Studies on Frequency Characteristics of Micro Inductors

We performed analyses of the frequency response of cloth inductors and thin-film inductors using an amorphous core, applying both to miniature dc-dc converters. Because these inductors are used in high-frequency bands from 1 to 100 MHz, the frequency dependence of the inductance L, capacitance C and resistance R in the inductors cannot be disregarded. The undetermined coefficients in a least-squares calculation were found by expressing L, C and R in terms of the coefficients of an expansion in powers of the frequency. In examining the coefficients of the first and second powers of the frequency, the hysteresis loss can be distinguished from the eddy current loss in the inductors. Moreover, the difference between the iron loss and the copper loss can be clarified. The maximum value of the quality factor is obtained at a frequency at which the iron loss is equal to the copper loss. The results calculated using this procedure are in approximate agreement with experiment.