Frequency-Dependent Permeability Evaluation by Harmonic Resonance Cavity Perturbation Method

An artificial material made by kneading magnetic metal flakes in plastic sheets has been used widely in PCs or mobile phone handsets. This sheet is called a noise suppression sheet to reduce unwanted coupling or unwanted signals in the device. The sheet has strong frequency-dependent characteristics in the permeability. It is essential to evaluate these characteristics accurately to develop the sheets and to design the device mentioned above. Currently, the sheets have been evaluated by the transmission line methods, but the accuracy was not enough. The evaluation by the resonance cavity perturbation method is proposed in this article. Although the accuracy of the resonance cavity perturbation method is high, it works well at only one resonance frequency. The expansion of the measuring frequency by using a harmonic resonance cavity is proposed in this article. A comparison of the proposed method to the transmission line method is also discussed.