MEASUREMENT OF SURFACE IMPEDANCE VERSUS TEMPERATURE USING A GENERALIZED SAPPHIRE RESONATOR TECHNIQUE

An automated measurement technique to measure the surface impedance, Z(s)=R(s)+iX(s),, as a function of temperature is presented. Based on the dielectric resonator measurement technique, a general purpose approach is developed which does not neglect dielectric loss and can accommodate a variety of sample sizes and measurement frequencies. By employing a parallel-plate geometry which has a known electromagnetic solution, both the surface impedance of the sample and the induced surface current can be related quantitatively to the measured and, the resonant frequency, and the applied power. Although the measurement sensitivity depends on the system design and choice of materials, comprehensive equations are presented which serve as a useful tool for designing the system and simulating the measurement. Using a sample size of 1X1 cm(2) and a measurement frequency of 19.6 GHz, a measurement uncertainty of 420 mu Omega for R(s) and 4800 mu Omega for Delta X(s) is demonstrated. For superconducting samples, this translates to a measurement uncertainty of 105 mu Omega for R(s) and 2400 mu Omega for Delta X(s) at 10 GHz, which is sufficient for routine measurements. Methods to improve the resolution and uncertainty of this measurement technique are discussed, and a general scheme to fully automate this measurement via computer is demonstrated.