Internal field of a hollow dielectric ellipsoid: the amplification effect

This study treats the quasistatic internal field of a hollow dielectric ellipsoid. The cavity is assumed to be a confocal ellipsoid relative to the dielectric ellipsoid. Special attention is paid to the amplification effect (the internal field amplitude is larger than the external uniform field) in hollow spheroids. The amplification effect is not very large: not more than 0.245 dB for a prolate spheroid and 9.5 dB for an oblate spheroid. The analysis is valid also for time-varying fields as long as the size of the ellipsoid is considerably smaller than the wavelength of the field.