Electromagnetic acoustic detection of defects in thick carbon steel plates using high frequency guided waves

Abstract

This paper reports on a new means of generating high frequency guided waves (HFGW) using pulsed meander coil electromagnetic acoustic transducer (EMAT) in thick carbon steel plates at significantly higher frequency–thickness (f × d) products i.e., 8 to 16 MHz-mm. Meander coil EMAT is ideal for generating HFGW and particularly attractive for probing steels and magnetic alloys because its transduction efficiency is larger due to magnetostriction. In this work, the meander coil EMATs were developed by using flexible printed circuit board (PCB) coils and sintered Neodymium Iron Boron (Nd-Fe-B) permanent magnets. Experimental measurements were carried out on carbon steel plates of 5 and 10 mm thicknesses using the developed meander coil EMATs. To optimize the excitation frequency and to understand the propagation characteristics of HFGW, several simulations were carried out using 2-D finite element (FE) models at different f × d products. The FE simulations captured all features observed in the experiments. The potential of HFGW was also examined to detect artificial machined notches of different sizes made on both carbon steel plates. From the transmission and reflection characteristics of HFGW, it was observed that the HFGW can effectively detect defects of 10% wall thickness in thick carbon steel plates.

Keywords

Meander coil EMAT high frequency guided waves carbon steel plate dispersion curves finite element simulation

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