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时间：2016年10月10日上午10:45-11:45

地点：水声楼15楼报告厅

报告题目：Use of Helmholtz Resonators for sound control

报告人：Olivier RICHOUX教授

主办单位：水声工程学院

报告人简介：Olivier Richoux, Professeur des UniversitésdepuisSeptembre 2015àl'Universitédu Maine (Le Mans), Enseignantàla Facultédes Sciences et Techniques, Chercheur au Laboratoired'Acoustique de l'Universitédu Maine, HabilitationàDiriger les Recherchesobtenue le 21 Mai 2012 à l'Université du Maine.

报告内容简介：In this presentation, devices using Helmholtz Resonators (HRs) are proposed to control the sound propagation. Firstly, linear propagation through a waveguide loaded by a periodic lattice of HRs is studied and the well-known characteristics of this type of media are recalled. The sound propagation in lossy, locally resonant periodic structures is investigated by taking into account the intrisicviscothermal losses. In particular, the limits and various characteristics of slow sound are studied. The propagation of a high amplitude wave is also examined and the existence of an acoustic soliton is demonstrated. Experimental, numerical and analytical results are shown and compared.

In a second part, experimental results of perfect acoustic absorption in devices using HRs are reported. We show that the interplay of the inherent losses and modes of the structure can lead to Coherent Perfect Absorption associated to Critical Coupling phenomenon. Different examples of one-port and two-ports systems exhibiting Perfect Absorption are proposed. The case of a high amplitude wave leading to nonlinear phenomena in the Helmholtz Resonators is also treated. We show that nonlinear absorption (due to high amplitude wave) can be used to critically coupling one HR with a waveguide and can lead to Coherent Perfect Absorption. Finally, experiments on metasurface made of Helmholtz Resonators are reported. Carpet cloaking for audible sound is demonstrated in the frequency domain. The reflection of a short pulse is also presented to inspect the broadband character of the cloak.