The Structural Optimal Design Of Omnidirectional Flexible Dielectric Elastomer Interdigital Transducer For SHM

Interdigital Transducer(IDT)is a Surface Acoustic Wave(SAW)device which can converse acoustic energy to electric energy by piezoelectric effect.It can transfer and intercept the guided wave signal,which was firstly used in the signal processing of SAW,such as filtering,dealy and superposition.IDT has been applied in SHM systems gradually since it has the advantanges of designed frequency,changed bandwidth and low insertion loss.The most popular one in them is the rectangle IDT based on Lamb Wave which is widly used in damage detection of plate structures for its large scale and rapid test.This thesis did some research on an annular flexible IDT with virable pitch on Dielectric Elastomer(DE)which has the characteristics of wide bandwidth and omnidirectional signal acquisition to overcoming the shortage of narrow bandwidth,single directivity and difficult to coupling with the surface of complex structure.The structure optional design of omnidirectional flexible PVDF-IDT and DE-IDT were calculated utilizing FEM method and the electric-field-driven jet deposition based micro-and nano-scale 3D printing method was chosen to manufacture the IDT.Finally,performance tests and preliminary application of SHM were carried out on the two IDTs.The main research work of this thesis is as follows:(1)The working principle and basic characteristics of IDT was studied.To achieve the purpose of optimizing the structure of IDT and improving its performance,this thesis firstly do some research on the ? function of IDT with equal pitch and virable pitch and analyze the frequency response.Meanwhile,the research on the constitutive equation of PVDF and DE was conducted to analyze the the force-electricity coupling relationship to design the optional omnidirectional flexible IDT.(2)The study on `propagation characteristics of Lamb wave in plate structure were conducted and the appropriate IDT frequency range is selected according to the dispersion curve.The COMSOL Multiphysics numerical simulation platform was used to calculate the surface stress changes of the flexible IDT on two different substrates,PVDF and DE,under different conditions.The optimal geometric and material parameters of DE-IDT were studied and optimized.(3)According to the FEM optimization design results,the annular flexible PVDFIDT and DE-IDT were fabricated by screen printing and the electric-field-driven jet deposition based micro-and nano-scale 3D printing method respectively.The driving / transmission of the two annular flexible IDTs were analyzed through experiments.The experimental results show that: PVDF-IDT has a full range of signal reception function,but its driving ability is extremely weak,and at the same time,it responds well in the range of 850 ~ 1050 kHz frequency and has a broadband effect.So that it can be used as a sensor for signal reception.The DE-IDT test results show that it also has a broadband effect at low frequencies,and can realize omnidirectional high-sensitivity driving and sensing functions.Finally,DE-IDT was initially used in the damage detection of the plate structure.