In multi-frequency ultrasonic system, transducer is one of the key components, it must have two resonant frequencies, and the impedance near its resonant point must be close to achieve the conversion of electricity and sound.
There are many resonant frequencies in the sandwich piezoelectric ceramic transducer, such as fundamental frequency vibration, 1st harmonic frequency, 2nd harmonic frequency, etc. . According to the design theory of sandwich composite transducer of ultrasonic cleaner, the transducer can work in both fundamental frequency and first harmonic frequency by changing its structure mode. There are two vibration modes of dual-frequency transducer, the fundamental vibration is half-wavelength with one node in the transducer, and the harmonic vibration is full-wavelength with two nodes in the transducer.
According to the study of the effect of the position of the ceramic plate in the Ultrasonic transducer on the performance of the transducer, the piezoelectric ceramic plate is placed near the vibration node of the transducer. Therefore, if the piezoelectric ceramic wafers are placed together in the traditional sandwich transducer mode, it is possible that the ceramic wafers are in the vicinity of their vibrating nodes for the half-wavelength vibration mode, and for the full-wavelength vibration mode, the ceramic plate will deviate from its vibrating node, which will reduce the power capacity of the transducer./n/nUltrasonic transducer is one of the most important parts of ultrasonic engineering technology and the fastest-growing branch of the field of acoustic transducers.
A transducer is an energy conversion device, which can convert one form of energy into another form of energy device, it can realize the conversion between electrical energy and sound energy.
The ultrasonic wave has many physical, chemical and biological effects when it propagates in the medium, and it is easy to realize fast and accurate on-line non-destructive detection and non-destructive diagnosis. A wide variety of Ultrasonic transducer are now used in industry, agriculture, defence, biomedicine and scientific research.

The application of Ultrasonic transducer is very extensive. It is divided into industry, agriculture, transportation, life, medical and military, etc. . According to the functions of ultrasonic processing, ultrasonic cleaning, ultrasonic detection, detection, monitoring, telemetry, remote control, according to the working environment is divided into liquid, gas, biological, etc.  It can be divided into power ultrasound, detection ultrasound, ultrasonic imaging and so on.