On-chip surface acoustic-wave driven microfluidic motors

Abstract

We report on the design of two different surface acoustic wave (SAW) driven rotary motors. Both designs use 20-30 MHz transducers patterned onto Lithium Niobate (LN), geometrically tailored to generate Rayleigh waves that are incident on opposing sides of each rotor. The first design exploits the efficient coupling between SAWs and fluids by use of a fluid coupling layer between the rotor and substrate, leading to rotations of a 5 mm disc shaped rotor over 2,500 rpm with a start-up torque of 60 nN m. The second design exploits a dry friction contact between the surface and rotors for further miniaturisation. In the latter design 1 mm steel rotors are driven up to 6,000 rpm with no external preload required.

Acoustic Vibration‐Induced Actuation of Multiple Microrotors in Microfluidics

“…Dincel et al [ 61 ] also utilized trapped oscillating bubbles to actuate microrotors and achieved a rotational speed of 450 RPM at a frequency of 5.6 kHz. 4) For microrotor fabricated with lithography, Shilton et al [ 16 ] have actuated the disc shaped rotor to a rotation speed ≈2500 RPM using 20–30 MHz transducers; Lu et al [ 11 ] have controlled multiple microrotors within a rotating magnetic field then achieved the rotational speed ≈800 RPM; Leonardo et al [ 30 ] have utilized motile Escherichia coli to achieve single microrotor rotation at rotational speed of 6 RPM where the bacteria could propel along the rotor boundary; Brooks et al [ 32 ] have adopted the catalytic self‐electrophoresis to immerse multiple microrotors within hydrogen peroxide and exhibited the rotational speed of 1.5 rad s −1 (≈14.3 RPM). Among the acoustic actuation microrotor, this current work is different with the microrotor fabricated through UV polymerization, [ 14 ] where the rotor was required to rotate within ethanol medium to avoid adhering to stator axle or substrate.…”

“…To produce the mechanical motion of microrotors, it can be generally classified into two categories according to the source of energy: One is driven by an external actuation, such as through acoustic, [ 14–17 ] electric, [ 18,19 ] magnetic, [ 11,20,21 ] optical [ 22–25 ] field, and external forces like hydrodynamic force [ 26,27 ] and bacterial movement. [ 28–30 ] The other type of actuation is relying on the chemical energy [ 19,31 ] conversion within the microfluidic system, which can obtain self‐sustaining energy from the surrounding environment and exhibit microrotor self‐propulsion [ 32,33 ] capability.…”

Acoustofluidic actuation of in situ fabricated microrotors

“…27–29 Yue et al fabricated laser-actuated microgears with rotation rates around 60 revolutions per minute (RPM) at 2 watts. 20 Their method enabled simple in situ fabrication of microstructures in various geometries inside microchannels.…”

“…Lu et al and Ahn et al utilized magnetic actuation for micromixing 14 and micropumping, 6 which require magnetic components and relatively complex operational setups. Shilton et al introduced micromotors driven by surface acoustic waves 27,28 and obtained high rotation rates with a drawback of laborious and expensive fabrication. A table of performance comparison of existing microrotors is given in Table S1†.…”

“…However, further improvements in fabrication 6,14,27,28 and performance are necessary to improve the practicality and applicability of these microrotors. 20,21 Continuous or stop-flow UV polymerization techniques can yield complex microstructures for microfluidics in a simple fabrication.…”