Magnetoinductive Waves and Wireless Power Transfer

Recent research in wireless power transfer has highlighted the potential benefits for relaying power from source to receiver by a number of resonating relay coils coupled via mutual inductance. A number of researchers have reported experimental systems based on relay coils and have noted that power transfer efficiency to loads located at different points on the structure can vary widely. Such structures, often known as magnetoinductive waveguides are well known to carry signals known as magnetoinductive waves (MIW) when excited with a frequency in their passband. This paper presents an investigation into their impact on wireless power systems and methods by which negative effects may be minimized. Using the physics of magnetoinductive waves it becomes possible to understand the behavior of relay coil systems and to model them in a closed form. The effects of reflections and standing waves on a one-dimensional system are considered and their effect on the input impedance and the variation of matching conditions determined. An optimum receiver load is proposed based on the results and tested experimentally. A simple experimental demonstrator is used as a model for study, which achieves 58% efficient power transfer to a single load at any point on its length.