Band gap structures in underwater screens of periodically spaced porous plates.
Acoustic properties of different periodic structures composed of alternating fluid and fluid-saturated porous layers obeying Biot's theory are investigated. At first, the network of modes and the transmission coefficients of finite structures of six plates are studied in the frequency-angle of incidence plane. It is shown that the network of modes concentrates in localized domains of the plane where the transmission coefficients will take the greatest values. With this minimum of six plates, the structures exhibit the main features as for structures containing more plates, especially those with an infinite number of plates. Then, considering infinite structures the band gap calculations are led using the Bloch-Floquet theorem. The evanescent and propagative zones in the frequency-angle of incidence plane are determined. What is proposed here is a class of underwater porous screens that exhibits band gaps extending over great angular domains and enlarging in the frequency domain when the pores at the interfaces of the porous plates are sealed. The effect of porosity on the band gaps is also investigated.
Laboratoire Ondes et Milieux Complexes (LOMC), UMR CNRS 6294, France; Université du Havre, Place R. Schuman, BP 4006, 76610 Le Havre, France.
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Trabelsi
Laboratoire Ondes et Milieux Complexes (LOMC), UMR CNRS 6294, France; Université du Havre, Place R. Schuman, BP 4006, 76610 Le Havre, France. Electronic address: herve.franklin@univ-lehavre.fr.
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Franklin
Laboratoire Ondes et Milieux Complexes (LOMC), UMR CNRS 6294, France; Université du Havre, Place R. Schuman, BP 4006, 76610 Le Havre, France.
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Tinel
Laboratoire Ondes et Milieux Complexes (LOMC), UMR CNRS 6294, France; Université du Havre, Place R. Schuman, BP 4006, 76610 Le Havre, France.
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Derible
Band gaps; Bloch–Floquet wavenumber; Porous plates; Transmission coefficient