Acoustofluidics 9: Modelling and applications of planar resonant devices for acoustic particle manipulation

This article introduces the design, construction and applications of planar resonant devices for particle and cell manipulation. These systems rely on the pistonic action of a piezoelectric layer to generate a one dimensional axial variation in acoustic pressure through a system of acoustically tuned layers. The resulting acoustic standing wave is dominated by planar variations in pressure causing particles to migrate to planar pressure nodes (or antinodes depending on particle and fluid properties). The consequences of lateral variations in the fields are discussed, and rules for designing resonators with high energy density within the appropriate layer for a given drive voltage presente

The development and deployment of formal methods in the UK

UK researchers have made major contributions to the technical ideas underpinning formal approaches to the specification and development of computer systems. Perhaps as a consequence of this, some of the significant attempts to deploy theoretical ideas into practical environments have taken place in the UK. The authors of this paper have been involved in formal methods for many years and both have tracked a significant proportion of the whole story. This paper both lists key ideas and indicates where attempts were made to use the ideas in practice. Not all of these deployment stories have been a complete success and an attempt is made to tease out lessons that influence the probability of long-term impact.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

Mode-switching: a new technique for electronically varying the agglomeration position in an acoustic particle manipulator

Acoustic radiation forces offer a means of manipulating particles within a fluid. Much interest in recent years has focussed on the use of radiation forces in microfluidic (or “lab on a chip”) devices. Such devices are well matched to the use of ultrasonic standing waves in which the resonant dimensions of the chamber are smaller than the ultrasonic wavelength in use. However, such devices have typically been limited to moving particles to one or two predetermined planes, whose positions are determined by acoustic pressure nodes/anti-nodes set up in the ultrasonic standing wave. In most cases devices have been designed to move particles to either the centre or (more recently) the side of a flow channel using ultrasonic frequencies that produce a half or quarter wavelength over the channel, respectively.It is demonstrated here that by rapidly switching back and forth between half and quarter wavelength frequencies – mode-switching – a new agglomeration position is established that permits beads to be brought to any arbitrary point between the half and quarter-wave nodes. This new agglomeration position is effectively a position of stable equilibrium. This has many potential applications, particularly in cell sorting and manipulation. It should also enable precise control of agglomeration position to be maintained regardless of manufacturing tolerances, temperature variations, fluid medium characteristics and particle concentration

An Experimental and Numerical Investigation of Drag Reduction Through Biomimetic Modelling

This paper characterises flow around a circular cylinder and investigates the potential of a non-smooth surface to reduce air resistance in a Reynolds number range between Red = 8.09 104 and Red = 2.02 105. The two- and three-dimensional numerical simulations were performed using a steady-state solution and the Reynolds-averaged Navier-Stokes (RANS) approaches. Three different mesh designs and four turbulence models with various treatments were assessed and compared against experimental data. A total of 26 uneven preparations in the two-dimensional analysis and two riblet structures in the three-dimensional analysis were designed to investigate the effect of drag reduction. The results reported hold the potential of uneven structures to reduce the air resistance in the case of a circular cylinder. This research further demonstrates that engineering applications can benefit from mimicking nature's details and functions

A Numerical Bubbly Flow Investigation of Drag Reduction for Underwater Vehicles

This paper discusses the numerical investigation of dispersed bubbly flow within the boundary layer of a fully submerged axisymmetric body in horizontal position. The aim is to analyse the influence of injection position and bubble parameters on the drag reduction behaviour. The numerical study is conducted with the commercial CFD package ANSYS Fluent using the Eulerian-Eulerian modelling approach. Several sets of simulations are carried out with air injection velocities in the rage of 1 m/s to 15 m/s, injection locations between 0 and 0.5 m, and bubble diameters from 0.1 mm to 2 mm. In order to obtain the percentage drag reduction the results are correlated with a model without air injection. The simulations demonstrate a different behaviour between small and large bubble diameters of 0.1 mm and 2 mm respectively. Small bubbles archive drag reduction rates around 10% almost independent from the injection velocity and position, while large bubbles are highly affected by those parameters. The maximum drag reduction of 20.67% is achieved by injecting bubbles of 2 mm diameter with a velocity of 12.5 m/s at the tip of the prow nose. It is presented that the drag reduction increases with increasing injection velocity and bubble diameter. These parameters enable the bubbles to build up a continuous film across large parts of the hull which is required for a sufficient drag reduction

Effects of surface profile on a boundary-driven acoustic streaming field

Acoustic streaming fields in two-dimensional rectangular enclosures that have structured boundaries are simulated and the effects of surface profile amplitude on a boundary-driven acoustic streaming field are numerically investigated. The standing wave fields in the enclosures are generated by excitation of a boundary and a sine-wave shaped profile on a boundary parallel to the particle oscillations is considered. This surface profile is found to have a large influence on the magnitude of both outer and inner streaming velocities. In terms of streaming pattern, it is found that the number of inner streaming vortices is dependent on the wavelength of profile while this profile has a less significant effect on the outer vortex pattern

Numerical simulation of 3D acoustophoretic motion of microparticles in an acoustofluidic device

Acoustic streaming is typically found in addition to acoustic radiation forces in acoustofluidic devices. Simulation of acoustic streaming is a crucial step for the understanding of its origins, which can provide efficient guidance on creating designs to limit or control this phenomenon. However, most existing methods can only simulate the streaming field in a local area, typically a cross-section of fluid channel. In this work, the three-dimensional (3D) Rayleigh streaming pattern in an acoustofluidic device is simulated and its effects on the movement of microparticles with various sizes are demonstrated. The viability of the simulation of 3D Rayleigh streaming presented here not only can provide better understanding and more comprehensive prediction of experiments in full acoustofluidic devices, but also can offer instructions on the simulation of unusual acoustic streaming patterns, e.g. transducer-plane streamin