Research And Design Of Ultrasonic Driving System Based On Frequency Tracking

Nowadays ultrasonic technology is widely used in many fields,such as ultrasonic detection,power ultrasonic treatment and so on.Ultrasonic generating system mainly consists of two parts:ultrasonic driving system and ultrasonic transducer.Ultrasonic driving system has always been the research focus of ultrasonic technology.This thesis focuses on the application of power ultrasonic driving system in ultrasonic therapy,and the frequency is mostly above 1MHz.The traditional power amplifier can not be used in this case,if the traditional power amplifier is used to amplify the ultrasonic excitation signal of high frequency,there would be problems such as low output efficiency and uncontrollable output power.At the same time,during in the working process,because of the wear and load change of the transducer,the resonant frequency of the transducer would have a shift,if just relying on the transducer matching network can not achieve an accurate frequency matching.Based on those problems,the ultrasonic driving system needs to have power control,transducer impedance matching and frequency tracking functions.In this thesis,the whole structure of the ultrasonic driving system is designed with the adjustable power output and driving frequency of 1MHz.According to the analysis of the impedance characteristics of the transducer,the T-type impedance matching network of the transducer is proposed,and the value of each electronic component in the network is calculated,and the phase difference detection circuit of the transducer is designed.Class E power amplifier is used to amplify the ultrasonic excitation signal,meanwhile the structure and parameters of the amplifier are deduced and calculated.Using PWM wave to control MOS gate driver can achieve indirect control of ultrasonic output power.Aiming at the problem of frequency drift of transducer,due to the nonlinear change of resonant frequency of transducer.In this thesis,a frequency control algorithm based on Fuzzy-DDS is proposed.The frequency of driving signal is adjusted by fuzzy controller and the establishment process of fuzzy controller is studied.The simulation model of ultrasonic driving system is built by MATLAB simulation tool,and the feasibility of fuzzy DDS frequency control algorithm is verified by the simulation results.At the end of the thesis,a prototype of the ultrasonic driving system is made,and an experimental platform is built to test the waveforms of each module of the prototype.At the same time,the ultrasonic output power of the driving system is measured and the conversion efficiency of the driving system is calculated.The driving frequency of ultrasonic driving system is 1MHz with frequency error of 1%,and the adjustable output power range is 0.5W?2.0W.The ultrasonic intensity of each gear is 0.193W/cm~2,0.306W/cm~2,0.447W/cm~2 and 0.642W/cm~2.The maximum electroacoustic conversion efficiency can reach 41.9%,and the system can operate safely and stably.