A New Procedure for Improving the Solution Stability and Extending the Frequency Range of the EBCM

The extended boundary condition method (EBCM) has been frequently used to obtain the absorption and scattering characteristics of axisymmetric dielectric objects. For applications involving relatively high-loss dielectric objects, however, the method was usable only at frequencies below resonance. In this paper a new procedure for improving the stability and extending the frequency range of the EBCM is presented. This new procedure has two main features: 1) it is iterative, since it starts with a known solution that approximates the scattering problem, and 2) it involves separate field expansions in each of the overlapping subregions which describe the total interior volume of the object. For example, for high-loss dielectric objects, such as the biological models of humans and animals, the first step in the procedure is to replace the lossy dielectric object with a perfectly conducting one of the same shape and solving the scattering problem to determine the current density on the surface of the conductor. This surface current is then used to calculate the induced field expansions inside the dielectric object. It is shown that the numerical stability of the solution is further improved by dividing the interior region of the object into overlapping subregions, in each of which a separate field expansion is assumed. The electric and magnetic surface currents so obtained from the solution of the internal problem are then used to improve the initial estimate of the current density on the surface of the object. The iterative procedure continues until convergent values of the surface currents and the fields are obtained. Numerical results illustrating the improved stability of the iterative EBCM (IEBCM) solution at higher frequencies as well as its accuracy in calculating the absorption characteristics of a spheroidal model of man in the resonance and the postresonance frequency range are presented.