Massively parallel iterative determination of stratified dielectric parameters from scattered-field measurements

The remote determination of dielectric constants of stratified dielectrics, through solution of the inverse-scattering problem, has practical application in many fields. We use a simple one-dimensional model to determine the salient characteristics of stratified layers of dielectrics given a finite number of reflection coefficients for various frequencies in the microwave X-band region. One of the key concepts of this research is the optimization that is necessary to find a global minimum of the highly nonlinear function that specifies the scattering coefficients. This was achieved by use of a simple iterative method whereby 16,384 iterative procedures that employ random starts are run simultaneously on a MasPar, which is a 16,000 processor single-instruction/multiple-data computer. Results show that one can solve for the refractive index or thickness of a number of dielectric layers with thicknesses of the order of one third of a wavelength or less by using this type of nonlinear optimization.