Computation of the magnetic polarizability of conducting disks and the electric polarizability of apertures

The electric polarizability of a small aperture of arbitrary shape is computed by solving the dual magnetostatic problem of a conducting disk. The method of moments is used to solve the integral equation for the current density induced on the disk. Charge-free expansion functions for the current density are introduced. The electric polarizability of the aperture is obtained from the magnetic polarizability of a complementary disk through the use of the duality principle. Results for five typical aperture shapes including the circle and ellipse are computed. The results of the computations are compared with available exact or measured data, and they show good agreement.