Electromechanical impedance of piezoelectric transducers for monitoring metallic and non-metallic structures: A review of wired, wireless and energy-harvesting methods

Electromechanical impedance–based structural health monitoring method had attracted several researchers in the recent past for aerospace, civil, mechanical, timber and biological structures. Smart materials such as piezoelectric (lead zirconate titanate) and macro fibre composite transducers are either surface bonded or embedded inside the host structure to be monitored. These smart materials with an applied input sinusoidal voltage interact with the structure, to sense, measure, process and detect any change in the selected variables (stress, damage) at critical locations. These can be categorized as wire-based ‘advanced non-destructive testing’, wireless-based ‘battery-powered lead zirconate titanate/macro fibre composite’ and energy harvesting–based ‘self-powered lead zirconate titanate/macro fibre composite’ methods. Most importantly, the effectiveness of these electromechanical impedance–methods can be classified into active and passive based on the properties of the material, the component and the structure to be monitored. Furthermore, they also depend on variables to be monitored and interaction mechanism due to surface bonding or embedment. This article presents some of the important developments in monitoring and the path forward in wired, wireless and energy harvesting methods related to electromechanical impedance–based structural health monitoring for metals and non-metals.