The capacitive sensor for liquid level measurement, fabricated with the inkjet printing technology

Abstract

The paper reports a capacitive multisection sensor for measuring level of various liquids. Presented sensor was fully fabricated with the inkjet printing technology on thin Kapton substrate. The measurement of liquids level based on capacitive sensing is already well known technique, however the novelty of presented sensor is the technology of fabrication that was used, approach to the pattern design which combines analog and digital capacitive section and obtained self-calibration feature of whole system independently on measured liquid type. Fabricated sensor structure has dimension of 210 mm x 12 mm and the thickness approximately of 27 μm. It contains 8 digital-like sections along the sensor and one analog section which allows to fine measurements. The sensor was tested in a vessel during filling and emptying with various liquids. Performed tests exhibited the linearity of the sensor characteristic and the lack of hysteresis. Obtained sensitivity of the sensor prototype was approximately 6.8 pF/mm, but it could be easily modify on the design stage due to the fast prototyping feature of inkjet printing technology. Thanks to the flexibility of the substrate, the sensor structure can be applied to any shape of vessel. Furthermore, the sensor construction is fairly simple and costs in mass production could be extremely low. This type of sensor was design especially for autonomous cleaning and washing robots for large areas operation.