The effect of microchannel height on the acoustophoretic motion of sub-micron particles

Tsz Wai Lai; Thilhara Tennakoon; Ka Chung Chan; Chun-Ho Liu; Christopher Yu Hang Chao; Sau Chung Fu

doi:10.1016/j.ultras.2023.107126

The effect of microchannel height on the acoustophoretic motion of sub-micron particles

Ultrasonics. 2024 Jan:136:107126. doi: 10.1016/j.ultras.2023.107126. Epub 2023 Jul 27.

Authors

Tsz Wai Lai¹, Thilhara Tennakoon¹, Ka Chung Chan¹, Chun-Ho Liu², Christopher Yu Hang Chao³, Sau Chung Fu⁴

Affiliations

¹ Department of Building Environment and Energy Engineering, The Hong Kong Polytechnic University, Hong Kong, China.
² Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China.
³ Department of Building Environment and Energy Engineering, The Hong Kong Polytechnic University, Hong Kong, China; Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hong Kong, China.
⁴ Department of Building Environment and Energy Engineering, The Hong Kong Polytechnic University, Hong Kong, China. Electronic address: schung.fu@polyu.edu.hk.

PMID: 37553269
DOI: 10.1016/j.ultras.2023.107126

Abstract

Acoustophoresis is an effective technique for particle manipulation. Acoustic radiation force scales with particle volume, enabling size separation. Yet, isolating sub-micron particles remains a challenge due to the acoustic streaming effect (ASE). While some studies confirmed the focusing ability of ASE, others reported continuous stirring effects. To investigate the parameters that influence ASE-induced particle motion in a microchannel, this study examined the effect of microchannel height and particle size. We employed standing surface acoustic wave (SSAW) to manipulate polystyrene particles suspended in the water-filled microchannel. The results show that ASE can direct particles as small as 0.31 µm in diameter to the centre of the streaming vortices, and increasing the channel height enhances the focusing effect. Smaller particles circulate in the streaming vortices continuously, with no movement towards the centres. We also discovered that when the channel height is at least 0.75 the fluid wavelength, particles transitioning from acoustic radiation-dominated to ASE-dominated share the same equilibrium position, which differs from the pressure nodes and the vortices' centres. The spatial distance between particles in different categories can lead to particle separation. Therefore, ASE is a potential alternative mechanism for sub-micron particle sorting when the channel height is accurately adjusted.

Keywords: Acoustic streaming; Acoustophoresis; Microfluidics; Particle concentration; Sub-micron particle separation.