中文摘要：

根据超声波压电换能器在谐振状态下工作电流最大的特点，针对因负载变化或扰动导致超声压电换能器工作频率偏离固有频率的问题，设计了由单片机组成的A／D转换器及其输入输出电路组成的共振频率单闭环跟踪系统。在软件的支持下，改变单片机输出给超声功率电源的PWM波的频率，使A／D转换采集到换能器的负载电流的分流值达到最大，从而保证了超声换能器工作在最佳谐振状态。该文对设计方案的硬件和软件部分作了较为详细的分析，并给出部分硬件原理图。设计方案应用在超声乳化装置上时，实测误差低于0．5％。

英文摘要：

With the feature of the greatest current in the state of resonance for piezoelectric ultrasonic transducer, a method has been proposed to solve the problem of frequency derivation caused by load changes or disturbances in this kind of transducer. And a single closed-loop system for tracking the resonance frequency has been designed, which was composed by A/D converters with single chip microprocessors and relating input/output circuit. In order to make the ultrasonic transducer work in the best state of resonance, a way to change the PWM frequency has been suggested to make sure the A/D converter acquired the maximum current value, and this current value is a segregate current for the transducer loads. The detailed analyses of the design including the hardware and the software, and the some hardware schematics have been described. And when this method was used in ultrasonic emulsification device, the measurement error has been less than 0.5%.