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 TE_0np modes. The calculated permeability using the TM₁₁₀ mode (where the sample experiences demagnetisation owing to the perpendicular field orientation) is verified using TE_0np 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.