Research On Concave Spherical Piezoelectric Ultrasonic Transducer Applied To SAM

Nondestructive testing,medical imaging,acoustic microscopy,etc.have always been the research hotspots and ultrasonic transducer,as a core part of them,have been widely used in various fields.For Mechanical scanning Acoustic Microscope(SAM),the conventional structure of planar ultrasonic transducer and the acoustic lens has been extensively studied and applied over the years.The structure of concave spherical ultrasonic transducer proposed earlier has higher resolution and better anti-noise than the conventional structure,but its research is not perfect.This thesis mainly studies the influence of the size and structure of the concave spherical ultrasonic transducer on its performance and the difference of performance between the concave spherical transducer and the conventional ultrasonic transducer.On the one hand,the purpose of optimizing the radial amplitude and resolution of the concave spherical ultrasonic transducer is achieved.On the one hand,the research of the concave spherical ultrasonic transducer can be further improved.The research work of this thesis mainly includes the research on the relationship between the structural parameters of the concave spherical ultrasonic transducer and its performance and its comparison with the performance of the conventional ultrasonic transducer.First,determine the structure,the materials applied and the operating frequency of the concave spherical ultrasonic transducer.and then the effects of piezoelectric layer thickness,spherical radius and spherical half-angle on the radial displacement of the radiating surface of the transducer and the resolution of transducer at a specific frequency are studied by theoretical calculation and the finite element method.In the finite element method,the thickness of the piezoelectric layer,the radius of the spherical surface and the half-angle of the spherical surface are grouped respectively by a certain variable interval,and then the harmonic response analysis is performed near the working frequency.Finally,the radial displacement or the resolution of the transducer at the working frequency is extracted.By collating the data,changes of transducer performance is studied as changes in the size of each structure and results are compared with the theoretical results.It is found that the half-angle of the spherical surface have a great influence on the radial displacement and resolution of the concave spherical transducer,and the change of the spherical radius does not affect the transducer.As the spherical half-angle increases,the resolution of the transducer gradually increases and its radial amplitude increases first and then decreases.When the spherical half-angle is between 40°~55°,the radial amplitude of the transducer is the largest.The radial displacement of the transducer decreases linearly with increasing thickness of the piezoelectric layer.And set the comparison of the group containing the matching layer of the machine glass and the group no matching layer,so that the other two parameters except the matching layer are the same,then establish the finite element acoustic model of the two sets of transducers respectively,and finally extract the acoustic pressure modulus values of the two sets of transducers in the focal zone.Comparing the acoustic pressure modulus values,it was found that the use of plexiglass as a matching layer did not significantly improve the emission performance of the concave spherical ultrasonic transducer.On the other hand,in order to more fully reflect the performance difference and advantages between the concave spherical ultrasonic transducer and the conventional ultrasonic transducer,the key size controlled of the two transducers are same and the voltage load of 10 V is applied,and there are five aspects compared and analyzed,including the focal length,output impedance,resolution,emitted sound pressure and receiving characteristics.The research found that: 1.The simulated focal lengths of the two transducers are slightly different from the theoretical focal length,and the focal length of the conventional transducer is larger than that of the concave spherical transducer;2.The acoustic pressure modulus of the conventional transducer is 106 MPa,the acoustic pressure modulus of the concave spherical transducer is 90.8 MPa,the sound pressure of the former is slightly larger than the latter,but the difference is not large,indicating that the emission performance of the two transducers is equivalent;3.The output impedance of the conventional transducer is approximately It is 2.95 times that of the concave spherical transducer;4.The resolution of the conventional transducer is 1.2?m,which is worse than the 0.8?m of the concave spherical transducer,which is also in accordance with the simulation results;5.Under the same point sound source,the output voltage of the conventional transducer is about 16 m V,and the concave spherical transducer is about 5.6m V.The former has better receiving characteristics than the latter.