Numerical modeling of a capacitance probe response

Capacitance sensors are one of the common means of characterizing the soil dielectric constant, Their design depends on their expected applications, I n particular, the electrode geometry has a critical influence on the extens ion of the probed region, Moreover, the soil may not always be viewed as a medium of statistically uniform dielectric constant (because of parking eff ects, air sheath in the vicinity of the electrodes, stones), Numerical mode ling for the behavior of a particular probe was developed. It is based on s olutions of the Maxwell's equations in the quasi-static approximation, by a finite element method. This modeling was compared with laboratory measurem ents in various media lair, ethanol) where heterogeneity was inserted in th e vicinity of the electrode, The numerical model reproduces very well the p robe response when millimetric scale perturbations were introduced, The num erical model appears to be a promising tool to investigate more deeply the capacitance probe measurements, for instance the extension of the measureme nt volume or the significance of measurements in highly structured soils.