Design And Test Of Capacitive Micromachined Ultrasonic Transducer Array

Capacitive Micromachined Ultrasonic Transducer(CMUT),as a new MEMS acoustic device,has a wide range of research prospects in defect detection,medical imaging,human-computer interaction and other fields.Compared to the traditional Piezoelectric Ultrasonic Transducer,the membrane structure of the CMUT makes it more efficient when it is working in the air.The size of the CMUT array is small and it is easy to be processed into a large scale array.Therefore,the research on the air-coupled CMUT array is of great value.In this paper,an air-coupled CMUT array was designed and fabricated.And,a system of the CMUT array was designed according to the test requirements of the array.The acoustic experiments of the CMUT array were completed by using this system.Specific research contents are as follows:(1)According to the Theory of Plate and Shell,single film resonant frequency of the CMUT was deduced and the size of the CMUT sensitive unit was calculated.The acoustic field directivity of the CMUT array was simulated by using Field II acoustic simulation toolkit.The parameters of the CMUT array were chosen by the results of the simulation.According to the phased array theory,the delay rules of the CMUT array were calculated.(2)The CMUT array test requirements were analyzed,and the overall structure of the test system was introduced.The components and functions of the test system were introduced from two aspects of hardware and software.The hardware part includes multi-channel pulse emitting unit,multi-channel acquisition unit,NCG200-D25 aircoupled probe,DC voltage source.Each part of the hardware system was introduced.(3)The structure and function of the software in the test system were introduced.The software part includes the delay algorithm and the data acquisition program.A FPGA was used to realize time delay algorithm.The program was tested by using ISim.The data acquisition program was written by LabView.(4)The processing technology of the CMUT array was introduced.The L-edit software was used to design the mask layout of the CMUT array.According to the test requirements,a PCB board was designed,and the CMUT was bound on it by the bonding technology.The surface morphology of the CMUT array was tested.The results showed that the surface of the CMUT array was intact without damage.(5)The acoustic emission intensity and the receiving sensitivity were tested in the acoustic experiments.A method was designed to eliminate the CMUT tailed signal.The directivity of the CMUT array was tested by the acoustic experiment.The results showed that the designed CMUT array met the design requirements.