A Procedure for the Extraction of Intrinsic AC Conductivity and Dielectric Constant of N87 Mn-Zn Ferrite Samples Based on Impedance Measurements and Equivalent Electrical Circuit Modeling

The nature of losses in ferrites has not been fully revealed yet. To achieve means for further investigation of ferrite core loss due to electric (E) field, we investigated the response of middle and side legs, cut from commercially available PQ core halves, to an applied E-field, by injecting a sine wave current in the samples. Using conventional laboratory instruments, we did impedance measurements in a wide frequency range (133 Hz-50 MHz) at temperatures that are typical for power electronics (25, 85, 100, and 120 degrees C). In this paper, we discuss a procedure for the extraction of intrinsic ac conductivity and dielectric constant of ferrites through an equivalent electrical circuit model based on the measured impedances. The examined material is of grade N87. The measurements show a clear influence of the investigated shapes. The results obtained start to deviate from "true" electrical properties at about 1 MHz. It appeared also that the inspected ferrites exhibit different conductivities and dielectric constants depending on the core of origin. It is obvious then that core shape, size, and production batch all have an impact on the core losses, which appear to be influenced by the E-field even at frequencies below 1 MHz.