Wireless underground sensor networks (WUSNs) can enable many important applications such as intelligent agriculture, pipeline fault diagnosis, mine disaster rescue, concealed border patrol, crude oil exploration, among others. The key challenge to realize WUSNs is the wireless communication in underground environments. Most existing wireless communication systems utilize the dipole antenna to transmit and receive propagating electromagnetic (EM) waves, which do not work well in underground environments due to the very high material absorption loss. The Magnetic Induction (MI) technique provides a promising alternative solution that could address the current problem in underground. Although the MI-based underground communication has been intensively investigated theoretically, to date, seldom effort has been made in developing a testbed for the MI-based underground communication that can validate the theoretical results. In this paper, a testbed of MI-based communication system is designed and implemented in an in-lab underground environment. The testbed realizes and tests not only the original MI mechanism that utilizes single coil but also recent developed techniques that use the MI waveguide and the 3-directional (3D) MI coils. The experiments are conducted in an in-lab underground environment with reconfigurable environmental parameters such as soil composition and water content. This paper provides the principles and guidelines for developing the MI underground communications testbed, which is very complicated and time-consuming due to the new communication mechanism and the new wireless transmission medium.
The MI technique is introduced to wireless underground communication in [8,10,16]. The MI techniques are shown to provide a more reliable underground communication channel. However, MI communication in their original form has a limited communication range due to the high attenuation rate in the near region. The MI waveguide concept is originally developed in [17-22], which is used for artificial delay lines and filters, dielectric mirrors, distributed Bragg reflectors, slow-wave structures in microwave tubes, among others. The channel model for both original MI communication and MI waveguide are maturely developed in recent years [8,10,11,16]. A model of 3D MI communication, is also introduced in @cite_3 .
@cite_3
2077428143
The real-time and in-situ monitoring capability in oil reservoirs is highly desired to increase the current recovery factor of crude oil and natural gas. To this end, the wireless sensor networks (WSNs) are envisioned to be deployed deep inside oil reservoirs to collect and report the physical and chemical information in real time. However, none of the existing wireless communication and networking technologies can support WSNs in oil reservoirs due to the very challenging environment and the extremely small device size. To address the problem, this paper proposes a new self-contained micro wireless sensor network framework based on the Magnetic Induction (MI) technique, which can enable the real-time and in-situ monitoring in oil reservoirs. Rigorous analytical models are developed to characterize the oil reservoir channel for both MI communication and energy transfer, which confirm the feasibility of the proposed self-contained sensor network framework. To enhance the system efficiency and reliability, high-permeability proppants are injected in the hydraulic fracture to increase mutual induction; while the tri-directional MI coil antenna is designed to achieve omnidirectional coverage. The theoretical models and numerical results are validated by the widely used finite element simulation software COMSOL Multiphysics.