Design and test of a microwave resonator for the measurement of resistivity anisotropy

The measurement of the microwave surface impedance is a fundamental characterization tool for a wide class of conducting, semiconducting and superconducting materials. In many cases, material anisotropy can show up as an intrinsic or tailored property, and its measure is often desirable. Microwave resonators can be designed to give at the same time non-destructive and highly sensitive measurements, in particular with the surface perturbation method for planar samples. Rectangular resonators can be designed to preserve sensitivity to the anisotropy of the samples under study, since they can induce straight currents on the sample. We designed a two-mode rectangular dielectric resonator with straight currents on the sample under testing, where the second mode can be used for validation of the results. We realized the rectangular dielectric resonator using a moderate-κ dielectric (LaAlO3) crystal, which showed the two designed microwave modes. Using the lowest mode, we tested the sensitivity of the device to the anisotropy using a graphite sample. The device was able to track the angular dependence of the microwave response, showing the effect of the anisotropy. The second mode confirmed the results. Thus, despite its low Q factor, the present device is able to track the anisotropy of highly lossy conductors.