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Computer codes that are based on Elson’s theory for light scattering by interfacial roughness in multilayer coatings were used to predict the bidirectional reflectance-distribution function (BRDF) of several opaque coatings from surface-roughness profiles measured by either a scanning–tunneling microscope or an atomic-force microscope. The predictions usually agreed with measured BRDF values to within a factor of 2. The coatings consisted of single layers of Ag or Ni and dielectric stacks with up to three layers.

Low-loss dielectric powders have been used as the core material of dielectric waveguides in the microwave and millimeter wave regions. Both flexible guides and planar circuits analogous to fiber and integrated optical components have been realized. Transmission losses Qs of 2000 are obtained at 94 GHz. Bending losses were found to be insignificant for radii of curvature greater than a few centimeters. Directional couplers with fixed and variable coupling were investigated. Barium tetratitanate, nickel aluminum titanate, and magnesium calcium titanate were among the lowest-loss powders studied, exhibiting effective dielectric constants of 3.5-6 in packed powder form. Teflon was used as the cladding material for flexible waveguides, and Teflon, polypropylene, and polystyrene were used as rigid substrates for the planar dielectric channel waveguides.