Wave Physics and Inter-Disciplinarity

Transcription

1 Wave Physics and Inter-Disciplinarity GDR: POAN, PRIMA, IMCODE, MESOIMAGE from 1993 to 2014 Primary goals of the GDR : (1) Bring people together (2) Make them speak the same language One (sometimes two) meeting per year since 1993 Next edition in May 2015 in Cargese (Corsica) Journées Interdisciplinarité CNRS 10/11 décembre 2014

2 Métamatériaux et Cloaking Sismo-Acoustique : Comment manipuler les ondes sismiques? Metamaterials and Seismo-Acoustic Cloaking : How to manipulate seismic waves? Philippe Roux ISTerre, Université Grenoble-Alpes, CNRS Journées Interdisciplinarité CNRS 10/11 décembre 2014

3 Concept : Manipulating the Wavefield Metamaterial Target WIKIPEDIA Metamaterials are artificial materials engineered to have properties that have not yet been found in nature.! Hot Topic! : 37 «Science Magazine» papers since 2001 A lot of Theory Only few Experimental Demonstrations

4 Concept : Manipulating the Wavefield Applications? The «cape of invisibility» (or «cloaking») Electromagnetic waves Simulation Experiment Schurig et al., Science (2006) WIKIPEDIA They are assemblies of multiple individual elements fashioned from conventional materials such as metals or plastics, but the materials are usually constructed into repeating patterns, often with microscopic structures.

5 10 cm Metamaterial: Spatial Distribution of Scatterers Acoustic waves Frahat et al, Institut Fresnel, Marseille Numerical simulation Laboratory experiment Wavelength

6 How to Manipulate the Wavefield? 1- Bragg scattering and Phononic crystals Negative Index of Refraction Guiding / Multiplexing Snell-Descartes Khelif et al., Applied Physics Letters (2004) Sukhovich et al., Physical Review B (2008)

7 How to Manipulate the Wavefield? 2- Multi-resonators Lemoult et al, Institut Langevin, Paris

8 Acoustic Meta-Materials

9 At Larger Scale : Cancellation of Seismic Waves? S. Guenneau, Institut Fresnel, Marseille

10 A City : Macroscopic Arrangement of Resonating Elements? Tall building : subwavelength resonator Cluster of buildings :meta-material?

11 Geophysical Observation (Courtesy P. Guéguen, ISTerre) Local damages in urban areas : site and site-structure effects. Site-city interaction : key role in sub-wavelength damages during Earthquakes

12 Numerical Approach so far : No Multi-resonators Involved Sismic radiation from a building

13 Experimental / Numerical Approach at ISTerre Coupling Surface wave (Geophysics) and Multi-Resonators (Acoustics) Vibrator 1.5 m x 2 m plate resonators Ricker 4 khz resonators 20 cm Z Laboratory set-up Simulation setup

14 Experimental Configuration

15 Experimental Configuration (1) 1.5 m Aluminium plate is 6mm thick. Its shape is an ergodic Bunimovich billard (1,5 m x 2 m => 2,52m²) 2.5 m

16 Experimental Configuration (2) Nota : Vertical field measurement is performed with a Laser velocimeter moved in 2D by motorized motors Seismo-acoustic source is a vibrometer (frequency range : [ khz]) Plate Lamb wave A0 Collection of 100 aluminium vertical beams (d=6.35mm; L=612.5mm) periodically attached to the plate on a 18-cm square with inter-beam spacing equal to 2 cm

17 Experimental Results : Metamaterial + Plate Outside the Metamaterial Inside the Metamaterial

18 Temporal / Spectral Responses Outside the Metamaterial Coupling between A0 Lamb wave and air

19 Temporal / Spectral Responses Inside the Metamaterial 3 Band-gaps

20 Temporal / Spectral Responses Outside the Metamaterial ZOOM

21 Temporal / Spectral Responses Inside the Metamaterial ZOOM

22 Spatial Distribution of the Wavefield Wavefield filtered in the first Band-gap (Ballistic Wave) Field Cancellation in the Metamaterial Distance (m)

23 Spatial Distribution of the Wavefield Wavefield filtered in the first Band-gap (Coda Waves) Field Cancellation in the Metamaterial Distance (m)

24 Temporal Evolution of the Wavefield Vertical Displacement filtered in [2100Hz Hz] 0,18 m 0,18 m Metamaterial 1,1m

25 Temporal Evolution of the Wavefield Vertical Displacement filtered in [2100Hz Hz] 0,18 m Bragg? 0,18 m Meta-material 1,1m

26 Periodic / Random Distribution of Beams Periodic configuration Random configuration

27 Periodic vs Random

28 Outside the Bandgaps : Sub- or Supra-Wavelength Modes Inside bandgap wavelength Outside bandgap

29 Metamaterial description through Dispersion relation Dispersion relation inside the Metamaterial S0 A0 Band-gap Modes sub-λ Modes supra-λ Band-gap Band-gap

30 Metamaterial description through Dispersion relation Role of the resonances Branche antiliante Milieu libre Branche liante

31 Metamaterial description through Dispersion relation Compression Resonances Flexion Resonances S0 Mode A0 Mode One Single Resonator

32 Numerical simulations : First Attempts Toward Seismo-Acoustic Cloaking

33 Numerical approach : Spectral Element Method with 3-D Adaptive Meshing

34 Numerical Results (drift) Vertical (x) and Horizontal component (y) of the displacement produced by a point force with central frequency 4kHz (wavelength~12cm and speed~700 m/s). Duration Time : 6 ms

35 Numerical Results Acceleration (vertical comp) power spectrum Band-gaps Local measurements a Frequency [khz]

36 Numerical Results (Filtered in the Bangap)

37 A Few Snapshots

38 Seismo-Acoustic Cloaking? Some Degrees of Freedom: - Length of the Beams - Spatial Distribution of the Beams

39 Effective Speed inside the Meta-Material

40 Toward Acoustic Cloaking (Numerical Results)

41 Toward Acoustic Cloaking (Numerical Results) Without Metamaterial With Metamaterial

42 First result : optimal Cloak for Backscattered field

43 Metamaterials at the geophysics scale? 120 m North of Villard-de-Lans, Vercors (38) Dense forest : 80 trees per 400 m 2 Dense geophone array with 31 x 31 = 961 sensors? ANR Meta-Forest? ( ) Wireless geophone Vibrating source : vibrometer

44 Spectral ratio Experimental result Frequency (Hz) Metamaterials at the geophysics scale Numerical study 10 m Layer 1 20 m Layer 10

45 Can we consider a Forest as a natural Metamaterial?