Application of Co-based amorphous alloy ribbons with various thicknesses to a noise filter

A large amount of electromagnetic interference (EMI) is caused by the radiated emission induced by the common mode noise current in cables used to connect digital equipment. We have investigated magnetic alloy ribbons in order to realize high loss characteristics and to fabricate very compact noise filters. It has been reported that annealed Co-based amorphous alloy ribbon provides the same noise attenuation as a conventional noise filter (ferrite core) but with ∼1/20th the volume. On the other hand, it is considered that impedance, especially resistance, depends on ribbon thickness, since eddy current loss is the main cause of the noise reduction. However, the relationship between ribbon thickness and impedance has not been yet investigated. Therefore, to reduce the noise filter volume, we examined the effect of annealing on the impedance in the MHz-GHz frequency range, for Co-based amorphous alloy ribbons of various thickness.