Measurements and modeling of HTS shielded dielectric resonators

摘要

We have performed accurate, reproducible and nondestructive measurements of the surface resistance of high quality YBa2Cu 3O7-x (YBCO) thin films in the temperature range 12 K to Tc using a compact rutile dielectric resonator method at 9.6 GHz. The absolute values of the HTS surface resistance have been measured to systematic errors of less than 10 μΩ at this frequency using this technique, which employs two resonator configurations with carefully chosen geometries. The resonators have unloaded Q factors of around 105 at 77 K, increasing to above 5.105 below 15 K. We have used three dimensional electromagnetic software (“Superfish”) to study the effects of the copper shield on these rutile (TiO2) measurements, and others using lanthanum aluminate (LaAlO3) as the dielectric material. In the latter case, there are significant uncertainties (as large as 100%) in the measurements of the surface resistance of the YBCO films owing to the smaller field energy filling factor for LaAlO3 since it has a lower relative permittivity than rutile