There are few of us who can go a whole day without checking the battery level on at least one of our devices — and between smart watches, fitness bands, e-readers and smartphones, we may have three or four constantly in danger of running out of juice. You can always find an outlet to top up, but researchers are discovering ways to charge that don't use the grid at all. Ambient noise, body-penetrating waves and even a person's own sweat are powering tiny devices — and soon, perhaps, larger ones.
One thing researchers are taken with, but that you might not have noticed, is that you're surrounded by energy. The noise from the street, the radio waves from cell towers and local stations, and of course the warmth and light from the sun — all these carry energy in some way or another, and if you can capture it, it's basically free power.
Take, for example, the ambient noise that we make our way through in the city: trains, cars, crowds. The minute vibrations from sound can be captured and turned into a modest, but usable, current. "Vibrational and movement energy harvesting is good because it can be very compact," Joe Briscoe of the Queen Mary University of London told NBC News via email.
Briscoe's team built a phone-sized device that catches everyday noise and converts it to electricity. "The power levels in sound are fairly low, so it's never going to fully power a phone, just make the battery last a bit longer," wrote Briscoe. "It can still go quite a bit further — we have a number of steps in mind to increase the efficiency and therefore the power that's generated."
Even energy you can't detect can contribute. The soup of Wi-Fi, TV and cellular radiation we walk through every day without noticing can be tapped into even if it can't be seen or heard.
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A number of teams around the globe are working on ways to catch these radio waves, which would otherwise go into space or dissipate in the air or ground, and put them to use. A broad-spectrum antenna being hit by such waves could power a tiny sensor like a thermometer or pollutant detector as it worked, and use the same energy to transmit that information wirelessly. No battery, no charging, nothing else necessary.
The space around us isn't the only place with "wasted" power. If your needs are small, you can find scraps of free power on your body, as well.
A "biobattery" in the form of a temporary tattoo, created by Joseph Wang's team at UC San Diego, uses chemicals naturally produced by the body to power itself. "This is the first example of a biofuel cell that harvests energy from body fluids like sweat," explains Wang in a video describing the invention.
Our muscles create a waste chemical called lactate and eject it through sweat — making it a good way to measure exertion and muscular activity. The biobattery uses the molecular properties of lactate itself to create a tiny current, which can be measured to determine the body's production of the chemical, a useful gauge in fitness testing.
Briscoe also points out that the same devices that gather energy from vibrations can get it by more direct means: "Another idea is to attach them to your arm or leg in clothing, or bag straps, so that as you walk and move around it's generating power."
And if you can't get the power from the body itself, you can send it straight through. The smaller and less obtrusive implanted devices like pacemakers and blood sugar sensors are, the better. But implants also need to stay in the body for a long time, which has generally required a battery — until Stanford's Ada Poon and John Ho found a way to beam energy directly to a device, right through the body. The result is an implant the size of a grain of rice.
As innovative as these techniques are, the researchers owe a lot to the same fundamental advances that have made things like smartphones possible. "The miniaturization of electronics definitely sets the stage for this work," wrote Ho. "The need for new powering techniques comes from the fact that implants can now be made incredibly small."
Every year researchers at ARM, Intel and elsewhere are working to shrink the size of transistors, the tiny electrical switches that make up computer processors. The latest generation is just 17 nanometers across — a fraction of the size transistors were a decade ago. That means chips are exponentially more powerful for their size, and they use far less power to boot.
"What is exciting is that as the devices continue to miniaturize and become cheaper, the capabilities multiply," Ho continued. "Researchers have already demonstrated tiny radios, sensors and even cameras that could be used inside of the body."
It may not be a bottomless battery pack for your iPhone (yet), but these researchers are thinking outside the "battery replacement" box. What if your phone didn't waste power checking the temperature via Weather.com, but just received that information from dozens of nearby embedded sensors? What if your fitness band ran entirely on the energy it got from your movement? Why include a heart rate monitor on your phone or a biometric lock if a perpetually powered implant can serve both purposes?
As the "Internet of Things" grows and proliferates, it may be able to take care of its own power needs, grabbing them from whatever trace energy is close at hand. It's a bit creepy, but it's also exciting — and it's also one less battery to worry about charging.