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Energy Harvesting and Power Management GUEST EDITORS’ INTRODUCTION Energy Harvesting and Power Management or over half a century, we have seen it’s often also possible for designers of mobile astonishing increases in the computa- devices, wireless sensors, and the like to em- tional, storage, and communications ploy other approaches to extend battery life- capabilities of embedded systems. But time. Two key techniques in this regard are en- while integrated circuit performance has, ergy harvesting and power management. Funtil recently, doubled every 18 months as predicted For this special issue, we invited authors to by Moore’s law, the same is far submit manuscripts describing new research from true for battery technology. contributions that advance the frontiers of per- Shwetak Patel Battery performance can be vasive and ubiquitous computing in the areas University of Washington evaluated in many different ways, of energy harvesting and power management, but no matter which metric you as well as advances relating to energy storage. Steve Hodges look at, it has taken more than We selected three articles that cover a range of Microsoft Research a decade to double performance. current research topics in this area. Joseph Paradiso As a consequence, in many cases MIT Media Lab an overriding factor limiting the In This Issue utility of pervasive computing In the first article, “Energy Provision and Storage hardware is battery lifetime. In for Pervasive Computing,” David Boyle, Michail addition to constraining indi- Kiziroglou, Paul Mitcheson, and Eric Yeatman at vidual, standalone devices, this limitation also en- Imperial College London review various types of compasses the maintenance and sustainability of wireless power transfer (WPT), including induc- large-scale deployments of sensor systems. tive, RF, and acoustic WPT, and other opportu- nistic energy harvesting techniques and methods of Overcoming Battery Limitations energy provisioning. They introduce some key fac- Although research to improve the energy den- tors for consideration when designing energy har- sity of batteries continues to be a high priority, vesting systems and energy-constrained systems. 26 PERVASIVE computing Published by the IEEE CS n 1536-1268/16/$33.00 © 2016 IEEE The article also includes a discussion of the AUTHORS modern energy storage and how it ad- Shwetak Patel is the Washington Research Foundation Endowed Professor in dresses or fails to address challenges in Computer Science & Engineering and Electrical Engineering at the University of modern device ecosystems. It addresses Washington. His research interests are in the areas of human-computer interac- tion, ubiquitous computing, sensor-enabled embedded systems, and user inter- very practical issues, such as choosing face software and technology. Contact him at [email protected]. between rechargeable battery technol- ogies and supercapacitors, the power consumption of various components and systems, the relative performance of Steve Hodges leads the Sensors and Devices research group at Microsoft Re- various energy harvesting sources, and search, Cambridge UK and is a Visiting Professor at the School of Computing characteristics of WPT systems. Science, Newcastle University. He creates compelling novel interactive experi- The second article in this special issue, ences for individuals, communities and organizations based on emerging hard- ware technologies. Hodges has a PhD in robotics and computer vision from “MIMO Wireless Power Transfer for Cambridge University. Contact him at [email protected]. Mobile Devices” by Daniel Arnitz and Matthew Reynolds from the University of Washington, describes a technique Joseph Paradiso is the Alexander W. Dreyfoos (1954) Professor in Media Arts for controlling the amount of power and Sciences at the MIT Media Lab, where he directs the Responsive Environ- delivered to mobile client devices in an ments Group. His research interests include sensor networks, energy harvest- RF-based WPT system. WPT has been ing, ubiquitous computing, computer music, and human-computer interac- tion. Paradiso has a PhD in high-energy physics from MIT. Contact him at explored by the research community for [email protected]. many years now, and consumer devices that incorporate some of these concepts for cord-free charging are starting to become available, although these are mainly low frequency and inductive in to power the monitoring device and esearchers continue to nature. While WPT offers tremendous directly drive the transmitted informa- make advances in energy benefits in terms of the convenience of tion. A variety of compact Monjolo style harvesting—both in terms powering mobile devices, the practical- energy harvesting sensor systems are of systems that capture ity of such systems depends on the ability described and implemented. These are Renergy naturally present in their op- to control the distribution of power to tailored to a wide range of applications, erating environments, and in terms many clients both spatially and tempo- such as monitoring door events for oc- of scenarios where intentional energy rally. The authors present their research cupancy, monitoring airflow, sensing the emission is introduced by a remote to leverage multi-input, multi-output state of illumination, determining device power source (such as WPT). None- (MIMO) techniques for controlling the operation via emitted heat, and perform- theless, to date, such systems have distribution of power for far-field wireless ing outlet-level power metering. rarely been adopted in commercial power systems. In addition to describing In addition to these three articles, this products. For this reason, continued the design of their WPT system, they pres- issue’s Spotlight department also relates research into power management and ent an evaluation of the system in opera- to energy harvesting and power manage- optimization techniques is also vitally tion. They also provide a short overview ment. One of us (Steve Hodges), along important. These techniques prom- of multipath propagation and previous with Ranveer Chandra and Anirudh ise to improve the performance of to- MIMO work in multipath environments. Badam from Microsoft Research and day’s predominant battery-powered The final peer-reviewed theme article Jian Huang from Georgia Tech, reprise products and at the same time accel- describes a new approach to “Perpetual several projects over the past 10 years erate the viability of harvested energy Sensing for the Built Environment.” Brad- that have sought to more effectively man- sources. ford Campbell, Meghan Clark, Samuel age the power consumption of mobile We hope the theme articles in this DeBruin, Branden Ghena, Neal Jackson, devices. In each case, this was done by special issue provide a useful over- Ye-Sheng Kuo, and Prabal Dutta from “offloading” operations from the device’s view of some of the current research the University of Michigan present an main processor in a way that reduced the in this field and, in so doing, inspire energy harvesting sensor system archi- energy requirements for the mobile de- others to pick up the challenge of in- tecture for smart building applications. vice in question. The article illustrates creasing battery lifetime. This work Guiding much of their work is some- that energy savings are possible through will literally fuel the next generation thing they refer to as the “Monjolo” phi- three different forms of offloading: com- of mobile and embedded devices and losophy—using the actual sensed signal putation, communication, and storage. experiences. OCTOBER–DECEMBER 2016 PERVASIVE computing 27.
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