chap9 - Chapter Nine Radiation Heinrich Rudolf Hertz (1857...

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Unformatted text preview: Chapter Nine Radiation Heinrich Rudolf Hertz (1857 - 1894) October 12, 2001 Contents 1 Introduction 1 2 Radiation by a localized source 3 2.1 The Near Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2 The Radiation or Far Zone . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Multipole Expansion of the Radiation Field 9 3.1 Electric Dipole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.1.1 Example: Linear Center-Fed Antenna . . . . . . . . . . . . . . 13 3.2 Magnetic Dipole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.3 Comparison of Dipoles . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.4 Electric Quadrupole . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.4.1 Example: Oscillating Charged Spheroid . . . . . . . . . . . . . 21 3.5 Large Radiating Systems . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.5.1 Example: Linear Array of Dipoles . . . . . . . . . . . . . . . . 24 1 4 Multipole expansion of sources in waveguides 26 4.1 Electric Dipole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5 Scattering of Radiation 31 5.1 Scattering of Polarized Light from an Electron . . . . . . . . . . . . . 31 5.2 Scattering of Unpolarized Light from an Electron . . . . . . . . . . . 34 5.3 Elastic Scattering From a Molecule . . . . . . . . . . . . . . . . . . . 35 5.3.1 Example: Scattering Off a Hard Sphere . . . . . . . . . . . . . 38 5.3.2 Example: A Collection of Molecules . . . . . . . . . . . . . . . 40 6 Diffraction 43 6.1 Scalar Diffraction Theory: Kirchoff Approximation . . . . . . . . . . 45 6.2 Babinets Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 6.3 Fresnel and Fraunhofer Limits . . . . . . . . . . . . . . . . . . . . . 53 7 Example Problems 55 7.1 Example: Diffraction from a Rectangular Aperture . . . . . . . . . . 55 7.2 Example: Diffraction from a Circular Aperture . . . . . . . . . . . . . 57 7.3 Diffraction from a Cross . . . . . . . . . . . . . . . . . . . . . . . . . 60 7.4 Radiation from a Reciprocating Disk . . . . . . . . . . . . . . . . . . 61 1 Introduction An electromagnetic wave, or electromagnetic radiation , has as its sources electric accelerated charges in motion. We have learned a great deal about waves but have not given much thought to the connection between the waves and the sources that produce them. That oversight will be rectified in this chapter. The scattering of electromagnetic waves is produced by bombarding some object (the scatterer) with an electromagnetic wave. Under the influence of the fields in that 2 wave, charges in the scatterer will be set into some sort of coherent motion 1 and these moving charges will produce radiation, called the scattered wave. Hence scattering phenomena are closely related to radiation phenomena....
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This note was uploaded on 01/08/2012 for the course PHYSICS 707 taught by Professor Electrodynamics during the Fall '11 term at LSU.

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chap9 - Chapter Nine Radiation Heinrich Rudolf Hertz (1857...

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