like perovskite, GaAs, and Cd compounds, hint at raising this efficiency by a factor of 2 to 3, albeit introducing some complexity in toxicity, manufacturing, etc.; the following chapters in this book explore this in detail. Similarly, needed power levels are still decreasing, not only for processing and sensing, but also for joining “heavier” mainstream networks like 801.11 or 5G, not to mention continued evolution in their low-power brethren like the now ubiquitous BLE and the multitude of other short-range contenders (e.g., ZigBee, Z-Wave, RF-backscatter, etc.).
The sheer number of wireless devices in the environments we live and work in will also continue increasing; at some point, this will cross a level at which battery replacement is less tolerable, together with a profusion of sensors in hard-to-access areas that still have low but usable levels of light (e.g., for environmental control, material integrity, leakage and structural assessment, safety, etc.). Also, as lighting has become more efficient and networked, and cheap renewable energy drops basic power costs, one possibility would be for areas of dwellings to illuminate for an interval when people aren’t present just to charge the sensors; they will tell the smart home or IoT servers when they are running low and need an illumination hit, or just raise the shades to let enough daylight in. Long-range inductive charging is a potential competitor here [25], but efficiency loss with range, orientation, and still unacceptably large EMI are show stoppers here, together with the lack of infrastructure; our homes and offices are amply lit, but don’t yet (and probably won’t) have large induction coils in the floors and walls (on the other hand, I see Helmholtz-coil-laden closets, draws, and shelves as potential ways to conveniently charge wireless electronics embedded in clothing).
Hence, we’re at a crossroads here—the dominance of batteries in low-power sensors and systems may well be close to ending as IPV technology advances and smart environments can coordinate their assets to conserve the energy of distributed wireless embedded systems and even recharge them when needed. Both batteries and photovoltaics are differently weighted in terms of manufacturing energy, toxicity, etc., and it’s not clear how much photovoltaics will come out ahead over a device’s lifetime, but the race is certainly on, and the incentives will continue.
I’m delighted to see this book arrive now—this is certainly the right time for it, and many of the things I’ve barely hinted at above are explored much more fully in the chapters ahead. But let’s check back in after another decade passes to see what will be energizing the low-power devices scattered throughout our environments—and, in what I currently find most exciting and profoundly important, how the data they produce is used and leveraged. In the context-driven world of the future, every bit will mean something—here’s hoping that they all will serve us well!
References
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Note
1 Email: [email protected]
2 Introduction to Micro Energy Harvesting
Monika Freunek (Müller)