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[EN] Acoustic vortex beams have great potential for contactless particle manipulation and torque-based biomedical applications. However, when focusing acoustic waves through aberration layers such as the human skull at ultrasonic frequencies results in strong phase aberrations which prevent the generation of sharp acoustic images. In the case of a wavefront containing phase dislocations, skull aberrations inhibit the focusing of acoustic vortex beams inside the cranial cavity. In this work, we demonstrate that phase-conjugated acoustic holograms can encode time-reversed fields simultaneously allowing the compensation of the aberrations of the skull and the generation of a focused vortex inside an ex-vivo human skull. The method is applied for single-element geometrically focused sources and results in a very simple and compact ultrasonic system. This work will pave the road to design low-cost particle trapping applications, clot manipulation, torque exertion in the brain and acoustic-radiation-force based biomedical applications. ; This research was supported by the Spanish Ministry of Science, Innovation, and Universities through "Juan de la Cierva-Incorporacion" Grants No. IJC2018-037897-I and No. PID2019-111436RB-C22, by the Agencia Valenciana de la Innovacio through Grants No. INNVAL10/19/016, No. INNVA1/2020/92, and No. INNCON/2020/009, and by the Generalitat Valenciana through Grant No. ACIF/2017/045. The action was cofinanced by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana, Grant No. IDIFEDER/2018/022. ; Jiménez-Gambín, S.; Jimenez, N.; Camarena Femenia, F. (2020). Transcranial focusing of ultrasonic vortices by acoustic holograms. Physical Review Applied. 14(5):1-10. https://doi.org/10.1103/PhysRevApplied.14.054070 ; S ; 1 ; 10 ; 14 ; 5 ; Elias, W. J., Huss, D., Voss, T., Loomba, J., Khaled, M., Zadicario, E., … Wintermark, M. (2013). A Pilot Study of Focused Ultrasound Thalamotomy for Essential Tremor. New England Journal ...

[EN] In this work we numerically and experimentally study the performance of large-volume hyperthermia induced by acoustic holographic-modulated high-intensity focused ultrasound (AHmHIFU) in gelatin phantoms. Excellent agreement was found between thermal simulations of the AHmHIFU system and temperature maps characterized with Proton Resonance Frequency Shift MR-thermometry at 1.5 T. ROIs inside which experimental temperature elevation was greater than 4 degrees were 11 mm by 16 mm and 7 mm by 30 mm with and without the holographic lens, respectively. Most importantly, standard deviation inside these ROIs were equal to 12% and 40% of the maximum temperature with and without the lens. This demonstrates that a wider and more uniform heated region can be generated using the holographic lens, showing the capabilities of acoustic holograms to be used as a low-cost alternative for large-volume hyperthermia treatments ; This research has been supported by the Spanish Ministry of Science, Innovation and Universities (MICINN) through grants IJC2018-037897-I, FPU19/00601 and PID2019-111436RBC22, by the Agencia Valenciana de la Innovaci o through grants INNCON/2021/8 and INNVA1/2020/92, by Generalitat Valenciana through grant AICO/2020/268. Action co-financed by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014-2020 (IDIFEDER/2018/022) and (IDIFEDER/2021/004). ; Andrés, D.; Vappou, J.; Jimenez, N.; Camarena Femenia, F. (2021). Ultrasonic Holograms to Enhance Hyperthermia Volumes. IEEE. 1-4. https://doi.org/10.1109/IUS52206.2021.9593807 ; S ; 1 ; 4

[EN] We present a novel method of elastography based on acoustic vortices to transfer angular momentum to tissue in addition to linear momentum. Focused vortex beams can push and twist tissue, and the rotation direction of the applied torque can be dynamically controlled by the modulation of the topological charge of the vortex. The technique results in a robust excitation of shear waves with quasi-omnidirectional radiation pattern and arbitrary waveform, which may have a great impact in imaging performance for elastography. ; This research has been supported by the Spanish Ministry of Science, Innovation and Universities through grants Juan de la Cierva - Incorporacion¿ IJC2018-037897-I and PID2019-111436RBC22, and by the Agencia Valenciana de la Innovacio through grants INNVA1/2020/92 and INNCON/2020/009. Action cofinanced by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014-2020 (IDIFEDER/2018/022). ; Jimenez, N.; Benlloch Baviera, JM.; Camarena Femenia, F. (2020). A new elastographic technique using acoustic vortices. IEEE. 1-4. https://doi.org/10.1109/IUS46767.2020.9251417 ; S ; 1 ; 4

[EN] Single-element focused ultrasound devices have demonstrated its ability to non-invasively open the Blood Brain Barrier. However, skull irregularities and absorption produce strong aberrations in the ultrasound focus. Recently, 3D-printed acoustic holograms were used to compensate aberrations and to produce a sharp focus. In addition, using this technology the geometry of the ultrasonic focus can be matched to the shape of the brain structure of interest. In this work, we experimentally and numerically report 3D-printed acoustic holograms for bilateral focusing through an ex-vivo human skull. Using holograms, we target different cerebral nuclei and the ultrasonic focuses are adapted to the target volumes, minimizing the acoustic field outside. Simultaneously, skull aberrations are corrected using phased-conjugation methods. The holographic surfaces were manufactured for a 100-mm aperture and 140-mm focal focused transducer at 500 kHz to focus through an ex-vivo human skull. Numerical and experimental results agree targeting several deep-brain nuclei: left-and-right putamen, caudate nuclei, and hippocampi, showing the potential of this low-cost technology to optimize BBBO or neuromodulation treatments. ; This research has been supported by the Spanish Ministry of Science, Innovation and Universities through grant Juan de la Cierva - Incorporacion (IJC2018-037897-I) and PID2019-111436RBC22, by the Agencia Valenciana de la Innovacio through grants INNVAL10/19/016 and INNCON/2020/009. Action cofinanced by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014-2020 (IDIFEDER/2018/022). ; Andrés, D.; Jiménez-Gambín, S.; Jimenez, N.; Camarena Femenia, F. (2020). Multifocal acoustic holograms for deep-brain neuromodulation and BBB opening. IEEE. 1-3. https://doi.org/10.1109/IUS46767.2020.9251769 ; S ; 1 ; 3

[EN] In solids, the constitutive relations between strain and stress lead in most cases to a dominant quadratic nonlinear response. However, there exist some solid materials that exhibit negative quadratic nonlinearity, as occurs in common glasses as borosilicate glass or fused silica. In this work, we present the dynamical response of a phononic crystal with modulated nonlinearity. In particular, we analyze a 1D phononic crystal composed of layers of alternating properties with quadratic nonlinearity, each layer presenting an alternating (positive and negative) nonlinear parameter value. First, we observe that the common distortion produced by the nonlinear steepening can be almost compensated. Thus, the propagation through the phononic crystal can be extended far beyond the shock formation distance, avoiding common saturation effects. Second, we show that in the absence of dispersion the artificial material exhibits weakly-cubic nonlinear effective properties. The structure presented here can be employed to avoid nonlinear distortion in waveguides, or to design metamaterials with effective cubic nonlinear properties using quadratic nonlinear building blocks. ; The work was supported by Spanish Ministry of Economy and Innovation (MINECO) and European Union FEDER through project FIS2015-65998-C2-2. NJ acknowledge financial support from Generalitat Valenciana through grant APOSTD-2017-042 ; Jimenez, N.; Tournat, V.; Romero García, V.; Sánchez Morcillo, VJ. (2018). Modulated-nonlinearity in phononic crystals: From extremely linear to effective cubic nonlinear media. Proceedings of Meetings on Acoustics. 34(1):1-5. https://doi.org/10.1121/2.0000908 ; S ; 1 ; 5 ; 34 ; 1

[EN] We report a method to monitor the setting process of bone-graft substitutes (calcium sulfate) using ultrasonic backscattering techniques. Analyzing the backscattered fields using a pulse-echo technique, we show that it is possible to dynamically describe the acoustic properties of the material which are linked to its setting state. Several experiments were performed to control the setting process of calcium sulfate using a 3.5-MHz transducer. The variation of the apparent integrated backscatter (AIB) with time during the setting process is analyzed and compared with measurements of the speed of sound (SOS) and temperature of the sample. The correlation of SOS and AIB allows us to clearly identify two different states of the samples, liquid and solid, in addition to the transition period. Results show that using backscattering analysis, the setting state of the material can be estimated with a threshold of 15 dB. This ultrasonic technique is indeed the first step to develop real-time monitoring systems for time-varying complex media as those present in bone regeneration for dental implantology applications. ; This work was supported in part by Universitat Politecnica de Valencia (UPV) and Fundacion para el Fomento de la Investigacion Sanitaria y Biomedica de la Comunitat Valenciana (FISABIO) through the project OSEODENT under Grant POLISABIO 2018, in part by the European Union, in part by Generalitat Valenciana through the European Regional Development Fund Program under Grant IDIFEDER/2018/022, and in part by the Agencia Valenciana de la Innovacio through the Unitat Cientifica d'Innovacio Empresarial under Grant INNCON00/18/9. The work of N. Jimenez was supported by Generalitat Valenciana under Grant APOSTD/2017/042. ; Rodríguez-Sendra, J.; Jimenez, N.; Picó Vila, R.; Faus, J.; Camarena Femenia, F. (2019). Monitoring the setting of calcium sulfate bone-graft substitute using ultrasonic backscattering. IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control. 66(10):1658-1666. ...

[EN] We report the optimal focusing of acoustic vortex beams by using flat lenses based on a Fresnelspiral diffraction grating. The flat lenses are designed by spiral-shaped Fresnel zone plates composed of one or several arms. The constructive and destructive interferences of the diffracted waves by the spiral grating result in sharp acoustic vortex beams, following the focal laws obtained in analogy with the Fresnel zone plate lenses. In addition, we show that the number of arms determines the topological charge of the vortex, allowing the precise manipulation of the acoustic wave field by flat lenses. The experimental results in the ultrasonic regime show excellent agreement with the theory and full-wave numerical simulations. A comparison with beam focusing by Archimedean spirals also showing vortex focusing is given. The results of this work may have potential applications for particle trapping, ultrasound therapy, imaging, or underwater acoustic transmitters. ; This work was supported by the Spanish Ministry of Economy and Innovation (MINECO) and European Union FEDER through Project Nos. FIS2015-65998-C2-1 and FIS2015-65998-C2-2. N.J. acknowledges financial support from Generalitat Valenciana through Grant No. APOSTD-2017-042. ; Jimenez, N.; Romero García, V.; García-Raffi, LM.; Camarena Femenia, F.; Staliunas, K. (2018). Sharp acoustic vortex focusing by Fresnel-spiral zone plates. Applied Physics Letters. 112(20):204101-1-204101-5. https://doi.org/10.1063/1.5029424 ; S ; 204101-1 ; 204101-5 ; 112 ; 20 ; J. Nye and M. Berry ,Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences(The Royal Society, 1974), Vol.336, pp. 165–190. ; Grier, D. G. (2003). A revolution in optical manipulation. Nature, 424(6950), 810-816. doi:10.1038/nature01935 ; Volke-Sepúlveda, K., Santillán, A. O., & Boullosa, R. R. (2008). Transfer of Angular Momentum to Matter from Acoustical Vortices in Free Space. Physical Review Letters, 100(2). doi:10.1103/physrevlett.100.024302 ; Anhäuser, A., ...

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, ...

543 554 17 5 ; Senia ; The propagation of intense acoustic waves in a one-dimensional phononic crystal is studied. The medium consists in a structured fluid, formed by a periodic array of fluid layers with alternating linear acoustic properties and quadratic nonlinearity coefficient. The spacing between layers is of the order of the wavelength, therefore Bragg effects such as band gaps appear. We show that the interplay between strong dispersion and nonlinearity leads to new scenarios of wave propagation. The classical waveform distortion process typical of intense acoustic waves in homogeneous media can be strongly altered when nonlinearly generated harmonics lie inside or close to band gaps. This allows the possibility of engineer a medium in order to get a particular waveform. Examples of this include the design of media with effective (e.g., cubic) nonlinearities, or extremely linear media (where distortion can be canceled). The presented ideas open a way towards the control of acoustic wave propagation in nonlinear regime. Work supported by Spanish Ministry of Economy and Innovation and European Union FEDER through projects FIS2011-29731-C02-02 and MTM2012-36740-C02-02. AM and LMGR acknowledge Generalitat Valenciana under grants Santiago Grisolia program (grant 2012/029) and BEST2015/279 respectively. RP and VJSM acknowledge the Spanish Ministry of Economy and Innovation under grants CAS14/00232 and PRX14/00705 respectively. Jimenez, N.; Mehrem, A.; Picó Vila, R.; García-Raffi, LM.; Sánchez Morcillo, VJ. (2016). Nonlinear propagation and control of acoustic waves in phononic superlattices. Comptes Rendus Physique. 17(5):543-554. doi:10.1016/j.crhy.2016.02.004

The propagation of intense acoustic waves in a one-dimensional phononic crystal is studied. The medium consists in a structured fluid, formed by a periodic array of fluid layers with alternating linear acoustic properties and quadratic nonlinearity coefficient. The spacing between layers is of the order of the wavelength, therefore Bragg effects such as band gaps appear. We show that the interplay between strong dispersion and nonlinearity leads to new scenarios of wave propagation. The classical waveform distortion process typical of intense acoustic waves in homogeneous media can be strongly altered when nonlinearly generated harmonics lie inside or close to band gaps. This allows the possibility of engineer a medium in order to get a particular waveform. Examples of this include the design of media with effective (e.g., cubic) nonlinearities, or extremely linear media (where distortion can be canceled). The presented ideas open a way towards the control of acoustic wave propagation in nonlinear regime. ; Work supported by Spanish Ministry of Economy and Innovation and European Union FEDER through projects FIS2011-29731-C02-02 and MTM2012-36740-C02-02. AM and LMGR acknowledge Generalitat Valenciana under grants Santiago Grisolia program (grant 2012/029) and BEST2015/279 respectively. RP and VJSM acknowledge the Spanish Ministry of Economy and Innovation under grants CAS14/00232 and PRX14/00705 respectively. ; Jimenez, N.; Mehrem, A.; Picó Vila, R.; García-Raffi, LM.; Sánchez Morcillo, VJ. (2016). Nonlinear propagation and control of acoustic waves in phononic superlattices. Comptes Rendus Physique. 17(5):543-554. https://doi.org/10.1016/j.crhy.2016.02.004 ; S ; 543 ; 554 ; 17 ; 5

[EN] We report a method to locally assess the complex shear modulus of a viscoelastic medium. The proposed approach is based on the application of a magnetic force to a millimeter-sized steel sphere embedded in the medium and the subsequent monitoring of its dynamical response. A coil is used to create a magnetic field inducing the displacement of the sphere located inside a gelatin phantom. Then, a phased-array system using 3 MHz ultrasound probe operating in pulse-echo mode is used to track the displacement of the sphere. Experiments were conducted on several samples and repeated as a function of phantom temperature. The dynamic response of the sphere measured experimentally is in good agreement with Kelvin¿Voigt theory. Since the magnetic force is not affected by weak diamagnetic media, our proposal results in an accurate estimation of the force acting on the inclusion. Consequently, the estimated viscoelastic parameters show excellent robustness and the elastic modulus agrees with the measurements using a quasi-static indentation method, obtaining errors below 10% in the whole temperature range. The use of the macroscopic inclusion limits the direct application of this method in a biomedical context, but it provides a robust estimation of the elastic modulus that can be used for material characterization in industrial applications. ; This work was supported in part by the Spanish Ministry of Science, Innovation and Universities through the "Juan de la Cierva - Incorporacion" under Grant IJC2018-037897-I, in part by the Program "Proyectos I+D+i 2019" under Grant PID2019-111436RB-C22, in part by the Agencia Valenciana de la Innovacio under Grant INNCON/2021/8, in part by Generalitat Valenciana under Grant AICO/2020/268, and in part by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 20142020 under Grant IDIFEDER/2018/022. The work of Alejandro Cebrecos was supported by the Universitat Politecnica de Valencia under Program PAID-10-19. ...

[EN] The unusual viscoelastic properties of silica aerogel plates are efficiently used to design subwavelength perfect sound absorbers. We theoretically, numerically and experimentally report a perfect absorbing metamaterial panel made of periodically arranged resonant building blocks consisting of a slit loaded by a clamped aerogel plate backed by a closed cavity. The impedance matching condition is analyzed using the Argand diagram of the reflection coefficient, i.e., the trajectory of the reflection coefficient as a function of frequency in the complex plane. The lack or excess of losses in the system can be identified via this Argrand diagram in order to achieve the impedance matching condition. The universality of this tool can be further exploited to design more complex metasurfaces for perfect sound absorption, thus allowing the rapid design of novel and efficient absorbing metamaterials. ; This work was funded by the RFI Le Mans Acoustique, Region Pays de la Loire. This article is based upon work from COST Action DENORMS CA15125, supported by COST (European Cooperation in Science and Technology). N.J. acknowledges financial support from Generalitat Valenciana through Grant No. APOSTD/2017/042. J.-P.G and V.R.G. gratefully acknowledge the ANR-RGC METARoom (No. ANR-18-CE08-0021) project and the HYPERMETA project funded under the program Etoiles Montantes of the Region Pays de la Loire. J.S-D. acknowledges the support of the Ministerio de Economia y Competitividad of the Spanish government and the European Union FEDER through Project No. TEC2014-53088-C3-1-R ; Fernandez-Marin, AA.; Jimenez, N.; Groby, J.; Sánchez-Dehesa Moreno-Cid, J.; Romero García, V. (2019). Aerogel-based metasurfaces for perfect acoustic energy absorption. Applied Physics Letters. 115(6):061901-1-061901-5. https://doi.org/10.1063/1.5109084 ; S ; 061901-1 ; 061901-5 ; 115 ; 6 ; Gesser, H. D., & Goswami, P. C. (1989). Aerogels and related porous materials. Chemical Reviews, 89(4), 765-788. doi:10.1021/cr00094a003 ; Herrmann, G., Iden, ...

[EN] We explore the use of a beamforming method intended for large-area scanning in optical-resolution photoacoustic microscopy. It has been evaluated in a experimental setup that comprises a low-cost laser diode and a phase array with a 128-elements linear probe. Three different beamforming strategies are discussed: no-beamforming, static beamforming and dynamic beamforming. The method has been tested in gelatine-based phantoms as well as ex-vivo organs. Results show that, compared with the other two, dynamic beamforming increases up to 15dB and homogenizes signal-to-noise ratio (SNR) along images of roughly 1 cm2. The method and system presented here could be the baseline for more advanced array-based systems that leverage the low-cost laser sources for clinical applications. ; This research has been supported by the Spanish Ministry of Science, Innovation and Universities through grant Juan de la Cierva - Incorporacion (IJC2018-037897-I), and program Proyectos I+D+i 2019 (PID2019-111436RB-C22). Action co-financed by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014-2020 (IDIFEDER/2018/022). A.C. received financial support from Generalitat Valenciana and Universitat Politecnica de Val ` encia through the grants APOSTD/2018/229 and program PAID-10-19, respectively. ; Cebrecos, A.; García-Garrigós, JJ.; Descals, A.; Jimenez, N.; Benlloch Baviera, JM.; Camarena Femenia, F. (2020). Dynamic beamforming for large area scan in array-based photoacoustic microscopy. IEEE. 1-4. https://doi.org/10.1109/IUS46767.2020.9251519 ; S ; 1 ; 4

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

6 12 ; S ; This work theoretically analyzes the sound absorption properties of a chirped multi-layer porous material including transmission, in particular showing the broadband unidirectional absorption properties of the system. Using the combination of the impedance matching condition and the balance between the leakage and the intrinsic losses, the system is designed to have broadband unidirectional and quasi perfect absorption. The transfer and scattering matrix formalism, together with numerical simulations based on the finite element method are used to demonstrate the results showing excellent agreement between them. The proposed system allows to construct broadband sound absorbers with improved absorption in the low frequency regime using less amount of material than the complete bulk porous layer. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). This work has been funded by the Metaudible project ANR-13-BS09-0003, co-funded by ANR and FRAE, and also by Ministerio de Economia y Competitividad (Spain) and European Union FEDER through project FIS2015-65998-C2-2-P. We acknowledge project AICO/2016/060 by Consellera de Educacion, Investigacion, Cultura y Deporte de la Generalitat Valenciana. Jimenez, N.; Romero García, V.; Cebrecos, A.; Picó Vila, R.; Sánchez Morcillo, VJ.; García-Raffi, LM. (2016). Broadband quasi perfect absorption using chirped multi-layer porous materials. AIP Advances. 6(12). https://doi.org/10.1063/1.4971274 Ma, G., Yang, M., Xiao, S., Yang, Z., & Sheng, P. (2014). Acoustic metasurface with hybrid resonances. Nature Materials, 13(9), 873-878. doi:10.1038/nmat3994 Ma, G., & Sheng, P. (2016). Acoustic metamaterials: From local resonances to broad horizons. Science Advances, 2(2), e1501595. doi:10.1126/sciadv.1501595 Merkel, A., Theocharis, G., Richoux, O., Romero-García, V., & Pagneux, V. (2015). Control of acoustic absorption in one-dimensional ...