Magnetic Hammer Testing With Tunnel Magnetoresistive Sensors

The magnetic hammer test (MHT) technique was developed using tunnel magnetoresistive (TMR) sensors that detect very weak magnetic signals generated by the natural vibration of steel plates. For the non-destructive testing (NDT) of infrastructures, which requires high accuracy and energy conservation, TMR sensors with high sensitivity have the potential to meet the NDT requirements. TMR sensors detected weak signals of nanotesla due to natural vibration and accurately evaluated the size of steel plates from the natural frequency. In addition, a finite element method (FEM) simulation analysis was conducted to elucidate the mechanism of the magnetic signals generated by the MHT. We concluded that the MHT technique using TMR sensors can be applied as a novel NDT method for detecting small fractures and corrosion in steel materials.