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Natural frequencies and eigencurrents of the elliptic disk
Author(s) -
Björkberg Jonas
Publication year - 1991
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/90rs02331
Subject(s) - physics , limit (mathematics) , harmonic , series (stratigraphy) , mathematical analysis , plane (geometry) , thin disk , excitation , computational physics , scattering , resonance (particle physics) , optics , mathematics , acoustics , geometry , atomic physics , quantum mechanics , paleontology , galaxy , biology
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.