Particle Deflection in a Poly(dimethylsiloxane) Microchannel Using a Propagating Surface Acoustic Wave: Size and Frequency Dependence

Abstract

We study the effect of a propagating surface acoustic wave (PSAW) with different frequencies on particles with different sizes in microfluidic channels. We find that the deflection critically depends on the applied frequency as well as on the particle size. For fixed frequencies, large particles are deflected and migrate perpendicular to the flow direction while smaller particles only follow the streamlines of the flow field. However, with increasing frequency of the PSAW above a size dependent limit, small particles are also actuated. This relation can be characterized by the wavenumber k and the particle radius r using the parameter κ = k · r. For the onset of deflection, we find a critical value κc ≅ 1.28 ± 0.20. Finally, we demonstrate how this device can be used for particle separation.

Acoustic impedance-based manipulation of elastic microspheres using travelling surface acoustic waves

“…It has been observed that a transition in particles' response occurs at k y 1 for most particle materials suspended in water. 3,29,30 However, the actual value can vary slightly with changes in uid composition and particle materials.…”

Vertical Hydrodynamic Focusing and Continuous Acoustofluidic Separation of Particles via Upward Migration

“…On the other hand, TSAWs have been used in cross‐type acoustic particle separators to laterally migrate particles and realize separation across the microchannel width or within a sessile droplet, because particles predominantly migrate within the horizontal plane 11, 25, 26, 27. Most SAW‐based acoustofluidic separation techniques utilize forces that act on micro‐objects suspended in a horizontal plane while pushing them laterally inside the microchannel 28, 29, 30, 31, 32. The interaction between TSAWs and the fluid results in leaky acoustic waves that radiate at an angle of ≈22° (in systems comprising water and a lithium niobate (LiNbO 3 ) substrate) inside the microfluidic channel, such that the vertical component ( F v ) of the acoustic radiation force (ARF) acting on the suspended particles is ≈2.5 times greater than the horizontal component of the force ( F h ), i.e., F v ≅ 2.5 F h 33.…”

“…The interaction between TSAWs and the fluid results in leaky acoustic waves that radiate at an angle of ≈22° (in systems comprising water and a lithium niobate (LiNbO 3 ) substrate) inside the microfluidic channel, such that the vertical component ( F v ) of the acoustic radiation force (ARF) acting on the suspended particles is ≈2.5 times greater than the horizontal component of the force ( F h ), i.e., F v ≅ 2.5 F h 33. The SAW‐based acoustofluidic devices that utilize the horizontal component of an ARF are composed of an interdigitated transducer (IDT) integrated into the side of a single‐layered PDMS microchannel 30, 34, 35, 36. (see Figure S1a in the Supporting Information).…”

“…(see Figure S1a in the Supporting Information). A multiple‐layered PDMS microchannel with a post beneath the micro‐object manipulation zone was also used in a similar fashion to deflect particles30 and sort cells or droplets 28. IDTs may also be positioned directly beneath a microchannel to induce desired particle migration.…”

Particle manipulation using macroscale angled ultrasonic standing waves

“…Acoustic radiation forces are widely used at the MEMS (Micro Electro Mechanical Systems) scale to manipulate particles. [9][10][11] Typically, the fluid channels are on the order of half a wavelength and the radiation force on the particles is used to cause particle deflections. These systems operate at low flow rates (µL/min) and are not directly scalable to high flow rates.…”