The Modelling and Experimental Study of the Piezofilm Transducer Waveforms in Cylindrical Geometry

Zhang, Zhong
Hsu, David
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Components with curved surfaces are very common in nondestructive evaluation. In order to detect flaws in curved components using the contact mode, transducers must be made to conform to the curvature of the component. The flexible polymer piezofilm transducers have a distinct advantage in such application. When applied on samples of a rod geometry, a film transducer assumes the shape of a part of a cylindrical shell. When a signal is generated by such a source, the received echo waveform will be significantly different from that of the initial excitation due to the effects of focusing and diffraction. This phenomenon was encountered when pulse-echo measurement was made on rod samples using PVDF polymer film transducers. A film transducers was wrapped around the rod surface covering approximately one sixth of the circumference. The first reflected echo was almost out of phase with the initial input signal and the second echo was out of phase with the first one. This phenomenon cannot be explained by ray approximation. An effort was therefore made to build a model to explain the pressure wave behavior in cylindrical field and to predict the received echo waveform. The efforts spent so far are concentrated on the longitudinal wave. A film transducer, conforming to the sample curvature and launching waves at normal incidence everywhere, can be considered as a longitudinal pressure wave source.