It has been demonstrated that magnetic resonant coupling is effective for improving the characteristics of ECT sensor, especially the lift-off-dependent reduced sensitivity and noise. The lift-off-dependent reduced sensitivity and noise are caused by the decrease of voltage gain from the exciter coil to detector coil. Magnetic resonant coupling is generally usable to increase the voltage gain from the transmitter coil to the receiver coil. Magnetic resonant coupling was applied to ECT in these experiments to investigate the phenomena of magnetic resonant coupling in the ECT. In the ECT setup, the voltage gain G increased more than 6 times by magnetic resonant coupling at a frequency of 105 kHz. The voltage gain ratio (GR/GNR) was rising 1.12 times when the lift-off length increased from 1mm to 2 mm. This result verified that magnetic resonant coupling has the potential for improving the characteristics of ECT. The EDM slit signal and the lift-off noise were calculated from the experimental results, respectively. Using magnetic resonant coupling, the EDM slit signal increased 1.5 times and the lift-off noise was reduced by 34 % at a lift-off length of 2mm. these results confirmed that magnetic resonant coupling is effective for improving the characteristics of ECT. Additional experiments were performed in order to verify the effect of magnetic resonant coupling for the wobbling (lift-off) noise in the tube inspection. In the vibration test of the ECT sensor inside the tube, the lift-off noise decreased by 28 % on average by magnetic resonant coupling. In the scanning test of the ECT sensor inside the tube, the wobbling and other noises were obviously reduced by magnetic resonance coupling.

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