Lukas et al. reported an electrospinning setup that used linear clefts as the spinneret (Fig. 7.6). The authors also developed a one-dimensional electrohydrodynamic theory to explain the process of electrospinning conductive liquids from an open plane surface (Fig. 7.6). During the electrospinning process, the amplitude of characteristic wavelength grew faster because of the electrical force. The fastest-growing stationary wave marked the onset of electrospinning from a free liquid surface. This theory not only predicated the critical value of the electrospinning process but also explained the upward needle-less electrospinning.