Research Of The Metal Plate Defect Detection Technology Based On Electromagnetic Ultrasonic Guided Wave

With the rapid development of China’s economy, sheet metal widely used inaerospace, defense industry, shipbuilding industry, high-speed railway project. Thedomestic demand for the metal plate is increasing. However, in metal processing andproduction processes, the environmental impact, there will inevitably be a variety ofdifferent types of defects, it is imperative that a reliable method of selecting a large areametal plate detector. Electromagnetic ultrasonic guided wave transducer because it has theelectromagnetic acoustic transducer (EMAT) and the respective advantages of ultrasonicguided waves, that is, non-contact detection area, high sensitivity, low attenuation, can bespread over long distances, very suitable for large area of sheet metal NDT. In this paper,electromagnetic ultrasonic guided wave theory, the study of electromagnetic ultrasonicguided waves in the sheet metal.In this paper, a theoretical study of the choice of metal plate Lamb wave generationand modal excitation frequency. Rayleigh-Lamb wave equations characterizing therelationship between the frequency and modal solving Rayleigh-Lamb wave equation,dispersion curves plotted. of the Lamb wave mode echo signal affected by the number ofparameters are analyzed to study the transducer excitation frequency Lamb waves, the coilspacing, the modal number is generated on the plate thickness, in order to determine Lambwave transducer structure parameters. In order to improve the electromagnetic ultrasonictransducer Lamb wave conversion efficiency was studied Lamb waves in the metal platedetecting transducer optimization. Optimized for Lamb wave transducer simulationcalculations, the magnet portion of the transducer is optimized to the magnetic inductioncoil and the Lorentz force size increased significantly, and the optimized Lamb wavetransducer applications defect detection in metal plates. The simulation and experimental results show that at different excitation frequencies,the number of the Lamb wave mode echo signal is changed with the increase of theexcitation frequency mode by the number of states increases. When the excitationfrequency is427KHz, the resulting S0, A0mode Lamb wave; when the excitationfrequency is521KHz, the resulting S0, A0, A1mode Lamb wave; When the frequency is400KHz, you can effectively inhibit the S0mode Lamb wave, so A0mode Lamb waveamplitude reaches the maximum, resulting in a single A0Lamb wave modes, and theexperimental results and numerical results coincide. Optimization of the Lamb wavetransducers can be detected from the position of the probe18m A0Lamb wave mode.Optimization Houlanmubo transducer effective detection distance is1.8times the originalmodel effective detection distance. Lamb wave mode conversion occurs in the event ofdefects increases with the depth of the defect, the amplitude of the received echo signalincreases, the amplitude of the flaw echo signals characterizing the size of the defect.