| To better meet the growing medical and health needs of the people,China’s medical equipment industry is also developing towards high quality.As an emerging device used in surgery,Radiofrequency(RF)Ablation is widely used in various minimally invasive surgeries because of its fast-cutting speed,good coagulation effect and small thermal damage to tissues.In the process of surgery,the system needs to output constant power to ensure the quality of surgery when the tissue location or ambient temperature and humidity change.It has important engineering application value to improve the control performance of the system based on power closed-loop control.Therefore,the hardware of RF Ablation system is designed in this paper,and the power closed-loop control is realized,with 4 MHz unipolar output and1.71 MHz bipolar output.This thesis completes the followings:Firstly,research and design are carried out for RF signal amplification circuit:Area Product(AP)method is used for RF transformer design.Furthermore,for avoiding the effect of skin effect on the Alternating Current(AC)resistance of the conductor,a 0.05 mm~2×250strand Litz wire is selected as the winding wire of the transformer;a class C push-pull circuit is used to invert the Direct Current(DC)signal into 4 MHz and 1.71 MHz RF signal,and a sixth-order LC resonant circuit is designed at the load end of the inverter circuit for frequency filtering;the parameters of the components in the resonant circuit are obtained by comparing the transfer function of the LC resonant circuit with those obtained at the preset resonant frequency points.A simulation is conducted,in which the resonant frequency point of the circuit is determined to be 4 MHz,and the actual resonant circuit is tested using an impedance analyzer.The results show that the LC resonant circuit obtained by using the method can achieve frequency filtering.Then the design is carried out for the software and hardware of the RF Ablation surgery system:the overall plan is formulated according to the performance indexes and functional requirements of the RF Ablation surgery system;the system uses a microcontroller STM32F303VCT6 with a sampling rate of up to 18 MHz and dual ADC alternate sampling method to require the RF output signal;the software design is carried out on the basis of the designed hardware platform,which enables the system to perform a switch of unipolar and bipolar output,and different cutting or coagulation effects can be achieved by controlling the crest factor of the output RF signal;the RF output power is obtained by frequency domain analysis of the sampled signal using the Discrete Fourier Transform(DFT)algorithm,and the power is controlled using a PID controller so that the actual output power quickly tracks the user-set power.Finally,the performance indicator of RF Ablation surgery system is tested,with the practicality of the system is tested according to the national standard GB9706.202-2021,and the test results show that the output power accuracy is less than 11%,which is better than the20%specified in the national standard;the power controller designed is tested,with experimental results showing that the controller is sufficient to adjust the power of the surgery system to the set value within 500 ms,without overshoot in the control process and within±1 W of power fluctuation after stabilization,and can achieve power tracking when the load changes;the output waveform crest factor of various modes is tested with results meeting the crest factor range specified in the Technical Specification for Quality Control Testing of Army Health Equipment;cutting and coagulation experiments are conducted to analyze the effect of different output power and crest factor on cutting and coagulation.A 3.5 mm chicken blood vessel is selected for the blood vessel closure experiment,and a digital display pressure gauge is used to test the burst pressure of the closed chicken vessels could reach 150 mm Hg or more to form an effective closure when the power is set at 25 W～40 W. |
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