Energy harvesting in the news
The world is starting to pay greater attention to energy harvesting, through which ultra-low power sensors and controls can be powered by ambient energy flows (like light, heat, motion, or stray radio and TV signals). This week, Electronics Weekly reported on a study that estimated the current market for energy harvesting at $19M/year, and projected that it will grow roughly tenfold by 2017. Putting aside the difficulty of projecting the future for economic and social systems, it’s clear that people are waking up to the potential for energy harvesting. Thus far it’s mostly been a niche application, the most widely used example of which is tire pressure sensors in cars (they use the motion of the wheel to power themselves).
There has also been more interest recently in biomedical applications. Proteus Digital Health has an ingestible sensor that has no battery. Instead, it has a cathode and anode, and uses your stomach juices as the electrolyte. It goes inside a pill, and when the pill dissolves in your stomach it sends a tiny signal to a patch on your skin, which relays the signal to your cell phone or other mobile device, recording accurately when you took your medicine. This is what Proteus calls “partial energy harvesting”, since the energy extracted is really embedded in the anode/cathode pair, and the electrolyte simple enables us to tap that energy for as long as the electrodes last.
Nature Biotechnology published an article recently on a device that can extract power from a biologic battery found in the inner ears of certain animals, including humans.
Mercier, Patrick P., Andrew C. Lysaght, Saurav Bandyopadhyay, Anantha P. Chandrakasan, and Konstantina M. Stankovic. 2012. “Energy extraction from the biologic battery in the inner ear." Nat Biotech. Advance online publication, 11/08/online. [http://dx.doi.org/10.1038/nbt.2394]
The Wall Street Journal reported on the Nature Biotechnology paper as well as some other examples of energy harvesting in medicine, where the concept seems to be taking off.
It’s important to remember that energy harvesting is still in its infancy, and that it’s competing against single use batteries that are also improving over time. Once an electronic device has achieved very low power (averaging micro watts or nano watts) then it’s relatively easy to attach it to a single use battery and achieve battery lifetimes in years (or even a decade or two). For many applications, that’s more than sufficient, so the cost of energy harvesting needs to be compared to that for a single use lithium or lithium thionyl chloride battery, and in many cases the battery will come out ahead. That won’t always be true, but it’s often true now.
