  Fast contact-line motion of a droplet spreading on a solid substrate under
the electrowetting effect generates strong capillary waves on the droplet's
surface. The capillary waves may be strong enough to induce ejection of a
satellite droplet from the primary one. In this study, we show that the size of
the satellite droplet and the ejection time are not only dependent on the
contact-line velocity, which directly relates to the applied voltage enabling
the electrowetting effect, but also affected by the ejection dynamics. We
derive a theoretical model of the criteria for droplet ejection and
experimentally verify the proposed criteria for wide ranges of viscosity,
droplet size and the applied voltage.
