Near-fields in attenuating media
Keywords: Attenuating Media
Metamaterials
Magnetoinductive waves
Electromagetic induction

Metamaterials are artificial materials that can exhibit extraordinary electromagnetic properties that have never been observed in nature. By engineering elements of metamaterials, one can achieve a so-called left-handed or double-negative medium, enabling new physics and new potential applications. Applications can be found in a wide variety of fields, such as invisibility cloaking, wireless power and data transfer, magnetic resonance imaging and body area networking. In addition, metamaterials are known to support magnetoinductive (MI) waves. By their very nature, magnetoinductive waves with strong inter-element coupling offers low loss and wide bandwidth channels. Recently, one of the new directions of research is low-frequency communications in RF-challenging environments (i.e., underground/underwater or in vivo medical diagnosis and treatment applications) with the aid of MI waves, due to their advantages over other transverse electromagnetic (TEM) wave-based techniques in penetrating lossy medium. Underground/underwater, or human body and tissues, are an extreme challenge for the conventional wireless links using TEM waves. TEM waves interact strongly with the lossy background medium resulting in high ohmic losses, the need for large antenna size and often rapid attenuation which increases in severity with frequency.
The use of arrays of resonating circuits forming MI waveguides therefore has been proposed in communications in lossy medium to achieve longer ranges as well as robust channels of transmission. Elsewhere, modelling of propagation of low-frequency waves in a lossy medium has been paid increasing attention to embedded biomedical systems and body area networking for health-related applications, due to the fact that the human body and organs are relatively conductive from about 0.05 S/m to about 1.5 S/m at microwave frequencies. In terms of signal propagation, the attenuation of a signal in a given medium is the most important parameter. The radiation of TEM waves in conductors was understood and described a long time ago by Maxwell’s equations. However, there is as yet no theoretical or numerical model to express the penetration of MI waves in conductive environments.
The main aims of this research are (i) firstly, to investigate the impact of an intervening conductive medium on the magnetic coupling of two low frequency coils which is usually presented by a questionable assumption in most literature, (ii) secondly to examine the field distribution and the mutual coupling, and by that, the attenuation and phase delay between two low-frequency coils embedded in a homogeneous dissipative medium and (iii) finally, study a completed circuit model, that takes into account all the effects of the background medium on coils coupled in close proximity and thereby, derive a new dispersion equation for the MI waves in these media. Since the dispersion equation is known, the propagation of MI waves will be fully understood and some relevant applications can be proposed. Besides, with the novel equivalent circuit model being considered, this research has laid the foundation for the theory of wireless power transfer in non-conventional environments.