Microwave characterization of magnetic materials under uniaxial and biaxial mechanical compressive stress

A new technique of determining the permittivity and the permeability of ferrite material from microwave measurements in a rectangular waveguide under biaxial mechanical stress is presented. Three measuring cells, corresponding to the application of uniaxial and biaxial compressive forces are developed, each in the range of 2.6 GHz to 3.95 GHz, and 3.95 GHz to 5.85 GHz. Measurements of the permittivity and the permeability of a sample of nickel-zinc ferrite are performed under stress levels up to 60 MPa. The results show that the permittivity remains isotropic and does not depend on the level of stress, and that the permeability is affected by the magnitude and direction of the stress applied.