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21 June 1999 Apodization of piezoelectric ceramics for ultrasound transducers
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Our objective in apodizing piezoelectric ceramic discs was to produce discs that vibrate more intensively in the central region than in the region near the edge in order to generate acoustic fields with minimum diffraction effects. A spherical poling electrode was used to format the electrical field across the ceramic disc in order to achieve a polarization stronger in the central region and weaker in the edges. The electrode radius was previously determined by simulation with finite element method. The frequency spectrum of the apodized ceramic discs showed that the resonance and the anti-resonance frequencies shifted to larger values. Ultrasound transducers were constructed with the apodized ceramics and with normal commercial ceramics in order to compare their acoustic fields. The apodized transducers showed an average value of the electromechanical coefficient of 0.576 while for the non-apodized transducers this value was 0.597. Their outputs were measured in a water tank, with a point hydrophone, and showed that the time duration of the pulses generated by the apodized transducers were shorter than the ones generated by the conventional transducers, even though the acoustic pressure output intensities were similar. We have also mapped their apodized and non-apodized transducers. The far field of the apodized transducers showed a smoother decay and extended to larger distances from their face, compared to that of the non- apodized transducers.
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Vera Lucia da Silveira Nantes Button, Eduardo Tavares Costa, and Joaquim Miguel Maia "Apodization of piezoelectric ceramics for ultrasound transducers", Proc. SPIE 3664, Medical Imaging 1999: Ultrasonic Transducer Engineering, (21 June 1999);

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