Development of a miniaturized piezoelectric ultrasonic transducer

A 421 kHz miniaturized piezoelectric ultrasonic transducer for portable and internal body therapeutic applications was developed. The weight, outer diameter, and length of the transducer are 0.15 g, 2 mm, and 10.35 mm, respectively. The transducer is a one-wavelength design based on the longitudinal vibration mode with a stepped horn to focus the energy. Finite element analysis and equivalent circuit models were applied for theoretical analysis. Q_m and k_eff of the transducer measured using the impedance analyzer were 393 and 0.21, respectively. The acoustic output properties of the transducer were measured based on the hydrophone measurements under the condition of 1/4lambda immersion depth. The maximum input electrical power, output acoustic power, sound intensity, radiation pressure, and vibration velocity at the radiation surface were derived to be 0.45 W, 0.11 W, 38 W/cm², 1.8 MPa, and 2.7 m/s, respectively. The directivity pattern shows that the pressure distribution is omnidirectional within the range from 30 to 150 degrees. The nonlinear effects of ultrasonic streaming in water and cavitation in silicone oil due to the intense ultrasound were also observed. The potential applications of the transducer are sonodynamic therapy, drug delivery, and microfluidic pumping.