Single crystal PZN/PT-polymer composites for ultrasound transducerapplications

摘要

Single crystal relaxor ferroelectrics of PZN-8%PT wereninvestigated for potential application in ultrasound transducers. Thenfull set of electromechanical properties was determined using combinednresonance and laser interferometry techniques. Ultra-high lengthnextensional coupling (k33) of 0.94 was observed, a 25%nincrease over Navy Type VI PZT ceramics. The thickness extensionalncoupling (kt) of 0.48 was comparable to PZT compositions, andnthe compliance S33E was a factor of six greater.nTo maximize height extensional coupling (k'33), whilenminimizing length extensional coupling k31 in array elements,nit was necessary to align the elements along the ⟨100⟩ncrystallographic direction in the x-y plane. Mode coupling plots andntest samples for array elements determined that width-to-height ratiosnof less than 0.5 were desired, similar to the requirement fornpolycrystalline PZT ceramics. Modeling of 1-3 composites andnexperimental results demonstrated that thickness coupling greater thann0.80 could be achieved with a 40% to 70% volume fraction of PZN-PT.nAlthough this is a substantial increase over PZT 1-3 composites, with anthickness coupling coefficient of 0.66, it represents a smaller fractionnof the length extensional coupling k33. This reduction may bena consequence of the increased compliance of PZN-PT, which results innsignificant clamping by the polymer matrix. Ultrasonic transducersnfabricated using PZN-8%PT 1-3 composites achieved experimentalnbandwidths as high as 141%. The pulse-echo responses displayed goodnagreement with modeled results using the Redwood equivalentncircuit