Scattering of elastic sound waves
When the frequency elastic waves in concrete is higher enough, the wavelength is smaller than the structure, but larger than the size of the heterogeneities, the sound interacts weakly with the heterogeneities and propagation takes place. When the frequency is still higher, the ultrasonic wavelengths are shorter than the size of the heterogeneities; the wave can interact with the heterogeneities several times before reaching the detector. In this case, the wave is forced to deviate from a straight trajectory by one or more paths then fall into the scattering regime.
Contributor: Xin Wang (ESR1)