Ultra-reliable and low-power wireless communications are desirable for wireless networking in extreme environments such as underground tunnels, underwater, and soil. Existing wireless technologies using electromagnetic (EM) waves suffer from unpredictable multipath fading and blockage. The recent development of magnetic induction (MI) communication provides a low-power and reliable solution, which demonstrates negligible multipath fading, high penetration efficiency, and low attenuation loss in lossy media. However, existing works neglect the fact that MI communication only demonstrates such advantages in the near-field, beyond which the MI communication converges to electromagnetic wave-based communication and all the aforementioned advantages disappear. This letter develops a magnetic field propagation model to show MI communication's different performances in the near-field and the far-field. We develop rigorous models to capture the multipath fading, the penetration efficiency through inhomogeneous media, and the attenuation loss in lossy media. The results show that although MI communication can provide reasonable signals in the far-field, it only demonstrates negligible multipath fading, high penetration efficiency, and low attenuation loss in the near-field.
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