Soil Moisture Sensor with Electrokinetic Ion Trap Mechanism

This study develops a real-time soil moisture sensor based on stainless planar electrodes to measure the capacitance changes of soil in the presence of water and an electrokinetic ion trap mechanism to move and attract ions in water for reducing ion effects on the sensor. As rain falls on -ground soil, its water content increases together with that of the soil in the sensor at the same ground level. This variation of water content causes a change in the dielectric constant of the sensing material (soil) in the sensor, and hence changes the measured capacitance between the measurement electrodes. For reducing the ion effect in water, an electric filed is applied to the web electrodes of the sensor, then anions and cations in water are trapped by the positive and negative electrodes (metal webs), respectively. The soil moisture is then determined from the change in the measured capacitance without ion effect. The experimental results show that not only the ions can be successfully trapped by the proposed mechanism but also the capacitive sensor yields a high degree of sensitivity (1.27 mu F/%gwgs(-1)) at different saline soils.