Sensitivity Enhancement of Piezoelectric Transducers for Impedance-Based Damage Detection via a Negative Capacitance Interface

Piezoelectric transducers are used in many applications due to electromechanical coupling, which allows mechanical and electrical quantities to be related. This principle is used in the development of structural damage detection techniques such as electromechanical impedance (EMI) commonly used in structural health monitoring (SHM), where structural health is monitored by measuring and analyzing the electrical impedance of a transducer. As a piezoelectric transducer is a primarily capacitive device, its reactance becomes small at high frequencies, reducing sensitivity to structural damage and increasing the excitation current required from the measuring system. Therefore, this paper proposes the use of a negative capacitance (NC) interface with the transducer to improve sensitivity to structural damage and reduce the excitation current. The improvement obtained with the NC interface is theoretically analyzed using an electromechanical model and experimentally validated with tests on an aluminum structure. The results conclusively indicate a significant improvement in the sensitivity to structural damage and a reduction in excitation current, which are critical for detecting incipient damage and developing onboard monitoring systems where the output current drive is usually low.