Đang tải... (xem toàn văn)
The electrical engineering handbook
Rawat, B. “Section IV – Electromagnetics” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000 High power gyrotron from CPI. The 110-GHz gyrotron is the current world record holder for high frequency power generation. This gyrotron is used in electron cyclotron reso- nance heating (ECRH) by producing extremely high frequencies of microwaves which heat a hydrogen gas — “plasma” — to very high levels in experimental fusion reactors. In the photo, the lower section is the electron gun region that generates extremely high-powered electron beam. Shown in the middle section of the gyrotron is an interactive window. The produced microwave power is transformed into a microwave beam that then passes through the high power interaction window. The large upper section is a fully instrumented collector of the “spent” electron beam. (Photo courtesy of Communications & Power Industries.) © 2000 by CRC Press LLC © 2000 by CRC Press LLC IV Electromagnetics 35Electromagnetic Fields J.A. Kong Maxwell Equations•Constitutive Relations•Wave Equations and Wave Solutions 36Magnetism and Magnetic Fields G. Bate, M.H. Kryder Magnetism•Magnetic Recording 37Wave Propagation M.N.O. Sadiku, K. Demarest Space Propagation•Waveguides 38Antennas N.J. Kolias, R.C. Compton, J.P. Fitch, D.M. Pozar Wire•Aperture•Microstrip Antennas 39Microwave Devices M.B. Steer, R.J. Trew Passive Microwave Devices•Active Microwave Devices 40Compatibility L.H. Hemming, V. Ungvichian, J.M. Roman, M.A. Uman, M. Rubinstein Grounding, Shielding, and Filtering•Spectrum, Specifications, and Measurement Techniques•Lightning 41Radar M.L. Belcher, J.T. Nessmith, J.C. Wiltse Pulse Radar•Continuous Wave Radar 42Lightwave S.O. Agbo, A.H. Cherin, B.K. Tariyal Lightwave Waveguides•Optical Fibers and Cables 43Solid State Circuits I.J. Bahl Amplifiers•Oscillators•Multipliers•Mixers•Control Circuits•Summary and Future Trends 44Three-Dimensional Analysis C.W. Trowbridge The Field Equations•Numerical Methods•Modern Design Environment 45Computational Electromagnetics E.K. Miller Background Discussion•Analytical Issues in Developing a Computer Model•Numerical Issues in Developing a Computer Model•Some Practical Considerations•Ways of Decreasing Computer Time•Validation, Error Checking, and Error Analysis Banmali S. Rawat University of Nevada, Reno LECTRIC AND MAGNETIC FORCES are among the five original forces in the universe. These forces are important as we are affected by them almost every instant. Electromagnetics is the combined effect of electric and magnetic fields. Today’s scientific development to a great extent is based on the electro- magnetic fields, their propagation, and varying effects under different boundary conditions. Very few subjects are understood as thoroughly as electromagnetics and have such wide applications. Electricity, telephones, radio, television, datalinks, medical electronics, radar, remote sensing, etc.—all have considerable impact on human life. Now that impact is being carried out further with optical fiber technology, which is also based on the concept of electromagnetic wave propagation. All of human society has been revolutionized by electromagnetics, but still our understanding is not complete. As H.G. Wells once wrote, and this is still true, “The past is but a beginning of a beginning, and all that is and has been is but the twilight of the dawn.” E © 2000 by CRC Press LLC This section focuses on the basic electromagnetic field concepts, wave propagation, devices, circuits, and other applications. The electric fields which are produced by stationary or moving charges are described in Chapter 35. Maxwell’s equations and their solutions under different boundary conditions help in determining the electric field components and resulting effects. The next chapter describes the magnetic fields and magnetic effects due to moving charges or current. These magnetic fields are also governed by Maxwell’s equations and their solutions are obtained for different boundary conditions. Particular magnetic materials with an assemblage of ferromagnetic particles in a nonferromagnetic matrix are useful as audio or video tapes. This subject is investigated in Chapter 36 to provide insight into the recording mechanism of the music we hear all the time. The time-varying electromagnetic field propagation in space or in transmission lines provides the concept of radio communication as discussed in Chapter 37. Another article in the chapter analyzes the transmission of energy through waveguides and microstriplines. Microstriplines have become the basic building blocks for microwave integrated circuits (MICS). For the propagation of electromagnetic fields in space, properly matched antennas between generator and space are required, as described in Chapter 38. Wire and aperture antennas are also described. The high-frequency or microwave-frequency electromagnetic field concepts are helpful in studying the micro- wave devices as discussed in Chapter 39. The electromagnetic compatibility (EMC) study in the following chapter is important for proper functioning of microwave devices and circuits. The important application of electro- magnetic radiation in the form of radar, discussed in Chapter 41, is useful not only for defense but in remote sensing and weather forecasting also. The next chapter explains the propagation of light through waveguides and optical fibers/cables. Optical fiber technology is an emerging technology and is affecting every facet of human life. Microwave circuits are the practical realization of electromagnetic field concepts and are discussed in Chapter 42. With the arrival of sophisticated software packages and high-speed computers, now it is possible and worthwhile to do 3-D analysis and computer modeling of electromagnetic fields in the circuits or devices, as discussed in the last two chapters of this section. This is helpful in the accurate design of microwave components and circuits. All the topics mentioned in this introduction are discussed in detail in their respective chapters. Nomenclature Symbol Quantity Unit A e actual effective aperture of m 2 antenna A em maximum effective aperture m 2 of antenna a attenuation constant neper/m b Doppler filter bandwidth Hz B magnetic flux density Wb/m 2 b phase constant rad/m c velocity of light in vacuum 2.998 ´ 10 8 m/s D electric displacement C/m 2 D divergent factor D directivity of antenna dB d penetrating depth m E electric field intensity V/m ⑀ permittivity F/m ⑀ 0 8.854 ´ 10 –12 F/m f D Doppler frequency Hz F receiver noise figure dB g m transconductance S G gain of antenna dB Symbol Quantity Unit g propagation constant m –1 G Fresnel reflection coefficient H magnetic field intensity A/m h intrinsic impedance W J electric current density A/m 2 J electric charge density C/m 2 k wavenumber k radiation efficiency factor L antenna loss dB l wavelength m m permeability H/m m 0 4 p ´ 10 –7 H/m P Poynting vector W/m 2 P T average power W Y grazing angle degree q electronic charge 1.6 ´ 10 –19 C R detection range of target m r s roughness coefficient S ( q ) shadowing function U unilateral power gain dB . Electromagnetics” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000 High power gyrotron from CPI. The 110-GHz gyrotron is the. reactors. In the photo, the lower section is the electron gun region that generates extremely high-powered electron beam. Shown in the middle section of the gyrotron