Smart materials for high power applications

Abstract

Various PZT/epoxy 1-3 composites were investigated for high power applications. "Hard" lead zirconate titanates (PZT4 and PZT8) were chosen for active piezoelectrics owing to their high mechanical quality factors, Q m s, while the passive polymers were selected based on the desired properties for high power composites -low elastic loss, low elastic modulus and high thermal conductivity. The results demonstrated that the composites with high thermal conductivity polymers generally have degraded electromechanical properties with significantly decreased mechanical quality factors, whereas the composites filled with low loss and low moduli polymers were found to have higher Q m s with higher electromechanical coupling factors k t : Q m ~ 200 and k t ~ 0.68 for PZT4 composites; Q m ~ 400 and k t ~ 0.6 for PZT8composites. The effects of high drive field on the behavior of 1-3 composites were further investigated by varying active and passive components. Improved high power characteristics of 1-3 piezoelectric composites were achieved by selection of optimized composite components, with enhanced electromechanical efficiency and thermal stability under high drive conditions. I． INTRODUCTIONPiezoelectric transducers are widely employed in a range of medical applications, including ultrasound diagnostic imaging and ultrasound therapy, such as high intensity focused ultrasound (HIFU), which has recently attracted lot of attentions as a therapeutic treatment for benign prostatic hypertrophy, prostate cancer, bladder cancer, liver cancer, and benign and malignant lesions of the kidney and breast, and expected to provide patients with a noninvasive, nonionizing therapy for these lesions [1] . HIFU destroy targeted tissues by rapidly heating them to temperatures approaching 60 o C or higher, as a result of absorption of high acoustic energy from the transducer. The single-transducer approach uses frequencies between 0.5 and 10MHz, with focusing the intensity varies per procedure between 10 2 and 10 4 W/cm 2 , over a time period of 1 to 30 seconds. A phased-array transducer designed for HIFU typically is constructed of 1-3 PZT/epoxy composite elements that provide high acoustic power over a higher bandwidth [2] .Currently, high power applications are limited by the internal power dissipation, which will generate heat and increasing hysteretic effects resulting in thermal instability. For the generation of high power ultrasound, high electromechanical coupling k ij and mechanical quality factor Q m of piezoelectric materials are desired, where the high electromechanical coupling factor permits effective energy conversion from electrical energy to mechanical energy and allows for increased transducer bandwidth, while the high mechanical quality factor reduces heat generation under high drive condition [3] .*

Characterization of an Improved 1-3 Piezoelectric Composite by Simulation and Experiment

“…However, the high cost and unstable performance of piezoelectric single crystal inhibit its application range. Some researchers have prepared 1-3 piezoelectric composites with other flexible polymers as the polymer material and with an improved electromechanical coupling factor (about 0.68) (3, 4). However, if Young's modulus of polymer is too low, composite easily generates bending deformation.…”