Wireless information and power transfer methods based on magnetic resonance in embedded sensor networks

Abstract

Recently, for various purposes, sensor networks have been deployed in which the sensors are embedded in dense media including rock, soil, and water. For example, in ubiquitous home networks, sensors are embedded in the walls of building for convenience and aesthetic reasons. In addition, sensors are sometimes buried underground so that environmental conditions, the state of infrastructure, and other situations can be monitored. However, the embedding of sensors can present two main challenges to be considered. Sensors cannot be effective in communicating with other sensors through the dense media where they are embedded. And, any battery is unlikely to be practical as a power supply because it is difficult to replace. Therefore, a solution needs to be found to deal with these obstacles so that embedded sensors can operate reliably in practice. Therefore, in this thesis, we focus on the communication using magnetic induction for the transfer of information and wireless power transfer using magnetic resonance for supply of energy in embedded sensor networks.

First, we attempt to maximize the capacity of magnetic induction communication in strongly and loosely coupled regions. In a strongly coupled region, we investigate frequency splitting, which disturbs the resonance of transmitter and receiver coils. We find a splitting coupling point, which is the value just before frequency splitting occurs, and propose an adaptive frequency-tracking scheme for finding an optimal frequency. The proposed scheme compensates for the degradation of capacity, so guarantees large capacity even at regions where frequency splitting occurs. Next, in a loosely coupled region, we derive an optimal quality factor for maximizing capacity in a two-coil system. As the distance between coils increases, strong resonance is needed to overcome the serious attenuation of signal strength. As a result, the optimal quality factor should be increased. In addition, we find an optimal quality facto...