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Scattering of electromagnetic waves by long radially inhomogeneous isotropic cylinders Parkinson, Robert George

Abstract

The problem of normal-incidence scattering by isotropic cylinders with arbitrary radial permittivity variation and by perfectly conducting cylinders surrounded by radially inhomogeneous isotropic shells is studied. Two types of approximation are considered, namely (i) an approximation of the permittivity variation which allows the use of a power series solution of the wave equation and (ii) approximation of the cylinder by a layered structure. For the latter type, computations are carried out for homogeneous shells and for shells with linearly-varying permittivities. The results are compared with those obtained by numerical integration of the Riccati-type differential equation for impedance or admittance. In general, the homogeneous-shell approximation appears to be easiest to apply and requires a relatively short computation time. It is shown that the scattered-field coefficients can be calculated from measurements of the scattered, field at a single radius by applying a Fourier least-squares fit to the data. The scattered field for plane-wave incidence can therefore be calculated from that for cylindrical-wave incidence, which suggests a more compact system for experimental investigation. Cylinders with a "smoothly" varying permittivity were constructed using a certain type of artificial dielectric. Measurements were carried out in a parallel-plate region for both plane and cylindrical wave incidence; the results obtained agree with computed results and disagree with some previously published theoretical results. As an application, an investigation is made of the range of validity of a planar model when interpreting phase angle measurements on dielectric-enclosed and -unenclosed cylindrical plasmas.

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