Assessment of the performance of different EMAT configurations for shear horizontal and torsional waves

Abstract

The fundamental shear horizontal (SH0) wave-mode in plates and the torsional mode T(0,1) in pipe-like structures are extensively used in guided wave inspection. Different Electromagnetic Acoustic Transducer (EMAT) configurations can be employed: Lorentz force Periodic Permanent Magnet (PPM) or magnetostrictive EMATs, directly applied on the sample or with a bonded strip of highly magnetostrictive material on the structure. This work compares the performance of these solutions on steel plates. The analysis shows that magnetostrictive EMATs directly applied on steel plates have comparatively poor performance, while large signal amplitudes can be achieved when a layer of highly magnetostrictive material is attached on the structure. PPM EMATs generate intermediate wave amplitudes while being non-contact.

Enhancement of the Excitation Efficiency of a Torsional Wave PPM EMAT Array for Pipe Inspection by Optimizing the Element Number of the Array Based on 3-D FEM

“…Guided waves have been widely used in pipe inspection due to their long range non-destructive detection features and their capability to detect hidden defects [ 1 – 3 ]. Among the various guided wave modes, the fundamental torsional wave of T(0,1) mode shows great advantages over other modes as it is non-dispersive, which simplifies the interpretation of signals [ 4 – 8 ]. The currently available transducers used for generating and receiving T(0,1) waves include piezoelectric transducers, magnetostrictive EMATs and Lorentz force EMATs.…”