Acoustofluidic manipulation of microparticles using surface acoustic wave induced streaming

Stringer Martin, Mercedes 2024. Acoustofluidic manipulation of microparticles using surface acoustic wave induced streaming. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Acoustofluidics enables contact-free manipulation of particles and fluids, offering transformative potential for biomedical applications. Recent advancements in acoustic streaming, driven by leaky surface acoustic waves (SAWs) generated through radio frequency signals applied interdigital transducers (IDTs) on piezoelectric substrates, have gained significant attention. This technique addresses challenges posed by low Reynolds numbers in micro- and nanoscale liquids, paving the way for applications such as isolating tumour cells, precise drug delivery, and tissue engineering. This thesis extensively reviews the mechanisms and applications of acoustic streaming, revealing promising new avenues. The primary aim was to investigate innovative configurations for producing acoustic streaming with SAWs to enable versatile applications. A reconfigurable device utilizing a Hexagonal Flexible Printed Circuit Board (FPCB) IDTs was developed for rapid investigations beyond the limitations of conventional IDTs. This approach, combined with numerical analysis using COMSOL Multiphysics, allowed exploration of wave mode characteristics at different angles and their resulting acoustic streaming actuation. Significant findings include enhanced acoustic streaming at 90° pseudo shear-horizontal-SAW (P-SH-SAW) compared to the conventional Rayleigh SAW (R-SAW at 0°) under identical power (30 dBm / 1 W) and fluid volume (100 μL) conditions. The 90° P-SH-SAW at 34.4 MHz achieved an average area streaming velocity of 1.58 mm/s - approximately 15% higher than the R-SAW at 0° (1.35 mm/s at 19.8 MHz) - despite having a Z-displacement magnitude that was ~40% of the R-SAW. At a constant fluid viscosity (60:40 water:glycerol), P-SH-SAW consistently outperformed R-SAW by ~50% across all tested powers (20, 27, and 30 dBm). When varying viscosity, P-SH-SAW maintained higher streaming velocities, with over 50% improvement at low viscosity and a 55% drop at high viscosity, compared to a 42% drop for R-SAW. Streaming of a 1 mL fluid volume (25 mm diameter PDMS ring) was achieved within 2 seconds using pseudo-SH-SAW at 30 dBm, whereas R-SAW showed minimal displacement. Notably, P-SH-SAW induced streaming through a standard 96-well culture plate at 30 dBm, achieving velocities of ≈1.2 mm/s, whereas R-SAW failed to generate effective streaming under the same conditions. These ii results highlight the potential of using combined wave modes and multidirectional SAW configurations on the 128° YX-cut LiNbO3 substrate for enhanced fluid manipulation. These combined wave modes achieved enhanced particle concentration for 10 μm, 1 μm, and 500 nm particles. For example, R-SAW plateaued early - often within the first 20% of the actuation time - while the combined wave modes continued to concentrate particles steadily throughout the duration, demonstrating superior performance for micro- and nanoparticle manipulation. The development and characterization of the Hexagonal FPCB IDT expanded understanding of how anisotropic properties affect acoustic streaming. This insight improves device optimization by shifting focus from altering IDT designs to manipulating the wave mode selection. These findings address key challenges such as excessive damping of R-SAW and low-power acoustic streaming, optimizing device performance. The Hexagonal FPCB IDT supports multiple applications by utilizing different IDTs, providing the foundation for future research.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	Acoustofluidics; Acoustic Streaming; Surface Acoustic Wave; Interdigital Transducer; Wave Modes; Particle Manipulation
Funders:	EPSRC
Date of First Compliant Deposit:	22 May 2025
Last Modified:	22 May 2025 14:19
URI:	https://orca.cardiff.ac.uk/id/eprint/178404

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