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We report experimental evidences of spatial (angular) filtering of sound beams propagating through sonic crystals. We show that at specific frequencies of the incident wave the paraxial plane wave compo- nents of the beam can be efficiently transmitted through the crystal, whereas the components propagat- ing at large angles are strongly reflected or deflected (filtered out) by the crystal. The modification of the angular field distribution results in formation of sound beams of relatively high spatial quality. ; The work was financieall supported by Spanish Ministry of since and Innovation and European Union FEDER through projects FIS2011-29731-C02-01 and -02, Generalitat Valenciana through the procect GV/2011/2055 and the UPV through PAID-05-12. ; Picó Vila, R.; Pérez Arjona, I.; Sánchez Morcillo, VJ.; Staliünas, K. (2013). Evidences of spatial (angular) filtering of sound beams by sonic crystals. Applied Acoustics. 74(7):945-948. https://doi.org/10.1016/j.apacoust.2013.01.003 ; S ; 945 ; 948 ; 74 ; 7

We propose an approach based on a local Hilbert transform to design non-Hermitian potentials generating arbitrary vector fields of directionality, p→(r→), with desired shapes and topologies. We derive a local Hilbert transform to systematically build such potentials by modifying background potentials (being either regular or random, extended or localized). We explore particular directionality fields, for instance in the form of a focus to create sinks for probe fields (which could help to increase absorption at the sink), or to generate vortices in the probe fields. Physically, the proposed directionality fields provide a flexible mechanism for dynamical shaping and precise control over probe fields leading to novel effects in wave dynamics. ; NATO SPS Research Grant[985048] ; Ministerio de Ciencia e Innovación ; Türkiye Bilimler Akademisi ; Spanish Ministerio de Ciencia e Innovacion[FIS2015-65998-C2-1-P] ; European Union FEDER[FIS2015-65998-C2-1-P] ; Erasmus Mundus Doctorate Program Europhotonics[159224-1-2009-1-FR-ERA MUNDUS-EMJD]

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Applied Physics Letters 107, 204103 (2015); doi:10.1063/1.4935917 and may be found at http://dx.doi.org/10.1063/1.4935917. ; We report the nonlinear focusing of ultrasonic waves by an axisymmetric diffraction grating immersed in water. In the linear regime, the system presents high focal gain (32 dB), with a narrow beam-width and intense side lobes as it is common in focusing by Fresnel-like lenses. Activating the nonlinearity of the host medium by using high amplitude incident waves, the focusing properties of the lens dramatically change. Theoretical predictions show that the focal gain of the system extraordinary increases in the strongly nonlinear regime (Mach number of 6.1 x 10(-4)). Particularly, the harmonic generation is locally activated at the focal spot, and the second harmonic beam is characterized by strongly reduced side-lobes and an excellent beam profile as experiments show in agreement with theory. The results can motivate applications in medical therapy or second harmonic imaging. (c) 2015 AIP Publishing LLC. ; The work was supported by Spanish Ministry of Science and Innovation and European Union FEDER through Projects FIS2011-29734-C02-01 and -02, MTM2012-36740c02-02, and PAID 2012/253. ; Jimenez, N.; Romero García, V.; Picó Vila, R.; García-Raffi, LM.; Staliünas, K. (2015). Nonlinear focusing of ultrasonic waves by an axisymmetric diffraction grating embedded in water. Applied Physics Letters. 107(20). doi:10.1063/1.4935917 ; S ; 204103 ; 107 ; 20 ; Farnow, S. A., & Auld, B. A. (1974). Acoustic Fresnel zone plate transducers. Applied Physics Letters, 25(12), 681-682. doi:10.1063/1.1655359 ; Sleva, M. Z., Hunt, W. D., & Briggs, R. D. (1994). Focusing performance of epoxy‐ and air‐backed polyvinylidene fluoride Fresnel zone plates. The Journal of the Acoustical Society of America, 96(3), 1627-1633. doi:10.1121/1.410242 ; Wang, ...

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 formation of high-order Bessel beams by a passive acoustic device consisting of an Archimedes' spiral diffraction grating is theoretically, numerically, and experimentally reported in this paper. These beams are propagation-invariant solutions of the Helmholtz equation and are characterized by an azimuthal variation of the phase along its annular spectrum producing an acoustic vortex in the near field. In our system, the scattering of plane acoustic waves by the spiral grating leads to the formation of the acoustic vortex with zero pressure on axis and the angular phase dislocations characterized by the spiral geometry. The order of the generated Bessel beam and, as a consequence, the size of the generated vortex can be fixed by the number of arms in the spiral diffraction grating. The obtained results allow for obtaining Bessel beams with controllable vorticity by a passive device, which has potential applications in low-cost acoustic tweezers and acoustic radiation force devices. ; We acknowledge financial support from MINECO of the Spanish Government under Grants No. MTM2012-36740-C02-02, No. FIS2015-65998-C2-1-P, and No. FIS2015-65998-C2-2-P. N.J. acknowledges financial support from PAID-2011 Universitat Politecnica de Valencia. ; Jimenez, N.; Picó Vila, R.; Sánchez Morcillo, VJ.; Romero García, V.; García-Raffi, LM.; Staliünas, K. (2016). Formation of high-order acoustic Bessel beams by spiral diffraction gratings. Physical Review E. 94(5). doi:10.1103/PhysRevE.94.053004 ; S ; 053004 ; 94 ; 5

We report the propagation of high-intensity sound beams in a sonic crystal, under self-collimation or reduced-divergence conditions. The medium is a fluid with elastic quadratic nonlinearity, where the dominating nonlinear effect is harmonic generation. The conditions for the efficient generation of narrow, nondiverging beam of second harmonic are discussed. Numerical simulations are in agreement with the analytical predictions made, based on the linear dispersion characteristics in modulated media and the nonlinear interaction in a quadratic medium under phase matching conditions. ; The work was supported by Ministerio de Economia y Competitividad of the Spanish government, and the European Union FEDER through Projects No. FIS2011-29734-C02-01 and -02, and No. MTM2012-36740-C02-02. We acknowledge A. Cebrecos and V. Romero-Garcia for their help in the band structure calculations. E.M.H. acknowledges EU-EMMAG program for his postdoctoral fellowship. ; Hamham, EM.; Jimenez, N.; Picó Vila, R.; Sánchez Morcillo, VJ.; García-Raffi, LM.; Staliünas, K. (2015). Nonlinear self-collimated sound beams in sonic crystals. Physical Review B. 92(5). doi:10.1103/PhysRevB.92.054302 ; S ; 054302 ; 92 ; 5

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 ...

This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.38.001890. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law. ; We predict the existence of evanescent modes with unlocked phases in two-dimensional (2D) dielectric periodic structures. Contrary to what is known for one-dimensional structures, where evanescent fields lock to the host modulation, we show that in 2D systems a new class of evanescent modes exists with an unlocked real part of the wave vector. Hence, beams constructed from such unlocked evanescent waves can exhibit spatial effects. A significant focalization of a beam propagating within the band gap of a flat photonic crystal slab is also shown. The predicted phenomenon is expected to be generic for spatially modulated materials. ; We acknowledge financial support by Spanish Ministerio de Ciencia e Innovacion and European Union FEDER through project FIS2011-29731-C02-01 and -02. V. R. G. is grateful for the contract UPV CEI-01-11. ; Botey, M.; Cheng, Y.; Romero García, V.; Picó Vila, R.; Herrero, R.; Sánchez Morcillo, VJ.; Staliünas, K. (2013). Unlocked evanescent waves in periodic structures. Optics Letters. 38(11):1890-1892. doi:10.1364/OL.38.001890 ; S ; 1890 ; 1892 ; 38 ; 11 ; Yablonovitch, E. (1987). Inhibited Spontaneous Emission in Solid-State Physics and Electronics. Physical Review Letters, 58(20), 2059-2062. doi:10.1103/physrevlett.58.2059 ; 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 ; Notomi, M. (2000). Theory of light propagation in strongly modulated photonic crystals: Refractionlike behavior in the vicinity of the photonic band gap. Physical Review B, 62(16), 10696-10705. ...

[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 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