Acoustic metamaterials and phononic structures

Acoustic metamaterials are artificial structures that present new striking and exotic properties that are not present in conventional or natural materials. In some frequency range, they can present dynamic negative compresibility and/or negative mass density, and strong dispersion and slow-sound. These new materials can be designed to obtain interesting properties such as perfect sound absorption, zero-sound transmission, focusing or specific scattering patterns.


Perfect acoustic absorbers

Artificial materials with strong dispersion can be designed by using locally resonant structures. Here, I'm working in the design of perfect acoustic absorbers composed of metamaterials. In the slow sound regime, the effective wavenumber inside the structures can be drastically increased, reducing the total thickness of the structure. Moreover, the tuning of the thermoviscous losses allows to critically couple the structure with the exterior medium, leading to perfect absorption.

In the top image, we present the absorption and the refelction in the complex plane of a perfect absorber panel working at 350 Hz. The panel is only 1.1 cm thick. Thus, the structure perfectly absorb an incoming acoustic wave with a wavelength 88 times longer than the panel thickness.

Moreover, slow sound can be generated in a panel in transmission, and using the Fabry-Pérot resonances to efficeintly absorb sound.

pdf link doi Ultra-thin metamaterial for perfect and quasi-omnidirectional sound absorption
N. Jiménez, W. Huang, V. Romero-García, V. Pagneux, J. Groby,
Applied Physics Letters, 109 (12), pp 121902, (2016)

pdflinkdoi Rainbow-trapping absorbers: Broadband, perfect and asymmetric sound absorption by subwavelength panels for transmission problems
N Jiménez, V Romero-García, V Pagneux, JP Groby,
Scientific Reports, 7, pp 13595, (2017)

pdflinkdoi Quasi-perfect absorption by sub-wavelength acoustic panels in transmission using accumulation of resonances due to slow sound
N. Jiménez, V. Romero-García, V. Pagneux, J. Groby,
Phys. Rev. B, 95, pp 014205, (2017)

pdflinkdoi Aerogel-based metasurfaces for perfect acoustic energy absorption
A. A. Fernández-Marín and N. Jiménez and J.-P. Groby and J. Sánchez-Dehesa and V. Romero-García,
Appl. Phys. Lett., 115, (6) pp 061901, (2019)

pdflinkdoi Broadband quasi perfect absorption using chirped multi-layer porous materials
N. Jiménez, V. Romero-García, A. Cebrecos, R. Picó, V. Sánchez-Morcillo, L. G. Raffi,
AIP Advances, 6, pp 121605, (2016)

Focusing devices

By the spefific control of the anisotropic dispersion of spacially modulated media and metamaterials, the phase of the transmitted field can be specially tailored to produce focusing and beam generation. Here, I'm working on focusing and vortex beam generation by periodic structures and metamaterials.

pdf link doi Nonlinear focusing of ultrasonic waves by an axisymmetric diffraction grating embedded in water
N. Jiménez, V. Romero-García, R. Picó, L. M. García-Raffi, K. Staliunas,
Applied Physics Letters, 107, pp 204103, (2015)

Scattering control by metasurfaces

The phase of the reflected waves by an spatially modulated media can also be tailored to obtain an specific phase pattern, leading to the precise control of the scattering of acoustic waves. Using metasurfaces based on Helmholtz resonators ultrathin sound diffusers can be designed. Another innovative application of this phenomena is to reduce the acoustic load and vibrations in the launch-pad during the litft-off of a rocket. We are appliying these concepts in collaboration with the European Space Agency (ESA)

pdf link doi Metadiffusers: Deep-subwavelength sound diffusers
N. Jiménez, T. J. Cox, V. Romero-García, J. Groby,
Scientific Reports, 7 (1), pp 5389, (2017)

pdf link doi Broadband reduction of the specular reflections by using sonic crystals: a proof of concept for noise mitigation in aerospace applications
LM García-Raffi, LJ Salmerón-Contreras, I Herrero-Durá, R Picó, J Redondo, V Sánchez-Morcillo, K Staliunas, A Cebrecos, N Jiménez, V Romero-García,
Aeroespace Science and Technology, 73, pp 300-308, (2018)

pdf link doi Experimental validation of deep-subwavelength diffusion by metadiffusers
E. Ballestero, N. Jiménez, J.-P. Groby, S. Dance, H. Aygun and V. Romero-García,
Applied Physics Letters, 115(8), pp 081901, (2019)

Nonlinear waves in phononic crystals

I'm studying nonlinear wave processes in spatially modulated media such as multilayered acoustic media, phononic crystals or sonic crystals. The rich nonlinear dynamics of these system are characterized by its strong dispersion. Here, harmonic generation processes and its relation with their band structure are explored. We found that the nonlinear processes can be enhanced, strongly minimized or simply modified by tuning the material dispersion relation. Thus, the combined action of nonlinearity (harmonic generation) and periodicity (different propagation velocities and attenuation for the different harmonics) results in novel and unexpected phenomena with respect to the linear counterpart, and opens the door to new mechanisms of acoustic wave control and manipulation.

pdf link doi Asymmetric propagation using enhanced self-demodulation in a chirped phononic crystal
A. Cebrecos, N. Jiménez, V. Romero-García, R. Picó, V. Sánchez-Morcillo, L. García-Raffi,
AIP Advances, 6, pp 121601, (2016)

pdf link doi Nonlinear propagation and control of acoustic waves in phononic superlattices
N. Jiménez, A. Mehrem, R. Picó, L. M. García-Raffi, V. Sánchez-Morcillo,
Comptes Rendus Physique, 17 (5), pp 543 - 554, (2016)

pdf link doi Nonlinear self-collimated sound beams in sonic crystals
E. M. Hamham, N. Jiménez, R. Picó, V. Sánchez-Morcillo, L. G. Raffi, K. Staliunas,
Phys. Rev. B, 92, pp 054302, (2015)

Nonlinear waves in lattices

I'm also exploring intense nonlinear waves in lattices of coupled oscillators. An example are strain waves in a chain of cations coupled by realistic interatomic potentials. In this case, the nonlinear ionic interactions and lattice dispersion lead to the formation of supersonic kinks. These intrinsically-nonlinear localized dislocations travel long distances without changing its properties and can explain the formation of dark traces found in muscovite-mica crystals.

pdf link doi Ultradiscrete kinks with supersonic speed in a layered crystal with realistic potentials
J. F. Archilla, Y. A. Kosevich, N. Jiménez, V. Sánchez-Morcillo, L. M. García-Raffi,
Phys. Rev. E, 91 (2), pp 022912, (2015)

pdf link doi Nonlinear dispersive waves in repulsive lattices
A Meherem, N Jiménez, LJ Salmerón-Contreras, X García-Andres, LM Raffi, R Picó, VJ Sánchez-Morcillo,
Physical Review E, 91 (1), pp 002200, (2017)

pdf link doi Macroscopic acousto-mechanical analogy of a microbubble
J. Chaline, N. Jiménez, A. Mehrem, A. Bouakaz, S. D. Santos, V. Sánchez-Morcillo,
The Journal of the Acoustical Society of America, 138 (6), pp 3600-3606, (2015)

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