102 research outputs found
Numerical modeling of underwater parametric propagation to detect buried objects
In underwater acoustics, detection of buried objects in sediments (cables, mines,…) is a complex problem. One reason is that acoustic attenuation in these sediments increases with frequency. To ensure sufficient penetration depth in marine sediments, low frequencies have to be used, implying a low resolution. A solution proposed to solve this problem is the parametric emission based on the nonlinear properties of the propagation medium. This method can generate a low frequency wave from two directional high frequencies beams. The parametric propagation is simulated in seawater and marine sediments. The model developed is based on the fractional-step numerical method introduced by Christopher and Parker [1]. In this method, the normal particle velocity is calculated plane by plane from the surface of the transducer to a specified distance. The effects of nonlinearity, attenuation and diffraction are calculated independently for each spatial step. Moreover, to reduce the number of spatial steps, a second order operator splitting scheme is used. The diffraction computation is based on a method of angular spectrum in the frequency domain where the field across a source plane is described by a spatial frequency distribution. To improve code stability, the effects of nonlinearity and attenuation are calculated and associated in shorter propagation substeps. At the interface between water and marine sediments, the transmission conditions are applied. Several tests have been carried out in different configurations (changing the primary frequencies, the parametric frequency, the source geometry, the inclination of the source with the interface, the focal distance,…). The 3D velocity field is calculated in each case, thereby allowing to know the directivity of the source, the velocity amplitude in sediments and the performance
The parametric propagation in underwater acoustics : experimental results
In underwater acoustics, detection of buried objects in sediments (cables, mines, . . . ) is a complex problem. Indeed, in order to ensure sufficient penetration depth in marine sediments, low frequencies have to be used, implying a low resolution. A solution proposed to solve this problem is the parametric emission based on the nonlinear properties of seawater. This method can generate a low frequency wave from two directional high frequencies beams. The aim of this work is to present experimental results of a parametric propagation. Experiments have been carried out in a water tank in various configurations. These experimental measurements are then compared with simulation results obtained with a numerical model based on a fractional-step method presented at the Underwater Acoustic Measurements conference in 2011
Taming the degeneration of Bessel beams at anisotropic-isotropic interface: toward 3D control of confined vortical waves
Despite their self-reconstruction properties in heterogeneous media, Bessel
beams are known to degenerate when they are refracted from an isotropic to an
anisotropic medium. In this paper, we study the converse situation wherein an
anisotropic Bessel beam is refracted into an isotropic medium. It is shown that
these anisotropic Bessel beams also degenerate, leading to confined vortical
waves that may serve as localized particle trap for acoustical tweezers. The
linear nature of this degeneration allows the 3D control of this trap position
by wavefront correction. Theory is confronted to experiments performed in the
field of acoustics. A swirling surface acoustic wave is synthesized at the
surface of a piezoelectric crystal by a MEMS integrated system and radiated
inside a miniature liquid vessel. The wavefront correction is operated with
inverse filter technique. This work opens perspectives for contactless on-chip
manipulation devices
Numerical modeling of underwater parametric propagation to detect buried objects
In underwater acoustics, detection of buried objects in sediments (cables, mines,…) is a complex problem. One reason is that acoustic attenuation in these sediments increases with frequency. To ensure sufficient penetration depth in marine sediments, low frequencies have to be used, implying a low resolution. A solution proposed to solve this problem is the parametric emission based on the nonlinear properties of the propagation medium. This method can generate a low frequency wave from two directional high frequencies beams. The parametric propagation is simulated in seawater and marine sediments. The model developed is based on the fractional-step numerical method introduced by Christopher and Parker [1]. In this method, the normal particle velocity is calculated plane by plane from the surface of the transducer to a specified distance. The effects of nonlinearity, attenuation and diffraction are calculated independently for each spatial step. Moreover, to reduce the number of spatial steps, a second order operator splitting scheme is used. The diffraction computation is based on a method of angular spectrum in the frequency domain where the field across a source plane is described by a spatial frequency distribution. To improve code stability, the effects of nonlinearity and attenuation are calculated and associated in shorter propagation substeps. At the interface between water and marine sediments, the transmission conditions are applied. Several tests have been carried out in different configurations (changing the primary frequencies, the parametric frequency, the source geometry, the inclination of the source with the interface, the focal distance,…). The 3D velocity field is calculated in each case, thereby allowing to know the directivity of the source, the velocity amplitude in sediments and the performance
Synthesis of anisotropic swirling surface acoustic waves by inverse filter, towards integrated generators of acoustical vortices
From radio-electronics signal analysis to biological samples actuation,
surface acoustic waves (SAW) are involved in a multitude of modern devices.
Despite this versatility, SAW transducers developed up to date only authorize
the synthesis of the most simple standing or progressive waves such as plane
and focused waves. In particular, acoustical integrated sources able to
generate acoustical vortices (the analogue of optical vortices) are missing. In
this work, we propose a flexible tool based on inverse filter technique and
arrays of SAW transducers enabling the synthesis of prescribed complex wave
patterns at the surface of anisotropic media. The potential of this setup is
illustrated by the synthesis of a 2D analog of 3D acoustical vortices, namely
"swirling surface acoustic waves". Similarly to their 3D counterpart, they
appear as concentric structures of bright rings with a phase singularity in
their center resulting in a central dark spot. Swirling SAW can be useful in
fragile sensors whose neighborhood needs vigorous actuation, and may also serve
as integrated transducers for acoustical vortices. Since these waves are
essential to fine acoustical tweezing, swirling SAW may become the cornerstone
of future micrometric devices for contactless manipulation
Cell detachment and label-free cell sorting using modulated surface acoustic waves (SAW) in droplet-based microfluidics
We present a droplet-based surface acoustic wave (SAW) system designed to
viably detach biological cells from a surface and sort cell types based on
differences in adhesion strength (adhesion contrast), without the need to label
cells with molecular markers. The system uses modulated SAW to generate
pulsatile flows in the droplets and efficiently detach the cells, thereby
minimizing SAW excitation power and exposure time. As a proof-of-principle, the
system is shown to efficiently sort HEK 293 from A7r5 cells based on adhesion
contrast. Results are obtained in minutes with sorting purity and efficiency
reaching 97 % and 95 %, respectively.Comment: Accepted for publication in Lab on a Chi
Multilayer modeling of thermoacoustic sound generation for thermophone analysis and design
International audienc
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