info:eu-repo/semantics/masterThesis
Acoustic rotational streaming and angular momentum transfer to matter driven by ultrasonic acoustic vortices
Autor
JUAN ISRAEL VÁZQUEZ LOZANO
Resumen
Mechanical effects of waves on material media is a powerful option to achieve contactless
manipulation in a controlled manner, which has already found numerous applications in optics and
acoustics. A basic example consists of absorption-mediated wave-matter exchange of linear and/or
angular momentum that light or sound may carry. To date, the demonstration of all kinds of
exchanges mediated by dissipative processes have been carried out experimentally. Moreover, nondissipative
exchanges of linear and angular momentum between waves and matter are also
possible.
Furthermore, recent works have observed indirectly that acoustic vortices impart momentum to a
fluid unveiling a rotational flow of the liquid. This rotational flow is the counterpart of the classical
acoustic streaming, which is the linear motion along the beam propagation direction that results
from momentum transfer due to thermoviscous dissipations induced sound absorption. This
rotational flow induced by the radiation torque exerted on the sound absorbing fluid through which
the acoustic beam propagates, circulates around the propagation direction of the acoustic vortex.
First we report on orbital angular momentum exchange between sound and matter
mediated by a non-dissipative chiral scattering process. The experimental demonstration is made
by irradiating a three-dimensional printed, spiral-shaped chiral object using an incident ultrasonic
beam carrying zero orbital angular momentum. This is the acoustic analog of an optical spiral phase
plate (SPP) but for sound waves. Chiral refraction is shown to impart a nonzero orbital angular
momentum to the scattered field and to rotate the object. This result constitutes a proof-of-concept
of a novel kind of acoustic angular manipulation of matter.
After that, we report the first direct experimental demonstration of acoustic rotational
streaming as result of the exchange of momentum between an acoustic vortex and fluid with PMMA
particles used as tracers of the flow. It is shown that the system behaves as a Fabry –Pérot like cavity
for acoustic waves. Experimental results and observations are sustained by a small model developed
for the system providing a first approach to this phenomenon.
Materias
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