Experimental investigation of the particle oscillation instability in a single-axis acoustic levitator

Marco A B Andrade,Spyros Polychronopoulos,Asier Marzo,Gianluca Memoli

doi:10.1063/1.5078948

Abstract

Single-axis acoustic levitators are employed in biomedicine, chemistry and physics experiments due to their ability to trap in mid-air objects of a wide range of materials and sizes. Although this type of levitator has been studied for decades, there are effects that are not well understood. One of these effects is the particle oscillation instability, in which the levitating particle starts to oscillate with increasing amplitude until it is ejected out of the levitator. Most of the operations performed with acoustic levitation require high accuracy regarding the positioning of the particle, thus a lack of stability severely hinders the experiments. In this paper, we present an experimental setup that consists of a single-axis levitator, a mechanized stage to control the separation between the emitter and the reflector, a scale to measure the radiation force and a high-speed camera. We experimentally investigate the effect of the distance between the emitter and the reflector on the apparatus resonant frequency and on levitation stability. In accordance with previous theoretical studies, three types of levitation behavior were experimentally identified: stable levitation, oscillation of constant amplitude and unstable oscillation. We also show that the type of levitation behavior can be controlled by changing the distance between the emitter and the reflector.

Highlights

Acoustic levitation[1,2] uses the radiation force[3] generated by sound waves to suspend liquids[4,5] and solids[6] in mid-air
The transducer emitted a sinusoidal wave of 25.25 kHz, and the levitator operated under the first mode (H ≈ λ 2), with λ being the acoustic wavelength (λ = 13.58 mm). This apparatus creates a standing wave where a small sphere can levitate at the pressure node
We presented an apparatus to measure the oscillations of a levitated sphere in a single-axis acoustic levitator

Summary

Introduction

Acoustic levitation[1,2] uses the radiation force[3] generated by sound waves to suspend liquids[4,5] and solids[6] in mid-air. There are various types of acoustic levitators.[17–21] The most commonly used and studied one is the single-axis levitator which consists of an emitter and an opposing reflector,[22–26] or two opposing emitters.[27,28]. In this type of levitator, a standing wave is formed between the two opposed elements and particles can be trapped at the pressure nodes.[3] There are various types of acoustic levitators.[17–21] The most commonly used and studied one is the single-axis levitator which consists of an emitter and an opposing reflector,[22–26] or two opposing emitters.[27,28] In this type of levitator, a standing wave is formed between the two opposed elements and particles can be trapped at the pressure nodes.[3]

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Conclusion