FDTD Analysis of Measuring Frequency-Dependent Properties Using Soil Samples

When conducting measurements with soil samples, various factors can lead to measurement errors (such as fringing or stray capacitances). This work aims to estimate those errors and make recommendations for reducing them. One of the factors that can lead to permittivity and resistivity errors is the excessive length of the sample (even though relatively long soil samples are practically more convenient for the four-terminal sensing). FDTD simulations have demonstrated that for relatively large permittivities, the errors are insignificant if the length of the sample is comparable to its width. However, when sample length is significantly bigger than its width, this can lead to errors even for large permittivities. The capacitance between measurement circuits should be minimized (as even 10 pF can lead to appreciable errors). The large length of the current and voltage measurement wires should be avoided.