Detecting Soil Moisture Levels Using Battery-Free Wi-Fi Tag

Abstract

Soil sensing plays an important role in increasing agricultural output. Existing soil sensing methods failed to achieve both high accuracy and low cost. This paper presents Soil-TAG, a battery-free Wi-Fi tag based high accuracy, low-cost and long range soil moisture sensing system. To measure the soil moisture, our idea is converting changes in soil moisture levels into the frequency response of the tag's resonator. To achieve high accuracy, we optimize key resonator parameters to increase the frequency response sensitivity for sensing even small soil moisture changes. To improve the working range, we design patch antenna array for the tag and employ beamforming and beam nulling at the transceiver side. Experimental results show that SoilTAG achieves a 2% high accuracy when the working range is less than 6 m, and when the working range is up to 10 m, it achieves 3.64% accuracy.