Novel Hilbert soil-moisture sensor based on the phase shift method

Abstract

In this paper, novel soil-moisture sensor based on the Hilbert fractal curve is proposed. The developed sensor is intended to be integrated into wireless sensor network whose goal is the monitoring of the agricultural soils. The operating principle of this sensor is based on the phase shift method which in essence represents the measurement of the soil permittivity. Analytical expressions for the calculation of optimal operating frequency and the absolute moisture content derived from effective permittivity are presented. The influence of the order and the number of fractal curves used to the sensor characteristics are analyzed. The proposed sensor operates at 1.2 GHz and provides phase shift in the range of 70.76° for the extreme cases of the soil moisture content (2 % and 20 %).