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Double-sided environmental sensor for high-efficiency particulate air filter

A capacitive environmental sensor pair is fabricated on a High-Efficient Particulate Air (HEPA) filter. The sensors are fabricated on both sides of the filter. The front side sensor is exposed to the conditions of the dirty side of a filter while the other is used as a reference on the back side. The capacitances on both sensors are measured to analyze particulate accumulation on the filter. It is observed that the capacitance of the front side sensor changes significantly, when the filter becomes dirty, whilst the reference capacitance has a minor change. The capacitance difference between the sensors was up to 45 %. After cleaning the filter, the capacitance values returned to the initial level on both sides. The proposed sensor concept is capable for a quantitative online monitoring of air filter condition, enabling interesting possibilities in IoT based automation systems.