Slow development in battery technology and rapid advances in ultra-capacitor design have motivated us to investigate the possibility of using capacitors as the sole energy storage for wireless sensor nodes to support ubiquitous computing. The starting point of this work is TwinStar, which uses ultra-capacitor as the only energy storage unit. To efficiently use the harvested energy, we design and implement feedback control techniques to match the activity of sensor nodes with the dynamic energy supply from environments. We conduct system evaluation by deploying sensor devices under three typical real-world settings -- indoor, outdoor, and mobile backpack under a wide range of system settings. Results indicate our feedback control can effectively utilize energy and ensure system sustainability. Nodes running feedback control have longer operational time than the ones running non-feedback control.

One of the most important requirements for a routing protocol in wireless body area networks (WBANs) is to lower the network's temperature increase. The temperature of a node is closely related to its activities. The proactive routing approach, which is used by existing routing protocols for WBANs, tends to produce a higher temperature increase due to more frequent activities, compared to the on-demand reactive routing approach. In this paper, therefore, we propose a reactive routing protocol for WBANs called priority-based temperature-aware routing (PTR). In addition to lowering the temperature increase, the protocol also recognizes vital nodes and prioritizes them so they are able to achieve higher throughput. Simulation results show that the PTR protocol achieves a 50% lower temperature increase compared to the conventional temperature-aware routing protocol and is able to improve throughput of vital nodes by 35% when the priority mode is enabled.