A Longitudinal Mode Guided Wave Transducer With the Ring Permanent Biased Magnet Based on Magnetostrictive Effect for Large Diameter Bridge Cables

The existing yoke magnetizers can be used for large diameter bridge cable detection, but cannot provide the optimal bias magnetic field due to the repulsion of the polarities arranged in the circumferential direction, which reduces the energy conversion efficiency of the magnetostrictive longitudinal mode guided wave transducer. A magnetostrictive longitudinal mode guided wave transducer with the ring permanent biased magnet is provided to improve energy conversion efficiency for large diameter bridge cables. Firstly, a ring magnetizer for the axial magnetization is proposed, which inspired by the structure of the yoke magnetizer and the adjustable bias magnetic field generated by the solenoid coil. Then, the specific transducer with the ring magnetizers is designed for PES(C) 7-127 cable. Based on the magnetostrictive coupling coefficient curves and magnetization curve of the cable steel wire, the finite element models verify that the magnetization effect of the ring magnetizer is better than the yoke magnetizer for PES(C) 7-127 cables. Furthermore, the structural parameters of the ring magnetizers are optimized based on magnetization strength and magnetization uniformity. Finally, the improved efficiency of the transducer is verified by experiments. The energy conversion efficiency of the transducer is increased by 43.65% at the transmitting side, 4.76% at the receiving side, 48.41% at the both sides. Besides, the weight of the ring magnetizers is 19.85% lower than the yoke magnetizers.