The dynamic characteristics of ultrasonic therapeutic transducers using lead-free Na_0.5K_0.5NbO₃, based ceramics

In this paper, lead-free Na_0.5K_0.5NbO₃ (NKN) based piezoelectric ceramics are synthesized by the conventional mixed-oxide methods with sintering temperature at 900-1050 °C. Microstructural analyses of un-doped and CuO-doped ceramics have been carried out and compared using X-ray diffraction (XRD) and scanning electron microscope (SEM). The dependence of the sintering temperatures of the CuO-doped NKN ceramics on the piezoelectric and dielectric properties have been investigated. The results show that the CuO-doped NKN specimens sintered at 1020 °C present the high thickness coupling factor, k_t (>0.50), mechanical quality factor Q_m = 1100 and the lower temperature coefficient of resonance frequency in thickness mode (df_r/f_r < 2%) within the temperature range 20-100 °C. Then, we successfully construct 3-MHz transducers (LF transducer) utilizing our fabricated piezoceramics and examine their static resonant characteristics. Simultaneously, their dynamic acoustic power is measured by the acoustic force balance under a power circuit driving with the intermittent pulse control as compared to the commercial transducers. We find the effective coupling factor of LF transducer (0.05) is superior to that of commercial transducer (0.45).