Optimized Design of Torsional Guided wave Magnetostrictive Patch Transducer Based on Reversed Wiedemann Effect

The torsional guided wave magnetostrictive transducer (MsT) based on the reversed Wiedemann effect has received much attention because of its high energy conversion efficiency and easy implementation of bias magnetic field. However, the coil is wound on the magnetostrictive patch which leads to the reduced coupling efficiency. And the coil winding process for MsT is also time-consuming. This paper proposes a new design of torsional guided wave MsT with circumferential alternating permanent magnet array. The permanent magnets with axial direction magnetization are alternately arranged along the circumference of the pipe. The meander coil is placed between the permanent magnet array and the pipe. On this basis, a magnetic circuit device is applied to increase the amplitude and uniformity of the bias magnetic field, making the transducer to achieve larger energy conversion efficiency. It has been proved experimentally that the designed MsT can generate T (0,1) guided wave with stronger energy. The amplitude of the guided wave signal increases by 2.8 times with the same excitation conditions. Moreover, the transducer has a wide bandwidth. Its center frequency corresponds to the wavelength λ, and the magnetostrictive patch width is about 0.5 λ or 1.5 λ. In conclusion, the proposed transducer has higher energy conversion efficiency and is also easier to design and install, making it more suitable for the health monitoring of large industrial equipment.