Miniaturized Sub-Megahertz Focused Ultrasound Transducer Composed of Multilayer Hard PZT Ceramics

Catheter-directed ultrasound transducer enables efficient delivery of ultrasound energy to targeted vessel lumens. For intravascular therapies, such as sonothrombolysis, a small size (<;8 Fr.), low frequency (<;3 MHz) transducer, particularly in sub-megahertz frequency range is preferable to enhance cavitation effects. Our previous studies demonstrated that the forward-looking multi-layer stack of soft PZT ceramic (PZT-5A) can generate moderate acoustic output to induce inertial cavitation of microbubble contrast agent (MCA). In this study, we aim to enhancing the transmitting power intensity by adopting hard PZT ceramic (PZT-4) as an active piezo material. In addition, a metallic concave lens was designed to focus ultrasound energy with an improved focal gain. The electrical and acoustic characteristics of the new transducer were analyzed through finite element analysis (FEA). The performance of the improved model was validated by experimental characterizations. As a result, the peak-negative-pressure reaches up to 2.4 MPa for 120 V_pp excitation, which is about 5.5 dB greater than that of the reference.