Abstract

ABSTRACT Composite structures have become a signi“cant part of modern lightweight aircrafts. Contrary to the aluminumpanels such structures are susceptible to catastrophic failure without noticeable forewarnings. One possible wayof preventing catastrophic failures is integrating health monitoring systems in the critical composite structuresof the aircraft. Ultrasonic resonance inspection is especially suitable for the inspection of multilayered compos-ite 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 frequencyresponse is monitored in a narrow frequency band. It has been proven that the NBUS method is capable ofdetecting both arti“cial disbonds and real impact defects in carbon “ber composites. 1 In this paper we presentdesign guidelines for optimizing narrow-band electromechanical impedance (NBE/MI) sensors that are to beintegrated with a monitored composite structure. The NBE/MI sensor takes the form of a piezoelectric elementbonded to the monitored structure. Parameter variations in the inspected structure result in the respectivevariations of the electrical impedance (admittance) of the piezoelectric sensor. Relation between the state ofthe inspected structure and the sensors admittance is estimated using the network representation. Conclusionsconcerning the proper choice of the operating frequencies suitable for various structures are presented.Keywords: structural health monitoring, narrowband ultrasonic spectroscopy, piezoelectric transducers

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