Influence of tough hydrophone shapes with titanium front plate and hydrothermal PZT thick film on distribution of acoustic bubbles around focal point of HIFU transducer

Novel tough hydrophones were developed by the depositing hydrothermally synthesized lead zirconate titanate thick film on the back-side surface of Ti plate to protect from acoustic cavitation. This hydrophone was resistant to damage at a high-intensity acoustic field formed by a high-intensity focused ultrasound (HIFU) transducer. Since the generation of acoustic bubbles cannot be avoided at high-intensity ultrasound field, an influence of the tough hydrophone´s shape on the spatial distribution of acoustic bubbles around focal point of HIFU transducer was investigated for accurate and precise evaluation of acoustic fields. As the result of the visualization by sonochemiluminescence in luminol, a stripe pattern derived from the standing wave was observed. Similarly, the trapping acoustic bubbles derived from the standing wave and moving acoustic bubbles derived from acoustic radiation forces were observed using visualization by the ultrasonic diagnostic equipment. By contrast, as the result of the observation using needle type hydrophone, the amount of the trapping acoustic bubbles reduced, while the moving bubbles remained and thinned in shape. The present shape of tough hydrophone tip was good use for low frequency ranges several tens kHz, whereas the influence of existence of the tough hydrophone with round shape tip was reduced as compared to that with flat shaped tip at high frequency.