Abstract
This paper presents a novel alternating current field measurement (ACFM) system, which is realized by tunneling magnetoresistive (TMR) sensors and a tradeoff (TO) wavelet denoising algorithm. The TMR sensor is characterized with a high sensitivity of 30 mV/V/Oe and a self-noise of less than 9pT/√Hz at driving frequency f = 3 kHz. TO algorithm is proposed to select the optimum combination of mother wavelet family and decomposition level. The combinations of wavelet Db5 with decomposition level 8 and Sym7 with decomposition level 8 are determined as the most suitable ones for x- and z-axis signal denoising respectively, which have been demonstrated to be better than the traditional low-pass filtering method. Finally, the efficiency of the proposed system is proved by an experiment under more pressing test conditions, for example, with increased lift-off distance of 10 mm. In particular, it leads to increased SNR (signal-to-noise ratio) by 25.5 dB and 16.5 dB for x- and z-axis ACFM signal, respectively.
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