Adaptive sub-MHz magnetic induction-based system for mid-range wireless communication in soil

Wireless communication in the subsurface has many scientific, commercial, disaster management, and security applications. The communications could be between two subsurface nodes, among many nodes of an underground sensor network, or between subsurface and surface nodes. However, no robust method has been practically proven for this application. Recently it has been shown that even at sub-MHz frequencies, the typical variations of the electrical properties of soils, for example due to rain or drydown event, significantly impact the wireless communication channel, particularly for mid-range distances, e.g., in the 15-30 m range. If one considers the trade-offs of a magnetic induction (MI) based system involving energy-efficiency and application bandwidth for two extreme soil conditions of very dry and very wet, it becomes apparent that a balanced solution is very hard to achieve. This is in large part because one of the main design parameters, the wire thickness of the MI node, is fixed and cannot be dynamically optimized for the entire range of dynamic soil dielectric properties. In this work, this problem is theoretically investigated and a solution is proposed based on a dual-wire coil to enable an adaptive front-end magnetic induction-based communication system for mid-range distances. Preliminary simulated and empirical results are discussed and design guidelines are proposed.