The electrodes are arranged such that given any two adjacent electrodes, one has positive voltage and the other has negative voltage. Each electrode is smaller than a scratch drive, so that no matter the position or orientation of a given scratch drive, it always lies above some area of positive voltage, and some area of negative voltage.
Because the scratch drive is made of conductive silicon but is coated with an insulating layer, charge flows within the scratch drive in response to the voltage on the underlying electrodes, but it will not flow into the electrodes. So, there is charge build-up on the underside of the scratch drive plate. This charge build-up causes the electrostatic attraction that results in motion of the scratch drive.
The typical drive voltage of a scratch drive actuator is 150 V . In order to achieve an equivalent voltage with the capacitive couple, approximately 300 volts must be applied between the high-voltage electrodes and the grounded electrodes.