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Towards high frequency electromagnetic induction sensing of soil apparent electrical conductivity

Electromagnetic properties of soil (electrical conductivity, dielectric permittivity, and magnetic susceptibility) depend on its physical and chemical properties that are of interest to applications such as precision agriculture or environmental monitoring. State-of-the-art electromagnetic induction (EMI) sensors operate in the lower frequency range well below 100 kHz in which they are most sensitive to the magnetic susceptibility of the soil, and to a lesser degree to its electrical conductivity. In addition to such EMI sensors, the ground-penetrating radar (GPR) is often employed for the dielectric permittivity mapping at the frequencies above several tens of megahertz. The EMI soil sensing in the higher frequency range from 1 MHz to 20 MHz can bridge the gap between the EMI sensors in the low frequency range and the GPR. In this frequency range, both electrical conductivity and dielectric permittivity of the soil affect the measurement. In this paper, we present a simple EMI sensor operating in the range between 1 MHz and 10 MHz with an estimated resolution of 15 mS/m. We evaluate the sensor sensitivity to the electrical conductivity and discuss the influences of the dielectric permittivity and liftoff. We compare the conductivity measurements with the presented analytical sensor model.