Search results for "ACOUSTIC"
showing 10 items of 1590 documents
Experimental realization of a pillared metasurface for flexural wave focusing
2021
International audience; A metasurface is an array of subwavelength units with modulated wave responses that show great potential for the control of refractive/reflective properties in compact functional devices. In this work, we propose an elastic metasurface consisting of a line of pillars with gradient heights, erected on a homogeneous plate. The change in the resonant frequencies associated with the height gradient allows us to achieve transmitted phase response covering a range of 2π, while the amplitude response remains at a relatively high level. We employ the pillared units to design a focusing metasurface and compare the properties of the focal spots through simulation and experimen…
Extraordinary nonlinear transmission modulation in a doubly resonant acousto-optical structure
2017
International audience; Acousto-optical modulators usually rely on coherent diffraction of light by a moving acoustic wave, leading to bulky devices with a long interaction length. We propose a subwavelength acousto-optical structure that instead relies on a double resonance to achieve strong modulation at near-infrared wavelengths. A periodic array of metal ridges on a piezoelectric substrate defines cavities that create a resonant dip in the optical transmission spectrum. The ridges simultaneously support large flexural vibrations when resonantly excited by a radio-frequency signal, effectively deforming the cavities and leading to strongly nonlinear acousto-optical modulation. The nano-o…
Acoustically tunable photonic band gap structures
2005
We discuss the formation of a tunable one-dimensional photonic band gap structure through the modulation of the resonance frequency of an optical microcavity by a surface acoustic wave (SAW). The microcavity consists of a λ/2 GaAs layer bounded by AlAs/GaAs Bragg mirrors. The SAW periodically modulates the optical thickness of the cavity layer, leading to a light dispersion relation folded within a mini-Brillouin zone (MBZ) defined by |k x |≤ π/λ SAW (k x denotes the photon wave vector component along the SAW propagation direction x-with-caret). In reflection and diffraction experiments, we observe photon modes bounding the gaps in the center and at the boundary of the MBZ as well as a reno…
Phonon-induced optical superlattice
2005
We demonstrate the formation of a dynamic optical superlattice through the modulation of a semiconductor microcavity by stimulated acoustic phonons. The high coherent phonon population produces a folded optical dispersion relation with well-defined energy gaps and renormalized energy levels, which are accessed using reflection and diffraction experiments.
Mobile Devices as Tools for Media and Communication Research: A Scoping Review on Collecting Self-report Data in Repeated Measurement Designs
2020
Mobile devices are deeply embedded in people’s everyday lives. On the one hand, this opens up a new field for media and communication research. On the other hand, the widespread diffusion allows fo...
The Diffusion of Humans and Cultures in the Course of the Spread of Farming
2017
The spread of farming into Europe some 9000–5000 years ago involved not only the advent of new plants and animals, but also of people, tools, technologies, and knowledge. While they all can be assumed to follow Fickian diffusion gradients, the mechanisms of spread can be quite different: when people migrate, there is mass balance in the number of people, but not in the knowledge and technologies brought along. Tools, plants and animals could also travel by trade, knowledge and technology by communication; there might even be local resistance to adoption of novelty. This chapter discusses these different diffusion mechanisms in the context of numerical trait- and agent-based socio-environmen…
Innovative user defined density profile approach to fsw of aluminium foam
2007
Metallic foams are one of the most exciting materials in the world of mechanical industry due to their reduced mass and the good mechanical, thermal and acoustic characteristics. Consequently, their application, is increasing day by day even with the important drawbacks that reduce their suitability and diffusion such as high manufacturing cost and difficulty in processing. An innovative approach is outlined in this paper that enables the production of complex shapes taking advantage of deformation processing and friction stir welding (FSW). The aim is to create customized tailored manufactured parts. The cellular construction of foams makes this approach rather challenging as the cell wall…
Diffusion stabilizes cavity solitons in bidirectional lasers
2009
We study the influence of field diffusion on the spatial localized structures (cavity solitons) recently predicted in bidirectional lasers. We find twofold positive role of the diffusion: 1) it increases the stability range of the individual (isolated) solitons; 2) it reduces the long-range interaction between the cavity solitons. Latter allows the independent manipulation (writing and erasing) of individual cavity solitons.
Forecasting the diffusion of hydrogen EV refuelling infrastructures in Italy
2019
In Italy the electric vehicle revolution is arrived but it still has difficulties to take off. At the moment hybrid technology would seem the most quoted, due especially to range anxiety. The aim of this work is to understand if the fuel cell technology can find place in Italy. The possibility to use fuel cell to storage electric energy is quite interesting: the charging times will be reduced, and heavy passenger transportation should be easily faced. Basing on the existing history and analysis of the information accessible, this paper addresses the existing e-mobility scenario in Italy and predicts the cities in which a hydrogen refuelling infrastructure should be more remunerative, in ord…
Transfer matrix method applied to the parallel assembly of sound absorbing materials
2013
International audience; The transfer matrix method (TMM) is used conventionally to predict the acoustic properties of laterally infinite homogeneous layers assembled in series to form a multilayer. In this work, a parallel assembly process of transfer matrices is used to model heterogeneous materials such as patchworks, acoustic mosaics, or a collection of acoustic elements in parallel. In this method, it is assumed that each parallel element can be modeled by a 2 × 2 transfer matrix, and no diffusion exists between elements. The resulting transfer matrix of the parallel assembly is also a 2 × 2 matrix that can be assembled in series with the classical TMM. The method is validated by compar…