Dual-frequency ultrasound is able to enhance the nonlinear effects of high-frequency ultrasound cavitation, improving its efficiency in HIFU applications. A multimodal DPLUS is proposed in this study. Through FEM design, two PZT rings operate in thickness modes to generate ultrasound. Due to different thicknesses, their resonance frequency ratio is close to 1:2. The excited sound waves are focused through a double-parabolic structure and finally output as dual-frequency ultrasound through a waveguide. To accurately couple the two modes, inductance is serially connected to the PZT for static tunning of the resonance frequency. Experimental results show that by connecting a 15.7 μH inductor to the thick PZT, the fundamental mode frequency was reduced from 1.084 MHz to 1.044 MHz, matching the second harmonic mode frequency of 2.084 MHz, and ultimately achieving dual-frequency ultrasound output.
