Study Of Longitudinal And Flexural Coupled Vibration Of Piezoelectric Compound Transducer

The new piezoelectric compound transducer which has the piezoelectriccomposite as the energy conversion component is a device that can implement energyconversion between sound and electricity. It has been an important part of theultrasonic non-detective system for its wideband, high sensitivity and acousticimpedance matching with material tested easier. Transducers for ultrasonic testing canproduce two vibrating modes that are longitudinal vibrating mode generated by thepiezoelectric vibrator and the flexural vibrating mode generated by front layer.Utilizing coupling between the two modes mentioned previously to expand theworking bandwidth of transducer, by adjusting the construction of transducer.In this article, the comprehensive review on ultrasonic non-detective testing,piezoelectric composite, piezoelectric transducer and the theory of expanding theworking band of frequency of transducer were firstly introduced. Then, the finiteelement method (FEM) for investigation of transducer was introduced. Finally, thefinite element model of1-3piezoelectric compound transducer was established, andthe relationships between its vibration modes and resonant frequencies and itscomponents were analyzed. The main contents and results are as following:(1) The effect of volume fraction (VF) on the vibrating modes and resonantfrequencies of transducer were studied. The FEM model of1-3piezoelectriccompound transducer was established, through the FEM analysis, the results showedthat the first two vibrating modes are longitudinal vibrating mode and flappingvibrating mode. With the VF increases, the first two resonant frequencies becomelarger, and the differences between the first two resonant frequencies become larger.With the components of1-3piezoelectric compound transducer kept changeless, theflexural resonant frequencies will be closer to the longitudinal resonant frequencies bythe VF decreases.(2) The effect of front layer on the vibrating modes and resonant frequencies oftransducer were studied. The FEM model of transducer on front layer was established,through the FEM analysis, the results showed that with the thickness of the rear-endof front layer increases, the first vibrating mode of transducer changes from flexuralvibrating mode to longitudinal vibrating mode, the second vibrating mode whichkeeps changeless is to be longitudinal vibrating mode, and the first two resonant frequencies of the first two modes also decrease. With the geometric dimensionsincluding radius and thickness of fore-end of front layer increase, the first tworesonant frequencies decrease, moreover the flexural frequencies decrease quicklythan the longitudinal one, differences between the two frequencies decrease too.(3) The effect of backing material on the vibrating modes and resonantfrequencies of transducer were studied. The FEM model of transducer on backingmaterial was established, through the FEM analysis, the results showed that the typesof backing materials are different, the vibrating modes also different. Using steel asthe backing material, at the same thickness of steel, the first two resonant frequenciesdecrease with the radiuses increase, differences between them also get larger.All in all, through the above research, the relationships between resonantfrequencies and vibrating modes and the construction of1-3piezoelectric compoundtransducer are obtained. The results offer useful guidelines to the design andapplication of wideband piezoelectric compound transducer used in ultrasonicnondestructive fields.