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The increasing emphasis over the past few years on intelligent material systems and structures has resulted in a significant research effort in the areas of embedded and bonded sensors and actuators. Of the many sensing materials available, piezoelectric sensors offer a number of advantages. The sensor output, proportional to changes in surface displacement over a large area, can be used to interpret variations in structural and material properties, e.g., the compliance of the material. This type of sensor has also been used as an ultrasonic transducer. It offers the advantage of having a low structural impedance, thus giving an accurate measurement of the change in area, and consequently can only be used as an actuator on flexible structural systems. The aim of this article is to demonstrate the use of piezoelectric film sensors as a structural integrity monitoring device for composite materials. Tests to date have been aimed at detecting and monitoring impact damage in composite materials, as well as detecting damage in composite-to-metal mechanically fastened joints.

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