Potential well of charged-walls

The potential well of the charged-wall in a contiguous disk device has been measured directly by a dynamlc equilibrium method using high speed photography. By applying a bias field gradient perpendicular to the propagation track, a bubble in the potential well of an attracting charged-wall is pulled out of the edge of track. The bubble stays in a dynamic equilibrium position where the pull out force due to the gradient field is equal to the force due to the attracting charged-wall. This equilibrium position depends on the magnitude of the gradient field. The slope of the potential well can be determined by the gradient field. The depth of the potential well is the difference between the collapse field at this position and that of the free bubble far away from the device structure. The width is given by the maximum distance of this equilibrium position. The detailed shape of the potential well can thus be measured directly by the experiments. The experimental results were taken on a 3 μm bubble contiguous disk device chip. This investigation includes various inplane field directions as well as magnitudes and at various bias fields. The results agree with ferrofluid pattern observations as well as the recent analysis of Shir and Lin. We did find, however, that the surface magnetic charges on the edge makes important contributions to the potential well, especially in the repelling charged-wall situation.