Design and Implementation of Low-Power and Mid-Range Magnetic-Induction-Based Wireless Underground Sensor Networks

摘要

Low-power wireless communication in underground settings and confined areas is considered one of last frontiers in communications. First, there is the energy challenge: because the nodes are embedded in some kind of medium, such as soil, concrete, or debris of a disaster event, many of the traditional energy solutions for communication devices are ruled out. Second, typical radio-wave-based solutions are significantly impacted in underground settings due to the high signal attenuation in lossy medium, such as wet soil. To address such challenges, wireless underground sensor networks (WUSNs) have been proposed. However, the lack of real-world deployments is an indication that some WUSN aspects still need to be addressed. In this paper, a soil path attenuation model for a magnetic induction (MI)-based WUSN is developed and the best operating frequency range is identified. Next, a strategic frequency and coil adaptation scheme is added to the design resulting in an efficient system in terms of energy and application bandwidth (BW), which can operate under typical variations of the electrical properties of soils, for example, due to a rain or dryout event. The model and design guidelines are validated by preliminary experiments in outdoors, and more recently, an indoor MI-based testbed is carefully developed. We concluded that this submegahertz MI-based communication testbed can also be perceived as an accurate noncontact sensor for dielectric spectroscopy. Such findings have the potential of not only helping in the proliferation of WUSNs but also providing the foundation for novel instrumentation possibilities in many fields of science.