An Eddy Current Detection Imaging Research Based On The Electromagnetic Acoustic Effect

Aircraft is the strategic support of national defense and air conveyance,and also a significant impetus for national financial growth and scientific and technological modernization.However,aircraft components and outer skin are prone to stealth fatigue damage in long-term service.If these damages are not checked and repaired in time,they can lead to serious aviation accidents.Therefore,the study of aircraft nondestructive testing(NDT)technology is the premise of improving its operation safety,and has irreplaceable significance for China’s national defense,conveyance and individual security.The current domestic aviation eddy current detection technology only relies on eddy current signals and it is difficult to quickly identify concealed defects.Only by realizing the visualization of eddy current inspection can the damage hidden on the surface and subsurface of aircraft skin be found quickly and accurately,so as to guarantee the flight safety.Therefore,in this article,a new imaging technique of eddy current detection on the based of electromagnetic acoustic effect is studied.In this study,the electromagnetic acoustic effect was combined with eddy current detection,and the electromagnetic acoustic signal was used as the carrier of defect information.The influence of flaw on the diffusion of induced eddy current area was used to change the waveform characteristics of the electromagnetic acoustic signal,and the flaw information was obtained and imaging was realized through the waveform characteristics of the electromagnetic acoustic signal.In this paper,the basic principle of electromagnetic acoustic eddy current detection is introduced firstly.Taking rectangular coil as an example,the model of inductive eddy current is analyzed,and the mathematical model of Lorentz force generation mechanism and surface wave motion is deduced.Then,according to the characteristics of the tested material,Rayleigh wave is selected as the carrier of defect information,and the corresponding combination of coil and permanent magnet is used to excite Rayleigh wave.A new type of transmitting coil is proposed,which can improve the excitation efficiency of ultrasonic signal and suppress the interference of electromagnetic shock.Then,the electromagnetic acoustic waveform characteristics under the condition of no defect and the condition of defect are analyzed.Considering the various factors affecting the electromagnetic acoustic waveform characteristics,the electromagnetic acoustic waveform is generalized from the specific defect length,defect position and defect number to the general situation,and the forward derivation of the electromagnetic acoustic signal model is completed.Finally,three defect information inversion methods based on pattern recognition are proposed to confirm the availability of the three methods and image them.This paper realizes the precise positioning and imaging of defects,which provides a new idea for the visualization of eddy current testing.