Clustering effect on permeability spectra of magneto-dielectric composites with conductive magnetic inclusions

摘要

Magneto-dielectric composites, promising candidate materials for next-generation microwave communication, require high permeability and low loss, which are closely related to the particle size of the magnetic fillers. However, clustering occurs when particles physically or electrically touch each other, resulting in effective particle clusters that are much larger than the individual particle size. In this paper, we extend the effective medium theory (EMT) to include the clustering effect, which describes a more accurate prediction of the effective permeability of magneto-dielectric composites over wide ranges of both particle concentration and frequency. A Monte Carlo simulation is applied to model the agglomeration of magnetic particles suspended within a polymeric matrix. The extended formula is experimentally verified by the measurement of constitutive parameters, for iron/paraffin composites with various filler concentrations, over the frequency range from 1MHz to 1GHz. Considering the clustering effect, the proposed EMT model corrects the overestimation of the traditional EMT models, especially near the percolation threshold where the cluster size grows comparable to the skin depth at a given frequency.