Noncontact methods used for characterization of high-<i>T</i> <i>c</i> superconductors

Abstract

Noncontact eddy-current techniques for characterizing superconductors between 5 MHz and 1 GHz are described. Both a transmission and a frequency-modulation technique rely on modification of the mutual inductance between a pair of coupled inductors. The sample is placed between the inductive sensors; the magnitude of eddy currents induced in the sample, a function of conductivity, modifies the mutual inductance. The frequency-modulation method (where the sensors are the inductive section of a series-resonant LC circuit in an oscillator) is particularly useful for determining the critical temperature (Tc) and transition width for superconducting samples.