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Engineering the Hypersonic Phononic Band Gap of Hybrid Bragg Stacks

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journal contribution
posted on 13.06.2012, 00:00 by Dirk Schneider, Faroha Liaqat, El Houssaine El Boudouti, Youssef El Hassouani, Bahram Djafari-Rouhani, Wolfgang Tremel, Hans-Jürgen Butt, George Fytas
We report on the full control of phononic band diagrams for periodic stacks of alternating layers of poly­(methyl methacrylate) and porous silica combining Brillouin light scattering spectroscopy and theoretical calculations. These structures exhibit large and robust on-axis band gaps determined by the longitudinal sound velocities, densities, and spacing ratio. A facile tuning of the gap width is realized at oblique incidence utilizing the vector nature of the elastic wave propagation. Off-axis propagation involves sagittal waves in the individual layers, allowing access to shear moduli at nanoscale. The full theoretical description discerns the most important features of the hypersonic one-dimensional crystals forward to a detailed understanding, a precondition to engineer dispersion relations in such structures.