M. Torres

Visualization of Bloch waves and domain walls

The theory of wave propagation in periodic structures and its major concept, Blochs theorem, have typically been assigned to the realm of solid-state physics, but they are now becoming useful in optics, acoustics and hydrodynamics. Blochs theorem is constructive and aesthetic, starting from the idea of perfect order and dealing with infinite extended states. But Blochs solution is unstable against a small amount of disorder.

Quasiperiodic bloch-like states in a surface-wave experiment

Bloch-like surface waves associated with a quasiperiodic structure are observed in a classic wave propagation experiment which consists of pulse propagation with a shallow fluid covering a quasiperiodically drilled bottom. We show that a transversal pulse propagates as a plane wave with quasiperiodic modulation, displaying the characteristic undulatory propagation in this quasiperiodic system and reinforcing the idea that analogous concepts to Bloch functions can be applied to quasicrystals under certain circumstances.

Five-fold quasicrystal-like germinal pattern in the Faraday wave experiment

Abstract A stable five-fold standing wave pattern exhibiting a germinal quasicrystalline structure has been found for the first time in a symmetry breaking Faraday instability experiment with a low aspect ratio and the liquid depth being less than the surface wavelength.

Conformal mapping of ultrasonic crystals: Confining ultrasound and cochlearlike waveguiding

Conformal mapping of a slab of a two-dimensional ultrasonic crystal generates a closed geometrical arrangement of ultrasonic scatterers with appealing acoustic properties. This acoustic shell is able to confine ultrasonic modes. Some of these internal resonances can be induced from an external wave source. The mapping of a linear defect produces a waveguide that exhibits a spatial-frequency selection analogous to that characteristic of a synthetic “cochlea.” Both experimental and theoretical results are reported here.

Extended and localized vibrational modes in (1‐3) Penrose‐like piezocomposites

Acoustic vibrational modes of piezocomposites with ceramic bars arranged at the vertices of both perfect Penrose tilings and random Penrose tilings have directly been observed by recording the corresponding standing vibration amplitude pattern. The random Penrose tiling exhibits similar although smoother spectrum than the perfect Penrose one. For both structures, the existence of extended and localized modes is shown. Resonances frequencies at the edges of the spectrum pseudogap correspond to localized and highly entropic modes. As expected, the modes are more localized in the random Penrose tiling case.

Acoustic Quasi-Crystals

A fivefold quasi-crystalline structure in a liquid has been obtained with five ultrasonic beams coming together in water according to a regular pentagonal array. A pressure scanning by means of a hydrophone probe has been made to show in a direct way the evidence of the quasi-crystalline pressure structure. Acousto-optic diffraction experiments by using a laser beam have also been performed.

Experimental assessment of an ultrasonic band gap in a periodic two-dimensional composite

An experimentally observed ultrasonic full band-gap in periodic two dimensional composites is described. The composite structure consists of an aluminum alloy plate with a square periodic arrangement of cylindrical holes filled with mercury. The band-gap found has a bandwidth of about 600 kHz around the first network resonance (750 kHz) along the [100] direction. The experimental test was performed by means of the through-transmission technique, exciting the structure with longitudinal waves. Moreover, different acoustic scannings of the vibration amplitude were also performed.

Nonisometric hyperlattices suitability to describe the approximant phases of the decagonal phase

Specific distortions of the five-dimensional cubic hyperlattice are proposed to describe the approximant phases of the decagonal phase in Al-Cu-Co-Si and Al-Cu-Co alloys. Density wave patterns are used to show the corresponding simulation of known high-resolution electron microscopy images.

An acoustic quasi-crystalline wave-field

Abstract In this note, the preview of quasi-crystalline acoustic structures in liquids is presented. The slow acoustic scanning of the standing structure, the optical diffraction pattern and the corresponding low contrast image of the instantaneous structure are shown.