Diffuse Ultrasonic Waves 

DUWsDiffuse Ultrasonic Waves are produced when a broadband source is able to generate many reflections and mode conversions within a component. These reflections and mode conversions are produced by multiple surface reflections and/or by strongly scattering media within the material. DUWs are a complex mix of different wave modes and frequencies. This makes interpretation of the signals difficult. The signal varies with transducer position and coupling, if separate measurements are made, and is susceptible to changes in temperature and surface condition.

Despite these disadvantages, DUWs are finding application in structural health monitoring (SHM) (see ‘What the Hec?!’, October 2010). DUWs are a global, active SHM technique. DUWs travel through a relatively large volume of the component and so have been shown to be sensitive to material changes. A smaller number of fixed transducers can be utilised compared to local bulk wave techniques and the permanent attachment of the transducers negates the susceptibility to changes in position and coupling between readings. There is still the need to compensate for temperature changes. Analysis of the DUW signal can be achieved by comparison with a baseline signal from a good structure.

DUWs have been used for the SHM of concrete, due to the presence of reinforcement bars and aggregates creating reflections at the boundaries and scattering from heterogeneities in the material.

For more information on DUWs see Chapter II of the PhD thesis (Yinghui Lu, ‘Analysis and modelling of diffuse ultrasonic signals for structural health monitoring’, Georgia Institute of Technology, August 2007) available at: https://smartech.gatech.edu/handle/1853/16141?show=full

For information on DUWs for SHM of concrete see: https://europepmc.org/article/PMC/6767232

WHAT THE HEC?! articles are not intended to be the definitive account on the topic or acronym in question. Readers’ comments and contributions are welcomed. Email: ndtnews@bindt.org