Perfectly conducting diffraction grating formalisms extended to good conductors via the surface impedance boundary condition.

The surface impedance boundary condition is used to include the effect of high conductivity of meals in the integral theory of perfectly conducting gratings. As an intuitive approach, the diffraction formalism proposed by Petit for the treatment of infinitely conducting gratings in P polarization is extended to highly conducting materials by introducing the concept of equivalent surface current density. Then, integral equations for both polarizations are deduced in a mathematically rigorous way. The new method is used to calculate the efficiencies of sinusoidal gratings at infrared and visible light, and the numerical results are compared with those obtained using Maxwell boundary conditions and also with the perfect conductivity model.