Design Of Driving Circuit For CMUT And Research On Acoustic Emission Characteristics

Traditional piezoelectric ultrasonic transducers have problems such as narrow bandwidth and large volume.A capacitive micromachined ultrasonic transducer（CMUT）is developed by using microelectromechanical systems（MEMS）,which has the advantages of small size,wide frequency bandwidth and good acoustic impedance matching performance.Features.In view of the working characteristics of CMUT,this paper establishes an equivalent circuit model,designs a multi-channel ultrasonic phased array drive circuit,explores the influence of pulse excitation parameters on the acoustic emission performance of CMUT,and proposes a solution to the problem of weak acoustic emission capability of CMUT.This paper firstly introduces the working principle of CMUT micro-element and ultrasonic phased array,and analyzes the equivalent circuit model of CMUT.The equivalent circuit model of the CMUT is established by testing the impedance characteristics of the self-made CMUT array elements in the laboratory.Secondly,the chips in the driving circuit are selected and modules such as pulse excitation,high voltage pulse gating,impedance matching,field programmable gate array（FPGA）control and power conversion are designed.The main logic control and data transmission in the drive circuit are realized by using Verilog hardware description language,and the method of FPGA to realize high-voltage pulse excitation signal and gate switch state control,pulse excitation signal channel delay and serial communication is described.Debug the circuit module,and use the signal integrity analysis and simulation to solve the overshoot problem of the pulse excitation signal.The AC/DC voltage ratio of 1:1,the number of pulses 5,and the pulse duty cycle of 50% were selected as the parameters to excite the CMUT through experiments.To test the effect of impedance matching on the directivity of the CMUT’s axial sound field,the output sound pressure amplitude before impedance matching within the measurement range is 5.45 m V-60.6m V,and the output sound pressure amplitude after impedance matching is 9.825 m V-94.75 m V.And does not affect the axial sound field characteristics;test the impact of impedance matching on the directivity of the radiated sound field of the CMUT,the output sound pressure intensity of the CMUT with impedance matching is always higher than the output sound pressure of the CMUT without impedance matching,and there is a main lobe with or without impedance matching.The widths are all about 6.2°.The resistance,reactance,and scattering coefficient before and after the comparison impedance matching test all tend to the target value.Combined with the phased array delay algorithm,the ability of the circuit to focus and deflect the sound beam of the CMUT array is verified.In the sound beam focusing experiment,the peak-to-peak output sound pressure of the CMUT array with delayed excitation is 187.5m V,which is significantly higher than that without delay.62.125 m V to excite the CMUT array output.This paper makes a preliminary exploration of the application of CMUT,and lays a foundation for the laboratory’s follow-up ultrasound imaging research on CMUT arrays.