Department of Applied Physics, Tohoku University, Sendai 980-8579, Japan.
Graduate Program in Spintronics, Tohoku University, Sendai 980-8578, Japan.
Sensors (Basel). 2019 Oct 30;19(21):4718. doi: 10.3390/s19214718.
Magnetic flux leakage (MFL) testing is a method of non-destructive testing (NDT), whereby the material is magnetized, and when a defect is present, the magnetic flux lines break out of the material. The magnitude of the leaked magnetic flux decreases as the lift-off (distance from the material) increases. Therefore, for detection at high lift-off, a sensitive magnetic sensor is required. To increase the output sensitivity, this paper proposes the application of magnetic tunnel junction (MTJ) sensors in a bridge circuit for the NDT of reinforced concrete at high lift-off. MTJ sensors were connected to a full-bridge circuit, where one side of the arm has two MTJ sensors connected in series, and the other contains a resistor and a variable resistor. Their responses towards a bias magnetic field were measured, and, based on the results, the sensor circuit sensitivity was 0.135 mV/mT. Finally, a reinforced concrete specimen with a 1 cm gap in the center was detected. The sensor module (with an amplifier and low pass filter circuits) could determine the gap even at 50 cm, suggesting that MTJ sensors have the potential to detect defects at high lift-off values and have a promising future in the field of NDT.
漏磁检测（MFL）是一种无损检测（NDT）方法，通过对材料进行磁化，当存在缺陷时，磁通线会从材料中逸出。随着提离（距材料的距离）增加，泄漏的磁通量会减小。因此，对于高提离检测，需要使用灵敏的磁传感器。为了提高输出灵敏度，本文提出将磁隧道结（MTJ）传感器应用于桥路电路中，用于高提离下的钢筋混凝土无损检测。MTJ 传感器连接到全桥电路中，其中臂的一侧有两个 MTJ 传感器串联连接，另一侧包含一个电阻器和一个可变电阻器。测量了它们对偏置磁场的响应，根据结果，传感器电路的灵敏度为 0.135 mV/mT。最后，检测了中心有 1 厘米间隙的钢筋混凝土试件。即使在 50 厘米处，传感器模块（带有放大器和低通滤波器电路）也可以确定间隙，表明 MTJ 传感器有潜力在高提离值下检测缺陷，并在无损检测领域具有广阔的前景。
