Measurements of backward wave propagation using the dynamic photoelastic technique

Guided waves in plates and cylinders exhibit the backward propagation that group and phase velocities have opposite directions. Backward waves might be used to control the acoustic energy flux. The existence of backward waves in acoustic waveguides has been well established, but the direct visualization of the propagation of backward modes has not been widely reported. The dynamic photoelastic method is able to present the stress distribution inside a solid material. In this paper, the photoelasticity has been used to measure backward-wave motions in plates, in order to obtain a better understanding of propagation characteristics of backward waves.