Non-contact Soil Moisture Content Determination System Using High Frequency Signal

Abstract

The non-contact measurement of soil moisture content is proposed by applying the reflected power of two signal frequencies based on the difference in electrical properties at each moisture content level. The strength of reflected signal is affected, and then data are collected, analyzed and decided the moisture content level. The measurement system consists of the transmitter and the receiver parts. The transmitter generates two signal frequencies at 2.40 and 2.45 GHz and switches one frequency at a time to transmit via the first designed patch antenna. The receiver receives the reflected signal from the soil sample under test via the second patch antenna. The received power is converted to DC voltage by the power detector circuit and then is converted to 10-bit digital data to process in a microcontroller board. In the experiments, the moisture content in soil was measured at eight levels from 0%, 5%, 10% to 35%, providing the average reflected powers of 8.06, 8.68, 9.07 to 11.94 mV, respectively. It can be noticed that the reflected power increases relatively with the increasing moisture content, with the maximum error at 3.18%. The sensitivity is not less than 0.065 V/5%, and the average SD is at 0.179. Consequently, the proposed system is stable and able to determine soil moisture content effectively.