Microfluidic actuation on lithium niobate and paper substrates using MHZ surface and bulk acoustic waves.

Rezk, A 2014, Microfluidic actuation on lithium niobate and paper substrates using MHZ surface and bulk acoustic waves., Professional Doctorate, Electrical and Computer Engineering, RMIT University.

Document type: Thesis
Collection: Theses

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Title Microfluidic actuation on lithium niobate and paper substrates using MHZ surface and bulk acoustic waves.
Author(s) Rezk, A
Year 2014
Abstract Surface acoustic waves are ~ 1 nm amplitude vibrations that can be generated on a piezoelectric material by applying an alternating current. Due to the relatively high frequency (MHz range), the generated surface vibration velocity is typically ~ 1 m/s with a tremendous acceleration of 107 m/s. For the last decade, SAW have found their way into a wide range of microfluidic applications, and a fascinating variety of fluid and micro-particle flow phenomena. However, the majority of these applications have been without a deep understanding of the governing physics in conjunction with a systematic experimental study; justifiably, due to the complexity of the interactions of these waves with fluids considering the high frequency used, (MHz range), compared to the natural resonance frequency of these fluids (Hz and KHz range). In this thesis, we demonstrate through experimental, theoretical, and limited numerical study how SAW interacts with microfluidic films and drops, and through the investigation we unravel two novel phenomena of unique fingering instability and soliton-like wave emergence and propagation, although the former — i.e. fingering instability — is akin in appearance to the classical viscous fingering instability, is distinct as the driving mechanism being the SAW diffraction. Beyond elucidating the underlying physics governing SAW-driven thin films, we designed an experimental setup comprising the integration of the SAW with microchannels patterned on a wet paper substrate, where a thin film at the paper’s tip was drawn out using SAW atomisation, which, led to driving the rest of the fluids at the channel’s other ends, leading to fluid mixing along the michrochannels. Mixing was quantified using a novel technique based on hue, which is shown to be more practical solution compared to the commonly known greyscale method, because of the latter’s lack of accuracy with limited colour contrast between fluids. Beyond the thorough experimental and theoretical understanding and integration with paper based microfluids, finally, for cost of effectiveness and simplicity of use we trade off SAW with a similar type of waves, in some aspects known as the Lamb waves to drive a range of microfluidic applications already achieved a SAW. The setup used here is exceptionally simple to the point that, in some cases, only standard aluminium foil is sufficient in simple contact with the lithium niobate substrate to good actuation. Large elastic deformations were achieved causing nebulisation of triggering a few mm mono-dispersed mist from a single microliter drop or a paper wick.
Degree Professional Doctorate
Institution RMIT University
School, Department or Centre Electrical and Computer Engineering
Keyword(s) microfluidics
surface acoustic waves
MHz vibrations
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Created: Fri, 11 Jul 2014, 15:37:39 EST by Lynne Johns
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