Precise measurements of the permittivity of microwave absorbing materials at microwave frequencies

With the development of electronic technology, microwave absorbing materials play an important role in aerospace, electromagnetic pollution, and other fields. However, the accurate measurement of dielectric properties at microwave frequencies has always been a difficult problem. In this work, the resonant perturbation method for the accurate measurement of microwave dielectric properties of microwave absorbing materials is proposed. Firstly, a series of samples are simulated by high frequency structure simulator (HFSS). Then the permittivity of paraffin, fused silica glass and alumina (99.6% purity) are measured by resonant perturbation method. The results of measurement are in good agreement with the simulation results, and it proves that this method is feasible. At last, a series of absorbing samples are prepared with different mass fractions of paraffin and carbon powder, and their permittivity and loss tangent are obtained by resonant perturbation method. The permittivity of the sample with 8% mass ratio is 2.42, and the tangent value of loss is 8.98 × 10⁻². Experiments show that the theoretical simulation results are in good agreement with the measurement results. Compared with coaxial air-line method, it can provide more accurate measurement results and also provide an idea for measuring the dielectric properties of materials with high loss and permittivity. It is believed that this method will have great application value in the future.