Advertisement

Experiments in Fluids

, 56:67 | Cite as

Mechanism and flow measurement of AC electrowetting propulsion on free surface

  • Junqi Yuan
  • Sung Kwon ChoEmail author
Research Article

Abstract

A free surface in contact with a floating object can be vertically oscillated by applying an alternating current electrowetting-on-dielectric (AC EWOD). The oscillation of the free surface generates a propelling force on the centimeter-sized floating object. This paper describes a propulsion mechanism in free-surface oscillation along with its experimental results. Flow visualizations, wave patterns measured by the free-surface synthetic schlieren method, and PIV measurements show that the oscillation generates a capillary Stokes drift on the water surface and two counter-rotating spiral underwater vortices, leading to an ejecting flow (streaming flow) normal to the wall of the boat. The momentum of the ejecting flow produces a reaction force on the wall and ultimately propels the floating boat. The propulsion speed of the boat highly depends on the amplitude, frequency, and shape of the AC EWOD signal. Curve fittings based on the Stokes drift well match the experimental measurements of propulsion speed. The width of the EWOD electrode also has significant effects on the boat speed.

Keywords

Contact Angle Free Surface Particle Image Velocimetry Contact Line Oscillation Amplitude 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols

A

Wave amplitude (m)

b

Width of electrode (m)

Aboat

Projected area of submerged boat part (m2)

CD

Drag coefficient

f

Frequency of applied AC signal (Hz)

Fdrag

Drag force (N)

Fprop

Propulsion force (N)

g

Gravitational acceleration (m/s2)

h

Water depth (m)

k

Wavenumber (1/m)

t

Thickness of dielectric layer (m)

udrift

Time-averaged drift velocity (m/s)

uboat

Boat propulsion speed (m/s)

V

Voltage applied to EWOD system (V)

Vd

Voltage across dielectric layer (V)

z

Vertical position from free surface (m)

γLV

Air–water surface tension (N/m)

ε0

Vacuum permittivity (8.854 × 10−12 F/m)

εr

Relative permittivity of dielectric layer

ω

Angular frequency of wave (rad/s)

ρ

Density (kg/m3)

θ

Contact angle (°)

θ0

Initial contact angle with no voltage applied (°)

C

Coefficient in Eq. (8)

Notes

Acknowledgments

This work is in part supported by the NSF Grant (ECCS-1029318).

Supplementary material

Supplementary material 1 (MOV 3024 kb)

Supplementary material 2 (MOV 5051 kb)

Supplementary material 3 (MOV 3167 kb)

Supplementary material 4 (MOV 2854 kb)

Supplementary material 5 (MOV 925 kb)

References

  1. Billingham J, King AC (2000) Wave motion. Cambridge University Press, CambridgezbMATHGoogle Scholar
  2. Cho SK, Moon H, Kim CJ (2003) Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits. J Microelectromech Syst 12:70–80CrossRefGoogle Scholar
  3. Chung SK, Ryu K, Cho SK (2009) Electrowetting propulsion of water-floating objects. Appl Phys Lett 95:014107CrossRefGoogle Scholar
  4. Craik ADD (1985) Wave interactions and fluid flows. Cambridge University Press, CambridgezbMATHGoogle Scholar
  5. Floyd S, Sitti M (2008) Design and development of the lifting and propulsion mechanism for a biologically inspired water runner robot. IEEE Trans Robot 24:698–709CrossRefGoogle Scholar
  6. Hocking LM (1987) Waves produced by a vertically oscillating plate. J Fluid Mech 179:267–281CrossRefzbMATHGoogle Scholar
  7. Hu DL, Prakash M, Chan B, Bush JWM (2007) Water-walking devices. Exp Fluids 43:769–778CrossRefGoogle Scholar
  8. Ko SH, Lee H, Kang KH (2008) Hydrodynamic flows in electrowetting. Langmuir 24:1094–1101CrossRefGoogle Scholar
  9. Kundu PK, Cohen IM, Dowling DR (2011) Fluid mechanics, 5th edn. Academic Press, AmsterdamGoogle Scholar
  10. Li F, Mugele F (2008) How to make sticky surfaces slippery: contact angle hysteresis in electrowetting with alternating voltage. Appl Phys Lett 92:244108CrossRefGoogle Scholar
  11. Luo C, Li H, Liu X (2008) Propulsion of microboats using isopropyl alcohol as a propellant. J Micromech Microeng 18:067002CrossRefGoogle Scholar
  12. Mesquita ON, Kane S, Gollub JP (1992) Transport by capillary waves: fluctuating Stokes drift. Phys Rev A 45:3700–3705CrossRefGoogle Scholar
  13. Miraghaie R, Sterling JD, Nadim A (2006) Shape oscillation and internal mixing in sessile liquid drops using electrowetting-on-dielectric (EWOD). Nanotechnology 2:610–613Google Scholar
  14. Mita Y, Li Y, Kubota M et al (2009) Demonstration of a wireless driven MEMS pond skater that uses EWOD technology. Solid-State Electron 53:798–802CrossRefGoogle Scholar
  15. Moisy F, Rabaud M, Salsac K (2009) A synthetic Schlieren method for the measurement of the topography of a liquid interface. Exp Fluids 46:1021–1036CrossRefGoogle Scholar
  16. Mugele F, Baret JC, Steinhauser D (2006) Microfluidic mixing through electrowetting-induced droplet oscillations. Appl Phys Lett 88:204106CrossRefGoogle Scholar
  17. Mugele F, Staicu A, Bakker R, van den Ende D (2011) Capillary Stokes drift: a new driving mechanism for mixing in AC-electrowetting. Lab Chip 11:2011–2016CrossRefGoogle Scholar
  18. Ozcan O, Wang H, Taylor JD, Metin Sitti (2010) Surface tension driven water strider robot using circular footpads. In: IEEE transactions of robotics automation, Anchorage, AK, pp. 3799-3804Google Scholar
  19. Phillips OM (1977) The dynamics of the upper ocean. Cambridge University Press, CambridgezbMATHGoogle Scholar
  20. Pollack MG, Fair RB, Shenderov AD (2000) Electrowetting-based actuation of liquid droplets for microfluidic applications. Appl Phys Lett 77:1725–1726CrossRefGoogle Scholar
  21. Ramshankar R, Berlin D, Gollub JP (1990) Transport by capillary waves. Part I. Particle trajectories. Phys Fluids 2:1955–1965CrossRefGoogle Scholar
  22. Sen P, Kim CJ (2009) Capillary spreading dynamics of electrowetted sessile droplets in air. Langmuir 25:4302–4305CrossRefGoogle Scholar
  23. Shin B, Kim HY, Cho KJ (2008) Towards a biologically inspired small-scale water jumping robot. In: IEEE international conference on biomedical robotics and biomechatronics, Scottsdale, AZ, USA, pp 127–131Google Scholar
  24. Song YS, Sitti M (2007) STRIDE: a highly maneuverable and non-tethered water strider robot. In: IEEE transactions on robotics and automation, pp 980–984Google Scholar
  25. Suzuki K, Takanobu H, Noya K, Koike H, Miura H (2007) Water strider robots with microfabricated hydrophobic legs 2007 IEEE/RSJ. In: International conference on intelligent robots and systems. San Diego, CA, pp 590–595Google Scholar
  26. ‘t Mannetje DJCM, Murade CU, van den Ende D, Mugele F (2011) Electrically assisted drop sliding on inclined planes. Appl Phys Lett 98:014102CrossRefGoogle Scholar
  27. Tejada-Martínez AE, Akkerman I, Bazilevs Y (2011) Large-eddy simulation of shallow water Langmuir turbulence using isogeometric analysis and the residual-based variational multiscale method. J Appl Mech 79:010909CrossRefGoogle Scholar
  28. Thorpe SA (2004) Langmuir circulation. Annu Rev Fluid Mech 36:55–79CrossRefMathSciNetGoogle Scholar
  29. Vallet M, Berge B, Vovelle L (1996) Electrowetting of water and aqueous solutions on poly(ethylene terephthalate) insulating films. Polymer 37:2465–2470CrossRefGoogle Scholar
  30. Vallet M, Vallade M, Berge B (1999) Limiting phenomena for the spreading of water on polymer films by electrowetting. Eur Phys J B 11:583–591CrossRefGoogle Scholar
  31. Zhang X, Zhao J, Zhu Q, Chen N, Zhang M, Pan Q (2011) Bioinspired aquatic microrobot capable of walking on water surface like a water strider. ACS Appl Mater Interfaces 3:2630–2636CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  1. 1.Department of Mechanical Engineering and Materials ScienceUniversity of PittsburghPittsburghUSA

Personalised recommendations