Improve charging distance with resonant repeaters

This chapter discusses opportunities to use the latest multi-hop wireless charging to improve recharge capability. Due to physical limitations, Mobile Chargers (MCs) only recharge one sensor node at a time, which has limited efficiency and scalability. With the short-range wireless charging reaching its maturity, recent advances in multi-hop wireless charging are gaining momentum and ready to provide fundamental support to address this problem. Unfortunately, the existing designs for single-node wireless charging cannot take advantage of such opportunities. In this chapter, we propose a new design that can relay wireless energy in multi-hops. Our method implements resonant repeater coils on sensor nodes. Once the MC is charging one sensor, the sensor can relay wireless energy to its neighbors. First, we present such novel design and discuss a method for estimating multi-hop charging efficiencies. Then we consider how to optimize network performance and achieve a balance between benefit and cost. A two-step approximation algorithm is proposed. We also discover there are more chances to further reduce the total system cost. Thus, we develop post-optimization procedures that can make use of the trade-offs between different types of energy cost. We also demonstrate simulation results to show significant improvements over single-node wireless charging.