Theoretical and Experimental Investigation into Stop-Band Properties of Sonic Crystals

Morandi, Federica (2016) Theoretical and Experimental Investigation into Stop-Band Properties of Sonic Crystals, [Dissertation thesis], Alma Mater Studiorum Università di Bologna. Dottorato di ricerca in Ingegneria energetica, nucleare e del controllo ambientale, 28 Ciclo. DOI 10.6092/unibo/amsdottorato/7652.
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The present work explores the theoretical basis of sound propagation through periodic media and provides experimental evidences of stop-band properties of sonic crystals, periodic arrays of scatterers immersed in air. In order to investigate the sound field generated by sonic crystals, three theoretical models are used. The band structures are analysed with the Plane Wave Expansion method, while the Multiple Scattering Theory is used to calculate the magnitude of the scattered sound field. The Finite Element analysis is used for both purposes and to provide a stronger bond between the calculations of the theoretical models and the experimental results. Experimental measurement campaigns are performed at the Open University, Milton Keynes (UK) and at the University of Bologna. The two laboratories offer different testing facilities, respectively an anechoic chamber and a large industrial hall. Three square unit cells are analysed, varying the lattice constant and/or the filling fraction in order to provide a correlation between the two experimental setups. Measurements are performed to assess the characteristics of the sound field transmitted and reflected from the arrays, posing a special attention to the contribution of side and top edge diffraction. The evanescent behaviour of modes inside the lattice has been investigated by carrying out Impulse Response measurements inside the crystal and testing, with an intensity probe, the components of the sound field that exit the crystal in the two main directions. Finally, standardised indices are calculated that allow to compare the screening performance of sonic crystals to those of common noise barriers. All measurements setups report coherent results among them and with respect to the theoretical calculations, representing a solid platform for further developments.

Tipologia del documento
Tesi di dottorato
Morandi, Federica
Dottorato di ricerca
Scuola di dottorato
Ingegneria industriale
Settore disciplinare
Settore concorsuale
Parole chiave
acoustics, sonic crystals, band gaps, EN 1793-6
Data di discussione
1 Giugno 2016

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