Resonant vibration and flashover phenomena of a water droplet located on a hydrophobic sheet under ac field

The electrohydrodynamic behavior of a single water droplet located on a hydrophobic silicone rubber sheet under an ac electric field was investigated. The water droplet under the ac electric field vibrates strongly at a particular frequency range. It corresponds to resonant vibration with natural frequency defined with the diameter of the droplet. To make the effect of resonant vibration on flashover via the water droplet clear, the time variation of the shape of a 30 μl droplet placed between the parallel electrodes was observed with a high-speed video camera. The flashover voltage via the droplet at the resonant frequency of 19 Hz was much lower than that at 50 Hz owing to larger deformation of the droplet.