Corona Enhanced Electrowetting and Dielectrophoresis in a Dielectric Fluid

The response to a step voltage of a system comprising a needle-like upper electrode partially immersed in dielectric oil, and a bottom flat electrode has been analysed. The fluid meniscus at the oil-air interface around needle electrode rises up when a voltage is applied and drops down on switch off with characteristic time constants. In the case where the interface has been charged by corona spraying, after the voltage is switched off and the meniscus has decayed, a secondary lift of the fluid occurs, which raises the fluid to a higher level than before. This is connected to the relaxation of the surface charges and it is present only when corona injection exists. Surprisingly, the system reacts in a similar way when a very low frequency is applied. In this case the fluid can rise to twice the height of that in the DC case