Test technique for arbitrary length high dielectric sheet materials based on perturbation method.

In this article, a very effective method is proposed to measure the permittivity of sheet materials with a high dielectric constant and loss. To meet the constraints of the perturbation method, controlling the magnitude of the perturbation by reducing the sample size is necessary. However, this will cause significant changes in the polarization field within the sample and, consequently, affects the accuracy of the calculations. To solve the problem, the effects of the polarized electric field and the non-uniformity of the electric field in the resonant cavity have been considered and an empirical model is developed based on this using curve fitting techniques. Taking the optimized depolarization factor into the resonant perturbation equation, the dielectric properties of arbitrary length of the sample can be accurately calculated when the frequency shift and the quality factor variation are known. Then, the method is validated and analyzed by numerical simulations. Finally, practical tests are carried out on a variety of materials at different sizes, and the results are stable and in excellent agreement with the simulated ones. Therefore, we can conclude that the method can accurately measure the complex permittivity of high dielectric sheet materials.