Sensitivity of a Torsional Guided Wave Signal using a Magnetostrictive Transducer Technique

To prevent the leakage of a buried pipe, several NDE (Nondestructive Evaluation) methods are proposed, and the guided wave method can be a promising technique. One promising feature of the magnetostrictive sensor technique is that the wave patterns are relatively clear and simple compared to a conventional piezoelectric ultrasonic transducer. If we can characterize the evolution of the defect signals, it can be a promising tool for the structural health monitoring of pipes for a long period as well as the identification of flaws. Among various vibration modes, the torsional guided wave T(0,1) mode has many advantages, such as no dispersion, no radial displacement, and a low attenuation. In this paper, we analyzed the amplitude of the wave reflected from several reflectors in a low alloy carbon steel piping. The torsional guided waves were generated and received by a coil and a DC magnetized nickel strip. The signal amplitude from various reflectors is compared with two different sensor techniques, one by a variation of DC bias and the other by a remnant magnetic bias technique. The amplitude of a magnetostrictive guided wave signal was analyzed to optimize the DC bias magnetization. The signal amplitude from various reflectors was compared with two different sensor techniques, one through the variation of DC bias and the other using a remnant magnetic bias technique. When we take a signal from the BW, the signal amplitude increases to a certain level, and saturates as the DC bias increases. The optimized DC bias is around 0.4 A for this the experimental setup and bias coil