Non-contact structural damage detection using magnetic admittance approach with circuitry tuning

One limitation of piezoelectric impedance/admittance approach is that the sensor is permanently fixed after it is bonded/embedded into the mechanical structure to be monitored. Recently, the magnetic transducer, which is essentially an electrical coil inserted with a permanent magnet, is explored for impedance/admittance-based damage detection. Since there is no direct contact between the magnetic sensor and the host structure, the magnetic impedance/admittance approach is capable of online health monitoring of structures with complicated geometries and boundaries. Also, the magnetic impedance/admittance sensor is moveable above the structure surface, which may reduce the number of sensors needed to cover a large structural area. In an earlier study a new magnetic impedance sensing scheme with circuitry integration is proposed, which can greatly enhance the signal-to-noise ratio and amplify the damage induced admittance change. In this research, we systematically study the sensor location on the performance of the magnetic impedance/admittance-based damage detection scheme with circuitry integration. By examining the resonant peaks in the circuitry impedance curves, the damage-induced change of circuitry admittance and the two-way magneto-mechanical coupling, the different amplification effects of the magnetic sensor on the dynamical responses around mechanical modes is investigated. The criteria of tuning the capacitance of the tunable capacitor to achieve significantly amplified admittance changes in a wide frequency range are also developed. Correlated numerical and experimental studies are carried out to validate our proposed tuning criteria.