Circular magnetization processes in CoFeNi electroplated wires

Circular magnetization processes in electroplated wires is an important topic having straight connection with sensor applications of these soft magnetic materials. In present work the longitudinal and circular hysteresis loops were measured and corresponding magnetization processes were studied in Cu(98)Be(2)/Co(16)Fe(20)Ni(64) wires. The longitudinal hysteresis loops, M(z)-H(z), were measured by inductive technique in a frequency range of 10 to 70 Hz. The circular magnetization curves (M(phi)-H(phi)) were measured for frequencies of 50 and 100 kHz in the H(phi) field up to 1500A/m for different values of the axial external field of 0 to 500 A/m. The longitudinal and circular magnetization curves are comparatively analyzed.García Miquel, ÁH.; García Chocano, VM.; Kurlyandskaya, G. (2009). Circular magnetization processes in CoFeNi electroplated wires. Solid State Phenomena. 152:341-344. doi:10.4028/www.scientific.net/SSP.152-153.341S34134415

Optimum control of broadband noise by arrays of cylindrical units made of a recycled material

[EN] We report acoustic barriers that are designed to attenuate efficiently broadband noise. The barriers are structures consisting of only three layers of cylindrical units containing rubber crumb, a sound absorbing material obtained from recycling used tires. An optimization algorithm is developed to obtain the material distribution and dimensions of the building units giving the best attenuation properties for traffic noise, which is here chosen as an example in which the design procedure is applied. A good agreement is found between predictions and measurements for a 3 m height barrier that has been characterized in a transmission room. (C) 2012 Elsevier Ltd. All rights reserved.Work supported by the Spanish MICINN under Contracts TEC2010-19751 and CSD2008-00066 (CONSOLIDER program). We acknowledge F. Simon for data acquisition, D. Torrent for useful discussions and L.-W. Cai for the critical reading of manuscript.García Chocano, VM.; Sánchez-Dehesa Moreno-Cid, J. (2013). Optimum control of broadband noise by arrays of cylindrical units made of a recycled material. Applied Acoustics. 74(1):58-62. https://doi.org/10.106/j.apacoust.2012.06.08S586274

In-plane omnidirectional magnetic field sensor based on Giant Magneto Impedance (GMI)

[EN] In this work the design and characterization of an omnidirectional in-plane magnetic field sensor are presented. The sensor is based on the Giant Magneto Impedance (GMI) effect in glass-coated amorphous microwires of composition (Fe6Co94)(72.5)Si12.5B15. For the first time, a circular loop made with a microwire is used for giving omnidirectional response. In order to estimate the GMI response of the circular loop we have used a theoretical model of GMI, determining the GMI response as the sum of longitudinal sections with different angles of incidence. As a consequence of the circular loop, the GMI ratio of the sensor is reduced to 15% instead of 100% for the axial GMI response of a microwire. The sensor response has been experimentally verified and the GMI response of the circular loop has been studied as function of the magnetic field, driven current, and frequency. First, we have measured the GMI response of a longitudinal microwire for different angles of incidence, covering the full range between the tangential and perpendicular directions to the microwire axis. Then, using these results, we have experimentally verified the decomposition of a microwire with circular shape as longitudinal segments with different angles of incidence. Finally, we have designed a signal conditioning circuit for the omnidirectional magnetic field sensor. The response of the sensor has been studied as a function of the amplitude of the incident magnetic field. (C) 2017 Elsevier B.V. All rights reserved.Hector Garcia-Miquel is grateful to the Universitat Politecnica de Valencia for the concession of a sabbatical year to have a research stay at the Cavendish Laboratory, and also want to express his gratitude to the Govern de la Generalitat Valenciana for financial support for this research stay at the Cavendish laboratory.S24925544

Anomalous sound absorption in lattices of cylindrical perforated shells

This work reports the enhancement of sound absorption by sonic crystals slabs made of cylindrical perforated shells. These building units, with perforations of millimeter size, show small losses and cannot explain the strong absorption observed at some specific frequencies when the slabs consist of just a few number of rows. It is found that this phenomenon is due to a resonant Wood anomaly which occurs when the incident wave couples with a leaky guided mode supported by the slab. This effect results in an enhancement of the absorption, since the energy transferred to the guided mode travels within the slab, along a direction perpendicular to the incident one. Multiple scattering and finite element simulations give support to the proposed behavior, the transmittance results being in good agreement with experimental data previously reported. (C) 2015 AIP Publishing LLC.This work was partially supported by the USA Office of Naval Research under Grant No. N000141210216 and the Spanish MINECO (Contract No. TEC2010-19751).García Chocano, VM.; Sánchez-Dehesa Moreno-Cid, J. (2015). Anomalous sound absorption in lattices of cylindrical perforated shells. Applied Physics Letters. 106(12):124104-1-124104-4. https://doi.org/10.1063/1.4916509S124104-1124104-410612Sánchez-Pérez, J. V., Caballero, D., Mártinez-Sala, R., Rubio, C., Sánchez-Dehesa, J., Meseguer, F., … Gálvez, F. (1998). Sound Attenuation by a Two-Dimensional Array of Rigid Cylinders. Physical Review Letters, 80(24), 5325-5328. doi:10.1103/physrevlett.80.5325Rubio, C., Caballero, D., Sanchez-Perez, J. V., Martinez-Sala, R., Sanchez-Dehesa, J., Meseguer, F., & Cervera, F. (1999). The existence of full gaps and deaf bands in two-dimensional sonic crystals. Journal of Lightwave Technology, 17(11), 2202-2207. doi:10.1109/50.803012Sanchis, L., Håkansson, A., Cervera, F., & Sánchez-Dehesa, J. (2003). Acoustic interferometers based on two-dimensional arrays of rigid cylinders in air. Physical Review B, 67(3). doi:10.1103/physrevb.67.035422Torrent, D., Håkansson, A., Cervera, F., & Sánchez-Dehesa, J. (2006). Homogenization of Two-Dimensional Clusters of Rigid Rods in Air. Physical Review Letters, 96(20). doi:10.1103/physrevlett.96.204302Sánchez-Dehesa, J., Garcia-Chocano, V. M., Torrent, D., Cervera, F., Cabrera, S., & Simon, F. (2011). Noise control by sonic crystal barriers made of recycled materials. The Journal of the Acoustical Society of America, 129(3), 1173-1183. doi:10.1121/1.3531815García-Chocano, V. M., Cabrera, S., & Sánchez-Dehesa, J. (2012). Broadband sound absorption by lattices of microperforated cylindrical shells. Applied Physics Letters, 101(18), 184101. doi:10.1063/1.4764560Umnova, O., Attenborough, K., & Linton, C. M. (2006). Effects of porous covering on sound attenuation by periodic arrays of cylinders. The Journal of the Acoustical Society of America, 119(1), 278-284. doi:10.1121/1.2133715Christensen, J., Romero-García, V., Picó, R., Cebrecos, A., de Abajo, F. J. G., Mortensen, N. A., … Sánchez-Morcillo, V. J. (2014). Extraordinary absorption of sound in porous lamella-crystals. Scientific Reports, 4(1). doi:10.1038/srep04674Van der Aa, B., & Forssén, J. (2014). Scattering by an array of perforated cylinders with a porous core. The Journal of the Acoustical Society of America, 136(5), 2370-2380. doi:10.1121/1.4896566Romero-García, V., Sánchez-Pérez, J. V., & Garcia-Raffi, L. M. (2011). Tunable wideband bandstop acoustic filter based on two-dimensional multiphysical phenomena periodic systems. Journal of Applied Physics, 110(1), 014904. doi:10.1063/1.3599886Maa, D.-Y. (1998). Potential of microperforated panel absorber. The Journal of the Acoustical Society of America, 104(5), 2861-2866. doi:10.1121/1.423870Wood, R. W. (1902). XLII. On a remarkable case of uneven distribution of light in a diffraction grating spectrum. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 4(21), 396-402. doi:10.1080/14786440209462857Rayleigh, L. (1907). On the Dynamical Theory of Gratings. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 79(532), 399-416. doi:10.1098/rspa.1907.0051Fano, U. (1941). The Theory of Anomalous Diffraction Gratings and of Quasi-Stationary Waves on Metallic Surfaces (Sommerfeld’s Waves). Journal of the Optical Society of America, 31(3), 213. doi:10.1364/josa.31.000213Maurel, A., Felix, S., Mercier, J.-F., Ourir, A., & Djeffal, Z. E. (2014). Wood’s anomalies for arrays of dielectric scatterers. Journal of the European Optical Society: Rapid Publications, 9. doi:10.2971/jeos.2014.14001Ingard, U. (1953). On the Theory and Design of Acoustic Resonators. The Journal of the Acoustical Society of America, 25(6), 1037-1061. doi:10.1121/1.1907235Allam, S., & Åbom, M. (2011). A New Type of Muffler Based on Microperforated Tubes. Journal of Vibration and Acoustics, 133(3). doi:10.1115/1.400295

Enhanced inertia from lossy effective fluids using multi-scale sonic crystals

n this work, a recent theoretically predicted phenomenon of enhanced permittivity with electromagnetic waves using lossy materials is investigated for the analogous case of mass density and acoustic waves, which represents inertial enhancement. Starting from fundamental relationships for the homogenized quasi-static effective density of a fluid host with fluid inclusions, theoretical expressions are developed for the conditions on the real and imaginary parts of the constitutive fluids to have inertial enhancement, which are verified with numerical simulations. Realizable structures are designed to demonstrate this phenomenon using multi-scale sonic crystals, which are fabricated using a 3D printer and tested in an acoustic impedance tube, yielding good agreement with the theoretical predictions and demonstrating enhanced inertia.This work was supported by the U.S. Office of Naval Research (Award N000141210216).Guild, M.; García Chocano, VM.; Kan, W.; Sánchez-Dehesa Moreno-Cid, J. (2014). Enhanced inertia from lossy effective fluids using multi-scale sonic crystals. AIP Advances. 4(12). https://doi.org/10.1063/1.4901880S412Dowling, J. P. (1992). Sonic band structure in fluids with periodic density variations. The Journal of the Acoustical Society of America, 91(5), 2539-2543. doi:10.1121/1.402990Sigalas, M. M., & Economou, E. N. (1992). Elastic and acoustic wave band structure. Journal of Sound and Vibration, 158(2), 377-382. doi:10.1016/0022-460x(92)90059-7Kushwaha, 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.71.2022Sánchez-Pérez, J. V., Caballero, D., Mártinez-Sala, R., Rubio, C., Sánchez-Dehesa, J., Meseguer, F., … Gálvez, F. (1998). Sound Attenuation by a Two-Dimensional Array of Rigid Cylinders. Physical Review Letters, 80(24), 5325-5328. doi:10.1103/physrevlett.80.5325Krokhin, A. A., Arriaga, J., & Gumen, L. N. (2003). Speed of Sound in Periodic Elastic Composites. Physical Review Letters, 91(26). doi:10.1103/physrevlett.91.264302Torrent, D., Håkansson, A., Cervera, F., & Sánchez-Dehesa, J. (2006). Homogenization of Two-Dimensional Clusters of Rigid Rods in Air. Physical Review Letters, 96(20). doi:10.1103/physrevlett.96.204302Torrent, D., & Sánchez-Dehesa, J. (2008). Anisotropic mass density by two-dimensional acoustic metamaterials. New Journal of Physics, 10(2), 023004. doi:10.1088/1367-2630/10/2/023004Zigoneanu, L., Popa, B.-I., Starr, A. F., & Cummer, S. A. (2011). Design and measurements of a broadband two-dimensional acoustic metamaterial with anisotropic effective mass density. Journal of Applied Physics, 109(5), 054906. doi:10.1063/1.3552990Torrent, D., & Sánchez-Dehesa, J. (2008). Acoustic cloaking in two dimensions: a feasible approach. New Journal of Physics, 10(6), 063015. doi:10.1088/1367-2630/10/6/063015Sanchis, L., García-Chocano, V. M., Llopis-Pontiveros, R., Climente, A., Martínez-Pastor, J., Cervera, F., & Sánchez-Dehesa, J. (2013). Three-Dimensional Axisymmetric Cloak Based on the Cancellation of Acoustic Scattering from a Sphere. Physical Review Letters, 110(12). doi:10.1103/physrevlett.110.124301Guild, M. D., Alù, A., & Haberman, M. R. (2014). Cloaking of an acoustic sensor using scattering cancellation. Applied Physics Letters, 105(2), 023510. doi:10.1063/1.4890614García-Chocano, V. M., Cabrera, S., & Sánchez-Dehesa, J. (2012). Broadband sound absorption by lattices of microperforated cylindrical shells. Applied Physics Letters, 101(18), 184101. doi:10.1063/1.4764560Christensen, J., Romero-García, V., Picó, R., Cebrecos, A., de Abajo, F. J. G., Mortensen, N. A., … Sánchez-Morcillo, V. J. (2014). Extraordinary absorption of sound in porous lamella-crystals. Scientific Reports, 4(1). doi:10.1038/srep04674Frenzel, T., David Brehm, J., Bückmann, T., Schittny, R., Kadic, M., & Wegener, M. (2013). Three-dimensional labyrinthine acoustic metamaterials. Applied Physics Letters, 103(6), 061907. doi:10.1063/1.4817934Climente, A., Torrent, D., & Sánchez-Dehesa, J. (2012). Omnidirectional broadband acoustic absorber based on metamaterials. Applied Physics Letters, 100(14), 144103. doi:10.1063/1.3701611Naify, C. J., Chang, C.-M., McKnight, G., & Nutt, S. (2010). Transmission loss and dynamic response of membrane-type locally resonant acoustic metamaterials. Journal of Applied Physics, 108(11), 114905. doi:10.1063/1.3514082Yang, Z., Dai, H. M., Chan, N. H., Ma, G. C., & Sheng, P. (2010). Acoustic metamaterial panels for sound attenuation in the 50–1000 Hz regime. Applied Physics Letters, 96(4), 041906. doi:10.1063/1.3299007Hussein, M. I., & Frazier, M. J. (2013). Metadamping: An emergent phenomenon in dissipative metamaterials. Journal of Sound and Vibration, 332(20), 4767-4774. doi:10.1016/j.jsv.2013.04.041Reyes-Ayona, E., Torrent, D., & Sánchez-Dehesa, J. (2012). Homogenization theory for periodic distributions of elastic cylinders embedded in a viscous fluid. The Journal of the Acoustical Society of America, 132(4), 2896-2908. doi:10.1121/1.4744933Carbonell, J., Cervera, F., Sánchez-Dehesa, J., Arriaga, J., Gumen, L., & Krokhin, A. (2010). Homogenization of two-dimensional anisotropic dissipative photonic crystal. Applied Physics Letters, 97(23), 231122. doi:10.1063/1.3526381Carbonell, J., Sánchez-Dehesa, J., Arriaga, J., Gumen, L., & Krokhin, A. (2011). Electromagnetic absorption in anisotropic photonic crystal of alumina cylinders. Metamaterials, 5(2-3), 74-80. doi:10.1016/j.metmat.2011.03.001Godin, Y. A. (2013). Effective complex permittivity tensor of a periodic array of cylinders. Journal of Mathematical Physics, 54(5), 053505. doi:10.1063/1.4803490Torrent, D., Sánchez-Dehesa, J., & Cervera, F. (2007). Evidence of two-dimensional magic clusters in the scattering of sound. Physical Review B, 75(24). doi:10.1103/physrevb.75.241404Martin, P. A., Maurel, A., & Parnell, W. J. (2010). Estimating the dynamic effective mass density of random composites. The Journal of the Acoustical Society of America, 128(2), 571-577. doi:10.1121/1.3458849Erokhin, S. G., Lisyansky, A. A., Merzlikin, A. M., Vinogradov, A. P., & Granovsky, A. B. (2008). Photonic crystals built on contrast in attenuation. Physical Review B, 77(23). doi:10.1103/physrevb.77.233102Song, B. H., & Bolton, J. S. (2000). A transfer-matrix approach for estimating the characteristic impedance and wave numbers of limp and rigid porous materials. The Journal of the Acoustical Society of America, 107(3), 1131-1152. doi:10.1121/1.42840

Broadband Acoustic Cloaking within an Arbitrary Hard Cavity

This paper reports the design, fabrication, and experimental validation of a broadband acoustic cloak for the concealing of three-dimensional (3D) objects placed inside an open cavity with arbitrary surfaces. This 3D cavity cloak represents the acoustic analogue of a magician hat, giving the illusion that a cavity with an object is empty. Transformation acoustics is employed to design this cavity cloak, whose parameters represent an anisotropic acoustic metamaterial. A practical realization is made of 14 perforated layers fabricated by drilling subwavelength holes on 1-mm-thick Plexiglas plates. In both simulation and experimental results, concealing of the reference object by the device is shown for airborne sound with wavelengths between 10 cm and 17 cm.W. W. K. and V. M. G.-C. contributed equally to this work. W. W. K., B. L., and J. C. C. acknowledge support by the National Basic Research Program of China (973 Program) (Grants No. 2010CB327803 and No. 2012CB921504), National Natural Science Foundation of China (Grants No. 11174138, No. 11174139, No. 11222442, No. 81127901, and No. 11274168), NCET-12-0254, a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions and a program supported by China Scholarship Council (CSC). W. W. K. was also supported by the program for outstanding Ph.D. students of Nanjing University. V. M. G.-C, F. C., and J. S.-D. acknowledge financial support from the U.S. Office of Naval Research under Grant No. N00014-12-1-0216 and from the Spanish Ministerio de Economia y Competitividad under Grant No. TEC2010-19751.Kan, W.; Garcia Chocano, VM.; Cervera Moreno, FS.; Liang, B.; Zou, X.; Yin, L.; Cheng, J.... (2015). Broadband Acoustic Cloaking within an Arbitrary Hard Cavity. Physical Review Applied. 3(6):064019-1-064019-9. doi:10.1103/PhysRevApplied.3.064019S064019-1064019-93

DC and AC linear magnetic field sensor based on glass coated amor- phous microwires with Giant Magnetoimpedance

Giant Magnetoimpedance (GMI) effect has been studied in amorphous glass-coated microwires of composition (Fe6Co94)(72.5)Si12.5B15. The impedance of a 1.5 cm length sample has been characterized by using constant AC currents in the range of 400 mu A-4 mA at frequencies from 7 to 15 MHz and DC magnetic fields from -900 to 900 A/m. Double peak responses have been obtained, showing GMI ratios up to 107%. A linear magnetic field sensor for DC and AC field has been designed, using two microwires connected in series with a magnetic bias of 400 A/m with opposite direction in each microwire in order to obtain a linear response from +/- 70 (A/m)(rms) for AC magnetic field, and +/- 100 A/m for DC magnetic field. A closed loop feedback circuit has been implemented to extend the linear range to +/- 1 kA/m for DC magnetic field. (C) 2014 Elsevier B.V. All rights reserved.Garcia Chocano, VM.; García Miquel, ÁH. (2015). DC and AC linear magnetic field sensor based on glass coated amor- phous microwires with Giant Magnetoimpedance. Journal of Magnetism and Magnetic Materials. 378:485-492. doi:10.1016/j.jmmm.2014.11.017S48549237

New devices for noise control and acoustic cloaking

[EN] The aim of this work is to design new acoustic devices based on arrangements of scattering units. First, the use of sonic crystals as noise barriers for traffic noise control is comprehensively analyzed. Due to the limitations of the conventional structures based on rigid scatterers, the inclusion of absorbing elements is proposed. Two different types of absorbers are here considered: porous materials and microperforated plates. In the first case, the attenuation characteristics of barriers made with cylinders containing rubber crumb is analyzed. The second proposal is based on the construction of cylindrical microperforated shells. Analytical approaches modelling the behavior of the barriers have been developed in both cases. These models show a satisfactory agreement with the corresponding experimental realizations. Finally, it is performed an optimization process in order to obtain efficient sound barriers intended to attenuate traffic noise. Another application considered in this work is the construction of cloaks to render objects acoustically invisible. In particular, cloaks made with rigid inclusions are designed to operate with airborne sound. The first proposal consists of a cloak that utilizes the temperature of the background to control the properties of the effective medium. In addition, two and three-dimensional cloaks have been developed through the scattering cancellation technique. These devices have been designed by means of an optimization procedure and their performance has been experimentally demonstrated.[ES] El objetivo de este trabajo es el diseño de nuevos dispositivos acústicos basados en disposiciones de centros de dispersión. En primer lugar, el uso de cristales sónicos como barreras acústicas para el control de ruido de tráfico es analizado en detalle. Debido a las limitaciones que presentan las estructuras convencionales basadas en centros de dispersión rígidos, se propone la inclusión de elementos absorbentes en los mismos. Se han considerado dos tipos distintos de absorbente: materiales porosos y placas microperforadas. En el primer caso se analizan las propiedades atenuadoras de barreras formadas por cilindros que contienen granza de caucho. La segunda solución se basa en la construcción de coronas microperforadas. En ambos casos se han desarrollado modelos analíticos que permiten determinar el comportamiento de las barreras. Dichos modelos muestran un acuerdo satisfactorio con las correspondientes realizaciones experimentales. Finalmente se ha realizado un proceso de optimización con objeto de obtener barreras eficientes para la atenuación de ruido de tráfico. Otra aplicación considerada en este trabajo es el desarrollo de dispositivos de invisibilidad acústica. Concretamente se pretenden diseñar mantos constituidos con elementos rígidos para ondas acústicas en aire. La primera propuesta consiste en un manto que utiliza la temperatura del medio externo para controlar sus propiedades efectivas. Además se han desarrollado mantos en dos y tres dimensiones a través de la técnica de cancelación de la dispersión. Los diseños han sido realizados por medio de un proceso de optimización y su funcionamiento ha sido demostrado experimentalmente.[CA] L'objectiu d'aquest treball és el disseny de nous dispositius acústics basats en disposicions de centres de dispersió. En primer lloc, l'ús de vidres sònics com barreres acústiques per al control de soroll de trànsit és analitzat en detall. A causa de les limitacions que presenten les estructures convencionals basades en centres de dispersió rígids, es proposa la inclusió d'elements absorbents en els mateixos. S'han considerat dos tipus diferents de absorbent: materials porosos i plaques microperforades. En el primer cas s'analitzen les propietats atenuadores de barreres formades per cilindres que contenen gransa de cautxú. La segona solució es basa en la construcció de corones microperforades. En tots dos casos s'han desenvolupat models analítics que permeten determinar el comportament de les barreres. Aquests models mostren un acord satisfactori amb les corresponents realitzacions experimentals. Finalment s'ha realitzat un procés d'optimització per tal d'obtenir barreres eficients per l'atenuació de soroll de trànsit. Una altra aplicació considerada en aquest treball és el desenvolupament de dispositius d'invisibilitat acústica. Concretament es pretenen dissenyar mantells constituïts amb elements rígids per ones acústiques en aire. La primera proposta consisteix en un mantell que utilitza la temperatura del medi extern per controlar les seves propietats efectives. A més s'han desenvolupat mantells en dues i tres dimensions a través de la tècnica de cancel·lació de la dispersió. Els dissenys han estat realitzats per mitjà d'un procés d'optimització i el seu funcionament ha estat demostrat experimentalment.García Chocano, VM. (2015). New devices for noise control and acoustic cloaking [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/53026TESISPremios Extraordinarios de tesis doctorale

Broadband sound absorption by lattices of microperforated cylindrical shells

Absorption of broadband noise by sonic crystals consisting of microperforated cylindrical shells is proposed and experimentally demonstrated. The theoretical study has been performed in the framework of multiple scattering method, where a model for the T matrix of the microperforated shells has been developed. It has been predicted an extraordinary broadband sound absorption that is explained in terms of the multiple scattering phenomena occurring at the surfaces of the absorptive units-the microperforated panels. Our proposal has been supported by experiments performed on a structure consisting of 3 rows of cylindrical shells 3 meters height. © 2012 American Institute of Physics.This work has been partially supported by the USA Office of Naval Research. We acknowledge D. Torrent for useful discussions. We thank A. Climente, R. Gracia-Salgado, E. Reyes-Ayona and F. Cervera for their technical help in building the barrier.Garcia Chocano, VM.; Cabrera García, S.; Sánchez-Dehesa Moreno-Cid, J. (2012). Broadband sound absorption by lattices of microperforated cylindrical shells. Applied Physics Letters. 101:1-4. doi:10.1063/1.4764560S1410

Reduced acoustic cloaks based on temperature gradients

This letter presents the design of a reduced acoustic cloak that uses a temperature gradient in order to obtain sound speeds larger than in air. The cloak consists of a circular acoustic crystal made of ten concentric layers of rigid cylinders whose surfaces are heated or cooled in order to get the temperature gradient needed for cloaking behavior. The total pressure field produced by the scattering of sound waves impinging this complex structure is computed and it is shown how acoustic waves are bent in a way similar to that predicted for perfect cloaking devices. © 2012 American Institute of Physics.Work partially supported by the Spanish MICINN under Grant Nos. TEC2010-19751 and CSD2008-66 (CONSOLIDER program) and by the U.S. Office of Naval Research. J.S.-D. acknowledges useful discussions with L.-W. Cai.García Chocano, VM.; Torrent Martí, D.; Sánchez-Dehesa Moreno-Cid, J. (2012). Reduced acoustic cloaks based on temperature gradients. 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