Analysis of the effect of ferrite tile gap on EMC chamber having ferrite absorber walls

It has been known that air gaps between ferrite tiles degrade the absorbing performance of the tile absorber wall installation. However, analysis of the effect has not been thoroughly well published. This paper presents two techniques to analyze gaps between ferrite tiles. A simplified magnetic circuit method is introduced to calculate the effective permeability of the tile wall with gaps. Then, a two-dimensional finite element method is used to analyze the same gap model to validate the simplified formula. The air gap formula is then incorporated into characterizing the ferrite tile absorber with or without a dielectric absorber as its matching element. The fully characterized ferrite absorbers can then be used to design EMC chambers. Design examples are, presented to demonstrate the correlation between calculated and measured normalized site attenuations for 10 m/3 m EMC semi-anechoic chambers.