The improvement of dynamic characteristics of ultrasonic therapeutic transducers using fine-grain PZT-based piezoceramics

Optimizing the dynamic resonant characteristics of ultrasonic therapeutic transducers depends most importantly on fine-grain piezoceramics with good resonant properties. In this paper, we prepare and compare modified Pb/_.99Sr_0.01[0.03(Mn_1/3Nb_2/3)-0.97(Zr_0.51Ti_0.49)]O₃ piezoceramics with 0.1 wt% CaCO₃ and 0.8 wt% PbO additives (PMZT3) synthesized by B-oxides precursor (BO) and conventional ceramic mixed-oxide methods (MO). Our experimental results show that the BO-type piezoceramics have better grain microstructure and better material properties [e.g., d₃₃= 340 pc/N, k_t= 0.52, Q_m= 1250, temperature coefficient of change rate of resonant frequency (TCF) = 0.01%/degC, and temperature coefficient of change rate of clamped capacitance (TCC) = 0.18%/degC]. We construct 1-MHz transducers using our BO and MO types of piezoceramics and examine their dynamic resonant characteristics as the transducers are driven by a power driver with open-loop control. Results show that the transducers with the BO-type piezoceramics have better dynamic characteristics, such as time stability (e.g., aging rate of resonant frequency at thickness mode = 0.26%/decade cycle, and aging rate of clamped capacitance = 0.55%/decade cycle) and temperature stability as BO-type piezoceramics. Furthermore, we observe that the clamped capacitance variation has more influence on the transducer dynamic characteristics than the resonant frequency variation, and we verify the observation from the partial derivative ratio of the transfer function derived by a simulated ultrasonic equivalent circuit system. It is concluded that the BO-type piezoceramics are better candidates than the MO-type samples for obtaining optimum dynamic resonant characteristics in ultrasonic therapeutic transducers.