Contents 1. INTRODUCTION
Now ultrasonic cleaning and ultrasonic extraction are widely used in industry, and sandwich piezoelectric ultrasonic transducers were usually used [1], [2]. In this type of transducer there is only one operating frequency and the ultrasonic waves were mainly radiated from one end. When the single frequency transducer works, the standing wave is produced in the liquid, which would seriously impact on the effect of the ultrasonic; this problem can be well solved by use of multi-frequency transducers. One of the developments of power ultrasonic piezoelectric transducer is to use more groups of piezoelectric ceramic crystal heaps to achieve multi-frequency. As the single frequency transducer design method, frequency equation is derived at first, and then the sizes are calculated by use of one operating frequency, the other frequency is determined in turn at last [3]. It is very complex and can not be used to design a multi-frequency transducer base on any two operating frequencies in this traditional design method, as a result that the application of the multi-frequency transducers would be prevented. A new invention patent of dual-frequency piezoelectric transducer which structure diagram is shown in Figure 1 was disclosed by Professor Mao Hanling. It has two groups of piezoelectric ceramic crystal heaps, two threaded transmission block for obtain radiation at two ends. The frequency equation set is deduced and verified based on the structure of Fig. 1 in this paper. The structure of dual-frequency piezoelectric transducers
