The effects of the numbers of fringing electric field (FEF) fingers on the performance of sensor for the water content in soil

Abstract

The use of fringing electric field electrode as a moisture sensor in low frequency has some limitations such as the measured capacitance value was small and it is hard to differentiate the capacitance value for several moisture level because the capacitance value are so close. Therefore, understanding the effect of the fringing electric field physical design and it working frequency on measured capacitance is needed in order to design a good moisture sensor for automation of water irrigation system. This work focused on identifying the right numbers of fringing electric field electrode finger and operating frequency for optimization. The samples were prepared with five different electrodes which have 5 to 9 electrode fingers and tested with five different moisture level. The supplied signal was within 100 kHz to 2 MHz operating frequency and tested in the room temperature. From the experiment, 6 FEF fingers showed the better result among the other at 900 kHz. The capacitance level has better separation with insulator compared to without it. The work identified that there are two stages where capacitance value are measured and choose the slope where it representing the dielectric of water content as reference. But it requires calibration to set the slope based on the soil type.