Surface impedance near edges and corners in three-dimensional media

Surface impedance expressions which express the AC electric field components on the surface of a conducting medium in terms of the magnetic field components are derived at and near 90° edges and full 90° corners in 3-D structures. These expressions are valid for differing conditions on the faces adjacent to an edge or corner, and for constant or linearly varying surface magnetic fields over those faces. When second-order variations are present, modified expressions must be used. The derived surface impedances depend on the direction of the surface magnetic field relative to the edge or edges, and are quite different in directions parallel to, and normal to, an edge. These expressions are suitable for use in 3-D finite-element computations using scalar magnetic potential in the air region, and to boundary-element methods. Application of the modifications to the Bath cube problem and to a boundary-element problem has shown major improvements in accuracy compared with results obtained using the simple one-dimensional surface impedance