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Energous and FCC Approval for Mid Range Device - What Does It Mean?

Six months ago wireless power company Energous claimed they'd have FCC approval for their at-distance charging, and I was highly skepti...

Monday, April 9, 2018

Energous FCC Approval Shows Weakness of WattUp Technology

More Energous news today with the announcement of another FCC approval, this time the "unlimited power" Part 18 approval for their Near-Field, contact only, system. You may remember this from May last year when it was approved under Part 18 at 5.8 GHz for 1 Watt transmitted output, but this time approved at 900 MHz at a staggering new 1 Watt transmitted output. Accounting for conversion efficiencies, that might be enough to charge your phone in 10 to 20 hours! Apparently this is momentous news and so WATT shares leapt 25% in after hours trading, because... well for no reason other than this is a volatile stock that trades on hope and greed, not an actual product or profits.

Why was this approval needed? Well, Energous had been advertising the WattUp family, that what charges with the Near-Field device will also work with their upcoming Mid- and Far-Field systems. Unfortunately, they learned in summer 2017 that the FCC would not allow the Mid-Field system to pass Part 18 at 5.8 GHz, and so they scrambled to change it and go with ~900 MHz, the only other frequency band realistically open to them. It got them the approval, for a pitiful amount of power (30 to 100 mW) at a small distance (0.5 to 0.9 meters) and a safety cutoff below 0.5 meters, but broke the promised compatibility with the contact version - the frequencies were just different. 

Now, this new approval allows them to market the compatibility, and it will be quite a campaign, I can just imagine it: 

"Charge your phone on a pad in around a day, and then charge at a distance in ten times as long! (Warning, charging only valid at 0.5 to 0.9 meters, safety cutoff closer than 0.5 meters)".

If you want to look at the data for yourself, look here, then search for Energous under the Applicant Name, and look up the product 2ADNG-NF230 at 918 MHz. You can see that transmitted power is limited to 29 dBm (basically, just under 1 Watt), and they likely have some antenna gain to pretend it's closer to 3 Watts. While there are two antenna to try and ensure the device charges at any angle, only one is active at any time.

Like the Mid-Field system approved at Christmas, the Specific Absorption Rate (SAR, a safety limit) seems to be what stops them, and is around 0.864 W/kg. While the limit is 1.6 W/kg, with safety margins it is hard to go much higher. Basically, this is as much power as they are ever going to put out. Further, unlike the Mid-Field, the CEO cannot pretend that the charge rate can be increased by altering the safety zone - there is none. This is as good as it gets. (Yes, Unlimited Power Part 18 does mean "around 1 Watt max").

For comparison, the Qi standard is around 5 Watts, with a high power version at 15 Watts - Qi is the resonant inductive method you're most likely to have seen, and that Apple has essentially chosen for AirPower. USB cables charge at anywhere from around 5 Watts to 100 Watts (though practically most today are around 10 Watts).

So at less than 1 Watt it's easy to see why Myant dropped Energous from their product. It would likely be ~10x slower than the cheaper, simpler cable they look to be providing instead. As a partner of Energous, Myant would have known this was coming, but still dropped it from the lineup. If "waiting for compatibility with long range charging" was the excuse, then that's gone, as both Near and Mid versions are at ~900 MHz now. Myant could put in the 900 MHz contact charging into their product now, and switch to the at-distance chargers later. If a key partner isn't taking advantage of this feature, IMO that's a major warning flag that something is rotten in the WattUp portfolio.

As with the Mid-Field FCC approval documents, this data shows how impractical the WattUp charging technology is, and how it can't be scaled up from here. This won't stop the Energous fans from claiming another victory, that the stock price boost is a sign of impending greatness, however it's just another well timed news dump of practical insignificance that will goose the stock for a few days. Just one of the occasional bounces you can expect to see on the way down and enabling some to make a profit from the volatility, not the value. I continue to admire Energous for their ability to boost the stock price and keep the game going longer. I wonder when we'll be seeing the next set of insider stock sales...

So is this overnight addition of $100 million to the market cap indicative of great things to come? I'll leave you with this, another reminder of what the Energous CEO said almost 2.5 years ago in the Q3 2015 earnings call:

"Here is a brief summary of the results of the amount of actual power delivered to a device at varying distances with a single WattUp transmitter. Power received at zero to five feet measured 5.55 watts compared to our targeted performance of 4 watts. Power received at five to 10 feet measured 3.74 watts compared to our targeted performance of 2 watts and power received at 10 to 15 feet measured 1.06 watts compared to our targeted performance of 1 watt."

They can barely do 1 Watt when in contact in Q2 2018. Still believing they'll deliver an actual product?

(My regular reminder, I have no financial position in Energous, long or short, or any other wireless power company)


  1. I really enjoy your blog and I find myself very entertained with Energous, Ossia, uBeam, etc. I'm curious and would like your opinion... in one of Energous' latest patents it's stated:

    "The efficiency of wireless power transmission as well amount of power that can be delivered may be a function of the total number of antenna elements used in a given receiver and transmitter system. For example, for delivering 1W at 15 feet, a receiver may include about 80 antenna and Transmitter may include about 256 antenna."

    If this is true, then perhaps Energous has been purposefully allowing videos, demos, and press of their technology at a lower or reduced rate of power transmission, as to not tip their hat to any competitors prematurely.

    Surely, if the new 918mhz near-field transmitter could only output 0.8W (29dbm), they would be doomed! But if the receiving device has, say 4 or 8 receiving antenna, then the harvested power would be 4x or 8x (ie 3.2 Watts or 6.4 Watts). The Dialog chipsets on their website hint at this too, the DA2210 chip can have up to 4 antenna and can be used in multiples for devices requiring more power.

    Thoughts on this? I think I'm right, but am only an amateur biochemist, not an EE!

    Thank you,

  2. Wireless power transfer via RF is not difficult, most EE undergrads can do it - but doing it safely and efficiently at any practical situation is nigh-on impossible (IMO).

    The limit to all of Energous' systems is not how hard they drive it, but that it hits a safety limit really quickly - look at my earlier posts on SAR that stops them going further. (There is also likely a limit on "contained pockets" of energy imposed by the FCC but it's complex and I'll take a whole post to cover that).

    The FCC are very clear and sum the output from all transmitters operating together, there's no dodging this. If Energous are at the SAR limit, and they double the number of antenna, they must halve the power from each to stay at the safety limit. Focusing of the arrays Energous use with the 33cm wavelength is just horrendous - this is not precise as you can see in some of their fieldplots from the FCC approval.

    If you want to ignore safety, then yes, you can add more antenna in the form of a very large array and get better focusing, better reception, and more power.

    I will say without fear of correction that Energous are not deliberately limiting the power output of their devices. Just not even vaguely true. They push every limit they can - and in fact if you look at one of my posts you can see they show demos "not limited by FCC" that show higher powers than the FCC approved versions do.

    Always remember with at-distance wireless power transfer - it's not if it's theoretically possible, it's "can it be done, safely, efficiently, economically, practically?"

    1. Thanks for the input. But I'm still curious about your thoughts on increasing power transmission efficiency by adding more RECEIVER antennas, not Transmitting antennas. I understand that power output by Tx's is limited by SAR and FCC part 15/18. But correct me if I'm wrong, you can harvest more energy with the more Receiving antennas/rectifiers you have in the device receiving the RF signals. If the NF130 only outputs 29dbm or 0.8W that's fine, as long as the device has multiple Rx antennas. If a phone has 4 Rx antenna, wouldn't the harvested power be 4 x 0.8W (minus efficiency loss of RF to DC conversion of course)?

    2. Another very quick answer - this is one of those "yes in theory, not so much in practice" responses, and I'll be simplifying things a lot. If the focal zone of the transmitted power is much larger than any single receive antenna can cover then yes, you can receive more power with more receive antenna.

      But, the receive antenna have a physical size - for example the half-wave dipole antenna will be more efficient in reception, but by definition will have to be a certain size. You can use patch antenna which are smaller but often less efficient. Generally you find yourself trying to be smart about using smaller things in combination and end up no better off than the simple basic methods. You also can't pack multiple antenna on top of one another and expect an increase, you want to separate them by a reasonable fraction of a wavelength (which here is 33cm, so likely more than a phone size separation)

      Looking at Energous' FCC approval, you can see the bulk of the power is delivered in a sphere about 50cm in diameter. So if you had a receiver that was a ball that size, you'd get more power, but it's not particularly practical to do.

      Also remember that the orientation of the antenna matters, so you're better off with a few antenna at an angle to one another.

      As for the last statement that if the NF130 only outputs 0.8W can 4 receivers harvest 4x0.8 - 3.2 W, I think you might have mistyped that. You can't harvest more than is transmitted. If the antenna on the receiver isn't capturing all the incident power, then more antenna may increase the efficiency of power gathered, but never to more than transmitted. If the second antenna is very close to the first one, in wavelength terms, the efficiency gain is likely to be very very small.