Investigation of a piezo-polymer array transducer for pulse-echo ultrasonic material examinations

摘要

The aim of this investigation was to make a flexible array ofpulse-echo ultrasound transducers by etching two orthogonal lineararrays of conducting elements into the metallisation of either side ofa sheet of PVdF. These would then be multiplexed under computercontrol in an X-Y raster, thereby forming an image of subsurfacedefects in a material specimen.A potential source model was used to predict the sensitivityof a single element air-backed transducer far from resonance. Initialinvestigations confirmed the predictions, and reaffirmed the resultsof previous workers.In making a prototype array, it was found necessary to use abi-laminar arrangement with a central ground plane, due todifficulties with crosstalk and charge leakage into the specimenmaterials. The radiation pattern of this array was tested and foundto agree with the predictions for Fraunhofer (Far-Field) radiation.A 10 MHz analogue to digital converter was constructed tointerface with the IBM-PC clone as a transient recorder, through adata capture program written in 'C'. However, the electrical noisegenerated by the PC was found to interfere strongly with the signalfrom the array transducer.A wide-band amplifier and full-wave rectifier was then addedto the multiplexer and A/D converter, and the system enclosed in anelectrically isolated environment, which made it possible to obtainclear signal data from the transducer.Non-linear regression was implemented in the software, tosmooth the data and locate echo peaks, and the most frequentlyoccurring peak separation was used to indicate sample thickness atthat location in a false-colour mapping on the screen of the PC.