Efficient counter-propagating wave acoustic micro-particle manipulation

Abstract

A simple acoustic system consisting of a pair of parallel singe layered piezoelectric transducers submerged in a fluid used to form standing waves by a superposition of two counter-propagating waves is reported. The nodal positions of the standing wave are controlled by applying a variable phase difference to the transducers. This system was used to manipulate polystyrene micro-beads trapped at the nodal positions of the standing wave. The demonstrated good manipulation capability of the system is based on a lowering of the reflection coefficient in a narrow frequency band near the through-thickness resonance of the transducer plates.

Ultrasound assisted particle and cell manipulation on-chip

“…Recently there has been substantial interest in building devices that allow more dexterous manipulation of particles through the use of planar arrays of transducers [44] and different configurations of opposing transducers [45,46].…”

Contactless Acoustic Manipulation and Sorting of Particles by Dynamic Acoustic Fields

“…However, this method presents several challenges, such as an unstable force resulting in movement among trapped particles. A different strategy to manipulate particles uses two acoustic emitters producing counter-propagating waves as demonstrated in liquid by Grinenko et al [20]. The superposition between these two propagating waves, results in a standing acoustic wave with fixed pressure nodes where the particles can be trapped.…”

“…The pressure nodes and thus the trapping positions can be translated and adjusted by changing the phase difference between the two emitters [21]. This technique has been applied in air [21] and in liquid media [20], [22]. In the ideal case, the wave generated by one sound emitter should be completely absorbed by the opposite emitter.…”

“…reflected by the emitter surface can superimpose on the acoustic standing wave, reducing the manipulation capability and interfering with the trapping process. In practice, acoustic manipulation can only be achieved when the reflection coefficient of the emitters is lower than 0.5 [20]. In the case of particle manipulation in liquid media, the reflection coefficient can be minimized by using piezoelectric transducers with matching and absorbing backing layers [20], [23].…”

Measurements of the force fields within an acoustic standing wave using holographic optical tweezers

“…24,25 In this work, we use the device for onedimensional trapping by driving a pair of oppositely mounted piezoelectric transducers to create a parallel set of acoustic pressure nodal planes throughout the sample (see Figure 1). The acoustic trap positions can be controlled in x by adjusting the relative phase of the transducers.…”