Design And Implementation Of Driving And Frequency Locking And Echo Circuits For Multi-frequency Ultrasonic Transducer

With the fast development of modern electronic technology ultrasonic technology has been widely used.No matter ultrasonic machining or ultrasonic testing and ultrasonic medical,ultrasonic technology is playing an increasingly important role.Ultrasonic transducer has an inherent resonant frequency,the output power of ultrasonic transducer maximum and most efficient when it works on the resonant frequency.However,the resonant frequency of ultrasonic transducer will be shifted by when it is processed or by the change of environment and temperature,self-aging and others factors.Multi-frequency of ultrasonic transducer can both realize detection depth and resolution ratio.So tracking and locking the resonant frequency of multi-frequency of ultrasonic transducer to make it works on the resonant frequency will be necessary.Besides,ultrasonic imaging technology plays an important part of the ultrasonic application technology.One of the key methods of ultrasonic imaging technology is to modulate and process the ultrasonic echo signal.This paper base on ARM Cortex-M4 architecture embedded microprocessor STM32F407ZGT6 to build the circuits of driving and frequency locking and echo for multi-frequency ultrasonic transducers.The main content of this paper includes:(1)Existing methods of frequency tracking and locking have the disadvantages of slow speed,low precision and rely on high performance microprocessor and hard to locking multi-frequency ultrasonic transducer.According to the working characteristics of the ultrasonic transducer,this paper makes a plan that tracking and locking multi-frequency of resonant frequency of ultrasonic transducer by using the phase difference of the voltage and current to convert high frequency signals into low frequency signals when the ultrasonic transducer working on the resonant frequency.This plan uses the DDS technology to generate the sine wave signal with variable frequency,before driving the ultrasonic transducer to work on continuous wave mode,the sine waves signal need to be power amplified by power amplifier module,and to collect voltage and current signals of ultrasonic transducer at the same time.The high frequency components of mixing signal in Multiplier filtered by high order low pass filter.The AD sampling method improved by average smoothing filtering algorithm to improve precision further,while the frequency tracking and locking by Size-Step-Size-Search method to reduce the frequency scan range greatly and reduce the speed of frequency tracking and locking.In order to tracking and locking multi-frequency of resonant frequency of the ultrasonic transducer,UCOS? system based on STM32F407ZGT6 microprocessor is adopted for task scheduling and switching.Theory analyzed by MATLAB and each module is simulated by Multisim.Finally,the board level with software and hardware coordination debugging is performed to realize the ultrasonic transducer frequency tracking and locking.(2)The echo signal is modulated by IQ modulating module based on AD9670.To configure the AD9670 the SPI communication protocol will be used by the microprocessor STM32F407ZGT6.Combined with UCOS? system for task allocation and scheduling,the resonant frequency of ultrasonic transducer will be track and lock,simultaneously the IQ modulation of echo signal will be achieved.Tested by experiment,the design of driving and frequency locking and echo circuits for multi-frequency ultrasonic transducers this paper proposed can track and lock two resonant frequency of ultrasonic transducer rapidly and precisely rely on ordinary performance microprocessor.At the same time,IQ modulation of echo signal is realized by output the low noise,stable the I signal and the Q signal.