A numerically efficient method of modeling interdigitated electrodes for capacitive film sensing

Interdigitated electrodes represent a commonly used planar structure when it comes to implementing capacitive sensors. The electric field decays strongly in the surface normal direction of the electrode arrangement. This can be used to estimate the thickness of dielectric films residing on the electrodes. A simple example for an application would be the detection of the build-up of biofilms. The exact expressions for the capacitance are relatively complex and can be provided in closed form only for the case without a cover layer. In this contribution we present an efficient modeling approach based on a physically motivated approximation of the charge distribution on the electrodes. Establishing a closed-form spectral domain representation of the associated electric potential distribution allows a numerically highly efficient calculation of the capacitance utilizing the FFT algorithm. In contrast to previous works, additional cover layers can be easily included in the model, which allows studying the aforementioned sensing effect.