Powered by small batteries, sensor nodes' lifetime has been constrained by the scarce energy supply. This has been a long-lasting, fundamental problem faced by sensor networks that are usually designed for long-term operation. The emerging wireless charging technology is a promising alternative to address such energy constraint problem in sensor networks. Together with the more and more mature and inexpensive mobile robots, this technology is able to replenish energy proactively to meet application requirements rather than passively adapted to the availability of environmental resources such as solar, wind etc. However, the application of wireless charging technology to sensor networks is still in its infancy stage. In this thesis, we study the network lifetime elongation problem in sensor networks. Specifically, through guiding the routing activities in the network and delivering energy to where it is needed, we not only replenishes energy into the network but also effectively improves the network energy utilization, thus prolonging the network lifetime. Small-scale testbed experiments and large-scale simulations are conducted to evaluate the effectiveness of our work.