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We propose and experimentally demonstrate a mechanism of sound wave concentration based on soft reflections in chirped sonic crystals. The reported controlled field enhancement occurs at around particular (bright) planes in the crystal and is related to a progressive slowing down of the sound wave as it propagates along the material. At these bright planes, a substantial concentration of the energy (with a local increase up to 20 times) was obtained for a linear chirp and for frequencies around the first band gap. A simple couple mode theory is proposed that interprets and estimates the observed effects. Wave concentration energy can be applied to increase the efficiency of detectors and absorbers. ; The work was supported by Spanish Ministry of Science and Innovation and European Union FEDER through projects FIS2011-29734-C02-01 and -02 and GVA/2011/055. V. R.-G. is grateful for the support of post-doctoral contracts of the UPV CEI-01-11. K. S. acknowledges the grant of UPV PAID-02-01. We acknowledge the CTFAMA and the Sonic Crystal Technologies Research Group at UPV for the use of the anechoic chamber and the 3DReAMS, respectively. ; Romero García, V.; Picó Vila, R.; Cebrecos Ruiz, A.; Sánchez Morcillo, VJ.; Staliünas, K. (2013). Enhancement of sound in chirped sonic crystals. Applied Physics Letters. 102(919):1-3. https://doi.org/10.1063/1.4793575 ; S ; 1 ; 3 ; 102 ; 919 ; Kushwaha, M. S., Halevi, P., Dobrzynski, L., & Djafari-Rouhani, B. (1993). Acoustic band structure of periodic elastic composites. Physical Review Letters, 71(13), 2022-2025. doi:10.1103/physrevlett.71.2022 ; Martínez-Sala, R., Sancho, J., Sánchez, J. V., Gómez, V., Llinares, J., & Meseguer, F. (1995). Sound attenuation by sculpture. Nature, 378(6554), 241-241. doi:10.1038/378241a0 ; Zhang, X., & Liu, Z. (2004). Negative refraction of acoustic waves in two-dimensional phononic crystals. Applied Physics Letters, 85(2), 341-343. doi:10.1063/1.1772854 ; Lu, M.-H., Zhang, C., Feng, L., Zhao, J., Chen, Y.-F., Mao, Y.-W., … Ming, ...

Phononic crystals are artificial materials made of a periodic distribution of solid scatterers embedded into a solid host medium with different physical properties. An interesting case of phononic crystals, known as sonic crystals (SCs), appears when the solid scatterers are periodically embedded in a fluid medium. In SCs only longitudinal modes are allowed to propagate and both the theoretical and the experimental studies of the properties of the system are simplified without loss of generality. The most celebrated property of these systems is perhaps the existence of spectral band gaps. However, the periodicity of the system can also affect to the spatial dispersion, making possible the control of the diffraction inside these structures. In this work we study the main features of the spatial dispersion in SCs from a novel point of view taking into account the evanescent properties of the system, i.e., studying the complex spatial dispersion relations. The evanescent behavior of the propagation of waves in the angular band gaps are theoretically and experimentally observed in this work. Both the numerical predictions and the experimental results show the presence of angular band gaps in good agreement with the complex spatial dispersion relation. The results shown in this work are independent of the spatial scale of the structure, and in principle the fundamental role of the evanescent waves could be also expected in micro- or nanoscale phononic crystals. ; This work was supported by MCI Secretaria de Estado de Investigacion (Spanish government) and the FEDER funds, under Grant Nos. MAT2009-09438, FIS2011-29734-C02-02, and from Generalitat Valencia through Project No. GV/2011/055. V.R.G. is grateful for the support of "Programa de Contratos Post-Doctorales con Movilidad UPV (CEI-01-11)." We acknowledge the Centro de Tecnologias Fisicas: Acustica, Materiales y Astrofisica and the Sonic Crystal Technologies Research Group of the Universitat Politecnica de Valencia for the use of the anechoic chamber and the ...

The enhancement of sound inside a two dimensional exponentially chirped crystal during the soft reflections of waves is experimentally and theoretically explored in this work. The control of this enhancement is achieved by a gradual variation of the dispersion in the system by means of a chirp of the lattice constant. The sound enhancement is produced at some planes of the crystal in which the wave is softly reflected due to a progressive slowing down of the sound wave. We find that the character of the sound enhancement depends on the function of the variation of dispersion, i.e., on the function of the chirp. A simple coupled mode theory is proposed to find the analytical solutions of the sound wave enhancement in the exponentially chirped crystal. Harmonic and time domain numerical simulations are performed to interpret the concept of the soft reflections, and to check the analytically calculated field distributions both in good agreement with experiments. Specially we obtain stronger sound enhancement than in linearly chirped crystals. This sound enhancement could motivate applications in energy harvesting, e.g., to increase the efficiency of detectors and absorbers. (C) 2014 Author(s). ; The work was supported by Spanish Ministry of Economy and European Union FEDER through project FIS2011-29731-C02-02. LMGR Acknowledges Supported by MINECO and FEDER, under Grant MTM2012-36740-c02-02. ACR is grateful for the support of Programa de Ayudas e Iniciativas de Investigacion (PAID) of the UPV. ; Cebrecos Ruiz, A.; Picó Vila, R.; Sánchez Morcillo, VJ.; Staliünas, K.; Romero García, V.; García-Raffi, LM. (2014). Enhanced of sound by soft reflections in exponentially chirped crystals. AIP Advances. 4(12):124402-124412. https://doi.org/10.1063/1.4902508 ; S ; 124402 ; 124412 ; 4 ; 12 ; Pennec, Y., Vasseur, J. O., Djafari-Rouhani, B., Dobrzyński, L., & Deymier, P. A. (2010). Two-dimensional phononic crystals: Examples and applications. Surface Science Reports, 65(8), 229-291. doi:10.1016/j.surfrep.2010.08.002 ...

Copyright 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Romero García, V.; Cebrecos Ruiz, A.; Picó Vila, R.; Sánchez Morcillo, VJ.; García-Raffi, LM.; Sánchez Pérez, JV. (2013). Wave focusing using symmetry matching in axisymmetric acoustic gradient index lenses. Applied Physics Letters. 103(26):264106-264106. doi:10.1063/1.4860535 and may be found at http://scitation.aip.org/ ; The symmetry matching between the source and the lens results in fundamental interest for lensing applications. In this work, we have modeled an axisymmetric gradient index (GRIN) lens made of rigid toroidal scatterers embedded in air considering this symmetry matching with radially symmetric sources. The sound amplification obtained in the focal spot of the reported lens (8.24 dB experimentally) shows the efficiency of the axisymmetric lenses with respect to the previous Cartesian acoustic GRIN lenses. The axisymmetric design opens new possibilities in lensing applications in different branches of science and technology. ; The work was supported by Spanish Ministry of Science and Innovation and European Union FEDER through Project Nos. FIS2011-29734-C02-01 and -02 and PAID 2012/253. V. R. G. is grateful for the support of post-doctoral contracts of the UPV CEI-01-11. ; Romero García, V.; Cebrecos Ruiz, A.; Picó Vila, R.; Sánchez Morcillo, VJ.; García-Raffi, LM.; Sánchez Pérez, JV. (2013). Wave focusing using symmetry matching in axisymmetric acoustic gradient index lenses. Applied Physics Letters. 103(26):264106-264106. https://doi.org/10.1063/1.4860535 ; S ; 264106 ; 264106 ; 103 ; 26 ; John, S. (1987). Strong localization of photons in certain disordered dielectric superlattices. Physical Review Letters, 58(23), 2486-2489. doi:10.1103/physrevlett.58.2486 ; Yablonovitch, E. (1987). Inhibited Spontaneous Emission in Solid-State Physics and Electronics. Physical Review ...

[EN] A theoretical and experimental study of the propagation of sound beams in- and behind three-dimensional sonic crystals at frequencies close to the band edges is presented. An efficient collimation of the beam behind the crystal is predicted and experimentally demonstrated. This effect could allow the design of sources of high spatial quality sound beams. © 2012 American Institute of Physics. ; The work was financially supported by Spanish Ministry of Science and Innovation and by European Union FEDER through projects FIS2008-06024-C02-02, -03 and MAT2009-09438. V.R.G. is grateful for the support of post-doctoral contracts of the UPV CEI-01-11. K.S. acknowledges the grant of UPV PAID-02-01. ; Cebrecos Ruiz, A.; Romero García, V.; Picó Vila, R.; Pérez Arjona, I.; Espinosa Roselló, V.; Sánchez Morcillo, VJ.; Staliünas, K. (2012). Formation of collimated sound beams by three-dimensional sonic crystals. Journal of Applied Physics. 111(10):104910-1-104910-4. https://doi.org/10.1063/1.4719082 ; S ; 104910-1 ; 104910-4 ; 111 ; 10

We propose a periodic structure that behaves as a fluid fluid composite for sound waves, where the building blocks are clusters of rigid scatterers. Such building-blocks are penetrable for acoustic waves, and their properties can be tuned by selecting the filling fraction. The equivalence with a fluid fluid system of such a doubly periodic composite is tested analytical and experimentally. Because of the fluid-like character of the scatterers, sound structure interaction is negligible, and the propagation can be described by scalar models, analogous to those used in electromagnetics. As an example, the case of focusing of evanescent waves and the guided propagation of acoustic waves along an array of penetrable elements is discussed in detail. The proposed structure may be a real alternative to design a low contrast and acoustically penetrable medium where new properties as those shown in this work could be experimentally realized. ; We acknowledge financial support by Spanish Ministerio de Economia y Competitividad and European Union FEDER through project FIS2011-29731-C02-01 and -02. VRG is grateful for the financial support of the post-doctoral grant from the "Pays de la Loire". ACR is grateful for the support of the Programa de Ayudas e Iniciativas de Investigacin (PAID) of the UPV. ; Cebrecos Ruiz, A.; Romero García, V.; Picó Vila, R.; Sánchez Morcillo, VJ.; Botey, M.; Herrero, R.; Cheng, YC. (2015). Acoustically penetrable sonic crystals based on fluid-like scatterers. Journal of Physics D-Applied Physics. 48(2):25501-25510. https://doi.org/10.1088/0022-3727/48/2/025501 ; S ; 25501 ; 25510 ; 48 ; 2

Copyright (2014) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in: Applied Physics Letters 105, 204104 (2014); doi:10.1063/1.4902387 and may be found at: http://dx.doi.org/10.1063/1.490238. ; We study the propagation of waves in a periodic array of absorbing layers. We report an anomalous increase of wave transmission through the structure related to a decrease of the absorption around the Bragg frequencies. The effect is first discussed in terms of a generic coupled wave model extended to include losses, and its predictions can be applied to different types of waves propagating in media with periodic modulation of the losses at the wavelength scale. The particular case of sound waves in an array of porous layers embedded in air is considered. An experiment designed to test the predictions demonstrates the existence of the enhanced transmission band. (C) 2014 AIP Publishing LLC. ; The work was supported by Spanish Ministry of Science and Innovation and European Union FEDER through Projects FIS2011-29731-C02-01 and -02, also MAT2009-09438. A.M.Y. would like to thank the Erasmus Mundus Project (WELCOME program) for supporting him. V.R.G. acknowledges financial support from the "Pays-de-la-Loire" through the post-doctoral program. ; Cebrecos Ruiz, A.; Picó Vila, R.; Romero García, V.; Yasser, AM.; Maigyte, L.; Herrero, R.; Botey, M. (2014). Enhanced transmission band in periodic media with loss modulation. Applied Physics Letters. 105(20):204104-1-204104-4. doi:10.1063/1.4902387 ; S ; 204104-1 ; 204104-4 ; 105 ; 20 ; Figotin, A., & Vitebskiy, I. (2008). Absorption suppression in photonic crystals. Physical Review B, 77(10). doi:10.1103/physrevb.77.104421 ; Figotin, A., & Vitebskiy, I. (2010). Magnetic Faraday rotation in lossy photonic structures. Waves in Random and Complex Media, 20(2), 298-318. doi:10.1080/17455030.2010.482575 ; Erokhin, S. G., ...

We present the design of a structured material supporting complete absorption of sound with a broadband response and functional for any direction of incident radiation. The structure which is fabricated out of porous lamellas is arranged into a low-density crystal and backed by a reflecting support. Experimental measurements show that strong all-angle sound absorption with almost zero reflectance takes place for a frequency range exceeding two octaves. We demonstrate that lowering the crystal filling fraction increases the wave interaction time and is responsible for the enhancement of intrinsic material dissipation, making the system more absorptive with less material. ; The work was supported by the Spanish Ministry of Science and Innovation and European Union FEDER through project FIS2011-29734-C02-01. J.C. gratefully acknowledges financial support from the Danish Council for Independent Research and a Sapere Aude grant (12-134776). V. R. G. gratefully acknowledges financial support from the ''Contratos Post-Doctorales Campus Excelencia Internacional'' UPV CEI-01-11. ; Christensen, J.; Romero García, V.; Picó Vila, R.; Cebrecos Ruiz, A.; Garcia De Abajo, FJ.; Mortensen, NA.; Willatzen, M. (2014). Extraordinary absorption of sound in porous lamella-crystals. Scientific Reports. 4(4674). https://doi.org/10.1038/srep04674 ; S ; 4 ; 4674 ; Mei, J. et al. Dark acoustic metamaterials as super absorbers for low-frequency sound. Nat. Commun. 3, 756 (2012). ; Leroy, V., Strybulevych, A., Scanlon, M. G. & Page, J. Transmission of ultrasound through a single layer of bubbles. Eur. Phys. J. E 29, 123 (2009). ; Leroy, V., Bretagne, A., Fink, M. H. W., Tabeling, P. & Tourin, A. Design and characterization of bubble phononic crystals. Appl. Phys. Lett. 95, 171904 (2009). ; Thomas, E. L. Applied physics: Bubbly but quiet. Nature 462, 990 (2009). ; Romero-García, V., Sánchez-Pérez, J. V. & Garcia-Raffi, L. M. Tunable wideband bandstop acoustic filter based on two-dimensional multiphysical phenomena periodic ...

We report Bessel-like beam formation of acoustic waves by means of an axisymmetric grating of rigid tori. The results show that the generated beam pattern is similar to that of Bessel beams, characterized by elongated non-diffracting focal spots. A multiple foci structure is observed, due to the finite size of the lens. The dependence of the focal distance on the frequency is also discussed, on the basis of an extended grating theory. Experimental validation of acoustic Bessel-like beam formation is also reported for sound waves. The results can be generalized to wave beams of different nature, as optical or matter waves. ; The work was supported by the Spanish Ministry of Science and Innovation and the European Union FEDER through projects FIS2011-29731-C02-01 and -02, also MAT2009-09438, MTM2012-36740-C02-02 and UPV-PAID 2012/253. VR-G acknowledges financial support from the "Pays de la Loire" through the post-doctoral programme. ; Jimenez, N.; Romero García, V.; Picó Vila, R.; Cebrecos Ruiz, A.; Sánchez Morcillo, VJ.; García-Raffi, LM.; Sánchez Pérez, JV. (2014). Acoustic Bessel-like beam formation by an axisymmetric grating. EPL. 106(2):240051-240055. doi:10.1209/0295-5075/106/24005 ; S ; 240051 ; 240055 ; 106 ; 2