arXiv subjects

R. Picó

Publications and source records attributed to R. Picó.

7 recordsLinked to original sources

arXiv2026

Acoustic wave scattering by spatio-temporal interfaces

Space-time materials are obtained by modulating a physical medium with a traveling-wave perturbation of one or several of its constitutive parameters, such as the density or the bulk modulus in the case of acoustic materials. When this modulation has the form of a moving and abrupt (subwavelength) transition between two parameter values, we refer to a spatio-temporal interface, which may be considered as a building block for more complex space-time materials. This work considers the problem interaction and scattering of acoustic waves with a single spatio-temporal interface, and a sequence of two interfaces forming a slab. Several regimes defined by the relation between the sound propagation velocities and the interface velocity (namely subsonic, intersonic, and supersonic regimes) are discussed. Analytical expressions for the frequency conversions and scattering coefficients are obtained, and compared with numerical simulations based on an equivalent FTFD squeme.

cond-mat.mtrl-sci↗

arXiv2019

Limits of flexural wave absorption by open lossy resonators: reflection and transmission problems

The limits of flexural wave absorption by open lossy resonators are analytically and numerically reported in this work for both the reflection and transmission problems. An experimental validation for the reflection problem is presented. The reflection and transmission of flexural waves in 1D resonant thin beams are analyzed by means of the transfer matrix method. The hypotheses, on which the analytical model relies, are validated by experimental results. The open lossy resonator, consisting of a finite length beam thinner than the main beam, presents both energy leakage due to the aperture of the resonators to the main beam and inherent losses due to the viscoelastic damping. Wave absorption is found to be limited by the balance between the energy leakage and the inherent losses of the open lossy resonator. The perfect compensation of these two elements is known as the critical coupling condition and can be easily tuned by the geometry of the resonator. On the one hand, the scattering in the reflection problem is represented by the reflection coefficient. A single symmetry of the resonance is used to obtain the critical coupling condition. Therefore the perfect absorption can be obtained in this case. On the other hand, the transmission problem is represented by two eigenvalues of the scattering matrix, representing the symmetric and anti-symmetric parts of the full scattering problem. In the geometry analyzed in this work, only one kind of symmetry can be critically coupled, and therefore, the maximal absorption in the transmission problem is limited to 0.5. The results shown in this work pave the way to the design of resonators for efficient flexural wave absorption.

physics.app-ph↗

arXiv2017

Nonlinear dispersive waves in repulsive lattices

The propagation of nonlinear waves in a lattice of repelling particles is studied theoretically and experimentally. A simple experimental setup is proposed, consisting in an array of coupled magnetic dipoles. By driving harmonically the lattice at one boundary, we excite propagating waves and demonstrate different regimes of mode conversion into higher harmonics, strongly influenced by dispersion and discreteness. The phenomenon of acoustic dilatation of the chain is also predicted and discussed. The results are compared with the theoretical predictions of $α$-FPU equation, describing a chain of masses connected by nonlinear quadratic springs. The results can be extrapolated to other systems described by this equation.

nlin.PS↗

arXiv2014

Acoustic Bessel-like beam formation by an axisymmetric grating

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.

cond-mat.mtrl-sci↗

arXiv2013

Wave focusing using symmetry matching in axisymmetric acoustic gradient index lenses

The symmetry matching between the source and the lens results of 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.

cond-mat.mtrl-sci↗

arXiv2013

Extraordinary absorption of sound in porous lamella-crystals

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.

cond-mat.mtrl-sci↗

arXiv2012

Enhancement of sound in chirped sonic crystals

We propose and experimentally demonstrate a novel 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. The results are obtained for the case of sound waves and sonic crystals, however they are extendable to other type of waves in modulated host matter.

cond-mat.mtrl-sci↗