Megahertz-range longitudinal guided wave excitation by a flexible magnetostrictive sensor for steel strand inspection

A new type of sensing coil for magnetostrictive sensor (MsS) is presented in this paper. The flexible printed meander coil (FPMC) can offer micron level dimensional accuracy for the structure parameters which link to the central frequency of the MsS. Thus, the actual central frequency of the FPMC-based MsS can precisely meet the expected value. The number of coil groups in the FPMC is optimised to maximise the excited and received energy of the megahertz-range longitudinal guided waves in the strand and its central rod. Meanwhile, the FPMC can be easily wrapped onto the twisted strand surface and also can be installed onto the central rod of the strand after being wrapped into multiple layers. With the proposed megahertz-range FPMC-based MsS, the rod/strand inspection system is potential to be applied for practical inspections, having higher axial inspection resolution and sensitivity to small defects.