Research Of The Steel Thickness Detection Technology Based On The Electromagnetic Ultrasonic

EMAT has the advantages of non-contact, no coupling, suitable for high temperature testing,and it easily inspires varieties of ultrasonic waveform. In recent decades, EMAT has graduallybecame a hot research topic, and has been widely used in industrial production. Metal plates arewidely used in the aerospace and automotive industries as well as the pressure vessel. In order toensure the safety of factory and equipment, the accurate measurements for thickness of the metalplate is very important. These advantages of EMAT can make it achieve high-speed automaticmeasurement of metal plate thickness, and have the ability to detect a wide range of corrosionand thinning of metal plates.In this paper, the research includes the basic theory of electromagnetic ultrasonic testingtechniques which is composed of the theory of the Lorentz force and the EMAT theory based onthe magnetostrictive mechanism. The mathematical relationship between EMAT physical of eachphysical field in non-ferromagnetic materials and ferromagnetic materials is derived. Thecoupling process between the various physical fields is analyzed. Study the electromagneticultrasonic shear and longitudinal wave generation mechanism, thickness measurement principleand the shear and compression thickness measurement transducer structure. The relationshipbetween structural parameters and conversion efficiency of EMAT are mathematically described.Based on the above theory, study transverse and longitudinal wave ultrasonic thicknessmeasurement transducers for solid modeling and simulation analysis using the finite elementsimulation software COMSOL. Among them, for thickness measurement of longitudinal wavetransducers, firstly establish horseshoe thickness measurement of longitudinal wave model, andthen improve its transducer structure, build circular thickness measurement of longitudinal wavetransducer model, doing the simulation analysis of two models, analyze the distribution of thestatic magnetic field and an alternating magnetic field. Then changing current frequency, coilparameters and permanent magnet structure, get the steel surface vortex density and sufferedLorentz force distribution. Study the effects of various parameters on the transducer conversionefficiency, determine the optimum parameters of the transducer structure. Combined theexperimental platform, do the thickness measurement experiments on the steel and aluminumplate using the transverse electromagnetic ultrasonic and longitudinal wave transducers thickness measurements respectively.By detecting different thickness of the steel plate and aluminum plate, verify the correctnessof the theory and simulation. Compared with the detection result of the aluminum plate, when theshear wave transducers detects the thickness of steel, the number of echoes is less, indicating thatthe acoustic wave decays more rapidly in the steel, it is necessary to select the appropriateexternal magnetic field for reducing the mutual interference between Lorentz force andmagnetostriction force and enhancing the conversion efficiency in the steel plate. The differencesof transverse and longitudinal waves thickness measurement were analyzed, transverse wavehave higher resolution, while the longitudinal wave can achieve faster thickness measurement.The transverse and longitudinal waves EMAT designed can be well applied to detect metal platethickness。...