光ポンピング磁気センサーを用いた渦電流探傷試験

抄録

Generally, in eddy current testing (ECT), magnetic field variations generated by induced eddy currents are detected using a pickup coil. However, according to Faraday’s law of electromagnetic induction, the sensitivity of a pickup coil decreases significantly at low frequencies, making the detection of low-frequency magnetic fields difficult. As a result, conventional ECT often have limited capability for detecting deep flaws in conductive materials. In this study, we propose an eddy current testing system based on an optically pumped magnetometer (OPM) with low-frequency excitation. The proposed method aims to improve the detectability of not only surface flaws but also deeper flaws that are difficult to detect using conventional ECT. To enable measurements under geomagnetic field conditions, the magnetic signal detected by the probe was transferred to an OPM inside a magnetically shielded box via a flux transformer. Furthermore, to suppress the effects of external magnetic noise and environmental disturbances, the probe was covered with an aluminum alloy magnetic shield. Experiments were conducted using a 12-mm-thick aluminum alloy plate containing artificial flaws with a diameter of 3 mm and depths ranging from 2 to 6 mm. The experimental results demonstrate that the proposed OPM-ECT system successfully detected all backside flaws in the specimen, indicating the potential of this method for deep-flaw inspection in conductive materials.