Analysis of acoustic surface waveguide for AE monitoring of concrete beams

The analysis of stress waves in an acoustic surface waveguide is presented. Elastic wave motions in a circular rod propagating through a rigid circular joint bonded on an elastic half-space were studied. The responses of four different harmonic wave motions-longitudinal, torsional, and two flexural-were investigated. Mode conversion, reflection, transmission, and phase change of these wave motions were observed. This analysis helps in understanding the signal transmission ability of a surface waveguide system, which is useful in the application of acoustic emission (AE) monitoring on high attenuation materials such as concrete. Numerical examples are presented to show the transmission and reflection coefficients at different frequencies and to examine the effect of mode conversion. The numerical analysis results were implemented into the design of an efficient waveguide system. Results from tests of concrete beams show that he AE monitoring range was significantly increased by using the proposed acoustic surface waveguide. The AE monitoring of a 210-cm concrete beam was accomplished by using only two sensors.