Over the past year or so, we've seen enough companies promising to deliver truly wireless power that we're almost, almost starting to believe in it. But there's an awful lot of hype, compounded by the fact that there are a bunch of very different technologies all targeting the same goal: charging everything, everywhere, without plugs or cables or pads. Recently, we've taken a closer look at a few of these technologies, including uBeam's ultrasonic power transmitters and Energous' WattUp pocket-forming antenna arrays.
Yesterday at CES, we were introduced to Ossia, another company that wants to transform how we power our devices using wireless energy. Ossia's solution, called Cota, uses thousands of tiny antennas to deliver substantial amounts of power directly to embedded receiving antennas in devices located up to 10 meters away. Cota emphasizes safety, efficiency, and reliability, and their technology seems pretty incredible.
Companies like Ossia aren't working on the kind of wireless power that you might already have in your toothbrush or cell phone, where you have to place the thing you want to charge in a specific orientation and specific place and then not touch it. You may not technically have to plug in a wire, but you might as well, for all the freedom such an arrangement provides. (And at least having a wire would let you use the device while it charges.) The wireless power that everybody wants and nobody has is the kind where all of your devices are charging themselves wherever they happen to be, whether you're using them or wearing them or not. That is what Ossia is offering with Cota.
Cota is based on the transmission of power using 2.4-gigahertz radio waves. Small antennas embedded in devices can receive up to 1 watt of power at up to 10 meters away. Rather than transmit this power in one concentrated beam, Cota uses a bunch of small antennas to transmit power to the receiver along multiple pathways. It’s not only safer, but it also helps to compensate for the position and orientation of the receiving antenna in real world environments.
So far, this sounds a lot like another wireless power technology we're familiar with: WattUp, from Energous, which uses multiple beams of 5.8 GHz RF energy to create a discrete “pocket” inside of which a device with a receiving antenna can charge. However, it's the details of how Ossia's technology works that sets it apart from anyone else in the wireless power space. What the company has managed to do with Cota seems kind of amazing.
Prototype of Ossia’s Cota wireless power transmitterPhoto: Evan Ackerman / IEEE Spectrum
The fundamental problem with wireless power is coming up with an efficient way to safely deliver a concentrated amount of energy to one specific (but arbitrary and sometimes moving) point in space where your device happens to be located. Ideally, to be safe and efficient, you'd want to transmit RF energy only to your receiving antenna and nowhere else. But how the heck would you project energy in the exact shape of an antenna out to a random point in 3-D space? That seems impossible, right? But it's exactly what Cota does.
Here's how Cota works: each device that you want to power contains an RF receiving antenna that also acts as a beacon. It sends out an RF “ping” 100 times a second. The Cota power transmitter (which is stationary) receives those pings across an array of thousands of small antennas, and each one of those antennas hears that “ping” from a slightly different angle. The transmitter responds by having each of its antennas send RF power straight back in the direction from which its particular ping came. Since all of those transmitting antennas are sending RF back to the ping’s point of origin, the RF is focused precisely on the shape of the receiving antenna with submillimeter accuracy.
This can be a little bit difficult to picture, I know, but fortunately, there's a totally cool experiment from Japan that handily illustrates the principle. Watch this:
To create an arbitrary shape in the water at an arbitrary point, this system uses a bunch of actuators all around the sides of the pool to generate small waves that constructively interfere with each other in very specific places. You could “teach” the system to make a new shape in a new location by dropping an object of that shape into the water, and then having the actuators all record the characteristics of the waves that reach them. By simply “replaying” those waves in reverse, you'd be able to precisely recreate the shape of the object in the pool. This would even work if you put a bunch of other static objects in the pool before you dropped the object in: just record and replay all the waves that you see, and you're good to go.
This is essentially how Cota's power transmission works, except in three dimensions, and with radio waves instead of water waves. The initial ping from the receiving antenna in the device provides the information that the transmitting antennas need to be able to precisely transmit power to the device and nowhere else. The device can be behind something, or you can be holding it; it doesn't really matter. As long as the transmitter hears that ping, all the transmitting antennas have to do is detect the phase and calculate the complex conjugate of the incoming signal, and then transmit power back in that direction.
Inside view of the Cota wirelessly chargeable AA batteryPhoto: Evan Ackerman/IEEE Spectrum
Okay, so now that we have a sense of how Cota works in principle, let's talk about how it performs in practice:
Efficiency: right now, Cota's transmitter uses about 8 watts to deliver 1 watt of power to a device. This is not end-to-end efficiency; Ossia says that including all the necessary conversions and computing and LEDs and stuff, a Cota transmitter will probably use a total of 60-70 watts to charge 4-5 devices remotely at 1 watt each. That 8:1 ratio is the significant one, though, because that's the measure of the efficiency of the wireless power delivery technique itself. Relative to other types of wireless power transmission, Ossia says that Cota is very well optimized, since it precisely targets the receiving antenna to minimize losses, including losses over distance. Ossia points out that if you use its system to charge something like a AA battery, it would be orders of magnitude more efficient and cost effective than buying even a single disposable AA.
Safety: Ossia’s engineers say that they deliberately chose 2.4 GHz because it's significantly safer than 5.8 GHz. None of their antennas emit that much power individually, and since the power is entirely focused on the receiver with submillimeter accuracy, it's safe to charge devices, even if they're right up against your skin like wearables. Furthermore, Cota doesn't interfere with WiFi networks, and can be used as a communication channel in addition to its role as a power delivery system. Ossia seems very confident about getting U.S. Federal Communications Commission approval for Cota: the technology is undergoing its third round of testing at an FCC certified lab, and Ossia “fully expects” to meet all SAR requirements with its current platform.
Cost: It might be a bit premature to talk about cost at this point; we've seen a sort of proof of concept demo, and that's it. (“We literally built this an hour before you came in,” said a product spokesperson.) Ossia still has a ways to go before it’s able (with the assistance of partners) to bring Cota to market. Having said that, we did get company reps to speculate a little bit on eventual cost, and the news is mostly good. The cost of the receiving antenna and associated hardware could probably be described as trivial, especially if it gets integrated directly to devices. The first generation of the transmitter (like the round one in the pictures except smaller in production) might run you a few hundred dollars. Ossia will be making more announcements about commercialization partnerships later this year.
There's a lot more to be said about Cota that we don't have time to put into this article in the midst of a jam-packed CES schedule. For example, since Cota can be used for data transmission as well as power, it opens up all kinds of possibilities for small Internet-Of-Things devices that won't require batteries. We spent an hour and a half talking with Ossia reps about their technology and vision for the future, and we were very impressed by how open they were about everything.
After CES, we'll have a more in-depth article on Ossia, but for now, if you have any questions, let us know and we'll try and get them answered at the show.
Updated on January 5 2016 with additional information on FCC certification.
Evan Ackerman is a senior editor at IEEE Spectrum. Since 2007, he has written over 6,000 articles on robotics and technology. He has a degree in Martian geology and is excellent at playing bagpipes.