We have written before about the computational power efficiency law know as Koomley’s Law which states that the computations one can do with the same amount of energy has been doubling every 1.57 years (for more info, please see my No power sensors surface … post).
The dawn of sub-threshold electronics
But just this week there was another article this time about electronics that use much less power than normal transistors. Achieving this in Internet of Thing (IoT) type sensors would take the computations/joule up by a orders of magnitude, not just ~1.6X as in Koomley’s law, although how long it will take to come out commercially is another issue
This new technology is called sub-threshold transistors and they use much less power than normal transistors. The article in MIT Technical Review, A batteryless sensor chip for the IoT, discusses the phenomenon used by sub-threshold transistors that normal transistors, even when they are technically in the “off” state, leak some amount of current. This CMOS transistor parasitic leakage had been considered a current drain that couldn’t be eliminated and as such, wasted energy up until recently.
Not so any longer, with the new sub-threshold transistor design paradigm, electronics could now take advantage of this “leakage” current to perform actual computations. And that opens up a whole new level of IoT sensors that could be deployed.
Prototype sub-threshold circuits coming out
One company PsiKick is using this phenomenon to design ASIC/chips that, depending on the application, using sub-threshold transistors plus extensive power reduction design techniques, only use 0.1 to 1% of the energy of similar functioning chips. Their first prototype was a portable EKG that uses body heat to power itself with a thermo-electric generator rather than a battery. The prototype was just a proof of concept but they seem to be at work trying to open the technology to broader applications.
One serious consideration limiting the types of sensors that could be deployed in IoT applications was how to get power to these sensors. The other thing was how to get information out of the sensor and out to the real world. There are a few ways to attack the power issue for IoT sensors, creating more efficient electronics, more effective/long lasting batteries, and smaller electronic generators. Sub-threshold transistor electronics takes a major leap forward to more efficient electronics.
In my previous post we discussed ways to construct smaller electronic generators used by low-power systems/chips. One approach highlighted in that paper used small antennas to extract power from ambient radio waves. But that’s not the only way to generate small amounts of power. I have also heard of piezoelectric generators that use force and movement (such as foot falls) to generate energy. And of course, small solar panels could do the same trick.
Any of these micro energy generators could be made to work, and together with the ability to design circuits that use 0.1 to 1% of the electricity used by normal circuits, this should just about eliminate any computational/power limits to the sorts of IoT sensors that could be deployed.
What about non-sensor/non-IoT electronics?
Not sure if this works for IoT sensors why it couldn’t be used for something more substantial like mobile/smart phones, desktop computers, enterprise servers, etc. To that end, it seems that ARM Holdings and IMEC are also looking at the technology.
Only a couple of years ago, everybody was up in arms about all the energy consumption of server farms, especially on the west coast of the USA. But with this sort of sub-threshold transistor electronics coming online, maybe servers could run on ambient radio wave energy, data centers could run desktop computers and led lighting off of thermo-electric generators inside their heat exchangers, and iPhones could run off of accelerometer piezoelectric generators using the motion a phone undergoes while sitting in a pocket of a moving person.
Almost gives the impression of perpetual motion machines but rather than motion we are talking electronics, sort of like perpetual electronics…
So can a no-battery iPhone be in our future, I wouldn’t bet against it. Remember, the compute engine inside all iPhones is based on ARM technology.
Photo credit(s): Intel Free Press: Joshua R. Smith holding a sensor