Design of piezoelectric transducers for health monitoring of composite aircraft structures

摘要

Composite structures have become a significant part of modern lightweight aircrafts. Contrary to the aluminum panels such structures are susceptible to catastrophic failure without noticeable forewarnings. One possible way of preventing catastrophic failures is integrating health monitoring systems in the critical composite structures of the aircraft. Ultrasonic resonance inspection is especially suitable for the inspection of multilayered composite structures. In our previous works we have described the principle of narrow-band ultrasonic spectroscopy (NBUS), where the surface of an inspected structure is scanned with a resonant transducer whose frequency response is monitored in a narrow frequency band. It has been proven that the NBUS method is capable of detecting both artificial disbonds and real impact defects in carbon fiber composites. In this paper we present design guidelines for optimizing narrow-band electromechanical impedance (NBE/MI) sensors that are to be integrated with a monitored composite structure. The NBE/MI sensor takes the form of a piezoelectric element bonded to the monitored structure. Parameter variations in the inspected structure result in the respective variations of the electrical impedance (admittance) of the piezoelectric sensor. Relation between the state of the inspected structure and the sensor's admittance is estimated using the network representation. Conclusions concerning the proper choice of the operating frequencies suitable for various structures are presented.