Extension of Babinet's Principle to Absorbing and Transparent Materials, and Approximate Theory of Backscattering by Plane, Absorbing Disks

A rigorous formulation of Babinet's Principle has been found by Copson and by Meixner for perfect conductors. A recently published theory of diffraction by holes in absorbing and transparent screens suggests a generalization of Babinet's Principle to absorbing and transparent materials. The generalized form of Babinet's Principle is not a rigorous statement; it holds only for certain approximate solutions. In this paper it is used to calculate backscattering by circular disks of various reflection coefficients from zero to unity. Experimental results by Severin and v.Baeckmann support this theory. It is expected that, in a succeeding paper, it can be shown that scattering by solid bodies may be calculated in a similar way if the bodies are bounded by plane surfaces large compared to wavelength.