Introduction to design techniques for energy harvesting

There is a growing interest in emerging energy harvesting methods, which have become more realistic in recent years. Thus, energy scavenging approaches are now considered real contenders as an alternative for powering ubiquitously deployed mobile and wireless electronic devices such as sensor network nodes. Low-power and energy-efficient circuits and systems have always attracted attention, however, there is a significant increase in demand for their usage and research to improve them in recent years. This demand is driven by several factors such as increasing energy costs for medium-to-large systems and the lack of sufficient battery power for ever increasing functionality of small and mobile devices. Further, mobility makes energy harvesting even more crucial. This special issue reports the recent advances in the emerging energy harvesting area as well as in energy-efficient circuits and systems. In the first article, by Wenck et al., the authors propose techniques to exploit the AC nature of mechanical vibration energy harvesting to increase efficiency and decrease cost. The techniques cover self-times circuits for maintaining the timing constrainst in wide voltage variations; fast power-on-reset circuits to initialize DSP pipelines; and dynamic memories to keep state information across supply cycles. The article by Wang et al. discusses design considerations of sub-mw indoor light energy harvesting for wireless sensor systems. A photovoltaic-panelbased energy harvesting is chosen for the wireless sensor system design. The authors employ a maximum power point tracking scheme to improve the power