Department of Electrical Engineering and Electrotechnologies, Lublin University of Technology, Nadbystrzycka 38A, 20-618 Lublin, Poland.
Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, 20-290 Lublin, Poland.
Sensors (Basel). 2020 Apr 22;20(8):2374. doi: 10.3390/s20082374.
Soil volumetric water content () is a parameter describing one of the most important factors conditioning proper plant growth. Monitoring soil moisture is of particular importance in the rational use of water resources for irrigation, especially during periods of water scarcity. This paper presents a method of measuring soil moisture in the vicinity of the plant root system by means of a probe designed to be mounted on a mobile device used for precise plant irrigation. Due to the specific field conditions of the measurement, the design of the probe was proposed as a monopole antenna. Electromagnetic simulations of the probe were carried out with Ansys HFSS software to optimise its dimensions. Then a prototype of the probe was manufactured to conduct laboratory measurements with the use of a vector network analyser (VNA) working in the 20 kHz to 8 GHz frequency range. The VNA analyser was configured to work in the time-domain reflectometry (TDR) mode. From measurements of the time distance between reflections from the probe's elements it is possible to calculate the bulk dielectric permittivity of the soil surrounding the probe. Next, based on commonly used soil moisture dielectric calibrations one can determine of the soil sample. The paper presents simulation results and laboratory tests of an antenna probe. Due to its tough and durable design, this type of probe gives the possibility of easy application in field conditions, which makes it especially suitable for mechanically demanding measurement systems. As the sensitivity zone is comparatively large, this probe is well-suited to measuring soil moisture in the vicinity of the plant root system.
土壤体积含水量 () 是描述影响植物生长的最重要因素之一的参数。监测土壤水分对于合理利用灌溉水资源尤为重要，特别是在水资源短缺时期。本文提出了一种通过设计用于精确灌溉植物的移动设备上安装的探头来测量植物根系附近土壤水分的方法。由于测量的特定现场条件，探头的设计被提出为单极天线。使用 Ansys HFSS 软件对探头进行了电磁模拟，以优化其尺寸。然后制造了探头的原型，以使用工作在 20 kHz 至 8 GHz 频率范围内的矢量网络分析仪 (VNA) 进行实验室测量。VNA 分析仪配置为在时域反射计 (TDR) 模式下工作。通过测量探头元件之间反射的时间距离，可以计算出探头周围土壤的体积介电常数。接下来，基于常用的土壤水分介电校准，可以确定土壤样本的 。本文介绍了天线探头的仿真结果和实验室测试。由于其坚固耐用的设计，这种探头可以很容易地应用于野外条件，特别适合机械要求较高的测量系统。由于灵敏度区域相对较大，因此该探头非常适合测量植物根系附近的土壤水分。
