SUPERCONDUCTOR SCREEN VIEWED AS ONE OR 2 INDUCTIVE LOOPS

Non-contact two-coil methods for the low-frequency electrodynamics of superconductors are analysed by representing the superconductor as one or two inductively-coupled loops with various voltage-current characteristics. Various types of behaviour can be explained without specific reference to granular or weak-link effects. For the one-loop model, flux-flow and surface flux-entry barrier characteristics are analysed for the first time. Fissured samples and films of uneven thickness may be modelled by two loops, which can exhibit ''overshoots'' and double loss-peaks. Attention is paid to the harmonic content and also, in the case of square-wave detection, to the distinction between pick-up coil and Hall-probe data. New YBaCuO ceramic, YBaCuO film and BiSrCaCuO crystal data are analysed.