The idea is that every parcel in a post office would transmit its position, origin and destination so that it can be tracked and routed more efficiently, that every product on a supermarket shelf would transmit its contents, price, shelf life and so on, that your smartphone would interrogate the contents of your fridge and cupboards every time you walk into the kitchen to warn you when the milk is running low. And so on.
Each of these things will enhance our businesses and lifestyles in a small way. But taken together, this Internet of Things will entirely transform the way we interact with the world around us. That’s the hope at least.
But there’s a problem: these tiny identifying devices require a power source. Batteries are expensive and impractical so computer scientists are hoping to harvest the necessary energy from the environment, in particular from lights and from human motion.
The question is how much energy is available in this way. That’s relatively straightforward to answer for indoor lights (about 50-100 microwatts per cm^2). But the energy available from human motion is much harder to assess.
That’s piqued the interest of Maria Gorlatova and pals at Columbia University in New York who have measured the inertial energy available from the activity of 40 individuals over periods up to 9 days. To do this they attached to each person inertial energy harvesting devices, essentially a mass attached a spring, that recorded their motion.
“To the best of our knowledge, the dataset that we analyze is the first publicly available acceleration dataset collected for a large number of participants,” they say.
They also measured the power available from the movement of objects such as doors, drawers and pencils to see how much might be harvested here.
The results are often surprising and sometimes counterintuitive. Here’s a list of their main findings:
- Periodic motion is energy rich. So writing with a pencil generates more power (10-15 microwatts) than the acceleration associated with a 3-hour flight flight including take off, landing and turbulence, which never generated more than 5 microwatts.
- Humans are passive most of the time. About 95 per cent of the total harvestable energy they produce is generated during less than 7 per cent of the day.
- Walking generates the same amount of power as indoor lighting (about 150 microwatts). Running generates around 800 microwatts.
- Purposeful shaking generates up to 3,500 microwatts, 30 times more than walking.
- Even though it requires less exertion, walking downstairs generates more power than going upstairs because of the higher accelerations involved.
- Taller people generate about 20 per cent more power than shorter people.
- The difference between people’s power output depends largely on the amount of walking they do. Sensor placement on the body makes little difference.
- Most people generate enough power to continuously transmit data at the rate of about 1 Kb/s (more than 5 microwatts).
That’s an interesting set of results. Engineers are already designing algorithms to manage the way energy is harvested, stored and then used. Gorlatova and co say this kind of work will help to make these as efficient as possible.
Beyond this, an interesting question is when we will begin to see commercial energy harvesting devices. Perhaps the first candidates are the increasing numbers of human motion sensors on the market.
Devices such as the Fitbit and the Nike Fuel Band have been continuously recording the daily activity of many thousands of individuals for some years now. It’ll be interesting to see how these companies use this data to improve their products which now require regular charging or disposable batteries.
Beyond that, substantial research dollars are currently being invested in designing computing devices that operate at low enough power levels to benefit from energy harvesting.
What seems clear from this and other work is that the Internet of Things is coming and that if the problem of power once looked like a showstopper, this is no longer a worry.
Ref: arxiv.org/abs/1307.0044: Movers and Shakers: Kinetic Energy Harvesting for the Internet of Things