Magnetic sensor arrays for the detection of 3D displacements of cracks in Structural Health Monitoring

In this paper, the authors propose a novel sensing technique for Structural Health Monitoring (SHM) based on the use of an array of magnetic field sensors to detect three-dimensional displacements of structural cracks, particularly in historical buildings. The proposed system employs at least three magnetic field sensors to measure variations in the magnetic field generated by a permanent magnet, enabling the detection of crack movements in all three spatial directions (x, y, z) exploiting the signals of three sensors. The sensor array is fixed on one side of the crack, while the permanent magnet is positioned on the opposite side using a cantilever-like structure. This configuration translates each crack movement into distinct variations in the sensor outputs, allowing for the continuous and real-time monitoring of the magnet's relative motion with respect to a reference position, with sufficient accuracy and low power consumption. The effectiveness of the proposed solution was validated through laboratory experiments over a displacement range of 10 mm along three orthogonal axes, demonstrating its potential to effectively track displacements associated with crack evolution. This provides a foundation for implementing non-invasive, low-cost distributed sensor networks in SHM applications.