Design Of Impedance Matching Network For Multi-Frequency Ultrasonic Transducers

With the continuous upgrading of medical equipment,High Intensity Focused Ultrasound(HIFU),which is non-invasive,harmless,safe and effective,has great potential for cancer treatment.In order to achieve optimal power output,an impedance matching network needs to be incorporated between the amplifier and the transducer.In this paper,an adaptive impedance matching network for HIFU applications is designed by analysing the BVD model of an ultrasonic transducer at multiple frequencies.In the context of this design,the proposed impedance matching network will adopt an L-shaped matching circuit.In order to solve the impedance drift caused by external factors during the operation of the transducer,the design adds a synchronous switching capacitor to the L-type impedance matching network through the idea of resonance method,and determines whether the best impedance matching state is achieved by detecting the phase difference between the output signal of the power amplifier and the input signal of the ultrasonic transducer,so as to output control signals for real-time The control signal is then output to regulate the synchronous switching capacitor in real time to ensure maximum power transfer efficiency between the power amplifier and the transducer.Unlike conventional adaptive impedance matching networks,the control circuit in this design does not require a microcontroller such as an MCU and relies on feedback signals to be automatically regulated by the control circuit.The control circuit consists of three main components:an automatic gain control circuit,a phase error detection circuit and a switching signal generation circuit.In particular,in order to adapt the circuit to normal operation in the frequency range of 1MHz to 10MHz,the circuit parameters are changed at different frequencies by means of switched capacitor arrays in the automatic gain control circuit and the phase error detection circuit,in order to improve the response speed of the circuit.The control circuit of the adaptive impedance matching network designed in this paper is based on a schematic and layout design using the AMS 0.35 μm process.The post-simulation results show that the overall control circuit can effectively adjust the duty cycle of the synchronous switching capacitor at both 1MHz and 10MHz operating frequencies during the simulated transducer impedance change,and verify that the control circuit can change the circuit parameters by frequency control signals to meet the response speed of the circuit at different frequencies.The simulation is performed with and without impedance matching network by simulating the transducer in the event of impedance change.The results show that the power transfer efficiency between the power amplifier and the ultrasonic transducer is improved by about 15%after the impedance matching network is added.