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Abstract

Droplet actuation using surface acoustic wave (SAW) technology has recently been widely employed in “lab-on-a-chip” applications. In this article, SAWs generated by interdigital transducers (IDTs) were used to actuate microdroplets, where their velocity and direction could be adjusted by changing only the excitation phase shift, θ , of the voltage applied to the two IDTs. Specifically, the equation of the vibration of the mixed traveling surface acoustic waves (TSAWs) and standing surface acoustic waves (SSAWs) formed on the substrate surface operating in the exciter–exciter mode has been reported by the authors. An analytical expression for the acoustic standing wave ratio has been derived and given as a function of θ and the spatial phase difference. It can be seen from the expression that the directions of the TSAWs will be opposite to each other, in the range of θ given by (0, π) and (π, 2π), and the component of the TSAWs can be adjusted by changing θ in each direction. Following the theoretical analysis discussed here, two IDTs have been excited to generate a mixture of TSAWs and SSAWs. A series of experiments was carried out to control the velocity and direction of the actuated droplets, by changing only θ . In addition, an experiment performed to compare the techniques shows that the upper limit of the velocity of the actuated droplets can be significantly increased using the exciter–exciter mode, showing that it has the potential to be an alternative method to the traditional exciter–absorber mode.

Publication Type:	Article
Additional Information:	© 2023 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
Publisher Keywords:	Surface Acoustic Wave (SAW), Inter-Digital Transducers (IDTs), Exciter-Exciter mode, excitation phase shift, Standing Wave Ratio (SWR)
Subjects:	Q Science > QC Physics T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > Engineering
SWORD Depositor:	Symplectic Administrator

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