Harmonic Analysis and Self-Tuning Control Combining Wavelet Analysis and Identification for High-Tc RF SQUID

High-T
_c
radio-frequency (rf) superconducting quantum interference devices are well understood and widely used in many areas of low-field measurement because of their high sensitivity and high resolution. Harmonic analysis has proven to be an efficient way for finding the optimum working point. However, there is a precondition for using harmonic analysis, which is not well understood so far. In this article, it is shown that the precondition can be fulfilled in the typical range of parameters and under our experimental conditions by using a direct mathematical derivation. It is demonstrated that the improvement of wavelet analysis in mean square error (MSE) is more than 50% for harmonic analysis. In addition, identification by forgetting factor recursive least square is a helpful way for self-tuning controller who gives fast tracking, small MSE and high coefficient of determination (R
²
) for harmonic analysis of different experimentally measured signals.