The guided wave ultrasonic testing (GWUT) has been widely utilized as a non-destructive inspection technique for its cost and time effectiveness with long distance travelling ultrasonic waves from a single location without loss of much energy to detect surface and internal defects, degradation in flat plate structures, pipes.&nbsp;&nbsp;The electromagnetic acoustic transducers (EMATs) with meander line coils can be designed to excite specific guided wave mode to some extent selectively by adjusting the coil pitch to the wavelength of the guided waves to be excited on flat plates with uniform thickness since guided waves has different modes at the same frequency due to dispersive property.&nbsp;Guided wave propagating modes are mainly separated into two groups such as symmetric and antisymmetric modes and it is essential to generate a specific mode for an effective inspection. Although the specific propagating wave mode has been excited effectively on the simple or uniform thickness shape plates or pipes, the guided wave propagation through specimens with thickness modification due to delamination, wall thinning is still considered complex because of amplitude attenuation by reflection and transmission and generation of other types of modes. In addition,&nbsp;recent years, the development of&nbsp;processing technology has increased the number of long and large structures with non-uniform cross-sections and complex shapes, and the demand for their inspection has also raised. There have been many studies on guided wave propagation in a specimen with changing shape and assuming a defect. However, studies over guided wave excitation by EMAT on non-uniform shapes has remained modest.In this research, the modal excitation characteristics of guided waves using meander line coil EMAT was focused on the inclined surface of aluminum plate. Specifically, the possibility of S0 mode excitation for plates with thickness varying uniformly in the propagation direction of wave packets was investigated considering importance of single mode propagation for the potential inspection of non-uniform plate like structures. It was&nbsp;shown&nbsp;that the wavelength variation could&nbsp;affect the mode excitation&nbsp;with respect to the thickness change of inclined plate at a given frequency. Furthermore, when the wavelength change was particularly large, it was confirmed by simulation and experiment that the desired mode can be generated with larger amplitude by gradually changing the coil pitch of the EMAT along the surface appropriately considering thickness variation of aluminum plate.

Guided Wave Mode Excitation on Inclined Surface by Meander Line Coil Emat

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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