Long range wireless power is one of the most exciting things we saw at CES this year. We've already talked about Ossia, and now, we're going to take a close look at Energous, whose WattUp technology we first saw at CES 2015. A few months ago, we spoke with Energous CTO Michael Leabman about the efficiency of his company’s system. Earlier this month, we spent over an hour in Energous' CES demo suite checking out demos, and speaking with Leabman about the future of wireless power and what the company has in store for 2016.
For details on how Energous' WattUp system works, it's worth reading our article from Last November. In summary, Energous uses multiple, steerable beams of 5.8-gigahertz radio waves emitted from an antenna array to form a small pocket of RF energy around a device. Inside the pocket, the device’s receiving antenna can harvest that RF energy and charge up the battery. This energy transfer can happen out to a range of several meters.
Does It Really Work?
Since its first demos were made public last year, Energous says that it’s had trouble convincing people that its not faking the whole thing. Most of its 2015 demos were wirelessly charging devices that already had batteries in them. Several of the demos that we saw at CES were designed to counter this, like this demo, which had a WattUp transmitter sending power to some green LEDs embedded in clear plastic along with Energous' receiver hardware:
Photo: Evan Ackerman/IEEE Spectrum
This shows that WattUp can, in fact, transmit power at range to a targeted device, but four LEDs (even if they're eyeball-searingly bright, which these were) don't need much juice. A second demo setup from Energous was much more interesting. This next pic shows a test setup, with an array of two WattUp transmitters (the white rectangles) placed maybe 4 or 5 feet from a WattUp receiver (in the foreground) with a LED hooked up to it to provide a load:
Photo: Evan Ackerman/IEEE Spectrum
This one shows the same antenna hooked up directly to a power meter:
Photo: Evan Ackerman/IEEE Spectrum
0.673 watt at just under 5 volts. A few inches away from the targeted location, the power drops off by a factor of several hundred. It doesn't work nearly as well if the receiver antenna isn't parallel to (and pointed at) the transmitter. But in practice, Lebman says, the antennas themselves are so cheap and easy to integrate that for a wearable, you could just put antennas on pretty much every surface to mitigate the orientation issue. The receiver in the background of that first picture, incidentally, has a larger antenna, and was getting about 1.6 watts from the same transmitter—although not at the same time as the smaller one. Leabman says that the small reciever was collecting about 10% of the power broadcasted from the transmitters.
Both of the transmitting antennas in the picture were being used in the demo; switching to just one cut the received power by a factor of four. Similarly, doubling the number of antennas in the array (and the amount of power being emitted) will increase the amount of received power by a factor of four. Furthermore, the larger antenna array enhances the precision with which that power can be focused. With these trade-offs in mind, you can shape and scale the antenna arrays however you want.
Leabman also told us that these particular transmitters (from a WattUp evaluation kit) used antennas that were not optimized, and that Energous is currently able to provide the same amount of power in a form factor that's about half the size. He also mentioned that they're now able to pack the transmitting antennas much closer together, further reducing the transmitter size, and increasing efficiency by a factor of two or three. We should see these smaller, more efficient transmitters this year.
An Energous RF to DC converter chip, a chip and antennal with green LEDs from the demo above, and an early generation antenna, with a nickel and a Fitbit for scale.Photo: Evan Ackerman/IEEE Spectrum
Energous is not a company that's particularly interested in producing consumer products. Like most wireless power companies, they'd much rather sell hardware to consumer electronics manufacturers, and have somebody else sweat the device integration. Consequently, Energous is all about making its hardware easy to stuff into wearables, cell phones, or anything else you might want to wirelessly charge.
Inside a device, you need two things from Energous: a 3-by-3-millimeter chip that converts RF to DC, and antennas to capture the RF energy beamed from the transmitter. The chip can actually be made even smaller if it's integrated with a Bluetooth or power management chip. And the receiving antenna is just two layers of PCB. It works over both 2.4-GHz and 5.8-GHz frequencies; and because it works for both power and communications, it's super easy to integrate into existing devices. It's also not especially complicated to attach a bunch of antennas to devices to maximize the amount of power they can receive. Perhaps most importantly, the cost for both the chip and antennas is trivial, perhaps a few cents.
Energous has been very focused this year on getting WattUp production-ready, in terms of size reduction, cost reduction, and ease of integration. It’s expecting to be able to ship “millions and millions” of chips by the end of 2016.
Because the amount of power that WattUp can deliver is based primarily on the size of the transmitting antenna array, the size of the receiving antenna, and the distance between the two, any instantiation can be scaled by manufacturers to fit whatever application they want. But it's this very flexibility that makes addressing the overall efficiency of WattUp a bit tricky.
Wireless Power Efficiency
What does the system’s efficiency depend on? There's the size of the transmitter, the size of the receiver, the orientation of the receiver, the distance between them, and even the characteristics of the surrounding space. Energous says that the total end-to-end efficiency could reach 50 percent—using a small transmitter with close-range optimized antennas—if a device were placed directly in contact with the transmitter. Leabman told us that “at a reasonable distance” of 1.5 to 2.5 meters, “maybe 10 or 15 percent” efficiency could be expected. We specifically asked about the demo that we saw earlier as an example to get a better sense of where the technology is now:
IEEE Spectrum: The sense that I’m getting is that, for consumers, in the home, it’s probably going to be one or two of those [transmitter] modules, and so you’re going to be consuming something in the 100-watt range to deliver one to two watts to a couple of different devices. Is that basically correct?
Michael Leabman: I would say probably more like 50 to 100 watts to deliver five to 10 watts. You’re not always going to be ten to fifteen feet away. Sometimes you’re going to be five feet away; sometimes you're going to be ten feet away. And, you know, cut from ten feet to five feet and you’re going to get four times more power.
Leabman went on to re-emphasize the scalability and consequent variability of the WattUp system, which leaves the efficiency question up to manufacturers—although there's definitely a range of efficiency that seems to be reasonable:
Leabman: It's really not up to us. We're not delivering products. We're delivering these reference designs and saying, “Hey, you guys figure it out.” I think a year and a half ago, people were really concerned about efficiency. Obviously, if you have a 200 to 300-watt power supply, it's not green and people aren't going to be happy with it. I think we all realize it's got to be less than 100 watt power supply, and it's got to have reasonable distance as well. So I think that's probably the sweet spot.
I made this point when talking about Ossia, and I'll make it again here: I don't feel like poor efficiency will be much of an issue for most consumers, considering the substantial benefits that wireless power will offer in terms of convenience. In principle, we can all bemoan the fact that we're wasting energy, but considering the amount of energy that we all waste daily and never think about, wireless power is a small drop in a large bucket. If someone were to hand you a cell phone and say, "You'll never have to think about charging this ever again, but it'll use 50 watts of power to charge as opposed to five," would you really refuse based on efficiency—when swapping out an incandescent light bulb or two would render the difference moot? Yes, wireless power is never going to be as efficient as plugging something in, and that's not great, but the efficiency is not so bad, I'm guessing, that most people would decide to avoid it based on that factor alone.
Furthermore, if your device can be charging almost all of the time, the amount of power required to charge it can be significantly less, which minimizes the impact of reduced efficiency. You shouldn't think of wireless charging as if it was a replacement for plugging your phone in when the battery gets low. Rather, think of it like having your phone plugged in and trickle charging all day. You simply won't need that high power charging, because your battery won't ever really run down as long as you're in the same room as a wireless charger.
Safety and Certification
Losing a bunch of RF energy into the environment is certainly inefficient, but the bigger question is whether it's unsafe. Radio frequency radiation isn't ionizing, meaning that it's not going to knock your DNA around and give you cancer. But it's still energy, though, and it can do other things—most notably causing localized heating if the radiation is strong enough. U.S. Federal Communications Commission regulations are designed to limit human exposure to RF radiation, with Part 15 applying to communications devices. Wireless power will be regulated under Part 18, which is a sort of catch-all for anything else in the RF spectrum, like medical and scientific devices.
Energous is is well aware of this as yet uncleared regulatory hurdle, and it hasn't completely addressed it for a few reasons. One is that it's not a fun process to go through; the plan was to wait until they had production hardware before starting it. And the other is avoiding the prospect of running the FCC gauntlet on its own. With that in mind, Energous has partnered with a tier 1 consumer electronics company (one of the five largest consumer electronics companies in the world, we're told) to get a little bit of experience (and clout) on its side. We asked Leabman for details:
IEEE Spectrum: How do you make sure that WattUp is going to be safe for people, and how do you make sure that it's going to be approved by the FCC?
Michael Leabman: We have to pass regulatory wherever there's power. RF has it's own regulation on what's safe and what's not safe. If we're going to deliver five watts into a small space, we're going to have to abide by those regulations. One of the advantages of picking up our tier 1 is that they're leading with the FCC. Their FCC team is larger than our entire company; they've done hundreds of products, so they know exactly what it's going to take. We've been working with them for a year, and the approach we're taking is something that they don't want us to share. But, you have to be safe, whether it's standing in front of the transmitter or out there with the device.
IEEE Spectrum: So there's a plan?
Leabman: Absolutely. When you have a multi-multi-billion dollar company, the last thing they want to do is ruin their image. So for them, this is very important. Safety is the highest thing, and we wouldn't have been engaged with them for a year if they didn't think there was a clear path. I think this is the year it's going to happen.
Anything wireless power has to pass FCC part 18. Part 18 didn't anticipate RF at a distance, so that's something we have to submit to the FCC, and they have to understand how the system works in order for us to get approval. That's something that takes time. We think we have a very clear path, driven by our tier 1, and that's all they're allowing us to say.
IEEE Spectrum: When you go through this process with the FCC, is it like they have this checklist of criteria you have to fulfill in order to be safe, or is it much more nuanced than that?
Leabman: Yes and no. Certainly there are regulations for RF, what's safe and what's not safe. There's SAR [specific absorption rate] for your phone. There's MPE [maximum permissible exposure]. The nice thing about RF is that they know what's safe, and they have regulations, so in that respect, that's known. The maximum power you can transmit under Part 15 is one watt. Obviously, to get one watt [at a power receiver], you have to transmit more than one watt. When Wi-Fi came out, it took time before people realized it was safe and people adopted it. And again, we have a very clear path.
IEEE Spectrum: If under Part 15 you can't transmit more than one watt, is that because transmitting more than one watt is unsafe somehow?
Leabman: Under Part 15, you can actually transmit significantly more power if you use directional antennas, like dish antennas. The conducted power is a watt, but the power out is more. But again, a lot of these rules are 20 years old. No one envisioned wireless power 20 years ago. A lot of these rules, at least for Part 18, are written very broadly, because no one knew what it would be like. So, for wireless charging that's contained, what does that mean? It's about working with the FCC to say, “This is how it works; it's safe in all the areas that you want.” And because it's new, you just have to go through all that.
I certainly wish that Energous would be more forthcoming about this process, and it’s unsettling that they aren’t, since it seems like such a major step between the technology that they have now and a marketable product. But if nothing else, I do have confidence in the aggressive self-interest of this unspecified tier 1 consumer electronics company. It's hard to believe that said company would be partnering with Energous if it didn't have a high level of confidence that making a product that's safe, and able to pass FCC certification, is a sure thing.
What’s Coming in 2016
The problem with developing a new platform-based technology is that it's hard to convince manufacturers to build it into devices without consumer demand, while it's hard to generate consumer demand without device integration.
I typify the problem: I'm interested in wireless power, but I'm not going to add a bulky case to my phone to take advantage of it. So, how do you break consumers in gradually without asking manufacturers to invest up front in an unproven technology? And with wireless charging, there's a more specific problem—the same one that users of USB-C have probably run into: Once you leave the house, you're in trouble, because the rest of the world hasn't caught up to your charging tech yet.
A WattUp USB power transmitter along with some demo wearables modified for wireless chargingPhoto: Evan Ackerman/IEEE Spectrum
Energous' solution to both of these problems is to start small. They've developed an inexpensive USB-powered WattUp dongle that can wirelessly charge a few small devices at once at very short range ("a couple of inches"). It's designed to be packaged and sold with wearables instead of a conventional power adapter or docking cradle.
The idea here is that you buy, say, a fitness band, and instead of a USB adapter and cable, it comes with this WattUp dongle thing. It doesn't cost extra, and you get the added benefit of a completely sealed band that you can wear in the shower. To charge the band, you just have to be wearing it while you're perhaps typing on your laptop and the WattUp dongle is plugged into a port on the side of the computer. Or, you can take it off, and place it on or near the dongle itself. It's not yet the dream for long-range wireless power, but it's about the same amount of effort (or less) as you'd spend with a conventional charger.
Later on, if you decide to upgrade to a larger, longer-range WattUp transmitter, your fitness band will be able to take advantage of that, since it's already part of the ecosystem.
The technology inside the dongle itself is similar to, although not identical to, WattUp's larger power transmitters. Because it's optimized for close-range transmission, it uses metamaterial antennas that are designed a bit differently, and it's not like you can crank the dongle way up and start charging devices meters away (although the pocket-forming technique works the same). What's important, though, is that the device that's being charged doesn't care whether you're using the close-range dongle or the longer range antennas. If it can charge from one, it can charge from the other, so even if you start with the close-range dongle, you're already equipped to charge at longer range too.
While starting with the dongle and small wearable or IoT devices seems like a reasonable idea, Energous' tier 1 partner will be embedding WattUp receivers directly into “certain mobile consumer electronics and certain related accessories,” which probably means something like a tablet or a phone. This tier 1 will also be making WattUp power transmitters. Energous tells us to expect to see consumer products with embedded WattUp technology from their partner to launch in late 2016 or early 2017.
The Future of Wireless Power
A prototype WattUp transmitter mounted underneath a monitor can charge a wireless mouse, a wireless keyboard, and anything else that you put in front of itPhoto: Evan Ackerman/IEEE Spectrum
While I've written articles about how exciting wireless power could be, I also want to add a note of caution. We've seen demos of a variety of technologies that work, but a demo and a working consumer product in your home are two very different things. And the stretch of road separating them can be long and fraught with bumps. Energous, and other wireless power companies, are very good at both communicating a dream, and at presenting that dream under controlled conditions while providing (necessarily) limited information.
The technology does certainly work. But it has to work reliably, cost effectively, safely, and be accepted by consumers. Will it change the world in the same way that replacing (or at least supplementing) phone lines with cellphones or ethernet with Wi-Fi has changed the world? Maybe. Personally, I hope so, because I really hate having to plug stuff in. But until we're able to try out a consumer product with built-in wireless charging enough so that we can say, “Yes, this works just like we've been promised,” maintaining reasonable amounts of pragmatism (and skepticism) are important.
We'll continue to follow Energous and other wireless power companies closely. In the next few months, look for an article on how wireless power fits in the scheme of FCC Part 18 regulations. For now, let us know if you have any questions, and we'll do our best to get you answers from Energous.
Updated on Friday January 22 with additional information on the efficiency of the demo and the difference between the demo hardware and Energous’ current generation of transmitter
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.