Fabrication And Application Research Of PZT Array Focused Ultrasonic Transducer

Crack is one of the most common defects in many engineering structures,widely exists in major parts such as impeller,shaft,cylinder and water turbine blades and other metal structure.Cracks have leaded to great potential safety problems in the engineering practice,therefore,timely detection for stress concentration area of bearing parts and surface cracks are of very importance significance.Ultrasonic microscope can obtained the inner structure information of body by the wave propagation characteristic in the materials.However,the conventional ultrasonic transducers all use a single piezoelectric sensing element,all of the obtained signal which reflected from the specimen,is the energy integral of the piezoelectric surface.So it is hard to describe the space distribution characteristics of the reflected sound filed better.In this dissertation,combining the thought of array distribution of sensing element,a PZT array focused ultrasonic transducer was designed and fabricated based on the principle of line focused ultrasonic transducer,and also studied the corresponding theory and experiment.The main contents are as follows.(1)The finite element model of line focused ultrasonic transducer is established,and the relationship between the parameters(width and depth)of surface crack and the echo signal is analyzed.The accuracy of the simulation results is verified by experiments,which lays the theoretical foundation for the research of surface crack detection by array focused ultrasonic transducer.(2)As the conventional focused ultrasonic transducer using a single sensing element,it can hardly describe the distribution of acoustic field,combined the formation mechanism of the back reflection of the sound field,it develops a new type of focused ultrasonic transducer,called PZT array focused ultrasonic transducer.The design of the sensing element of the transducer,the layout,the positioning bracket and the design of the transducer shell are analyzed in detail,the sound field distribution is analyzed by array ultrasonic transducer at the focusing and defocusing position by the finite element software.(3)Combined with theoretical analysis and finite element simulation results,a PZT array focused ultrasonic transducer was developed.The ultrasonic testing system based on FPGA was built and used to detect the excitation response characteristics of the PZT array focused ultrasonic transducer,then the performance of the transducer was determined.(4)By using the spatial distribution characteristics of the transducer sensing element,the back scattering sound field is obtained through detecting the non-defect specimen at the focusing position.The experimental results are consistent with the simulation results.Based on the theoretical basis of the surface crack detection,the surface crack depth was measured by array ultrasonic transducer,and the measured results were accurate.The results show that the surface array ultrasonic transducer has a good application value and academic significance.