Dimensional Resonances in Magnetic Powder Cores

The existence of dimensional resonances in magnetic powder cores is investigated. Dimensional resonances are a well-known and important phenomenon occurring in ferrite cores, causing a significant inductance drop above a certain frequency. In this work, permeability measurements of commercial powder cores with typical core dimensions are outlined for frequencies up to $\mathbf{1 G H z}$. Moreover, full-wave simulations are conducted. It is demonstrated that dimensional resonances occur in powder cores between 40 MHz and 200 MHz, depending on powder material and core size. Accordingly, this effect needs to be considered when using powder cores as inductors in, e.g., EMI filters. To accurately include their high frequency properties in circuit simulations, a physics based model of powder cores is proposed and first steps towards an equivalent circuit representation are outlined.