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Radio Science

Natural frequencies and eigencurrents of the elliptic disk

Authors

  • Jonas Björkberg


Abstract

The natural frequencies of an object determine the late time response of a transient excitation and govern the time harmonic scattering in the resonance region. In this paper the natural frequencies and the corresponding eigencurrents of a perfectly conducting elliptic disk are treated using the null-field approach. The elliptic disk is obtained as the zero thickness limit of a general ellipsoid. It is found that the dominant frequencies, i.e., the frequencies that stay in the finite complex frequency plane when the disk approaches the “wire limit,” line up in two series. The first series, closest to the real axis, can be identified as the resonances of a thin wire antenna, corresponding to quasi-stationary current waves on the disk. The second series has more involved nonstationary current patterns. The theoretical results are illustrated with numerical calculations.

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