Novel piezoelectric structures for sensor applications

Piezoelectric ceramic devices have been formed into the helical spring shap es from tubular extrudates. These structures are shown to possess low compl iance and low natural resonant frequencies. Equations are presented allowin g the prediction of the resonant frequencies of the devices; these are show n to be in good agreement with measured responses. Using the design criteri a a device has been constructed to exhibit a low fundamental resonance and a clear spectrum up to 500 Hz. The frequency response is shown for this dev ice and compared to a conventional electromagnetic geophone. The results sh ow that the device acts as a displacement sensor providing an output charge of 0.427 mC/m with no observed spurious resonances. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.