270 research outputs found
Adaptive locomotion of artificial microswimmers
Bacteria can exploit mechanics to display remarkable plasticity in response
to locally changing physical and chemical conditions. Compliant structures play
a striking role in their taxis behavior, specifically for navigation inside
complex and structured environments. Bioinspired mechanisms with rationally
designed architectures capable of large, nonlinear deformation present
opportunities for introducing autonomy into engineered small-scale devices.
This work analyzes the effect of hydrodynamic forces and rheology of local
surroundings on swimming at low Reynolds number, identifies the challenges and
benefits of utilizing elastohydrodynamic coupling in locomotion, and further
develops a suite of machinery for building untethered microrobots with
self-regulated mobility. We demonstrate that coupling the structural and
magnetic properties of artificial microswimmers with the dynamic properties of
the fluid leads to adaptive locomotion in the absence of on-board sensors
Adaptive locomotion of artificial microswimmers.
Bacteria can exploit mechanics to display remarkable plasticity in response to locally changing physical and chemical conditions. Compliant structures play a notable role in their taxis behavior, specifically for navigation inside complex and structured environments. Bioinspired mechanisms with rationally designed architectures capable of large, nonlinear deformation present opportunities for introducing autonomy into engineered small-scale devices. This work analyzes the effect of hydrodynamic forces and rheology of local surroundings on swimming at low Reynolds number, identifies the challenges and benefits of using elastohydrodynamic coupling in locomotion, and further develops a suite of machinery for building untethered microrobots with self-regulated mobility. We demonstrate that coupling the structural and magnetic properties of artificial microswimmers with the dynamic properties of the fluid leads to adaptive locomotion in the absence of on-board sensors.ER
Numerical analysis of a planar wave propagation based micropropulsion system
Micropropulsion mechanisms differ from macro scale counterparts owing to the domination of viscous forces in microflows. In essence, propulsion mechanisms
such as cilia and flagella of single celled organisms can be deemed as nature’s solution to a challenging problem, and taken as a basis for the design
of an artificial micropropulsion system. In this paper we present numerical analysis of the flow due to oscillatory planar waves propagating on microstrips. The time-dependent three-dimensional flow due to moving boundaries of the strip is governed by incompressible Navier-Stokes equations in a moving coordinate system, which is modeled by means of an
arbitrary Lagrangian-Eulerian formulation. The fluid medium surrounding the actuator boundaries is bounded by a channel, and neutral boundary conditions
are used in the upstream and downstream. Effects of actuation parameters such as amplitude, excitation frequency, wavelength of the planar waves are
demonstrated with numerical simulations that are carried out by third party software, COMSOL. Functional-dependencies with respect to the actuation
parameters are obtained for the average velocity of the strip and the efficiency of the mechanism
Active Brownian motion in a narrow channel
We review recent advances in rectification control of artificial
microswimmers, also known as Janus particles, diffusing along narrow,
periodically corrugated channels. The swimmer self-propulsion mechanism is
modeled so as to incorporate a nonzero torque (propulsion chirality). We first
summarize the effects of chirality on the autonomous current of microswimmers
freely diffusing in channels of different geometries. In particular, left-right
and upside-down asymmetric channels are shown to exhibit different transport
properties. We then report new results on the dependence of the diffusivity of
chiral microswimmers on the channel geometry and their own self-propulsion
mechanism. The self-propulsion torque turns out to play a key role as a
transport control parameter.Comment: to be published in Eur. Phys. J Special Topic
Control and controllability of microswimmers by a shearing flow
With the continuing rapid development of artificial microrobots and active particles, questions of microswimmer guidance and control are becoming ever more relevant and prevalent. In both the applications and theoretical study of such microscale swimmers, control is often mediated by an engineered property of the swimmer, such as in the case of magnetically propelled microrobots. In this work, we will consider a modality of control that is applicable in more generality, effecting guidance via modulation of a background fluid flow. Here, considering a model swimmer in a commonplace flow and simple geometry, we analyse and subsequently establish the efficacy of flow-mediated microswimmer positional control, later touching upon a question of optimal control. Moving beyond idealized notions of controllability and towards considerations of practical utility, we then evaluate the robustness of this control modality to sources of variation that may be present in applications, examining in particular the effects of measurement inaccuracy and rotational noise. This exploration gives rise to a number of cautionary observations, which, overall, demonstrate the need for the careful assessment of both policy and behavioural robustness when designing control schemes for use in practice
Physics of Microswimmers - Single Particle Motion and Collective Behavior
Locomotion and transport of microorganisms in fluids is an essential aspect
of life. Search for food, orientation toward light, spreading of off-spring,
and the formation of colonies are only possible due to locomotion. Swimming at
the microscale occurs at low Reynolds numbers, where fluid friction and
viscosity dominates over inertia. Here, evolution achieved propulsion
mechanisms, which overcome and even exploit drag. Prominent propulsion
mechanisms are rotating helical flagella, exploited by many bacteria, and
snake-like or whip-like motion of eukaryotic flagella, utilized by sperm and
algae. For artificial microswimmers, alternative concepts to convert chemical
energy or heat into directed motion can be employed, which are potentially more
efficient. The dynamics of microswimmers comprises many facets, which are all
required to achieve locomotion. In this article, we review the physics of
locomotion of biological and synthetic microswimmers, and the collective
behavior of their assemblies. Starting from individual microswimmers, we
describe the various propulsion mechanism of biological and synthetic systems
and address the hydrodynamic aspects of swimming. This comprises
synchronization and the concerted beating of flagella and cilia. In addition,
the swimming behavior next to surfaces is examined. Finally, collective and
cooperate phenomena of various types of isotropic and anisotropic swimmers with
and without hydrodynamic interactions are discussed.Comment: 54 pages, 59 figures, review article, Reports of Progress in Physics
(to appear
- …