Piezopolymer Interdigital Transducers for a Structural Health Monitoring System

摘要

The flexible piezopolymer transducers made with thin 100 μm PVDF film were proposed by the authors in previous works [1-3]. The proposed technology uses an array of transducers which can be designed to excite particular types of ultrasonic Lamb waves in laminate materials (metallic or composite). The finger to finger distance of interdigital electrode patterns determines the central wavelength of the transducer (λ) and then the corresponding Lamb waves mode. The piezoelectric polymer film can operate in a range of temperature (-80 to +60 °C) that is broader than that of ceramic transducers. Furthermore, the high mechanical compliance makes it adaptable to curved surfaces. A laser-based microfabrication design process can be tuned for efficient excitation and reception of selected Lamb waves. This property depends on the characteristics of laminate material and defect types. In our case we adopted 8 mm finger distance and four pairs of electrodes (see Fig. 1). Permanently glued on the vessel surface, a series of PZTs (Acellent Technologies, Inc., Sunnyvale, CA) used during previous tests is still present.