9F-2 Heat Conductive Array Transducer for Phase-Conversion Molecular Imaging

Abstract

A heat conductive array transducer was designed for transmitting high power ultrasound as well as transmitting and receiving wideband pulse waves. In phase-conversion ultrasonic molecular imaging, tissue-selective nano-droplets are converted to contrast microbubbles by a long duration ultrasonic pulse with a relatively high amplitude. When a conventional imaging array transducer was used, sensitivity of transducer decreased caused by some breakdown processes. In this study, we firstly examined the breakdown process based on experiments and numerical simulations. The experimental result was consistent with the simulation result assuming peeling of the adhesive between two PZT layers. A new transducer structure using a heat conducting acoustic isolation layer (AIL) on a metal heat sink block was conceived to inhibit this type of breakdown while maintaining the wide bandwidth for imaging with a high resolution. Heat generated in the PZT and adjacent layers can diffuse into a metal heat conductor through the AIL. Since the AIL reflects pulses, a possible unwanted response due to reflection at the opposite side of the metal block will be suppressed. The temperature rise and the ultrasonic pulse response of the transducer were calculated using PZFlex. The temperature rise in the transducer immediately after driving at 40 V for 25 s with 1% duty ratio was 37 degrees for the proposed structure, much lower than that for the conventional structure of 56 degrees. No serious unwanted response was observed for the proposed structure. These results show that the proposed structure will be useful for a high-power wideband phased array transducer.