The wireless communications in complex environments, such as underground and underwater, can enable various applications in the environmental, industrial, homeland security, law enforcement, and military fields. However, conventional electromagnetic wave-based techniques do not work due to the lossy media and complicated structures. Magnetic induction (MI) has been proved to achieve reliable communication in such environments. However, due to the small antenna size, the communication range of MI is still very limited, especially for the portable mobile devices. To this end, Metamaterial-enhanced MI (M2I) communication has been proposed, where the theoretical results predict that it can significantly increase the data rate and range. Nevertheless, there exists a significant gap between the theoretical prediction and the practical realization of M2I; the theoretical model relies on an ideal spherical metamaterial, while it does not exist in nature. In this paper, a practical design is proposed by leveraging a spherical coil array to realize M2I communication. The full-wave simulation is conducted to validate the design objectives. By using the spherical coil array-based M2I communication, the communication range can be significantly extended, exactly as we predicted in the ideal M2I model. Finally, the proposed M2I communication is implemented and tested in various environments.
The effect of surrounding an electrically small dipole antenna with a shell of double negative (DNG) material ( spl epsiv sub r <0 and spl mu sub r <0) has been investigated both analytically and numerically. The problem of an infinitesimal electric dipole embedded in a homogeneous DNG medium is treated; its analytical solution shows that this electrically small antenna acts inductively rather than capacitively as it would in free space. It is then shown that a properly designed dipole-DNG shell combination increases the real power radiated by more than an order of magnitude over the corresponding free space case. The reactance of the antenna is shown to have a corresponding decrease. Analysis of the reactive power within this dipole-DNG shell system indicates that the DNG shell acts as a natural matching network for the dipole. An equivalent circuit model is introduced that confirms this explanation. Several cases are presented to illustrate these results. The difficult problem of interpreting the energy stored in this dipole-DNG shell system when the DNG medium is frequency independent and, hence, of calculating the radiation Q is discussed from several points of view. Metamaterials are compound materials exhibiting electromagnetic properties not readily found in nature. Novel antennas, couplers, imaging systems and methods for the reduction of the radar cross-section based on these properties have been proposed in literature. In this thesis a systematic synthesis technique for metamaterials is presented. The foundation of this approach is that metamaterials consist of unit cells that are small compared to the wavelength. The topology of the unit cell's network representation can be derived from first-order space-discretising schemes in 1D, 2D, and 3D. Using this technique two novel isotropic 3D metamaterials are synthesised. Maximally-symmetric and planar physical realisations are proposed and verified by full-wave simulation and experiment, respectively. Magnetic induction (MI) communication technique has shown great potentials in complex and RF-challenging environments, such as underground and underwater, due to its advantage over EM wave-based techniques in penetrating lossy medium. However, the transmission distance of MI techniques is limited since magnetic field attenuates very fast in the near field. To this end, this paper proposes metamaterial-enhanced magnetic induction ( @math ) communication mechanism, where an MI coil antenna is enclosed by a metamaterial shell that can enhance the magnetic fields around the MI transceivers. As a result, the @math communication system can achieve tens of meters communication range by using pocket-sized antennas. In this paper, an analytical channel model is developed to explore the fundamentals of the @math mechanism, in the aspects of communication range and channel capacity, and the susceptibility to various hostile and complex environments. The theoretical model is validated through the finite element simulation software, Comsol Multiphysics. Proof-of-concept experiments are also conducted to validate the feasibility of @math .