Q&A: Harvesting energy
What if our devices didn’t need recharging or new batteries? University of Cambridge researchers are hoping to build wearables that harvest energy from transistors and can last years without a recharge
The devices that glean power from transistors.
rather than improve batteries, why not reduce the need for them? Researchers at the University of Cambridge have designed transistors that scavenge for energy from their own environment, meaning devices could have power for years without a new battery.
The ultra-low-power transistor borrows from computers in sleep mode, harnessing leaked electrical current from transistors. The experts compare it to water dripping from a faulty tap, and such leaks are characteristic of all transistors, offering a free energy source – if only it can be captured and used.
To do so, the researchers made use of the point of contact between the metal and semiconducting points of a transistor, known as the Schottky barrier. Transistor engineers usually try to avoid such barriers, but the Cambridge researchers instead tapped it for power.
Harvesting that energy means low-power devices won’t need new batteries or recharging for years, with the researchers claiming that the energy in an AA battery could be made to last for a billion years using their transistor design.
We spoke to researcher Arokia Nathan, professor at the University of Cambridge’s Department of Engineering, to see why it was worth harvesting energy to cut battery use and what devices such a design could be used to develop.
What innovation did you come up with for this to work? You do have this in silicon, the kind of thing that’s already used in computers [such as low power draws when they’re put to sleep]. But what we’ve done is basically use technology used in a lot of displays. This is very nice for wearable applications.
Wearable technology is fussy about how much energy you consume, because you don’t want to be carrying around batteries when you wear something. We were looking at how to cut back on the energy consumption… in thin films, you get a much better performance than with silicon technology. That’s why we went with the non-silicon approach. We actually had to come up with a new device architecture from the start, which provided this performance.
What devices could this work with? It’s ideal for cases where speed isn’t important… It’s [not ideal for] application in the very high-frequency stuff that you use in cell phones; it’s more for wearables and IoT.
That could be monitoring health, the body or even buildings. Basically, anything that you would want to monitor remotely, so that you don’t keep going back to change the battery all the time.
The most obvious things are wearables, healthcare monitoring (heartbeat, blood pressure): we design sensors for these things. We develop circuits using this architecture to read out sensory information.
Degradation in matter – buildings or anything else – is a very slow process so we’d be looking at constantly monitoring.
Thinking longer term, could this ever work for smartphones? Smartphones constantly go for higher frequencies – they’re going to 5G now. What comes after that will be even faster, right? For that there are well-established silicon technologies. They may have to think about how to cut back on power, but not using our approach.
Why are you looking at cutting power rather than boosting batteries? Many people are working on increasing the energy-storage capacity of batteries, but they’re not really addressing how to cut down the use of batteries. If we were restricted in terms of energy storage or battery capacity, how do we make electronics that would consume very, very little? That’s what we were thinking.