Finite Element Analysis of Uncovered Coplanar Interdigital Electrodes for Capacitive Sensor Applications

In this paper, COMSOL simulations are used to analyze the capacitance of uncovered coplanar interdigital capacitors of two configurations varying the dimensions, but with constant finger electrode spacing and active area: one of 8 mm × 4 mm, and the second with 4 mm × 8 mm. The expression of a finite-layer conformal mapping model has been modified to consider the finger electrode thickness which is in very good agreement with the simulations. The results indicated that the capacitance for the two configurations is insignificantly different, so either can be used in a sensing application. It has been verified the designs with the highest capacitances are those that have a smaller electrode width, higher thickness of the dielectric substrate, and higher thickness of the electrode, but a capacitance saturation exits when the ratio of substrate thickness and electrode width is approximately 2.5 or the substrate thickness is half of the periodicity ratio. Electrostatic simulations showed a higher concentration of 2D electrical potential in the active area when electrode width decreases, reason why the capacitance is increased. The finding found should be taken into account by designers to fabricate capacitive sensors and micro-supercapacitors based on interdigital electrodes.