Apparatus used to study charge shuttling. (a) Schematic of the system. A droplet of insulating oil containing a single Wood’s metal (WM) sphere is placed between two flat electrodes. The current carried by the moving sphere is measured as a function of the voltage applied across the electrodes, . (b) An optical microscope image of the electrodes and a single -radius WM sphere in silicone oil. When the voltage is applied, the sphere picks up charge from one electrode and is pushed toward the other, where the charge is reversed and the sphere returns. (c) A scanning electron micrograph of a WM sphere in vacuum.
Plot of measured current vs time for an -radius shuttle in silicone oil with and . The large spikes correspond to transfer of charge during contact between the shuttle and one of the electrodes. In this case, the gap traversal time, , is .
Measured time-averaged current, vs applied voltage for shuttles in relatively high-viscosity silicone oil . The plots show different radii , 53, and and different electrode spacings . The open circles (squares) are for increasing (decreasing) . The heavy black curves represent the results of the model described in Sec. IV.
(Color online) Plot of the current as a function of the current predicted from the overdamped-motion model described in the text. All of the data for silicone oil are shown here, with different colors representing different devices.
Measured shuttle frequency in high-viscosity silicone oil as a function of applied voltage. Top: and ; was measured using light scattering. Bottom: and ; was measured from the current-vs-time trace of Fig. 2.
Measured time-averaged current, vs applied voltage for shuttles in relatively low-viscosity hexadecane . The plots show different radii , 73, and (from left to right) and different electrode spacings . The open circles (squares) are for increasing (decreasing) . The heavy black curves represent the results of the model described in Sec. IV.
Plot of measured vs for two hexadecane samples. Top: . The discontinuous change in the slope is seen in the log-log-scale plot at ; the straight lines are guides to the eye (inset). Bottom: , showing a slope discontinuity at .
Plot of normalized measured current as a function of the forcing, where and is the viscous relaxation time, as described in the text. The data for hexadecane appear at the upper left and that for silicone oil at the lower right. The dashed curve shows the prediction from the model in which the elastic rebound is ignored (dashed curve).
Summary of the fit, theory, and measured capacitances and the voltage-scaling exponent . The fit capacitance was obtained by fitting to ; measured capacitance was obtained from the plots of vs ; the calculated (“theory”) capacitance is .
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