  A droplet of millimeter-to-centimeter scale can exhibit electrostatic
levitation, and such levitated droplets can be used for the measurement of the
surface tension of the liquids by observing the characteristic frequency of
oscillatory deformation. In the present study, a simple mechanical model is
proposed by considering a single mode of oscillation in the ellipsoidal
deformation of a levitated rotating droplet. By measuring the oscillation
frequency with respect to the rotational speed and oscillation amplitude, it is
expected that the accuracy of the surface tension measurement could be
improved. Using the proposed model, the dependences of the characteristic
frequency of oscillatory deformation and the averaged aspect ratio are
calculated with respect to the rotational angular velocity of a rotating
droplet. These dependences are found to be consistent with the experimental
observations.
