VP16-12 Indirect Current Feedback of Low-Frequency Signals in Rectangular Wave Eddy Current Testing of a Tunnel Magnetoresistive Sensor
Creators: Ziwei Guo and Teruyoshi Sasayama
Publisher: name: IEEE
Year: 2025

The rectangular wave eddy current testing method can be used to detect conductor metal defects and simultaneously obtain multiple signals to distinguish defect information. In a previous study, we proposed a method for improving the sensitivity of deep defect detection using a magnetoresistive (MR) sensor [1]. However, signal-to-noise ratios at low frequencies were low because the MR sensor was affected by excitation fields. Therefore, we developed a method to eliminate the effect of the excitation field by using an external coil. Moreover, a digital-to-analog converter (DAC) compensation method proposed in a previous study could not be applied to the MR sensor because of the differential output of the MR sensor [2]. Therefore, we developed a method to apply a DAC compensation to MR sensors using an indirect current feedback (ICF) circuit. The experimental setup is illustrated in Fig. 1. A rectangular current flowed in an excitation coil. A cancellation coil generated a proximity field to counteract the excitation field. A tunnel magnetoresistive (TMR) sensor was placed at the center of the cancellation coil to receive the magnetic field generated by the eddy currents and convert it into differential voltage signals. Then, an ICF circuit was constructed using an instrumentation amplifier, and a 1 μF capacitor was connected in parallel to form an integration circuit to minimize the effects of harmonics. Moreover, the voltage signals were compensated for by generating a compensation waveform via the DAC to decrease the harmonic noise generated. The processed voltage signal was captured using an analog-to-digital converter (ADC). A 12-mm-thick aluminum plate specimen with three artificial circular defects (φ3 mm × 2, 4, and 6 mm) on the specimen surface or back surface was used. Fig. 2 shows the contour maps of the voltage signals of the third harmonic. The results show that the proposed method can improve the detection of surface and back-surface defects with low-frequency signals. This work was supported by JST SPRING, Japan (grant number: JPMJSP2136).References: [1] Z. Guo and T. Sasayama, IEEE Trans. Magn., Vol. 59, No. 11, Art. No. 6200505 (2023) [2] T. Sasayama and Z. Guo, Int. J. Appl. Electromagn. Mech., Vol. 71, No. S1, pp. S39–S46 (2023)
The rectangular wave eddy current testing method can be used to detect conductor metal defects and simultaneously obtain multiple signals to distinguish defect information. In a previous study, we proposed a method for improving the sensitivity of deep defect detection using a magnetoresistive (MR) sensor [1]. However, signal-to-noise ratios at low frequencies were low because the MR sensor was affected by excitation fields. Therefore, we developed a method to eliminate the effect of the excitation field by using an external coil. Moreover, a digital-to-analog converter (DAC) compensation method proposed in a previous study could not be applied to the MR sensor because of the differential output of the MR sensor [2]. Therefore, we developed a method to apply a DAC compensation to MR sensors using an indirect current feedback (ICF) circuit. The experimental setup is illustrated in Fig. 1. A rectangular current flowed in an excitation coil. A cancellation coil generated a proximity field to counteract the excitation field. A tunnel magnetoresistive (TMR) sensor was placed at the center of the cancellation coil to receive the magnetic field generated by the eddy currents and convert it into differential voltage signals. Then, an ICF circuit was constructed using an instrumentation amplifier, and a 1 μF capacitor was connected in parallel to form an integration circuit to minimize the effects of harmonics. Moreover, the voltage signals were compensated for by generating a compensation waveform via the DAC to decrease the harmonic noise generated. The processed voltage signal was captured using an analog-to-digital converter (ADC). A 12-mm-thick aluminum plate specimen with three artificial circular defects (φ3 mm × 2, 4, and 6 mm) on the specimen surface or back surface was used. Fig. 2 shows the contour maps of the voltage signals of the third harmonic. The results show that the proposed method can improve the detection of surface and back-surface defects with low-frequency signals. This work was supported by JST SPRING, Japan (grant number: JPMJSP2136).References: [1] Z. Guo and T. Sasayama, IEEE Trans. Magn., Vol. 59, No. 11, Art. No. 6200505 (2023) [2] T. Sasayama and Z. Guo, Int. J. Appl. Electromagn. Mech., Vol. 71, No. S1, pp. S39–S46 (2023)