Research On Electromagnetic Ultrasonic Guided Wave Inspection In Metal Plates

Metal plates can be considered as the primary material for industry, and their large scale production contributes to the rapid increase of national economy, especially national defense technology. As flaws may be inevitably generated in metal plates, ultrasonic testing (UT) is required to pick out the defect. Presently, bulk wave inspection is in low-efficiency, and traditional ultrasonic testing based on piezoelectric sensors applys in limited occasion due to its high dependence on the acoustic couplant. So research on electromagnetic ultrasonic guided wave inspection in metal plates is made in this paper. Ultrasonic guided wave has obvious advantages in high-efficiency detection and long-range testing, and electromagnetic ultrasonic technology is free of couplant, and it can easily produce the guided waves. As a result, electromagnetic ultrasonic guided wave inspection that integrates the two advantages can accomplish metal plates detection in high-efficiency.This paper makes a detail analysis on the principle of guided wave inspection and the characteristic equations of Lamb wave, Rayleigh wave and SH guided wave in solids, and explain the features and applications in inspection.For ferromagnetic and nonferromagnetic metal plates, the Lorentz force and magnetostriction mechanism have been analyzed, and four types of EMATs (Electromagnetic Acoustic Transducers) have been designed to excite the three kinds of guided waves. Through the relation between the parameters of coils and wave'characteristic equations, the excitation equations have been established and excitation curves have been plotted; Through the analysis the frequency spectrum of exciting current and the wave-number spectrum of meander-line coils, the operating point and operating zone have been studied to the emergence and remove of multi-modes and dispersion to optimize guided wave inspection.Experimental research of electromagnetic ultrasonic Lamb wave, Rayleigh wave and SH guided wave inspection in metal plates, including steel plates and aluminum plates, has been accomplished to verify the validity and practicability of this technology. The achievement of excitation and optimization of electromagnetic ultrasonic guided wave inspection in metal plates is a solid basis for the further application of the technology in industry field.