307 research outputs found
Harnessing Electric Fields for Microfluidics – From Lightning Sparks to Tiny Tornadoes
The dominance of surface tension and viscous effects over body forces such as inertia, gravity or centrifugal force makes fluid actuation and particle manipulation at microscale dimensions extremely difficult. We demonstrate the possibility of exploiting electric fields to drive unstable turbulent-like flows for micromixing and complex flows for efficient particle separation and concentration. In particular, the ions resulting from the breakdown of air surrounding a theoretically singular sharp electrode tip due to corona discharge is employed to accelerate the air towards the surface of a liquid in a cylindrical microchamber. Through interfacial shear, the surface liquid layer is recirculated to produce a Batchelor-type flow within the chamber that spirals suspended colloidal particles to a stagnation point at the bottom no-slip plane. We show the use of this technology for rapid and efficient separation of red blood cells from plasma for the development of miniaturised point-of-care diagnostics. Such liquid flows also become unstable at high applied voltages and frequencies leading to the generation of vortices that span a cascade of length scales, which can be exploited for micromixing
Design, Optimization, and the Prototyping of a Small Tuning-Fork Ultrasonic Piezoelectric Linear Motor
The design, optimization, and properties of a prototype small traveling-wave ultrasonic piezoelectric linear motor design are described. A method for optimizing the geometry of the motor to maximize its mechanical output for a given electrical input is described, as is the inherent properties of the design to maximize the motors durability and utilization of the piezoelectric material. Results from testing the motor demonstrate the design and indicate a maximum speed of 2.5 cm/s with a preload of 16 g due to an applied voltage of 80 V/RMS/ at an applied current of 15 mA
Driving Cell Seeding Using Surface Acoustic Wave Fluid Actuation
In this paper, we investigate the ability to drive fluid streaming via a surface acoustic wave (SAW) into a porous bioscaffold structure, and to exploit this effect to deliver fluorescent particles/yeast cells into the scaffold as a potential rapid and efficient method for cell seeding in tissue engineering. The results demonstrate that the seeding process takes approximately 10 seconds, much shorter than that if the cell suspension were to perfuse through the scaffold under the effects of gravity alone (approximately 30 mins). By increasing the input power, both the velocity of the fluid flow and the particle seeding efficiency can be enhanced. At 560 mW, fluid velocities of the order 10 mm/s were achieved; in this case, the particle/yeast seeding efficiency is around 92%. In addition to rapid seeding, the SAW streaming induced perfusion is observed to significantly improve the uniformity of the scaffold cell distribution due to greater penetration into the scaffold. Finally, we verify using a methylene violet staining procedure that 80% of the yeast cells seeded by the SAW method within the scaffold remained viable
Extensional viscosity of copper nanowire suspensions in an aqueous polymer solution
Suspensions of copper nanowires are emerging as new electronic inks for
next-generation flexible electronics. Using a novel surface acoustic wave
driven extensional flow technique we are able to perform currently lacking
analysis of these suspensions and their complex buffer. We observe extensional
viscosities from 3 mPas (1 mPas shear viscosity) to 37.2
Pas via changes in the suspension concentration, thus capturing low
viscosities that have been historically very challenging to measure. These
changes equate to an increase in the relative extensional viscosity of nearly
12,200 times at a volume fraction of just 0.027. We also find that interactions
between the wires and the necessary polymer additive affect the rheology
strongly. Polymer-induced elasticity shows a reduction as the buffer relaxation
time falls from 819 to 59 s above a critical particle concentration. The
results and technique presented here should aid in the future formulation of
these promising nanowire suspensions and their efficient application as inks
and coatings.Comment: 7 pages, 5 figures, under review for Soft Matter RS
Ultrasonic Characterization of Poling in Lead Zirconate Titanate Ceramics
A method for measuring the spatial variation of the macroscopic poling state of a piezoelectric material using an ultrasonic transducer is described. The relatively simple method clearly indicates the distribution of poling within the material, demonstrated by the testing of a collection of partially poled lead zirconate titanate samples
Describing the Sward Structure of Wheat and Annual Ryegrass Swards Grazed by Lambs in Southern NSW
Dual-purpose wheats are now an established part of the feed base on many mixed-farms in southern NSW. However agronomic practices can vary and it is unknown whether row spacing will impact the availability of forage for grazing by sheep. Intake has been shown to be affected by a range of factors including tiller length, pasture height, sward density and pasture mass (Allden and Whittaker 1970; Black and Kenney 1984). This study sought to describe the differences in sward structure of grazed wheat swards at two different row spacings in terms of mean height, row height and bulk density and compare this to an annual ryegrass pasture presented as a continuous pasture
Motility induced changes in viscosity of suspensions of swimming microbes in extensional flows
Suspensions of motile cells are model systems for understanding the unique
mechanical properties of living materials which often consist of ensembles of
self-propelled particles. We present here a quantitative comparison of theory
against experiment for the rheology of such suspensions. The influence of
motility on viscosities of cell suspensions is studied using a novel
acoustically-driven microfluidic capillary-breakup extensional rheometer.
Motility increases the extensional viscosity of suspensions of algal pullers,
but decreases it in the case of bacterial or sperm pushers. A recent model
[Saintillan, Phys. Rev. E, 2010, 81:56307] for dilute active suspensions is
extended to obtain predictions for higher concentrations, after independently
obtaining parameters such as swimming speeds and diffusivities. We show that
details of body and flagellar shape can significantly determine macroscale
rheological behaviour.Comment: 12 pages, 1 appendix, 7 figures, submitted to Soft Matter - under
revie
A Single-Element Tuning Fork Piezoelectric Linear Actuator
This paper describes the design of a piezoelectric tuning-fork, dual-mode motor. The motor uses a single multilayer piezoelectric element in combination with tuning fork and shearing motion to form an actuator using a single drive signal. Finite-element analysis was used in the design of the motor, and the process is described along with the selection of the device\u27s materials and its performance. Swaging was used to mount the multilayer piezoelectric element within the stator. Prototypes of the 25-mm long bidirectional actuator achieved a maximum linear no-load speed of 16.5 cm/s, a maximum linear force of 1.86 N, and maximum efficiency of 18.9%
On-chip unidirectional waveguiding for surface acoustic waves along a defect line in a triangular lattice
The latest advances in topological physics have yielded a rich toolset to
design highly robust wave transfer systems, for overcoming issues like beam
steering and lateral diffraction in surface acoustic waves (SAWs). However,
presently used designs for topologically protected SAWs have been largely
limited to spin or valley-polarized phases, which rely on non-zero Berry
curvature effects. Here we propose and experimentally demonstrate a highly
robust SAW waveguide on lithium niobate (LiNbO3), based on a line defect within
a true triangular phononic lattice, which instead employs an intrinsic
chirality of phase vortices and maintains a zero Berry curvature. The guided
SAW mode spans a wide bandwidth and shows confinement in the lateral direction
with 3 dB attenuation within half of the unit-cell length. SAW routing around
sharp bends has been demonstrated in such waveguide, with less than ~4%
reflection per bend. The waveguide has also been found robust for defect lines
with different configurations. The fully on-chip system permits unidirectional
SAW modes that are tightly bound to the waveguide, which provides a compact
footprint ideal for miniaturization of practical applications and offers
insight into the possibility of manipulating highly focused SAW propagation
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