Design And Characteristic Analysis Of Broadband Capacitive Micromachined Ultrasonic Transducer

Broadband Capacitive Micromachined Ultrasonic Transducer(CMUT)has good application prospects in ultrasonic imaging,ultrasonic identification,flow measurement and nondestructive testing due to its excellent characteristics.At present,some progress has been made in the research of CMUT in China,but the research of broadband CMUT is still in its infancy.Therefore,it is of great research significance and practical value to design and analyze the characteristics of broadband CMUT in this paper.The specific research contents are as follows:(1)Two theoretical models of CMUT are established: thin plate vibration model and plate capacitance model.Through theoretical model analysis and derivation,the calculation formulas of characteristic frequency,vibration displacement,collapse voltage,transmitted sound pressure,received sensitivity and other parameters of CMUT are obtained,and the design ideas of broadband CMUT are introduced respectively from the aspects of cell and array element.(2)The finite element model of the CMUT cell is established by COMSOL Multiphysics,and the modal simulation,static simulation,collapse voltage simulation,harmonic response simulation and transient simulation are carried out.The resonance frequency,static displacement,collapse voltage and other parameters of CMUT were obtained respectively;Then,by changing the DC bias voltage amplitude and the AC excitation voltage signal,amplitude,frequency and period between the electrodes of the CMUT cell,the influence of the applied voltage on the emission performance of the CMUT cell is studied.Finally,by changing the cell’s size,number and spacing of the CMUT array elements,the effects of the parameters of the array element on the characteristics are analyzed.The analysis of the factors affecting the performance of CMUT cell and array element lays a foundation for the design of broadband CMUT.(3)The method of increasing the bandwidth of CMUT cell and array element is studied,and the design principle of the structure of the broadband CMUT array element is analyzed.By increasing the radius-thickness ratio of the membrane and designing a multi-frequency mixeddecreasing diaphragm structure,the bandwidth of the CMUT cell and array element are respectively increased.Then by changing the cell spacing and the number of cells of different sizes that make up the CMUT array element,the effect of the spacing and number on the bandwidth of the array element is simulated and analyzed,thereby optimizing the bandwidth characteristics of the CMUT array element.Finally,the selection principle of the main structural parameters of the broadband CMUT array element is analyzed.According to the proposed principle,three CMUT array elements with a resonance frequency of 3MHz in the air domain and-6d B relative bandwidth of 50% are designed.The crossover ranges are 20%,50%,and80%,respectively,and then the COMSOL finite element software is used for simulation analysis.The result proves that the bandwidth characteristic of the CMUT array element is better when the frequency crossover range of adjacent cell is larger.The design rules obtained in this paper can provide theoretical guidance for the selection of the main structural parameters of the broadband CMUT array element.