Piezoelectric transducers have a long history of applications in nondestructive evaluation of material and structure integrity owing to their ability of transforming mechanical energy to electrical energy and vice versa. As condition based maintenance has emerged as a valuable approach to enhancing continued aircraft airworthiness while reducing the life cycle cost, its enabling structural health monitoring (SHM) technologies capable of providing on-demand diagnosis of the structure without interrupting the aircraft operation are attracting increasing R&D efforts. Piezoelectric transducers play an essential role in these endeavors. This paper is set forth to review a variety of ingenious ways in which piezoelectric transducers are used in today’s SHM technologies as a means of generation and/or detection of diagnostic acoustic waves. 1. Introduction Piezoelectric transducers are omnipresent in modern human life, from a kitchen gas lighter to popular gadgets such as smart phones and tablet computers, from submarine sonar to medical echography systems, and from electric watches to more dedicated measurement devices such as accelerometers for aircraft vibration monitoring and pressure sensors in jet engines for engine operation monitoring. Piezoelectric transducers can be used either as an actuator, for example, as the ultrasonic motor in a camera lens, or as a sensor, as in the case of an ultrasonic fish finder. These transducers can be used stand-alone, as are the case of conventional ultrasonic nondestructive evaluation (NDE) and nondestructive inspection (NDI) sensors, or be an integrated part of microelectro-mechanical systems (MEMS). The piezoelectric elements can also be used as harvesters of mechanical vibration energy. From an acoustic point of view, there is no difference between SHM and conventional NDE/NDI since both rely on the same physics in the sense that in either case acoustic waves need to be generated and then detected, independently of the acoustic wave mode or method used. What truly differentiate an SHM approach from an NDE/NDI approach is that the former usually requires the sensing elements to be permanently mounted on or embedded in the structure to be evaluated while allowing the wave generation elements, if active wave generation is used by the inspection method, to be either permanently mounted or mobile, whereas in the latter case both wave generation and detection elements are mobile. The requirement of permanently installed SHM sensors, and in some cases, of acoustic wave generation devices, poses challenges and at the same
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