Method of Measuring Permittivity of Composite Materials with Hexagonal Ferrite Inclusions

A new simple method for measuring complex permittivity of substantially lossy composite materials is presented. In this method, a sample of the material under study should completely fill in the cross-section of the single-mode transmission line (waveguide), and the length of the sample must be an integer of a half-wavelength in the waveguide filled with this material. The oscillator frequency is swept linearly, the minima of the reflection coefficient are measured, and then analytical formulas are used to calculate real and imaginary parts of permittivity. The method was tested on magneto- dielectric samples containing hexagonal ferrite powders, as well on such dielectric materials, as PMMA, schungite composites, and alabaster. This method can be a useful technique for measuring dielectric properties of absorbing materials designed, for example, for electromagnetic shielding purposes.