Scattering by gaps and cracks

The contribution from gaps and cracks where two component structures come together is a matter of increasing concern in radar scattering. For the two-dimensional problem of a narrow gap filled with a resistive or impedance material in an otherwise perfectly conducting plane, the integral equations for the currents induced in the gap are approximated under the assumption that w≪λ, where w is the gap width and λ is the wavelength. Exact solutions are derived in special cases and used to guide the development of approximate analytical expressions for the diffracted fields that are valid for almost all resistivities of the gap material. By comparison with data obtained from a moment-method solution of the problem, it is demonstrated that the results are accurate even for gap widths as large as λ/8 for H-polarization and λ/4 for E-polarization, and the application of these formulas to realistic gap geometries is discussed