Electromagnetic wave absorbing characteristics of Ni-Zn ferrite grid absorber

The reflection loss of Ni-Zn ferrite grid absorber is studied in the low frequency limit which the period of the array is small compared with wavelength. The relative equivalent complex permeability and permittivity with air volume fraction is obtained using the Hashin-Shtrikman (1962) upper-bound formula. The impedance matching conditions for maximum electromagnetic wave absorption are obtained by the “contour map method.” Two impedance matching thicknesses and frequencies are compared with theoretical matching relationships derived under the limiting case of impedance matching formula. As the air volume fraction increases, the first matching frequency, f_m1 remains nearly constant, while the second one, f_m2 decreases and approaches f_m1. Therefore, the absorption band of a ferrite grid absorber is broader than that of the single layered ferrite plate absorber