Focusing electromagnetic waves into an anisotropic conducting half-space

Abstract

The authors consider a two-dimensional model of an aperture excited homogeneous half-space whose admittivity (or complex conductivity) is different in the horizontal and vertical directions. The criterion for focusing the aperture, of finite width, to a point in the half-space is developed. It is demonstrated that, for an electrical field perpendicular to the axis of the aperture, the anisotropy can be allowed for by a suitable scaling of the isotropic model. The numerical results show that there is a significant enhancement of the fields (and the power dissipation) at the focus point provided that the conduction currents are relatively small compared with the displacement currents in the half-space. Also the width of the aperture should be about 3 or 4 wavelengths for effective focusing.

A viable model for power focusing in a lossy cylinder

“…We define , , , ( denotes the speed of light in free-space and is the permittivity of free-space), tan . As a numerical test case, we con-sidered that the required axial field is given by (4) and, for this case, the real and imaginary parts of the normalized surface field (with ) are plotted as a function of over the length of the cylinder, where the total normalized length of the cylinder is equal to one. The parameters used are indicated on the figures.…”

“…Then, clearly, if and zero otherwise. Thus (4) where . In this case, the aperture distribution harmonic content has the same form as the axial field, but enhanced by the complex factor .…”

“…The field (or power) distribution on the axis of the lossy cylinder may be assumed to have any desired form and their sources can then be calculated. The approach presented here may be viewed as an alternative to phase and compensated focusing [2]- [4], which assumes a given relationship between the phases and amplitudes of the distributions on the array elements. Therefore, the idea Manuscript received September 14, 1999; revised July 11, 2000.…”