Microwave complex permeability of magnetite using non-demagnetising and demagnetising cavity modes

This paper investigates the use of a cylindrical microwave cavity resonator to measure the complex permeability of mixtures of magnetite (Fe3O4) and silicon dioxide (SiO2) using different field orientations. The weight percentages of the mixtures are varied and the effective bulk permeability is measured at frequencies from 3.8GHz to 10.16GHz using the TM110 and TE0np modes. The calculated permeability using the TM110 mode (where the sample experiences demagnetisation owing to the perpendicular field orientation) is verified using TE0np modes (where the sample demagnetisation is small). The TM110 measurement follows the permeability and loss trends with frequency, demonstrating the effectiveness of this non-invasive technique for measuring the broadband magnetic properties of powder mixtures at microwave frequencies