Manipulation of particles in two dimensions using phase controllable ultrasonic standing waves

Abstract

The ability to manipulate dense micrometre-scale objects in fluids is of interest to biosciences with a view to improving analysis techniques and enabling tissue engineering. A method of trapping micrometre-scale particles and manipulating them on a twodimensional plane is proposed and demonstrated. Phase-controlled counter-propagating waves are used to generate ultrasonic standing waves with arbitrary nodal positions. The acoustic radiation force drives dense particles to pressure nodes. It is shown analytically that a series of point-like traps can be produced in a two-dimensional plane using two orthogonal pairs of counter-propagating waves. These traps can be manipulated by appropriate adjustment of the relative phases. Four 5 MHz transducers (designed to minimize reflection) are used as sources of counter-propagating waves in a waterfilled cavity. Polystyrene beads of 10 mm diameter are trapped and manipulated. The relationship between trapped particle positions and the relative phases of the four transducers is measured and shown to agree with analytically derived expressions. The force available is measured by determining the response to a sudden change in field and found to be 30 pN, for a 30 V pp input, which is in agreement with the predictions of models of the system. A scalable fabrication approach to producing devices is demonstrated.

Acoustically trapped colloidal crystals that are reconfigurable in real time

“…The metadevice consists of three orthogonally arranged systems: the levitation system, arranged vertically, which lifts the particles and holds them in horizontal planes, and two orthogonal manipulation stages, which use the counterpropagating wave method to produce a grid of acoustic traps in the horizontal plane. The lattice spacing can be controlled by the frequencies of the standing waves and the form and location of the lattice by the phase differences (16). The…”

Counterpropagating wave acoustic particle manipulation device for the effective manufacture of composite materials

“…Initially, the particle is assumed to be at a position x(0) = /8, where the acoustic force is a maximum. Analytical predictions are the solution to (6). An experimental value for the assembly time of a single particle is also indicated around t ⇠ 667 ms ± 200 ms.…”

“…The most common of these devices produce a standing wave between a transducer and a reflector (see reviews by Laurell et al [1] and Evander et al [2]) and have seen application, particularly in the biomedical field to, for example, tissue engineering [3], [4]. Devices with additional transducers have also been explored and shown to be able to create a wide range of patterns [5], [6], [7] and allow these patterns to be translated [8], [9], [10], [11].…”

Integrated ultrasonic particle positioning and low excitation light fluorescence imaging

“…Eight 5 mm × 5 mm plates of (NCE51 Noliac ceramic) lead zirconate titanate (PZT) had an alumina loaded epoxy acoustic matching layer applied. The thickness of the matching layer was optimised using a one-dimensional transmission line model to minimise the reflection of the incident waves 9 . The matching layers reduce resonances that would result in unwanted standing waves with nodal positions that were fixed by the geometry thus inhibiting translation of the field by phase variation.…”