Research Of Impedance Matching Optimal Design For Multi-array Focused Ultrasound System

Focused ultrasound focuses high-energy ultrasound beams in the focal tissue to form thermal ablation damage,as a noninvasive and minimally invasive treatment technique,it has more and more clinical application due to its safety,efficacy and repeatability,especially in uterus,breast and prostate and other parts of the tumor treatment and also acquired good results.The core modules of focused ultrasound system include: the amplifier drive circuit,the phase control module,the matching circuit,the transducer array,the therapeutic moving machine and the water treatment,etc.With the development of technology,the new generation of focused ultrasound treatment equipment have higher requirement about high power output and miniaturization.High-intensity sound power output is the guarantee of achieving effective treatment,however,piezoelectric ultrasonic transducers have different input impedance at different operating frequencies,resulting in power reflection and energy loss when the drive signal output and the transducer input impedance mismatched.Therefore,in order to achieve the maximum power transmission,designing an impedance matching network between the power source and the transducer is the optimal technical proposal.The performance of the impedance matching network circuit determines,whether the system can transmit energy efficiently,so that improve the power transfer efficient and the electroacoustic transformation efficiency of focused ultrasound system.This paper focuses on the driver circuit and impedance matching optimal design of focused ultrasound system.Based on the optimization theory and the equivalent circuit of ultrasonic transducer,a new multichannel focused ultrasound power drive system had been developed.Mainly work is as follows:In the designing of impedance matching network optimization,we used the network test analyzer to measure the impedance curve of the ultrasonic transducer.According to the Butterworth-Van-Dyke(BVD)model,the equivalent circuit had been built,after derived the transmission parameters of the two-port network and evaluation index of the matching network,the component values corresponding to the different structures of the matching network were calculated,then they were verified with the optimal function model Nelder-Mead method based on the Matlab platform.In terms of the system drive and power amplifier circuit,the traditional Class-A,B,C and the new Class-D,E amplifier circuits were analyzed respectively,including their working status,output efficiency and other parameters.Based on the results and requirements,we selected the appropriate chip to build the Class-D amplification drive circuit,then used FPGA platform and PC software system as a control signal to complete the waveform generation module and digital phase shift module development,which could generate the 1.36 MHz multi-channel digital square wave output with phase accuracy at 1.5 ° to drive the multi-array ultrasonic transducer.Finally,in the experimental and test analysis of the focused ultrasound system power drive performance,the accuracy and the stability of the signal were verified.At the same time,impedance matching networks of different structural corresponding to multiple ultrasound transducers were tested and analyzed,the experiment result proves that the impedance matching network based on optimization theory could be accurately fitted to the target impedance as needed,meanwhile the three-element network intersect have better filtering and frequency selection function than two-element network,the results lay a foundation for the subsequent function expansion.