Dielectric Measurements on Polymeric Materials by Using Superconducting Microwave Resonators

This paper deals with the theoretical and practical investigation of a test method using superconducting cavity and helical resonators in an oscillator loop, which aIIows precision measurements to be performed on solid dielectrics in the range of 0.1-10 GHz, and below 9 K. The underlying formulas are an extension of the well-known perturbation formalism and are not restricted to low temperatures. Our experiments resulted in unloaded quality factors of Q = 5˙ 10⁷, between 0.2 and 10 GHz, with a maximum Q (2.2 K, 0.19 GHz) of 9˙ 10⁸, which enabled us to observe the smallest loss tangent so far: tan delta (2.2 K, 6.5 GHz) = (3.7 ± 5 percent)˙ 10^-7 in polyethylene.