Improving Structural Health Monitoring Techniques Based on Electromechanical Impedance by Exploiting Mutual Impedance Effect

The Electromechanical Impedance (EMI) method has been widely employed in several Structural Health Monitoring (SHM) applications. Its basic principle relies on a piezoelectric transducer (PZT) bonded to a host structure, operating simultaneously as both an actuator and a sensor. The transducer is excited over a wide frequency range to compute the EMI. Conventional EMI-based SHM systems sequentially apply this procedure to each PZT when multiple transducers are used. Here, a novel approach is proposed in which all PZT transducers, bonded to the structure, are excited simultaneously, whereas the EMI is individually computed for each sensor, a fundamental distinction from parallel excitation methods that measure only total impedance. Since a PZT transducer can be modelled as a transmission line, the EMI measured at a given transducer includes the effects of crosstalk between adjacent sensors. To assess the proposed method, a simulation study was conducted on OnScale software to model an aluminium plate measuring 200 × 40 × 2 mm instrumented with two PZT transducers. Structural changes were simulated by adding an iron mass, with dimensions of 12 × 4 × 5 mm, to the plate. The EMI was computed from each sensor using both methods. The results obtained indicate that the proposed method increases the sensitivity of the EMI response for damage detection when compared to the conventional sequential EMI approach, which may support the development of improved damage detection and localisation methods.