Reflection of the Fundamental Torsional Wave from a Stepwise Thickness Change in a Pipe

The reflection properties of the fundamental torsional guided-wave mode from a stepwise change in pipe wall thickness are investigated experimentally from 40 to 250 kHz. When incident from a thicker section, the wave undergoes a phase reversal upon reflection from the step, and the reflection coefficient increases with increasing wave frequency. When incident from a thinner section, no phase change occurs in the reflected wave, and the reflection coefficient decreases with increasing frequency. Because of the opposite frequency dependences on the wave’s incidence direction, the disparity in the two reflection coefficients, which is negligible in the low-frequency limit, is significantly large at high frequencies. The above frequency dependences indicate that, at low frequencies, the wave interaction with the step discontinuity follows the behavior of a plane wave incident at right angles to the boundary of two different media of constant (frequency-independent) acoustic impedances, and with increasing frequency, gradually shifts to the behavior of geometrical ray acoustics. KCI Citation Count: 5