The Structure Optional Design Of Broad Bandpass TIDT For Structure Damage Detection

The interdigital transducer(IDT)can realize the electro-acoustic conversion through piezoelectric effect,which is the first used in the surface acoustic wave(SAW)device.In recent years,IDT has been gradually applied in Structural Health Monitoring(SHM)system for its characteristics of designed working frequency,low cost,adjusted frequency band and low loss.Among them,the most common one is the formation of ultrasonic Lamb wave IDT,which can quickly realize a wide range of detection and is applied in the damage detection of plate structure.At present,the rectangular IDT,whose interfinger-spacing determines the natural frequency,is the most common method for damage detection of plate structures with specific frequency.When the structure under test is transformed,the rectangular IDT with different geometric sizes needs to be redesigned,and only valid signals of a specific frequency can be transmitted and received.Therefore,improving the performance of the existing rectangular IDT is crucial for structural damage detection.To the deficiency of the existing rectangular IDT in the narrow frequency band,the study of Trapezoidal Interdigital Transducer(TIDT)was presented,and the finite element method was used to optimize the size of TIDT.Finally,the performance of the designed TIDT is tested and preliminary discussion is made for structural damage detection.This paper main research content is divided into the following four parts:(1)The research background and significance of this paper are proposed.According to the status of IDT research at home and abroad,the application of TIDT in structural nondestructive testing is proposed.(2)The working principle and basic characteristics of IDT are introduced,its frequency response curve is analyzed,the propagation characteristics of the Lamb wave structure are introduced,and the geometric size design of the TIDT for damage detection is analyzed.(3)Building 3D model and designing different geometric parameters of TIDT,the two different base material(PZT-5A,(Polyvinylidene fluoride,PVDF))and under horizontal unit voltage changes under different thickness of base and strain value was analyzed,and the performance was compared.(4)According to results of optimization design,TIDTs with base PZT-5A and PVDF were made,and through experiment the driving performance of TIDT with base PZT-5A was analyzed(orthotropic、wide band).The results show that TIDT has the strongest excitation signal in the horizontal direction and the weakest in the vertical direction.The designed TIDT has a good excitation signal in the range of 100-450 kHz and can be used as a driver in this frequency range.The sensing property of TIDT of two kinds of substrate materials was tested.The results show that the PVDF-based TIDT sensing performance is better than the PZT-5A-based TIDT.The initial test of damage detection was carried out on the aluminum plate,and the image was performed by the elliptical positioning method.The imaging results were in good agreement with the actual results.