Research On Working Mechanism And Application Foundation Of CMUT And CMUT Array

Ultrasonic imaging technology is widely applied in many fields such as medicine,military,industry,agriculture and so on.Ultrasonic transducer is one of the key components of ultrasonic imaging system.Capacitive micromachined ultrasonic transducer(CMUT)based on micro-electro-mechanical systems(MEMS)technology has significant advantages over traditional piezoelectric ultrasonic transducers.CMUT has emerged as a promising alternative to traditional piezoelectric ultrasonic transducer and will become the market mainstream products.Consequently,It has an important research value and practical significance to study the theory and application foundation about capacitive micromachined ultrasonic transducer.The main contents of this dissertation are listed as follows:Firstly,it can provide foundation for optimizing design parameters to analyze characteristics of CMUT before processing and manufacturing.CMUT modeling theory was studied based on CMUT working mechanism and relevant theories.Small signal equivalent circuit model and finite element model were built for CMUT cell.The static analysis,modal analysis and harmonic analysis were implemented by using finite element model.In particular,for purpose of quick and effective characteristics analysis,a state equation-SIMULINK model was derived and established and applied to analyze the radiation and receiving characteristics systematically and comprehensively.The analysis results may provide an important theoretical basis and reference for subsequent actual application and measurement.Secondly,it is generally known that the directivity is one of the important characteristics of CMUT and CMUT array in the far field.The design principles of reasonable parameters selection were proposed by considering design parameters influence on directivity and structural features of CMUT and CMUT array.Three different directivity functions of CMUT and four different directivity functions of CMUT array were derived respectively and analyzed contrastively.In view of sidelobe in directivity diagram,a variety of methods were researched and demonstrated to suppress sidelobe effectively.Again,it is certain that the acoustic field distribution characteristics of ultrasonic transducer have a direct affect on its imaging quality.In accordance with related sound field theory,three kinds of sound field analysis methods including Rayleigh-Sommerfeld integral formula,angular-spectrum method and spatial impulse response were studied.The corresponding analysis methods on CMUT and CMUT array were studied according to their characteristics.Not only the focusing and deflection performance of CMUT array but also the influence of array aperture size on focusing distance was analyzed by calculating the radiation sound field.Furthermore,analysis of the effect of CMUT array design parameters on its pulse echo response was implemented by computing the response.Then,it is obvious that various imaging methods have some difference in their performance and features.Consequently,many factors should be taken into synthetic consideration to choose an appropriate method in the practical application.Three imaging methods including phased array imaging,synthetic aperture focusing imaging and phased subarray imaging were discussed respectively.Their contrastive analysis was conducted by calculating the corresponding effective apertures and synthetic beams.Their imaging effects were verified and analyzed on the basis of CMUT linear array.Specially,several particular imaging methods were designed,for CMUT planar array composed of a large number of elements,in order to reduce the complexity of the imaging system and improve the real-time performance of imaging effectively.Last but not least,the CMUT linear array was tested and analyzed comprehensively.The results further validate the performance of the CMUT and CMUT linear array,and they can provide valuable reference data for development of ultrasonic imaging system in the future.