Increasing the Capacity of Magnetic Induction Communication Using MIMO Coil-Array

Magnetic Induction (MI) is a promising solution for wireless communications in complex environments, such as oil reservoir, underground, indoor, and underwater. Due to the inherent electrically small size and simple structure of the magnetic coil antenna, it suffers from low radiation efficiency, extremely narrow bandwidth, and dramatic polarization loss. Recently, significant efforts have been made to increase MI communication's performance, for instance, the metamaterial- enhanced magnetic induction has been developed to increase the signal strength, the tri-directional coil antenna is used to overcome the polarization loss, among others. However, increasing the bandwidth of MI communication is still a great challenge. In this paper, we propose a MIMO antenna array with each antenna element having its own resonant frequency. Due to the strong coupling in the deep near field, the antenna elements mutually affect each other. Instead of eliminating this coupling, we rigorously derive a model to capture it and use metamaterial-inspired method to find the optimal configuration of the antenna array to achieve multiple bands. As a result, the overall bandwidth can be significantly increased. Meanwhile, the enhanced wireless channel can provide much better signal strength. Finally, we theoretically analyze the channel gain in comparison with the original MI to demonstrate the benefits of MI MIMO.