In this thesis we investigate acoustic metamaterials and how they can influence incident sound waves. Specifically we are interested in the mathematical technique of transformation acoustics and how several simple examples of metamaterials, devised via transformation acoustics, can be realised physically. We present a simple methodology for optimising microstructure consisting of rods with elliptical cross sections arranged on a rectangular array in order to best fit the material properties required by a desired transformation. We present in detail three such examples: a one dimensional scaling, the beam shifter, and a right angle bend. We apply the one dimensional scaling to a quarter wavelength resonator, theoretically predicting that we are able to lower the active frequency of the resonator without increasing its physical length. This result is then confirmed experimentally. We provide further experimental evidence of the broad band nature of the microstructure and suggest how it could be applied as a one dimensional acoustic cloak. Finally we present numerical simulations of acoustic propagation through microstructure chosen to realise a beam shifter and right angle bend. These are devices associated with more complicated two dimensional transformations that may prove useful in the field of noise control and redirection.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:764627 |
| Date | January 2018 |
| Creators | Rowley, William |
| Contributors | Parnell, William |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/mathematical-modelling-of-novel-metamaterials-for-noise-reduction-applications(7ce8e9fb-4c2c-4637-ac89-c156949f9a27).html |
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