Battery-Free Sensor Array for Wireless Multi-Depth In-Situ Sensing

Underground in-situ sensing plays a vital role in precision agriculture and infrastructure monitoring. While existing sensing systems utilize wires to connect an array of sensors at various depths for spatial-temporal data collection, wireless underground sensor networks offer a cable-free alternative. However, these wireless sensors are typically battery-powered, necessitating periodic recharging or replacement. This paper proposes a battery-free sensor array which can be used for wireless multi-depth in-situ sensing. Utilizing Near Field Communication (NFC)-which can penetrate soil with negligible signal power loss-this sensor array can form a virtual magnetic waveguide, achieving long communication ranges. An analytical model has been developed to offer insights and determine opti-mal design parameters. Moreover, a prototype, constructed using off-the-shelf NFC sensors, was tested to validate the proposed concept. While this system is primarily designed for underground applications, it holds potential for other multi-depth in-situ sensing scenarios, including underwater environments.

I. Introduction

Multi-depth in-situ sensing systems are extensively used in agriculture and water management [1], [2]. In precision agriculture, soil sensors are placed at various depths to comprehensively monitor attributes like salinity, moisture, and nitrogen density and distribution. This sensing data aids in the intelligent management of irrigation and nitrogen usage. Unlike single sensors, multi-depth sensory arrays gather rich information, providing a deeper understanding of a crop's root nutrition.