Characterisation of the acoustic properties of viscoelastic materials
The measurement of the acoustic properties of highly attenuative materials such as bitumen is very difficult. One possibility is to use measurements of the extent to which filling a cylindrical waveguide with the material affects the dispersion relationships of the cylinder. It has been shown that the bulk velocities and attenuation of the material may be obtained by measuring the phase velocity and attenuation of guided waves over the frequency range of interest. This method is feasible when the material flows sufficiently easily for the cylinder to be filled. An alternative when the material does not flow easily is to clamp a sample of the material between two rod waveguides and to measure the reflection and transmission of guided waves across the sample; again the bulk velocities and attenuation of the material can be extracted over the frequency range of the measurements.