土壤含水率测量探头特性阻抗的镜象解

A Solution to Characteristic Impedance of the Measuring Probe of Soil Water Content

摘要: 在基于驻波比原理的土壤含水率测量仪中，探头特性阻抗是影响土壤含水率快速、准确和可靠测量的关键参数。基于静电场中的镜象原理，该文推导出三针、四针土壤含水率测量探头特性阻抗的镜象计算公式。各种规格尺寸下，该镜象解与高精度边界元法数值解的比较结果表明：当探头尺寸满足D/d≥5时，该镜象解与高精度边界元数值解间的相对偏差不大于0.18%，可应用于土壤含水率测量仪中。

Abstract: The characteristic impedance of the probe is critical to determine soil water content for the measuring instrument based on the principle of standing wave ratio. In this paper, solution to the characteristic impedance of three-wire and four-wire probes are derived by image method. The results of the image method solution are compared with the reliable data obtained by boundary element method. It was shown that the image method solution can be used in caluclating the probe characteristic impedance when (D/d)≥5.