Selection of frequency and mode for guided wave detection of steel pipe using magnetostrictive sensor technology

Ultrasonic guided wave propagating in a steel pipe has a dispersive and multimode characteristic, which bring some difficulties. to analyze the guided wave reflection signals. The guided wave dispersive characteristics depend on the selected frequency and the guided wave multimode characteristics are related with the designment of the magnetostrictive sensor So it is very important for optimal setup and analysis the relationships between the magnetostrictive sensor, frequency and mode of guided wave. For a given steel pipe, the dispersion curves can be calculated by using the related dispersion software, which determines the range of the exciting frequency, and the cutoff frequency can also be calculated by the specific formulas, then the optimal exciting frequency is determined to compare two type frequencies. Experimental observation the reflection signals using the selected different frequency. By changing the magnetostrictive sensor configuration and the distribution of the bias magnetic field applied to the steel pipe, the magnetostrictive sensor can produce the longitudinal, torsional, and flexural guided wave modes. In this paper, the longitudinal wave mode is discussed in the experiment arrangement. The theoretical computation values are compared very well with the experimental results.