Steel strands and ropes are widely used to support heavy structures, such as bridges, buildings, lifts, and cable cars. They are also used in transmission lines to deliver power to cities as well as electrical trains. Failures occurring in strands/ropes may cause serious casualties and suspension of services. Therefore, it is of prime concern to provide advanced warnings prior to fatal failures. Magnetostrictive sensor (MsS) has become popular in generating and receiving desired ultrasonic guided waves to detect strand/rope defects. Conventional MsS usually uses hard sensing coils to generate the necessary dynamic magnet field to excite the desired guided waves for defect inspection. However, the hard coils are bulky and difficult to install on strands/ropes with different diameters. Such inflexibilities limit the use of MsS in many practical situations. This paper reports the design of a new type of MsS that uses innovative flexible coils, called flexible printed coil (FPC). The FPC is made of flexible film with the desired printed circuit pattern so that it can replace the conventional hard coils. The FPC-based MsS can be easily installed on or removed from the inspected strand/cable because of its flexible structure and the wrapped around type of mounting fashion. Moreover, the inspection performance of the new FPC-based MsS has been greatly increased because the FPC can be wrapped into multiple layers. The more the layers, the higher the wave energy can be emitted. The results obtained from the experiments conducted on seven-wire steel strand samples have proven the superior abilities of FPC than the conventional hard coils. The multi-layer FPC-based MsS has longer inspection range and higher sensitivity in detecting small cracks.

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