5,357 research outputs found
In-channel experiments on vertical swimming with bacteria-like robots
Bio-inspired micro-robots are of great importance as to implement versatile microsystems for a variety of in vivo and in vitro applications in medicine and biology. Accurate models are necessary to understand the swimming and rigidbody
dynamics of such systems. In this study, a series of experiments are conducted with a two-link cm-scale bioinspired robot moving vertically without a tether, in siliconefilled narrow cylindrical glass channels. Swimming velocities are obtained for a set of varying tail and wave geometries, and employed to validate a resistive force theory (RFT) model using modified resistance coefficients based on measured forward velocity and body rotation rates
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
Flow induced ultrasound scattering: experimental studies
Sound scattering by a finite width beam on a single rigid body rotation
vortex flow is detected by a linear array of transducers (both smaller than a
flow cell), and analyzed using a revised scattering theory. Both the phase and
amplitude of the scattered signal are obtained on 64 elements of the detector
array and used for the analysis of velocity and vorticity fields. Due to
averaging on many pulses the signal-to-noise ratio of the phases difference in
the scattered sound signal can be amplified drastically, and the resolution of
the method in the detection of circulation, vortex radius, vorticity, and
vortex location becomes comparable with that obtained earlier by time-reversal
mirror (TRM) method (P. Roux, J. de Rosny, M. Tanter, and M. Fink, {\sl Phys.
Rev. Lett.} {\bf 79}, 3170 (1997)). The revised scattering theory includes two
crucial steps, which allow overcoming limitations of the existing theories.
First, the Huygens construction of a far field scattering signal is carried out
from a signal obtained at any intermediate plane. Second, a beam function that
describes a finite width beam is introduced, which allows using a theory
developed for an infinite width beam for the relation between a scattering
amplitude and the vorticity structure function. Structure functions of the
velocity and vorticity fields deduced from the sound scattering signal are
compared with those obtained from simultaneous particle image velocimetry (PIV)
measurements. Good quantitative agreement is found.Comment: 14 pages, 23 figures. accepted for publication in Phys. Fluids(June
issue
Improved kinematic models for two-link helical micro/nano-swimmers
Accurate prediction of the three-dimensional trajectories of micro/nano-swimmers is a key element as to achieve high precision motion control in therapeutic applications. Rigid-body kinematics of such robotic systems is dominated by viscous forces. The induced flow field around a two-link swimmer
is investigated with a validated computational fluid dynamics (CFD) model. Force-free-swimming constraints are employed in order to simulate motion of bacteria-like swimmers in viscous medium. The fluid resistance exerted on the body of the swimmer is quantified by an improved resistance matrix, which is
embedded in a validated resistive force theory (RFT) model, based on complex-impedance approach. Parametric studies confirmed that the hydrodynamic interaction between body and tail are of great importance in predicting the trajectories for such systems
Nonreciprocity Applications in Acoustics and Microfluidic Systems
Breaking reciprocity in linear acoustic systems and designing a novel actuator for the nonreciprocal valveless pumps are studied in this dissertation. The first part was started by deriving the acoustic governing equations in a moving wave propagation medium. It was shown thatthe Coriolis acceleration term appears ina cross-product term with the wave vector. It means the main reason for breaking reciprocity in the circular fluid flow is the Coriolis acceleration term. Finally, the governing equations were solved numerically by COMSOL Multiphysics software. Moreover, Green`s second identity was used as a complimentary method to prove breaking reciprocityin such a system with moving medium. It is concluded that the non-reciprocity is magnified by increasing the angular velocity of the fluid system. The second part of this thesis is about achieving non-reciprocity utilizing the arrangement of a nozzle and diffuser as the inlet and outlet ports. This part’s goal is to design a novel flexible actuator design for a valveless pump. The actuation mechanism which is novel in its own term, uses liquid metal called galinstan, a non-magnetic but electrically conducting alloy. In the designed device, an alternating current (AC) is applied onto a microchannel filled with galinstan. This device is placed between two permanent magnets with opposing poles. Due to the Lorentz force law, there will be radial in-plane forces on the polymeric flexible substrate. These in-plane forces radially contract and expand the circular diaphragm to provide an upward and downward out of plane bending moment, which causes an oscillatory reciprocating movement similar to a piezoelectric actuator`s movement. Compared to the traditional piezo electric materials such as Lead Zirconate Titanate (PZT), this actuator has numerous advantages such as being flexible, having the ability to be scaled down, being formed as an integrated structure, and being fabricated by a considerably simple process. The prototype of the pump could be fabricated easily with Platinum Silicone rubber and some low-cost 3D printed elements. Although the prototype has been fabricated in a relatively large size, it is considered as a proper conceptual model representing the performance of the pump
Index to NASA Tech Briefs, 1975
This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs
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