Flexible inkjet printed sensor for liquid level monitoring

In this work a method for liquid level measurement is presented, with a support of experimental results. The presented liquid-level measurement method uses two sensors: level and reference interdigital capacitors. Proposed sensors are fabricated in low-cost inkjet printing technology with nanoparticle silver ink on a Novele™ coated polyethylene terephthalate (PET) substrate. The sensors comprise a two interpenetrating comb electrodes with 1.5 mm width of comb electrode, 1.5 mm spacing between each comb and 15 fingers with length of 135 mm and 8 fingers with length of 19 mm for level and reference sensor, respectively. Capacitance of the level sensor fixed on a test tube increases as the liquid level increases (up to 43.5 mm). The sensor characteristics for three liquids with different permittivity are presented. The reference sensor at the bottom of the tube is completely covered by liquid and its capacitance changes as the permittivity of the liquid changes. Experimental results for three different liquids confirmed simple liquid level measurement method which enables the measurement regardless of the liquid type.