Sensing field analysis of 3D direct capacitance imaging sensor

Classic electrical capacitance tomography (ECT) provides 2D images of a process cross section, and a “quasi” 3D image can be generated by stacking up the 2D images. But the 2D image obtained is a combined result of the medium in ECT sensor´s 3D sensing space, not of a slice of medium, which will reduce the degree of realism of the 3D image. 3D direct capacitance imaging acquires the 3D image directly from the measured capacitance data, transforms the inconveniences of the 3D sensing space into the benefit of 3D tomography. Analysis of the sensing fields of an ECT sensor should be carried out in the first design phase, so that the optimum result can be achieved. In this paper, the 3D sensitivity distribution of a 3D direct capacitance imaging sensor with 12-electrodes was studied by finite element method. The axial sensitivity distribution and the influence of the axial gap between measurement electrodes on the sensor´s sensitivities were focused on. Research shows that the change of axial gap between electrodes will result in non-notable difference in axial sensitivity distribution, while the position is radial (x- and y- axes) will result in notable difference in axial sensitivity distribution.