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# Acoustic, elastic and thermal metamaterials II

## 14:00 Invited talk : Acoustic transparency and opacity using Fano Interferences in Metamaterials

### Abdelkrim Khelif (1),A. Elayouch M. Amin (2),M. Farhat (2),M. Addouche (1),H. Bagci (2)

#### (1)Franche-Comte University (France) , (2)King Abdullah University of Science and Technology (Saudi Arabia)

We investigate both experimentally and theoretically how to generate the acoustical analogue of the Electromagnetically Induced Transparency. This phenomenon arises from Fano resonances originating from constructive and destructive interferences of a narrow discrete resonance with a broad spectral line or continuum. Measurements were realized on a double-cavity structure by using a Kundt's Tube. Transmission properties reveal an asymmetric lineshape of the transmission that leads to acoustic transparency.

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## 14:20 Invited talk : Locally resonant acoustic metamaterials beyond homogenization: subwavelength control of waves, slow waves, negative index and other exotic phenomena

### Fabrice Lemoult, Nadege Kaina, Mathias Fink, Geoffroy Lerosey

#### ESPCI ParisTech (France)

Starting from the very simple example of a soda can metamaterial (an acoustic medium made of Helmholtz resonators), we explain the propagation of waves in locally resonant media without claiming homogenized parameters. This allows to highlight the importance of multiple scattering even at this deep subwavelength scale where usually the quasi-static approximation is performed. This then permits to envisage exotic phenomena such as subwavelength control of waves, slow waves or even negative refraction with a single negative medium.

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## 14:40 Invited talk : Total absorption in waveguides by admittance conjugation

### Vincent Pagneux

#### LAUM - CNRS Le Mans (France)

We present a method to achieve perfect total absorption for a wall with local admittance (thin coating) by putting inhomogeneities in front of the wall. The first step, using the eigenvectors of the Dirichlet-to-Neumann Admittance operator, is to construct a solution with only outgoing waves from a wall with a local gain admittance. Then, by conjugating this solution, we get a new solution where the incident wave is perfectly absorbed by a wall with a local absorptive admittance.

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## 15:00 Invited talk : Spectral Effectiveness of Engineered Thermal Devices in the Frequency Regime

### David Petiteau (1),Sebastien Guenneau (1),Michel Bellieud (2),Myriam Zerrad (1),Claude Amra (1)

#### (1)Institut Fresnel (France) , (2)Montpellier University (France)

We analyse several thermal devices such as thermal cloaks or concentrators designed via different geometric transforms. We evaluate quantitatively in the frequency regime the effectiveness of these thermal devices through the calculation of the standard deviation of the isotherms and of the heat flux distribution. Through homogenization process, we also study the effectiveness of engineered multilayered thermal devices using concentric or orthoradial layers. Thus, we determine the number of layers required to approach ideal thermal devices effectiveness.

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## 15:20 Invited talk : Towards multi-physical fields camouflage using natural materials

### Cheng-Wei Qiu, Tianzhi Yang, Tiancheng Han, Xue Bai, Baowen Li, John Thong

#### National University of Singapore (Singapore)

Manipulation of various physical fields, including optics, electromagnetics, acoustics, thermotics, etc. through different materials has been a long-standing dream for many researchers over the decades. Analogous to invisible cloak and wave-dynamic illusion, thermal metamaterials can potentially transform an actual perception into a pre-controlled perception, thus empowering unprecedented applications in thermal cloaking and camouflage. Here we report our recent works about thermal cloak and multi-physics invisible sensor. The approach can be readily extended and applied in other static fields.

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## 15:40 Invited talk : Geometric phase and topological transition point in acoustic systems

### M. Xiao, G. Ma, Z. Yang, P. Sheng, Z. Q. Zhang, C. T. Chan

#### Hong Kong University of Science and Technology (Hong Kong)

We constructed a phononic crystal with a topological transition point in the acoustic band structure where the frequencies of an odd mode and an even mode become degenerate. The Zak phases of the bulk bands change upon a shift in system parameters across this transition point. This is an analog of band inversion behavior in the acoustic system. We present a theoretical framework, together with two methods to experimentally determine the Zak phase in this acoustic system.

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