An Innovative Design for Flexible Magnetostrictive Sensors with Optimized Parameters for the Integrity Inspection of Cables/ropes

Description

Ropes and cables are widely used to hoist or support heavy objects. They must bear heavy loads during operation, but repeated loading and unloading make them prone to fatigue. The saline and humid environment of Hong Kong escalates the wear on ropes and cables, which can lead to their sudden breakage. For instance, rope accidents have caused hoist lifts to suddenly plunge to the ground, resulting in human casualties. The structure of ropes is complex, as they are formed by many twisted and inter-locked wires. Currently, lift maintenance still mainly depends on human visual inspection, which is obviously unable to detect sub-surface defects in ropes and cables. Other existing inspection techniques suffer from shortcomings such as difficulty in installing the sensors, and often generate inaccurate results. There is thus an urgent need for a well-designed sensor that is easy to install and provides accurate detection results for sub-surface defects in ropes and cables.Recently, ultrasonic guided waves have become popular due to their long-range inspection ability and high degree of sensitivity in detecting defects. Magnetostrictive sensors (MsS) are promising guided wave technology applications because they are noncontact and can cover long distances during inspection. Conventional MsS are made from hard coils. This means that each sensor is tailor-made to fit a particular diameter of rope/cable, and must be mounted to a rope/cable that has a free end. We propose an innovative MsS that is made of flexible printed coil (FPC) to replace the conventional hard-coil MsS. The FPC-based MsS is flexible, and can form any cylindrical shape to fit different diameters of rope/cable, and can be mounted onto a rope/cable without a free end. Most importantly, the FPC-based MsS can be wrapped around itself to form multiple layers of coil, which substantially increases the excited wave energy. A major problem that must be overcome is the dispersion effect of guided waves, which inevitably introduces a high level of complexity into the process of detecting rope defects. This effect becomes more severe with the complexity of the structure of the rope/cable under inspection. We propose an innovative optimization scheme embedded with an effective algorithm to adjust the operating parameters of the FPC-based MsS and its excited guided wave. Our FPC-based MsS can excite guided wave that has a minimal dispersion effect and contains high wave energy, which significantly increases its accuracy in defect detection.