Research On Linear Coil EMAT Finite Element Calculation And Sound Field Characteristic Analysis Of Shear Wave And Lamb Wave

Aluminum alloy plates of various thicknesses are important raw materials in the manufacturing industry,and are widely used in manufacturing,aviation,transportation and other fields.Therefore,non-destructive testing of plate quality is particularly important.In recent years,various non-destructive testing technologies have developed rapidly.Ultrasonic shear waves are suitable for the detection of medium-thick aluminum alloy plates(thickness≥6mm),and ultrasonic lamb waves are suitable for thin aluminum alloy plates(thickness<6mm).Compared with the conventional piezoelectric ultrasonic detection technology,the electromagnetic ultrasonic detection technology has the advantages of noncontact,no coupling agent,and is suitable for extreme high and low temperature detection.Therefore,the use of electromagnetic ultrasonic shear waves for flaw detection of thick aluminum alloy plates,and the use of electromagnetic ultrasonic guided wave technology for defect detection of thin aluminum alloy plates are currently the most effective detection methods.Electromagnetic ultrasonic transducer(EMAT,Electromagnetic Acoustic Transducer)is the core of electromagnetic ultrasonic detection technology,which is easy to generate different types of ultrasonic waves.However,the characteristic analysis of EMAT radiation sound field when using shear wave detection,single mode when using Lamb wave detection Control excitation is a difficult problem to be solved urgently in practical engineering applications,but it has not yet been solved well.To this end,this research mainly focuses on two problems that need to be solved urgently in this field,the linear coil EMAT transverse wave radiation sound field distribution law,and the Lamb wave mode control excitation method in the plate.Aiming at the problem of analyzing the characteristics of EMAT radiation sound field during shear wave detection,the electro-magnetic-acoustic multi-physics coupling model of recetrack coil EMAT detection medium-thick aluminum plate was established and the finite element solution was carried out.Sound field amplitude,sound field width,sound field directivity and other sound field characteristics,and the influence of factors such as coil width,excitation frequency,magnet placement and other factors on the characteristics of radiation sound field were studied.A sound field measurement system was built to measure the EMAT shear wave radiation sound field of the racetrack coil,and the distribution characteristics and influence laws of the EMAT radiation sound field of the racetrack coil were experimentally studied.Through the analysis of simulation calculation results and experimental verification,the characteristics of the linear coil EMAT radiation sound field are summarized,and the influencing factors are analyzed.Aiming at the problem of single-mode Lamb wave control excitation in the board,the linear coil EMAT multi-channel array finite element simulation model is first established,then the delay of each channel is calculated by the orthogonal mode expansion method,and finally the delay of each channel is calculated by Excitation,in the finite element model,realizes the control excitation of the specific mode of the Lamb wave.The multi-channel array EMAT Lamb wave experimental system was built,and the multi-channel array EMAT was used to conduct the Lamb wave mode control excitation experiment,which further verified the effectiveness of the orthogonal mode expansion method to solve the delay parameter for controlling the single mode Lamb wave excitation.