Additive manufacturing for capacitive liquid level sensors

A new manufacturing wave concerning the Additive Manufacturing of sensors is spreading: several benefits, such as cost, time, and manual task reduction, can be achieved. The aim of the present research is the one-shot Additive Manufacturing of a low-cost capacitive sensor for liquid level sensing. The Material extrusion (MeX) technology was used to fabricate the proposed sensors (composed of a flexible substrate, two conductive electrodes, and a top flexible coverage), and a Design for Additive Manufacturing (DfAM) approach in conjunction with the 3D printing force analysis was performed. Very thin conductive tracks (0.5 mm) were manufactured to obtain a sensor having a final capacitance value of 125 pF, readable by common laboratory instrumentation. The sensor has been tested for the liquid level sensing using two different liquids, i.e., sunflower oil and distilled water, exhibiting very good sensitivity of 0.078 pFmm and 0.79 pFmm, respectively, with high repeatability, thus obtaining sensing performances comparable with that of more expensive sensors found in literature. Moreover, the proposed sensor showed high linearity (R2 ≥ 0.997), which resulted in a maximum propagated level error of 1.4 mm. The present research proves that the inexpensive MeX technology can be successfully employed for the fabrication of high-performance capacitive sensors: the sensor manufacturing cost (related to raw materials) is 0.38 €, and no manual assembly tasks were performed. This study lays the foundation for the one-shot fabrication of smart structures with capacitive sensors on board, saving manufacturing time and cost.