Ossia and FCC Approval

Earlier today (Thu 27th) the FCC published that Ossia, the RF at-distance wireless power company, had been granted Part 18 approval for their charging system. This has many similarities to the Energous system that got similar approval around 18 months ago, but also a number of differences. The first similarity is that it seems a lot of cost and effort to deliver very little power across an annoyingly short distance though in a more elegant manner than Energous. If you want to look up the data for yourself, you can go the the FCC OET Authorization Search page and enter "Ossia" under Applicant Name. Ossia are clear in its intended application:

The Cota power system is intended to power sensors, actuators, small displays and other devices in a commercial or industrial environment for which changing batteries and/or connecting wires is impractical.

So no charging your phone, or any other significant electronics, and also it seems to be for fixed receivers, not mobile.

This is a large area transmitter, around 0.36m^2 (imagine a ceiling tile), and outputting 5 Watts, not that much more than a cellphone or a wireless router. For comparison, at the claimed 145 dB SPL uBeam would be emitting 100 Watts acoustic from the same area panel.

Having had a little time to read the 100+ pages of data, I'll summarize the results:

• Uses 2.45GHz band (12.25cm wavelength), compared to ~900 MHz used by Energous (33cm)
• Tries to be tightly +/-10MHz, to limit interference with WiFi?
• A 16 by 16 antenna array (256 total), compared to the linear 12 antenna used by Energous
• A 60 by 60cm ceiling tile size transmitter, compared to a flat bar for Energous
• Means a 0.3 wavelength spacing, so good steering possible
• A maximum of 5 Watts emitted, compared to 10 Watts max for Energous
• Claiming 1 Watt delivered, unclear if to the receiver or battery, possibly 500 mW to 1 Watt actual, max. Energous in the 30mW to 150 mW range.
• Limited by a SAR of ~1.42 W/kg, compared to ~0.97 W/kg for Energous (FCC limit is 1.6)
• No increasing power from here
• Max range 1 meter, compared to 90 cm for Energous
• Creates a more confined beam, better steering, but no "hotspot"
• They claim to be able to steer around objects, some viability to that claim with a large phased array and test results 
• A 15 by 15cm receiver with unspecified output
• Ossia website says "meaningful power at 1 meter" but no numbers given
• No indication of a "keep out zone" that Energous 
• Ossia website claims the phased array steering means it's not needed
• Fans on the transmitter, possibly for compute/ADC heat phase-shift electronics
• If 30+ Watts for electronics, efficiency is likely ~1.5 to 3.0%
• ~10 mW CW output from the receiver, for location
• No consumer use allowed, professional installation only and a 20cm offset from people from transmitter and receiver
• I cannot see a significant business case for this system, even at OK power the range and stationary nature limits it
• No personalized message of congratulations from Ajit Pai, FCC Chair

So the summary seems to be that Ossia have a larger 2D phased array at a higher frequency and so can control the beam better than Energous, transmit half the power, to a fixed receiver the size of two phones, needs professional installation and never closer than 20cm to people, barely enough power to charge a phone, but potentially a very low efficiency. They also cannot increase the power beyond where they are without breaching the SAR safety limit (I'd guess they scaled down to the 20mW per antenna to get under the SAR limit, and some indication they started at 40 mW per antenna). The worst case seems to be immediately behind the receiver, on page 94 of the RF Exposure report Part 2.

Front of the Ossia Cota Transmitter Panel

Without impedance information it's hard to calculate what the power is even if we assume a half-wave dipole and multiple antenna, and know the field strengths. Obviously it's less than 5W received, they claim "meaningful power at 1 meter" but no numbers given, and no use cases such as "charge your phone" so I would guess it's starting to confirm the low power number in the high 100s of mW. (Update: This article claims around 1 Watt delivered so I'll guess it's somewhere from 500 mW to 1 Watt at the battery, max under ideal conditions) If it were much greater than a Watt I think they'd be saying that very loudly, so ~10 to 20% efficient on receive (emitted to battery and *not* overall system efficiency, which is wall socket to battery). (These are estimates, I will reserve the right to update later! Which I did...) I'd be interested to see how WiFi and Bluetooth work around this, even if they have restricted to one or two of the channels.

Back of the Ossia Cota Transmitter Panel

The receiver outputs a signal at a constant 9dBm, which is <10 mW. This is the signal that's used to determine location. Now that signal I expect gets received at up to 256 channels on the transmitter, sampled (assuming the same number as transmit), so Analog to Digital Conversion (ADC). Sampling will likely be in the high GHz to get the phase accuracy needed. You can look at ADCs in the 10GHz+ range, such as this AD913 part, and they are going to consume (say) 5 Watts per channel. If sensing/location duty cycle is 100% then that's 1.25 kW of heat just from the ADCs, and so fans will be needed. Wording in the report indicates they do this 50 times a second, so I expect a lower duty cycle, let's guess 10%? Even at 100 Watts for this with simplifications and good engineering, the system is using 105 Watts to charge ~1 Watt, so overall end-to-end efficiency is <1% which is not good. (This is not certain it's what they do, but given what I'd guess the phase delay precision requirements are to make this work, it's the most obvious solution).

Update 29th June 19. I'm glad I left the caveat on different ways of doing things, as a conversation with a colleague who has a lot of narrowband phased array radar experience covered alternative ways of doing this. My expertise is most heavily in broadband ultrasound for medical, and applications of using time reversal have been really precise in sending back the exact same signal, not just phase shifting a CW train. It's a reminder that general engineering expertise gets you so far, but specialized knowledge is invaluable. If anyone from Ossia was reading it they were probably rolling their eyes :). Very quickly, they would expect that they use phase shifters rather than ADCs, and that they'd expect the electronics to be around 30+ Watts to do this. With distributed electronics, it's just easier to put a fan on the back rather than heatsink everything. They also estimated you'd manage to contain about 80% of the power into the beam, would have around 75% loss of power in the 1 meter propagation path, and then around 50% receive efficiency, so you'd see about 1 Watt RF at the receiver, and about 500 mW converted to usable power. Assume they do a good job, that's in line with the 500 mW to 1 Watt estimate. That would put it at around 35 Watts in to get between 0.5 and 1 Watt out, so 1.5 to 3% overall end-to-end efficiency.

The compute on this to work out how to send the signal back should be pretty minimal. As an alternative to this system (barring, of course, a length of wire) I note the receiver is about a 15 x 15 x 3cm block so about 775 cm^3. At 500 Wh per L, that means around 390 Wh in a Li-ion battery that size, so anywhere from 2 to 4 weeks runtime at 0.5 to 1 Watt requirement.

Why limit to 1 meter? Well with a panel 60cm across, and 12.25cm wavelength, the near/far field boundary is at around 75cm, so it gets hard to have a bounded energy region beyond about 1 meter. That may be a consideration here on the regulatory side.

The report also makes it seem like the phased array nature of the array is used not to track a moving receiver, but to act as the safety system and try to route the signal around obstructions. Both the transmitter and receiver are likely fixed. How this is then useful in most circumstances is very questionable.

I'd be interested to compare this to a modern multi-antenna wifi router with MIMO like the ASUS AC5300 with the firmware hacked to up the power transmitted and see what gets received. Might be a fun 1 to 1 comparison.

What Ossia Want the Public to Think Their Tech Is

Most of the press articles on this are pretty light reading, simply regurgitating the talking points handed to them by Ossia. In the 18 months since Energous manipulated them, the press still fall for this approach, and it remains as frustrating as ever. Interestingly, what Ossia wants them to talk about is not this system, but mythical future ones, that what they have here is "a critical first step". It's like they are embarrassed by it, even the pictures they've given out are for non-existent desktop products. This is a shame as I think the engineering team has done as good a job as could be expected, this data shows they are ultimately limited by laws of physics and regulatory safety rules - ultimately I think this is as good as it gets. It's a successful approach though, they get the press talking about phone charging even in the headlines - something that's hard to do when you can't be within 20cm of your phone... Read for yourself the similarity in articles from IEEE Spectrum, Tom's Hardware, Tom's Guide, and VentureBeat.

What's the importance of this approval? The nominal use case of charging sensors in an industrial environment IMO doesn't hold up when everything is fixed and <1m distant, a wire or large battery does the job cheaper and better. It seems to me about as important as Energous' equivalent approval from 18 months ago, good for marketing/smoke and mirrors, but meaningless if you want to charge anything.

As far as I can see, no-one has beaten Powercast yet for just getting the job done without hype.

Note: I posted a version of this article earlier, but wrote it late at night and realized when I got up I had made some mistakes, and didn't have time to correct, so took the article down for a few hours until I had a chance to fix. So if you think you saw it and then disappear, you are correct.

Powercast and Ossia

This blog spends a lot of time covering Energous, the RF based at-distance wireless power company, as in my opinion it's such a good example of how to manipulate the press, public, and markets with not much more than great PR and a willingness to be 'flexible with the truth'. In their own little world there's some competition from other companies essentially doing the same thing, in a technical sense. The most prominent of these are Ossia and Powercast.

I've been asked a few times about these companies and why I don't really cover them, and the basic reasons are these - they've not been blatantly lying about technical capabilities (to date, read on for some concerns), deliberately creating multiple product lines to confuse media and consumers, or funneling money from the general public straight into the pockets of the executives. There have been enough questions though that I wanted to clarify who these companies are, what they offer, and the (minor) technical differences between them and Energous.

Powercast

Powercast have been in operation since 2003, and have had an at-distance RF based wireless power system available and FCC approved since 2010. Like Energous they operate in the ~913MHz band, and the physics involved is essentially identical. They have a number of patents in the area. You can actually buy development kits to test them out, their website has detailed technical datasheets on all products, a simple but realistic spreadsheet for calculating actual power that can be delivered. The datasheets make it clear that they should be useful for wireless sensors and low power electronics, and never mention phones, tablets, TVs, cars, or any of the other ridiculous items other wireless power companies talk about. They don't spout techno-babble about "energy pockets" that they can't deliver on (like Energous' demonstrated inability to accurately focus in their FCC Part 18 filing).

The two product lines for receivers state up to 100 mW for the short range (over 2 days to charge a phone), and 10 mW for the long range (nearly 3 weeks for a phone), and that's maximum. More realistic is 1/10th of that, and that's reflected in the Powercast descriptions of 'microWatt to low milliWatt' levels. Powercast products are FCC Part 15 approved, which is the same rules under which your WiFi router operates - yes, it's that kind of power level we're talking about here. Could they get FCC Part 18 'unlimited power' certification? Yes, I think they could, and they might up their power output by a factor of 2 before all sorts of other safety limitations kick in. In practical terms Part 18 would buy them limited benefits with a number of restrictions, though clearly from the Energous buzz around their Part 18 approval it's worth a lot marketing wise.

So what does Energous have that Powercast doesn't? In my opinion basically nothing, except a marketing department willing to push the boundaries of truth, and an FCC Chairman willing to use his public position to promote a private company. Powercast appear to me to be a genuine engineering company, following all the rules and regulations, that has a product that you can buy, and are completely upfront and clear as to the technical capabilities and limitations. 

They may not have a desperately useful consumer-level product, but that's not to say it does not have its application. With regards to phones, if someone like Apple had wanted to, they could easily have made an offer that Powercast couldn't turn down and incorporate this tech into their equipment. But they didn't, and is a firm and clear datapoint that RF wireless charging isn't really viable in the consumer space. Powercast's website lists a number of design wins that may well have specific demands that make the technology appropriate for that case. I can see it being used in industrial settings, charging large numbers of extremely low power sensors in awkward to reach locations. They mention RFID on their site, and it seems like a good fit for those conditions. Use of this technology may also grow as the number of "Internet of Things" devices increase.

In my opinion, Powercast should be commended for sticking to an honest approach to their business in the face of what must be incredibly frustrating marketing and publicity from Energous. Like many engineering led companies that focus on delivering a product and not on marketing hype, their approach probably gives them a good business but fails to deliver them the riches that the less scrupulous get. The price of a conscience?

Ossia

Ossia have been going since about 2008 and are still privately held, having raised at least $25 million from industry and Venture Capital groups including Intel. Their technology, which they brand 'Cota', is also RF based, but this time at 2.4 GHz, same as some WiFi routers. Their founder/CTO writes blog posts and technical white papers available from their website, but they are exceptionally light and free from any real information with which to analyze their products in detail. There are no products, datasheets, or evaluation kits of Ossia technology that I am aware of. (Update, In June 2019 Ossia received FCC Part 18 Approval for a system.)

Their choice of 2.4 GHz results in a smaller wavelength than the 900 MHz band (around 12.5 cm vs 33 cm), so in theory can lead to greater control over small focal zones and beamforming. At best the focus will be at least a phone sized sphere in any practical situation, but it's better than the beachball sized 'pocket' Energous have. By creating a large phased array of many small transmitters, and sending the right signal to each, a beam could be steered with reasonable precision - their 'ceiling tile' size array (pictured above, from here) could have 10 by 10 emitters each spaced at half a wavelength, and according to this article is closer to 16 by 16, so 1/3 wavelength spacing.

Larger arrays mean greater control, I covered some of the maths behind this here. Ossia claim this allows them to be much more precise in targeting the receiver, and 'bounce' signals around the room so that direct line of sight isn't needed. The image below from Ossia shows this in operation, with the receiver sending out a location signal about 100 times a second. This is a pretty well known engineering technique, sometimes called time-reversal, so under the right conditions it will work. It does not, however, reduce the size of the smallest possible focal zone, remove safety limits, or increase the amount of power legally transmittable.

Under Part 15 rules, Ossia can still only transmit as much power as Powercast, which means the entire system is just a more precise way of delivering microWatts to low milliWatts and leaves phone charging as an impossibility. Much of Ossia marketing material in the last few years has made it clear they're looking at similar low power situations as Powercast. Their statements are sometimes questionable, for example that 2.4 GHz is 'safer' than 5.8 GHz, can allow more precise targetting, and won't interfere with WiFi. I wonder if they'd say the same now that Energous have moved from 5.8 GHz to 913 MHz?

What about Part 18 and 'unlimited power'? There's no reason that Ossia can't do this, and once again will be limited not by transmit power, but the various safety restrictions, which like Powercast means perhaps a factor of two increase in power delivered. Why haven't Ossia done this, as it's not a complex set of tests to go through? While the FCC have not made specific statements on this, it seems they are unwilling to give Part 18 certification on wireless power devices in the 2.4 and 5.8 GHz ranges. Energous started at 5.8 GHz, but rapidly moved to 913 MHz when they repeatedly failed to get FCC approval in 2017, skipping 2.4 GHz entirely (there are limited frequency bands that are available in Part 18). 

One school of thought is that the FCC isn't allowing Part 18 at 2.4/5.8 as they are the main WiFi bands, and that communications will suffer interference, so the options left are 913 MHz and ~25 GHz. Another is that the FCC isn't allowing 'unbounded' energy above a certain level - that you need control of that region of power, a peak with clearly defined edges. This would mean charging would have to happen within the near field, or at best at the near/far field boundary. No matter what your technology, that is set by the laws of physics - basically your frequency and size of transmitter are all that matter. Bigger transmitters are less practical but will allow you to push that boundary out further. Higher frequencies lead to more precise control over the beam and spot due to the smaller wavelength, as well as more transmitting elements in the same space leading to precision.

While Ossia have been playing by the rules and not putting out highly misleading marketing, I've been disturbed by some of their recent press. This article looked at both Ossia and Energous, and reached the usual level of in-depth analysis by a tech journalist that I'm used to (i.e. none). At first, Ossia demonstrate a transmitter with 10 Watts of output power - that's clearly well beyond Part 15 limits, and matches the 10 Watts of the Energous Part 18 transmitter.

"The maximum range is somewhere around 30 feet, but at that distance you can only receive a very small amount of power. Within 6 feet of the transmitter, you’ll get somewhere around 1 watt from the 10 watts being transmitted. At longer distances, you might expect 100 or perhaps 200 milliwatts, which isn’t enough to charge up a smartphone, though it can slow down the discharge."

Since they don't have Part 18 approval, that device needed to have a clear notice that it was not FCC approved and is not available for sale. I wonder if they had it and the journalist simply failed to notice? I also find their numbers disturbingly high - remember Energous transmits 10 Watts to get 30 mW at 90 centimeters, are Ossia really getting 33 times the power at twice the distance? That implies some massive directionality and antenna gain, and regions of space between transmitter and receiver going well over safety limits like SAR and MPE.

They then go on to talk about safety:

“We have established that this technology achieves the same level of safety as Wi-Fi and Bluetooth, so there is no issue with exposing people.”

This is bordering on deliberately misleading, having talked about the power levels with a non-approved device, (which seem to be vastly beyond anything realistic even under Part 18), to then go on to talk about safety numbers from WiFi type equipment of Part 15. Poor journalism may be to blame here, but I don't see Ossia rushing to correct it. I've refrained from talking about Ossia too much as they had not been making outrageous claims, or deliberately confusing the press and consumers by talking about two very different products in subsequent sentences, and allowing the listener/reader to assume they are the same. If they keep this up, in all fairness to Energous, I'll need to start covering them in the same way. Ossia, please don't make me do that, I've little enough time as it is to write...

Summary

There are at least two other RF based wireless power companies out there besides Energous. One of them has had an approved device on the market for years, but has minimal traction in the consumer market. The other seems to be trying a more technically sophisticated version of the same thing, but are now watching Energous getting away with very misleading marketing. Both are limited by the laws of physics, and safety rules, that mean powering phones or any other sizeable devices is out of reach. Despite that, tech journalists will continue to publish puff pieces on how wireless power for phone charging is just around the corner.

I can't blame companies who follow the law from trying to get favourable coverage. The tech press, however, need to wake up to the fact that they are now reporting on products and markets that directly affect our health and safety. Despite high profile cases like Theranos, it seems to be business as usual. The usual cursory coverage and regurgitation of company PR doesn't cut it in these situations, this isn't the latest iPhone or a dating app, and they need to step it up before something hurts more than investors wallets.

Those Other Guys, Pt 1

Having made comment about others' concerns over tech startups like Theranos ability to fleece investors and the public, I thought I would make some comments regarding Energous, another wireless power company getting some press. I'll point out here that I have no inside knowledge of the workings of Energous, just that I've spent a lot of time in the last few years looking at the physics of transferring power via waves (acoustic and electromagnetic waves have a lot of similarities in the maths and fundamental behaviours, much of what I say below can be applied to ultrasound phased arrays), and how investors in tech companies think.

For the less technically minded among you, I'll summarise in the next part the key points from here, and you can just skip straight to part II.

Energous uses RF electromagnetic waves, similar to those used in the higher speed wifi signals, to transfer the energy. At the 5.8GHz they claim, wavelength is going to be around 5.2 cm (divide the speed of light at 3e8 m/s by the frequency of 5.8e9 Hz). Why is this important? Here's an image from their patent filings, with the power transmitter in the top left, labelled 706:

It's clear from the patent they intend to use a phased array, similar to what is done in radar, and what uBeam has claimed to do. Essentially, it's a large regular grid of transmitters, like a chessboard, and by sending the signals from each small piece at slightly different times, you can send a beam to a chosen location. An image below shows a beam from an array from a standard computer simulation package. This is a well known phenomena and has been for many years, there are few surprises.

Notice as well as the main lobe (big red bit where most of the energy is going), there are lots of little peaks going in other directions called side lobes. These are an inevitable consequence in any practical system, and involve energy wasted and going places you don't want. You can also get even worse lobes called 'grating lobes' if you don't put those transmitters close enough together, less than half a wavelength or around 2.5 cm. Let's assume, like any good engineer would if designing a phased array where you are sending power and don't want to cook anything off to the sides, that you go with 2.5 cm spacing.

Now Energous have been claiming 'hundreds of small elements' so in the great power analysis here let's assume around 500, or about a 22 by 22 grid, which at 2.5cm spacing is 55cm on each side. Wow, that's a big panel. Let's make it closer to the size of a speaker, which is what the press is describing here and make it to 100, that's a 25 by 25cm plate, still pretty sizeable. That's not out of scope - if you look at the scale of array that Ossia, also using RF to do charging, is showing in their patents. (Ossia work at half the frequency, so wavelength is 2x bigger).

Anyway, Energous claim to create 'pockets of 3D energy' which is marketing speak for 'beam'. No pocket of energy magically appears with none elsewhere, like a magnifying glass with sunlight, it concentrates more and more until your point focus is very intense. How small you can make that focus is related to the wavelength L (smaller wavelength for smaller focus) and transmitter size relative to wavelength D (bigger transmitter is smaller focus), and how far away you are trying to focus F (further away is larger focus). Generally, your focus (pocket of energy) is given by L*F/D. That's not exact, but is close enough for a blog, and the fact that the energy slowly dies off, like in the image below, would certainly be a safety concern. Not something I want to be near even away from that pocket.

So using the above numbers, at 5 meters range (just beyond the 15 feet they state), the focus is 0.05 * 5 / .25, or around 1 meter in size. That's a big 'pocket'. Even at 1 meter range that's still a 20 cm focus which is larger than any phone, and will catch your hand, head, and anything else nearby. In an IEEE Spectrum article they state the pocket is larger than the receiver, so not unbelievable. (Note to uBeam: Energous seem to know how to handle a skeptical technical press, despite similar incredulity from the experts)

The 'mini-transmitters' they talk about are ridiculous though - do the above calculation with a USB sized device. It's no wonder it would literally take years to charge a phone with it, even before you consider you need to reach a level of 0.5 to 1 Watt these days to trigger charging.

And then there's directivity where the amplitude falls off with angle as you move away from the beam pointing straight ahead - by the time you get to 60 degrees, you're at half-power, and down to 0 when pointing to the side. This simply doesn't mesh with Energous' claims of a '30 foot diameter bubble'. In summary - with a phased array it's easy to point straight ahead, and harder as you move to the side. This means it gets less efficient - a significant problem when imaging, a killer if you're transferring power.

I won't go into other numbers showing that their claims of power delivery capability are not just difficult but defying laws of physics - the only thing more ridiculous would be claiming that ultrasound could charge a device that's in your pocket. Anyway, you can find information demolishing Energous' claims here including mention of the regulatory issues they face with the FCC, though everyone seems to forget the FDA can choose to become involved in any radiation emitting device (and ultrasound is radiation, FYI).

Confused, bored, lost? No? Then you probably knew most of this anyway, are technically proficient, and were already skeptical of Energous. Yep? That's what 95% of people who read this will feel like, and switch off. And that's the point.

That's the tech side - next part, the business side and their novel approach to fundraising.