Physical Explanation to the Electromagnetic Scattering of a Thin Metallic Plate at Very Low Frequencies

The scattering of a thin metallic plate at very low frequencies is investigated by using the method of moments (MoM) with loop/tree basis function. Calculations show that at low frequencies the scattering of a very thin plate and the scattering of a zero-depth plate are very different not only for the current distribution but also for the RCS. However, the differences are very small at high frequencies. A physical explanation is given to the phenomenon: both the electromagnetic dipole and magnetic dipole are excited simultaneously when illuminated by a very low frequency electromagnetic wave for a general three-dimensional object but the magnetic dipole could not be excited for a zero-depth plate. The appearance of the magnetic dipole makes the scattered electric far field unstable due to the finite digital precision of the computer. A simple method is shown how to make the far field calculation stable.