Dual-Frequency Ultrasound Transducer Using Inversion Layer Technique for Therapeutic Ultrasound Surgery

High intensity focused ultrasound surgery still requires relatively a long surgical time due to small size of coagulative necrosis per each sonication. In order to increase a region of coagulative necrosis, dual-frequency ultrasound scheme has been proposed and showed notable results. In this paper, a novel dual-frequency ultrasound transducer based on the inversion layer technique is presented. Finite element analysis simulation was conducted, and the prototype transducer was fabricated to demonstrate the performance of the proposed method. The optimized thickness ratio between the inverted and non-inverted piezoelectric layers was chosen as 0.3:0.7. The proposed transducer with the chosen ratio generated the fundamental (at 1.2 MHz) frequency and the second harmonic frequency (at 2.4 MHz) ultrasound at the same time. The performance of the proposed transducer was numerically and experimentally verified through electrical impedance, pulse-echo response, and beam profile tests.