Analysis of natural frequencies of cavities and scatterers using an impulsive current model

A recently suggested (see Y. Leviatan et al., ibid., vol.36, p.1722-1734, Dec. 1988) method of moments solution to generalized formulations of electromagnetic scattering from perfectly conducting and material bodies of smooth shape is used to compute the natural frequencies of such bodies. The field inside the body and the field scattered from the body are expanded by means of the field of impulsive current sources (elemental dipoles) situated a distance away from (rather than on) the boundary. The key feature of this approach is the fields anywhere in space can be evaluated analytically, yielding a substantial saving of computation time in comparison with standard on-surface formulations. Impulsive expansion functions are used for the fictitious currents that simulate the source-free fields in the relevant regions, and a point matching procedure is adopted for the enforcement of the boundary conditions. The result is a generalized impedance matrix whose singularities in the complex frequency plane represent the natural frequencies of the body. The numerical solution is simple to execute, computationally efficient, and can be applied to a broad class of bodies of smooth shape. Results demonstrating the excellent accuracy of the procedure are given