Universal Characteristic Charts for Ferrite EM Absorbers.

Ferrite electromagnetic absorbers making use of the frequency dispersion of the ferrite permeability are very superior to other absorbers in terms of thickness and bandwidth. Their basic properties have been found by extensive research in the past. However, no theoretical and systematic explanation has yet been given. This paper discusses the electromagnetic absorbing characteristics based on the material dispersion of the ferrite. It is shown that the previous findings can be derived systematically. Because of a significant dispersion in the permeability, the ferrite absorber becomes reflectionless only for the frequency f and the thickness d (matching point) characteristic to each ferrite material. The traditional methods for determining the matching point are based on the impedance matching and require solution of complex transcendental equations of two variables (f and d). Hence, these methods are not suited for systematic derivation of theoretical explanation. In this paper, the reflection coefficient itself is treated and the equation for the matching condition can be separated into the determining equation for the matching frequency and that of the matching thickness. By means of this new method, the basic absorbing characteristics such as the matching frequency, matching thickness, and relative bandwidth are given in the form of nomographs applicable to any ferrite. In addition, the relationship between the permittivity of the ferrite and the absorbing characteristics is derived. [ABSTRACT FROM AUTHOR]