properties, which may indicate a material parameter such as moisture level. In that case, the field strength—and therefore the level of energy imparted into the material—is small and is enough for sufficient signal strength over the noise level. Typically, this signal level is far below the level needed to heat the material. There are cases, for example, magnetic resonance (nuclear magnetic resonance, electron spin resonance [ESR]), where the same device can act as both applicator and sensor.

While the fundamental physics are similar, there are practical differences between applicators and probes that make the design considerations quite different. These differences are mostly related to far higher levels of power, voltage, and current in the case of applicators versus signal levels in the case of probes. In addition to size differences, the choice of frequency for probes is far wider because of low power levels, which allow probes to work outside of allowed ISM frequency bands.

2.1.2 Far-field and near-field: antennas versus applicators/probes

Most applicators and probes discussed in this book are near-field, which is generally defined as having the distances between the applicator and the material small compared with the wavelength. In most cases of near-field systems, the material is actually enclosed within the applicator structure; an obvious example is the domestic microwave oven, where the food item is placed within the microwave cavity.

In far-field systems the distances between the antenna and the material can be large compared with the operating wavelength, and instead of applicator/probe terminology, antenna terms are used. In far-field systems, the field interacting with a material is in the form of traveling plane waves, with the ratio of electric field to magnetic field (wave impedance) at the free space level of 377 Ω, while in near-field systems, the fields interacting with the material have impedances that typically deviate greatly from this value. The wave impedance issue was discussed in Chapter 1 and will be covered in the context of applicators and probes in this chapter as well.

Another distinctive feature of near-field applicators/probes is that the presence of the material load typically has a significant impact on the device’s field configuration and some circuit variable such as impedance, voltage, and current. In essence, the subject material, through its electrical properties, becomes a part of the circuit. In far-field (antenna) systems, on the other hand, the effect of the material on the circuit variables is negligible. This book mainly deals with near-field systems. There are, however, excellent references for far-field material interaction systems that deal with microwave and millimeter-wave imaging, sensing, and tomography [1].

Applicators for field–material interactions are somewhat analogous to transmitting antennas in communication systems, and probes are analogous to receiving antennas. In the same manner as in communication systems, the reciprocity theorem [2] holds for applicators and probes.

2.1.3 Electrically small and electrically large applicators

High-frequency applicators can be categorized from the standpoint of electrical size, which is the relative size of an applicator compared with the operating wavelength. Obviously, in most cases, the physical size of an applicator is mainly set by the size of the material load. The electrical size is a very important factor in applicator design and determines the geometry, materials of construction, and method of analysis and design.

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Produkt-Details

• Erscheint lt. Verlag: 16.9.2015
• Sprache: englisch
• Themenwelt: Mathematik / Informatik ► Informatik
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Elektrodynamik
• Themenwelt: Technik ► Bauwesen
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Nachrichtentechnik
• ISBN-10: 0-323-32842-3 / 0323328423
• ISBN-13: 978-0-323-32842-5 / 9780323328425