The Sommerfeld method of solving diffraction problems is essentially a way of extending the range of applications of the image method originated by Lord Kelvin. For this reason, some insight into the Sommerfeld method can be gained through a brief review of the Kelvin image method.
Kelvin’s image method extends the region on which a solution to the given problem is originally defined in order to make it easier to represent the solution in part of the original region. However, the new solution may not conform to physical reality in all of the extended region. To illustrate the essentials of this approach, a simple example can be presented that emphasizes those aspects relevant to the Sommerfeld method.
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