Discrete Fourier transformation analysis of AC Hall sensor magnetometer measurements of high temperature superconductor tapes

During the last five years, the AC performance of high temperature superconductor (HTS) tapes has been under intense development due to the needs of practical applications. Previously, a system capable of measuring time dependent, spatial distribution of the magnetic flux density at a selected distance above the HTS tape has been presented. The tape can carry any cyclic current signal in the frequency range of 0-400 Hz. In this paper, a calculation model to extract information about the current densities, which create the measured magnetic flux density, is developed and used to interpret these measurements. Discrete Fourier transformation is found to provide a numerically stable method that is well suited to the interpretation of results and also for the signal noise exclusion. The third harmonic of the measured Hall voltage is seen to play an integral role in the comparison of the penetration models.