A Capacitance PCB Sensor for Granular Material with Increased Accuracy

Granular materials like cereals and sands are widely present in different industrial fields like food and agricultural industry. Capacitive planar sensors for granular materials suffer from an additional source of uncertainty related with the random distribution of the grains inside the sensitivity volume. In this letter, we propose a capacitive planar sensor with a new electrode geometry for increasing the sensitivity volume, thus improving the accuracy of the measurements. The geometry is optimized through a design based on numerical simulations in order to maximize the sensitivity volume without reducing the dynamics of the capacitance variation. Experimental results obtained by considering two different granular materials show a reduction of the standard deviation due to granularity of 20% with respect to a classical interdigital electrode structure. Finally, it is experimentally shown that the increased accuracy of the proposed geometry can be fruitfully used for contaminant detection in a mixture of granular materials.