An integrated structural health monitoring system based on electromechanical impedance and guided ultrasonic waves

We propose a structural health monitoring (SHM) paradigm based on the simultaneous use of ultrasounds and electromechanical impedance (EMI) to monitor waveguides. Methods based on the propagation of guided ultrasonic waves (GUWs) are increasingly used in all those SHM applications that benefit from built-in transduction, moderately large inspection ranges, and high sensitivity to small flaws. Meantime, impedance-based SHM promises to adequately assess locally the structural integrity of simple waveguides and complex structures such as bolted connections. As both methods utilize piezoelectric transducers bonded or embedded to the structure of interest, this paper describes a unified SHM paradigm where pulse-echo and pitch-catch GUWs as well as EMI are employed simultaneously and are driven by the same sensing/hardware/software. We assess the feasibility of this unified system by monitoring a large flat aluminum plate with two transducers. Damage is simulated by adding small masses to the plate. The results demonstrate that the proposed system is robust and can be developed further to address the challenges associated with the SHM of complex structures