Microwave Electrical Properties of Nanocomposites

Abstract

Several techniques have been proposed for the measurement of the complex dielectric permittivity at microwave frequencies. The cavity resonant method presents good accuracy, in particular for low loss materials, using the small perturbation theory. In this method, the resonance peak frequency and the quality factor of the cavity, with and without a sample, can be used to obtain the complex dielectric permittivity of the material. We measure the shift in the resonant frequency of the cavity Δf caused by the insertion of the sample, which can be related to the real part of the complex permittivity ε′ and the change in the inverse of the quality factor of the cavity, Δ(1/Q), which gives the imaginary part, ε″. The relations are simple when we consider only the first order perturbation in the electric field caused by the sample. This technique is presented to study polymer nanocomposites that will be used in microwave oven doors, which purpose is to confine the energy to the cavity, where the microwave leakage must be strictly controlled.