Soil Moisture Sensor with Electrokinetic Ion Trap Mechanism

附有離子捕捉機制之土壤濕度偵測器

李明熹(Ming-Hsi Lee) ； 簡士濠(Shih-Hao Jien) ； 蔡得建(De-Jian Tsai) ； 楊志安(Jason Yang) ； 李佳言(Chia-Yen Lee)

《中國機械工程學刊》 35卷2期 (2014/04) Pp. 109-114

摘要

本研究發展出一種即時土壤溼度偵測器，該偵測器係使用不鏽鋼平面電極以量測土壤在不同水份含量時之電容變化量及離子捕捉電極可以移動與吸附土壤水分中之離子以降低離子效應對於上述電容量測的影響。當有降雨發生在地表土壤時，其土壤中水份含量之增加將一併造成埋在同一土壤高程之土壤溼度偵測器內土壤感測層水分含量增加，此土壤溼度偵測器內土壤感測層水分含量變化可引土壤感測層之介電係數變化，因而可使位於土壤感測層兩側之量測電極量得之電容值產生變化。本研究為避免進入土壤中水份內不同離子濃度對於介電係數量測造成影響，本感測器藉由網格狀之離子捕捉電極對於土壤感測層中施加電場，可使土壤中水份內的陰、陽離子分別被電場吸附於離子捕捉電極之正、負極表面。故土壤含水量即可在不被水中離子影響之狀況下準確地量測得知。本研究之實驗數據清楚呈現本研究發展之土壤含水量偵測器不僅可以利用上述離子捕捉機制降低離子效應外，並成功地達到不論土壤中之鹽度大小皆可具有極高之土壤含水量偵測靈敏度（1.27μF/%g_wg_s^(-1)）。

並列摘要

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 (1.27μF/%g_wg_s^(-1)) at different saline soils.

並列關鍵字

dielectric constant ； ion trap ； landslide ； soil moisture ； TDR