Magnetic Hammer Testing with Tunnel Magnetoresistive Sensors

For the nondestructive inspection for infrastructures required both high accuracy and energy conservation, the tunnel magneto-resistive (TMR) sensors with high sensitivity have the potential to meet the requirements. In this study, the magnetic hammer test (MHT) technique was developed using TMR sensors that detect very weak magnetic signals generated by the eigen-oscillation of steels. TMR sensor detected the weak signals below 1 nT by natural vibration and the size of steel plates was accurately evaluated from the eigen-frequency. In addition, a finite element method (FEM) simulation analysis was conducted to confirm the validity of experimental results. We concluded that the MHT technique using TMR sensors can be applied to a novel nondestructive inspection for detecting small fractures and corrosion in steel materials.