Design Of Ultrasonic Transmitting Circuit And Research On Ranging Applications For CMUT Device

The capacitive micromechanical ultrasonic transducer（CMUT）is manufactured by MEMS（Micro Electro Mechanical Systems）technology,which has advantages such as wide frequency band,easy integration with electronic circuits,and has been applied in fields such as medical science.This paper is aimed at the acoustic characteristics of CMUT device and designs transmitting circuits of square wave pulse to drive CMUT device to send out ultrasonic waves,further conducts ranging research.This paper studies the acoustic characteristics of close-packed CMUT devices.Based on the theory of thin plate vibration,the emitted sound field P（x,y,z）of CMUT element is calculated from the acoustic properties of CMUT cell.The correctness of the first-order vibration mode equation of the thin plate vibration theory was verified through experiments on the vibration distribution of CMUT cell diaphragm.Simulations and analyses were conducted on the sound field distribution of CMUT device under different arrangements of CMUT cells and conditions at distances below 40 mm,and the sound axis pressure was simulated and experimentally verified.Simulate and analyze were conducted on the sound axis pressure of CMUT device under different arrangements of CMUT cells and conditions at distances over 40 mm,also simulate and analyze were conducted on the far-field sound axis pressure of CMUT device in seawater and air at distances over 40 mm.This paper adopts two design schemes and designs two transmitting circuit boards of square wave pulse.The first scheme is a clock,three-level and five-level pulse transmitting circuit,while the second scheme is a multi-channel transmitting circuit.Both schemes have hardware design and FPGA programming（Verilog language）.The first scheme has three modes related to clock:transparent mode,single ended clock mode,and differential clock mode.At the same time,three-level pulse excitation of NRZ and RZ waveforms related to clock can be achieved in three-level mode,and five-level pulse excitation of NRZ and RZ waveforms related to clock can be achieved in five-level mode.The second scheme designs a multi-channel transmitting circuit,which can achieve the functions of pulse excitation and encoding excitation.This paper conducted ranging experiment of CMUT device in three modes related to clock with distances of 5 cm～25 cm.A formula for calculating the average distance is obtained through typical ranging applications.By comparing the experimental values with the simulated theoretical value P₂（x,y,z）of the far-field sound axis pressure of CMUT device through ranging experiment in three modes related to clock,the theoretical value P₂（x,y,z）was corrected;And the influence of input condition Vpn of the transmitting circuit on ranging was added,the theoretical value P₂（x,y,z）was supplemented;Thus,the actual ranging formula can be obtained.At the same time,the advantages,disadvantages,and characteristics of ranging experiment of three modes related to clock were compared.This study provides a theoretical basis for the design and performance analysis of CMUT.Provide new references for the front-end circuit design of ultrasound imaging systems.It is of great significance to link the far-field sound axis pressure theory of CMUT device with practical applications.