Estimation of Attenuation Characteristics of Feed-Through Type EMI Filters using Fe-Si Alloy Flake-Polymer Composite

The authors have constructed a prototype feedthrough type EMI filter by filling the hollow portion of a coaxial structure having an outer diameter of 7.00 mm and an inner diameter of 3.04 mm with composite magnetic material made up of Fe-Si alloy flakes and polyphenilene sulfide resin. Insertion losses were measured in the frequency range from 100 MHz to 20 GHz for filter specimens containing different length of composite magnetic material, and an insertion loss of 10 dB and greater was observed from 1 GHz to 20 GHz in the case of 20 mm. In addition, using material constants of the composite magnetic material measured beforehand, insertion losses were calculated, and it was found that the results of calculation agreed relatively well with the above measurements. On the basis of the above, the authors have been able to clarify how the material constants of the composite magnetic material affect insertion loss.