Electromagnetics Explained (eBook)

A Handbook for Wireless/ RF, EMC, and High-Speed Electronics

Ron Schmitt (Autor)

eBook Download: EPUB

2002 | 1. Auflage
410 Seiten
Elsevier Science (Verlag)
978-0-08-050523-7 (ISBN)

Infos

Based on familiar circuit theory and basic physics, this book serves as an invaluable reference for both analog and digital engineers alike. For those who work with analog RF, this book is a must-have resource. With computers and networking equipment of the 21st century running at such high frequencies, it is now crucial for digital designers to understand electromagnetic fields, radiation and transmission lines. This knowledge is necessary for maintaining signal integrity and achieving EMC compliance. Since many digital designers are lacking in analog design skills, let alone electromagnetics, an easy-to-read but informative book on electromagnetic topics should be considered a welcome addition to their professional libraries.

Covers topics using conceptual explanations and over 150 lucid figures, in place of complex mathematicsDemystifies antennas, waveguides, and transmission line phenomenaProvides the foundation necessary to thoroughly understand signal integrity issues associated with high-speed digital design

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Approx.410 pagesApprox.410 pages

Inhalt

Cover 1
Electromagnetics Explained: A Handbook for Wireless/RF, EMC, and High-Speed Electronics 4
Copyright Page 5
Contents 6
Preface 12
Acknowledgments 16
Chapter 1. Introduction and Survey of the Electromagnetic Spectrum 18
The Need for Electromagnetics 18
The Electromagnetic Spectrum 20
Electrical Length 25
The Finite Speed of Light 25
Electronics 26
Analog and Digital Signals 29
RF Techniques 29
Microwave Techniques 33
Infrared and the Electronic Speed Limit 33
Visible Light and Beyond 35
Lasers and Photonics 37
Summary 38
Chapter 2. Fundamentals of Electric Fields 42
The Electric Force Field 42
Other Types of Fields 43
Voltage and Potential Energy 45
Charges in Metals 47
The Definition of Resistance 49
Electrons and Holes 50
Electrostatic Induction and Capacitance 51
Insulators (Dielectrics) 55
Static Electricity and Lightning 56
The Battery Revisited 62
Electric Field Examples 64
Conductivity and Permittivity of Common Materials 64
Chapter 3. Fundamentals of Magnetic Fields 68
Moving Charges: Source of All Magnetic Fields 68
Magnetic Dipoles 70
Effects of the Magnetic Field 73
The Vector Magnetic Potential and Potential Momentum 85
Magnetic Materials 86
Magnetism and Quantum Physics 90
Chapter 4. Electrodynamics 92
Changing Magnetic Fields and Lenz's Law 92
Faraday's Law 93
Inductors 93
AC Circuits, Impedance, and Reactance 95
Relays, Doorbells, and Phone Ringers 96
Moving Magnets and Electric Guitars 97
Generators and Microphones 97
The Transformer 98
Saturation and Hysteresis 99
When to Gap Your Cores 99
Ferrites: The Friends of RF, High-Speed Digital, and Microwave Engineers 100
Maxwell's Equations and the Displacement Current 101
Perpetual Motion 103
What About D and H? The Constituitive Relations 104
Chapter 5. Radiation 106
Storage Fields versus Radiation Fields 106
Electrical Length 108
The Field of a Static Charge 111
The Field of a Moving Charge 113
The Field of an Accelerating Charge 113
X-Ray Machines 115
The Universal Origin of Radiation 115
The Field of an Oscillating Charge 116
The Field of a Direct Current 116
The Field of an Alternating Current 119
Near and Far Field 122
The Fraunhoffer and Fresnel Zones 124
Parting Words 125
Chapter 6. Relativity and Quantum Physics 128
Relativity and Maxwell's Equations 128
Space and Time Are Relative 132
Space and Time Become Space-Time 137
The Cosmic Speed Limit and Proper Velocity 137
Electric Field and Magnetic Field Become the Electromagnetic Field 141
The Limits of Maxwell's Equations 142
Quantum Physics and the Birth of the Photon 143
The Quantum Vacuum and Virtual Photons 147
Explanation of the Magnetic Vector Potential 150
The Future of Electromagnetics 150
Relativity, Quantum Physics, and Beyond 151
Chapter 7. The Hidden Schematic 156
The Non-Ideal Resistor 156
The Non-Ideal Capacitor 159
The Non-Ideal Inductor 160
Non-Ideal Wires and Transmission Lines 163
Other Components 166
Making High-Frequency Measurements of Components 167
RF Coupling and RF Chokes 167
Component Selection Guide 168
Chapter 8. Transmission Lines 170
The Circuit Model 170
Characteristic Impedance 172
The Waveguide Model 174
Relationship between the Models 176
Reflections 176
Putting It All Together 178
Digital Signals and the Effects of Rise Time 180
Analog Signals and the Effects of Frequency 182
Impedance Transforming Properties 184
Impedance Matching for Digital Systems 188
Impedance Matching for RF Systems 189
Maximum Load Power 190
Measuring Characteristic Impedance: TDRs 192
Standing Waves 194
Chapter 9. Waveguides and Shields 198
Reflection of Radiation at Material Boundaries 199
The Skin Effect 200
Shielding in the Far Field 201
Near Field Shielding of Electric Fields 207
Why You Should Always Ground a Shield 207
Near Field Shielding of Magnetic Fields 208
Waveguides 211
Resonant Cavities and Schumann Resonance 221
Fiber Optics 221
Lasers and Lamps 222
Chapter 10. Circuits as Guides for Waves and S-Parameters 226
Surface Waves 227
Surface Waves on Wires 230
Coupled Surface Waves and Transmission Lines 231
Lumped Element Circuits versus Distributed Circuits 234
./8 Transmission Lines 235
S-Parameters: A Technique for All Frequencies 236
The Vector Network Analyzer 240
Chapter 11. Antennas: How to Make Circuits That Radiate 246
The Electric Dipole 246
The Electric Monopole 247
The Magnetic Dipole 247
Receiving Antennas and Reciprocity 248
Radiation Resistance of Dipole Antennas 248
Feeding Impedance and Antenna Matching 249
Antenna Pattern versus Electrical Length 253
Polarization 256
Effects of Ground on Dipoles 258
Wire Losses 261
Scattering by Antennas, Antenna Aperture, and Radar Cross-Section 262
Directed Antennas and the Yagi-Uda Array 263
Traveling Wave Antennas 263
Antennas in Parallel and the Folded Dipole 265
Multiturn Loop Antennas 266
Chapter 12. Emc 268
Part I: Basics 268
Self-Compatibility and Signal Integrity 268
Frequency Spectrum of Digital Signals 269
Conducted versus Induced versus Radiated Interference 272
Crosstalk 274
Part II: PCB Techniques 276
Circuit Layout 276
PCB Transmission Lines 277
The Path of Least Impedance 279
The Fundamental Rule of Layout 281
Shielding on PCBs 282
Common Impedance: Ground Rise and Ground Bounce 284
Star Grounds for Low Frequency 286
Distributed Grounds for High Frequency: The 5/5 Rule 286
Tree or Hybrid Grounds 287
Power Supply Decoupling: Problems and Techniques 288
Power Supply Decoupling: The Design Process 295
RF Decoupling 299
Power Plane Ripples 299
90 Degree Turns and Chamfered Corners 299
Layout of Transmission Line Terminations 300
Routing of Signals: Ground Planes, Image Planes, and PCB Stackup 302
3W Rule for Preventing Crosstalk 303
Layout Miscellany 303
Layout Examples 304
Part III: Cabling 304
Ground Loops (Multiple Return Paths) 304
Differential Mode and Common Mode Radiation 307
Cable Shielding 313
Chapter 13. Lenses, Dishes, and Antenna Arrays 324
Reflecting Dishes 324
Lenses 328
Imaging 330
Electronic Imaging and Antenna Arrays 333
Optics and Nature 336
Chapter 14. Diffraction 338
Diffraction and Electrical Size 338
Huygens' Principle 340
Babinet's Principle 341
Fraunhofer and Fresnel Diffraction 342
Radio Propagation 343
Continuous Media 344
Chapter 15. Frequency Dependence of Materials, Thermal Radiation, and Noise 348
Frequency Dependence of Materials 348
Heat Radiation 355
Circuit Noise 360
Conventional and Microwave Ovens 360
Appendix A. Electrical Engineering Book Recommendations 366
Index 370

Textauszug

2 FUNDAMENTALS OF ELECTRIC FIELDS

THE ELECTRIC FORCE FIELD

To understand high-frequency and RF electronics, you must first have a good grasp of the fundamentals of electromagnetic fields. This chapter discusses the electric field and is the starting place for understanding electromagnetics. Electric fields are created by charges; that is, charges are the source of electric fields. Charges come in two types, positive (+) and negative (–). Like charges repel each other and opposites attract. In other words, charges produce a force that either pushes or pulls other charges away. Neutral objects are not affected. The force between two charges is proportional to the product of the two charges, and is called Coulomb’s law. Notice that the charges produce a force on each other without actually being in physical contact. It is a force that acts at a distance. To represent this “force at distance” that is created by charges, the concept of a force field is used. Figure 2.1 shows the electrical force fields that surround positive and negative charges.

Figure 2.1 Field lines surrounding a negative and a positive charge. Dotted lines show lines of equal voltage.

By convention, the electric field is always drawn from positive to negative. It follows that the force lines emanate from a positive charge and converge to a negative charge. Furthermore, the electric field is a normalized force, a force per charge. The normalization allows the field values to be specified independent of a second charge. In other words, the value of an electric field at any point in space specifies the force that would be felt if a unit of charge were to be placed there. (A unit charge has a value of 1 in the chosen system of units.)

Electric field = Force field as “felt” by a unit charge

To calculate the force felt by a charge with value, q, we just multiply the electric field by the charge,

The magnitude of the electric field decreases as you move away from a charge, and increases as you get closer. To be specific, the magnitude of the electric field (and magnitude of the force) is proportional to the inverse of the distance squared. The electric field drops off rather quickly as the distance is increased. Mathematically this relation is expressed as

where r is the distance from the source and q is the value of the source charge. Putting our two equations together gives us Coulomb’s law,

where q1 and q2 are the charge values and r is the distance that separates them. Electric fields are only one example of fields.

OTHER TYPES OF FIELDS

Gravity is another field. The gravitational force is proportional to the product of the masses of the two objects involved and is always attractive. (There is no such thing as negative mass.) The gravitational field is much weaker than the electric field, so the gravitational force is only felt when the mass of one or both of the objects is very large. Therefore, our attraction to the earth is big, while our attraction to other objects like furniture is exceedingly small.

Another example of a field is the stress field that occurs when elastic objects are stretched or compressed. For an example, refer to Figure 2.2. Two balls are connected by a spring. When the spring is stretched, it will exert an attractive force on the balls and try to pull them together. When the spring is compressed, it will exert a repulsive force on the balls and try to push them apart. Now imagine that you stretch the spring and then quickly release the two balls. An oscillating motion occurs. The balls move close together, then far apart and continue back and forth. The motion does not continue forever though, because of friction. Through each cycle of oscillation, the balls lose some energy until they eventually stop moving completely. The causes of fiction are the air surrounding the balls and the internal friction of the spring. The energy lost to friction becomes heat in the air and spring. Before Einstein and his theory of relativity, most scientists thought that the electric field operated in a similar manner. During the 1800s, scientists postulated that there was a substance, called aether, which filled all of space. This aether served the purpose of the spring in the previous example. Electric fields were thought to be stresses in the aether. This theory seemed reasonable because it predicted the propagation of electromagnetic waves. The waves were just stress waves in the aether, similar to mechanical waves in springs. But Einstein showed that there was no aether. Empty space is just that—empty.* Without any aether, there is no way to measure absolute velocity. All movement is therefore relative.

Figure 2.2 Two balls attached by a spring. The spring exerts an attractive force when the balls are pulled apart.

VOLTAGE AND POTENTIAL ENERGY

A quantity that goes hand in hand with the electric field is voltage. Voltage is also called potential, which is an accurate description since voltage quantifies potential energy. Voltage, like the electric field, is normalized per unit charge.

Voltage = Potential energy of a unit charge

In other words, multiplying voltage by charge gives the potential energy of that charge, just as multiplying the electric field by charge gives the force felt by the charge. Mathematically we represent this by

Potential energy is always a relative term; therefore voltage is always relative. Gravity provides a great visual analogy for potential. Let’s define ground level as zero potential. A ball on the ground has zero potential, but a ball 6 feet in the air has a positive potential energy. If the ball were to be dropped from 6 feet, all of its potential energy will have been converted to kinetic energy (i.e., motion) just before it reaches the ground. Gravity provides a good analogy, but the electric field is more complicated because there are both positive and negative charges, whereas gravity has only positive mass. Furthermore, some particles and objects are electrically neutral, whereas all objects are affected by gravity. For instance, an unconnected wire is electrically neutral, therefore, it will not be subject to movement when placed in an electrical potential. (However, there are the secondary effects of electrostatic induction, which are described later in the chapter.)

Consider another example, a vacuum tube diode, as shown in Figure 2.3. Two metals plates are placed in an evacuated glass tube, and a potential (10 V) is placed across them. The negative electrode is heated. The extra electrons in the negative electrode that constitute the negative charge are attracted to the positive charge in the positive electrode. The force of the electric field pulls electrons from the negative electrode to the positive electrode. (The heating of the electrode serves to “boil off” electrons into the immediate vicinity of the metal.) Once free, the electrons accelerate and then collide with the positive electrode where they are absorbed. Just before each electron collides, it is traveling very fast because of the energy gained from the electric field. Its kinetic energy can be easily calculated, in terms of electron-Volts (eV) and in terms of Joules (J):

Figure 2.3 A vacuum tube diode, showing electrons leaving the negatively biased cathode to combine with positive charge at the anode.

From this example, you can see how natural the unit of electron-Volts (eV) is for describing the energy of an electron.

The most important thing for you to remember is that voltage is a relative term. On a 9 volt battery, the (+) contact has a voltage of 9 volts relative to the (–) contact. Furthermore, the battery has a net charge of zero, although the charge is separated into negative and positive regions. The charge on the positive side is drawn to the charge on the negative side. Connecting a wire between the terminals allows the charges to recombine. The same result is true for a charged capacitor. What would happen if you brought a neutral unconnected wire close to one of the battery’s terminals? Nothing, the wire is neutral. It has no net charge. We’ll revisit the details of this situation a little later in the chapter.

CHARGES IN METALS

In electronics you will only encounter two types of charged particles, electrons and ions. To understand each, let’s review the basic building blocks of matter. Matter consists of tiny particles called atoms. In each atom is a core or nucleus that contains protons and neutrons. The nucleus is very compact. Surrounding the nucleus are electrons. For a neutral atom, there are equal numbers of electrons and protons. The protons possess positive charge, and the electrons possess an equal but opposite charge. The neutrons in the nucleus are neutral. The electrons orbit the nucleus in a special way. You might imagine the electron as a small ball orbiting the nucleus in the same way that planets orbit the sun. However, this analogy is not quite correct. Each electron is smeared out in a three-dimensional cloud called an orbital. Atoms can lend out or borrow electrons, which leaves the atom with a net charge. Such atoms are called ions and they can be positively charged (missing electrons) or negatively charged (extra electrons). Ions of opposite charge can attract one another and form ionic bonds. These bonded ions are called molecules. Table salt, NaCl,...

Produkt-Details

• Erscheint lt. Verlag: 12.6.2002
• Sprache: englisch
• Themenwelt: Mathematik / Informatik ► Informatik ► Software Entwicklung
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Elektrodynamik
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Nachrichtentechnik
• ISBN-10: 0-08-050523-6 / 0080505236
• ISBN-13: 978-0-08-050523-7 / 9780080505237