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.

Further Safety Limits for Energous? MPE

It's just as well Energous got their FCC Part 18 approval in a holiday period - any other week and I simply wouldn't have had the time to read the reports, analyze them, and write these blog posts. (You can find these earlier posts here) Over the last four days it's been around 7,500 words and 15 pages worth of writing, and there was a lot of reading and work for each of those pages. This will likely be the last in-depth analysis for a few days, as I actually have to get back to real work tomorrow - the exception possibly being a short piece on Powercast I'm working on and may finish tonight (Edit: nope, that didn't happen).

Here's the main point of this post - Maximum Permissible Exposure is a further safety limitation for RF radiation that has not been applied to the approved Energous system, as far as I can see. If it were, using limiting power density for the general public, my calculations say they're over the limit by a factor of 3. If they use the "Controlled Exposure" higher limits, then they are within the limit (just) - however in that case this is a system that would not be allowed to be used around the general public. I can't find exemptions that would apply so I'm wondering why it's not implemented for Energous, or if they are simply not admitting this is a system not fit for consumers.

Update: Energous may be classifying their transmitter as "mobile" to allow them to select the more lenient SAR tests than the MPE. 

Maximum Power Exposure - MPE

Re-reading FCC regulations (fun times!) I found another safety limitation for RF that I had forgotten about. While the FCC Part 18 approval documents cover the Specific Absorption Rate (SAR), where Energous sit right at the limit of at 50 centimeters (hence the keep-out/danger zone), there is also Maximum Permissible Exposure or MPE. The FCC document detailing this can be found here, it's Title 47, Section 1, 1310. Table 1 lists the exposure limits for the general public.

The power density limit is set as f/1500, where f is the frequency in MHz. Given the frequency for Energous is 913 MHz that sets the maximum power per cm² at 0.61mW/cm². An iPhoneX has a surface area of 14.4 by 7.1 = 102 cm², so if the MPE limit is to be observed then maximum power to an iPhone X at any distance, in a perfect orientation, is 62 mW. Assuming a 60% conversion efficiency from RF to DC that means no more than about 37 mW at the battery.

Energous are claiming 100 mW received or more at the 50 cm mark, so I'm now confused as to how this is possible without exceeding the MPE. There are apparently exemptions for mobile transmitters, listed here under 2.1093, but they define this as:

For purposes of this section, a portable device is defined as a transmitting device designed to be used so that the radiating structure(s) of the device is/are within 20 centimeters of the body of the user. 

Given there is a "keep-out" zone at 50 centimeters and it is supposed to be "at-a-distance" wireless charging, it's really hard to imagine how they can get this exemption. Even then the only benefit seems to be that the system can use duty cycle to calculate the power - so if Energous were to, at the 100 mW received range, run their system for 3.7 seconds on then 6.3 seconds off, constantly repeating (or equivalent) then they could meet the 62 mW RF power density limit. 

So if MPE were to be applied Energous would, in addition to their (IMO) half-assed and useless safety zone, need to switch the system off about 2/3 of the time in any 30 minute period of charging. If they manage to up the power from where they are now, not only will the keep-out zone increase in size, they'd have to decrease the duty-cycle further as well.

Not Usable by the Public?

The only other way I can see this regulation not applying is if they use the less stringent safety limits for Occupational/Controlled Exposure. These are 5 times higher than for the general public (f/300 rather than f/1500). This would place the maximum RF power received by an iPhone X under ideal circumstances at 310 mW, which at 60% efficiency translates to 186 mW at the battery - barely more than the 100 mW currently received (apparently), and essentially within a 2 to 3 dB safety margin usually required. Once again, by my calculations, the Energous system as-is sits at the safety limit and cannot increase power from here. Worse, if the general public exposure limits are applied then the system power, these numbers say it would have to be reduced by a factor of 3 from the already low values.

Wearables and MPE

Things get much worse now for consumer wearables as well - for a 2 by 2 cm patch (big for a wearable), that 4 cm² will get you a stunning 2.44 mW of RF power, or 1.5 mW after conversion. That would be enough to charge your AirPods in about 4 days. Patch antenna would also be highly directional.

Does MPE Apply to Energous?

So how do Energous get away without meeting the Maximum Power Exposure limit? I don't see it referenced anywhere in the FCC Part 18 approval documents. It's not as if they don't know about it, an IEEE Spectrum interview with CTO Leabman in January 2016 has him admitting the MPE applies:

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. 

I've tried to find other exemptions to MPE in the regulations, but so far have not. If there are any readers with a knowledge of FCC RF regulations and MPE who care to let me know, I'd appreciate that. I'll update this post should I find that.

Edit: In discussion with some other engineers, the KDB 447498 D01 General RF Exposure Guidance document may offer some insight here. Energous may be classifying their device as "mobile" under 47 CFR 2.1091 by meeting the requirement that it is not "physically secured at one location", is "able to be easily moved to another location", and that the user is at least 20 cm from the transmitter. In this case, they may be using this section to choose between SAR or MPE as the limit. Given MPE is the more stringent of the two, I can see why they chose SAR instead. Further, this document shows why they picked 50 cm as the "keep-out zone" as there appears to be a different way SAR is calculated when you cross that 50 cm boundary, and the safety limit is even lower. It also seems to definitively limit the RF power at 50 cm and 913 MHz to 158 mW. (I misread units here, it's 50mm not 50cm, hence the scorethrough)

So the questions here are: "Would this exclusion still apply if the transmitter were "portable" and not potentially mobile?" but mostly "Have Energous chosen SAR instead of MPE knowing they would fail MPE?"

Looks like lots of gaming the system is going on.

Unsafe Demo, Faked, or Something Else?

Last point: The IEEE Spectrum article has a Jan 2016 demonstration of their system charging via an antenna at 5 feet at 1.6 Watts, while in a Las Vegas hotel room with a journalist present. They state that 0.673 Watts is about 10% of power transmitted, so 7 Watts total or so. At 5.8 GHz the MPE limit for an iPhone X receiver would be about 100 mW and 500 mW RF received, "general public" and "controlled" respectively. This was a demonstration then that exceeds regulatory limits, and if we scale linearly from the approved system I'd guess the entire room exceeded the SAR safety limit. So did Energous give an unregulated demonstration that exceeded safety limits, was it faked, or were they otherwise somehow exempted?

Yet More Energous

It's been a busy few days on the Energous front, and will likely stay that way with CES coming up, along with watching how their share price will fluctuate and if any more insiders have cashed in. We'll almost certainly see plenty of new information and revelations, which will come in a little at a time, and it's hard to judge if they should just be included as addenda or merit a post in themselves. My last post had a few additions to it since I first published it, and it got to the point where I'm going to regurgitate some of it in a new post. If you read that post really recently, there won't be too much new here for you.

Before I begin though, I just want to remind everyone that this is a system that needs a safety cutoff and an exclusion-zone larger than the operating-zone to charge your phone in about a week, at closer than 1 meter (if at all), if you hold it perfectly in alignment. Sounds amazing, doesn't it?

Energous have, until now, relied on ambiguity and vague promises which could not be argued with due to lack of information, but data is now public due to the FCC filing. This data now gives us the first concrete (though incomplete) numbers to show what those with an understanding of physics and RF have always suspected - there's nothing new or amazing here. Energous are not finding that "one weird trick" that bypasses the laws of physics, or have a Nobel-prize level discovery. The emperor really does have no clothes, but instead has an awesome marketing and PR department.

A summary of what's here:

1) Energous could increase the power delivered, but would then have to increase the size of the keep-out-zone, likely to room-scale for most reasonable charge rates. This is also dependent upon perfect receiver alignment.

2) Charge rates shown in the FCC report look to be for phone-sized objects. Move to wearables and the power delivered will drop, likely significantly.

3) The system has very poor beamforming capabilities and the point of highest power is not often at the target location. It is not a precision system, comforting when it can hurt you...

4) Some people are mistakenly reporting that the system transfers power at ~2.4GHz with a max 400 microWatts. This is the communications part of the system, not for power transfer.

5) The system shown in the FCC filings is vastly inferior in every regard to the promises from January 2015.

More Power!

Energous appear limited in how much power they transmit primarily due to the SAR restrictions, which they are currently at. The FCC data shows they are at 0.966W/kg at 50cm, while the limit is 1.6 W/kg. If we assume a measurement and manufacturing tolerance of 2 dB total (63%) then that takes the 0.966 to 1.58 W/kg - basically they are working at the limit, there's no more headroom here to expand.

What can get them more power at any given location is to extend the "keep-out-zone" further, essentially the distance from the transmitter at which the SAR value is around 0.97 W/kg. Now we are dealing with near-field effects so it's hard to say exactly, but let's for now say that the SAR power value increases linearly with the receiver power value. Let's increase the power at 90 cm from 30 mW to 45 mW - in this case the keep-out-zone moves to 75 cm and your phone still isn't charging. Now double to 60 mW and the zone is at 1 meter - you're standing inside the unsafe perimeter and the system will of course shut off, your charge rate is zero. And your phone wouldn't charge anyway. Now let's raise the power to 500 mW, the bare minimum to charge a phone, and the keep-out zone is now 8.3 meters - larger than the room you're in and probably the room next to it, and the one after that as well.

Depending on beamforming the exclusion zone may increase slower than that, but even under best case assumptions it's still expanding to room-sized danger zones for pretty pathetic charge rates.

No! You're not holding your phone correctly!

Also remember that these numbers in the FCC report are for a receiver in perfect alignment for the transmitter - rotate 90 degrees in two out of three axes and you get nothing. Even rotating in the other axis reduces power by around 20% at 50 cm. 

Consider how you stand and hold your phone while using it - likely at around 45 degrees to the floor. You'll probably lose a good 30% of power at least, not including what your hand might absorb instead. Now consider how you place your phone on a table when you're not using it - flat. With that orientation, you're getting close to the "nothing" for power delivery. Actually use your phone, and charge rate will vary considerably but the key thing is this - the numbers you see reported by Energous are as good as it will get, under perfect circumstances.

Low Power for Phones - Ideal for Wearables!

As the initial excitement of the Part 18 approval fades, it's becoming clear to even the most ardent Energous supporter that the power levels here are so low as to be useless for phone charging, even if they increase by near an order of magnitude. What I'm seeing though from the Energous faithful is grasping at "charging wearables" as the killer app for Energous. Unfortunately, that's just not going to happen either.

The receive antenna Energous use is likely a half-wave dipole antenna (think the bars in a TV antenna), and given wavelength at 913 MHz is 33cm, a half wavelength in free space is 16.5 cm (half wave dipole antennas are actually slightly shorter than the free space half wavelength). Given a phone is usually 10 to 14 cm long, the antenna will be close to that, not perfect but some dielectrics around it and it's close enough. Some info on effective antenna area is here.

Now look at your watch - how large is that? What's the size of an antenna you can put in there? It's much smaller, with a reduced size comes reduced power delivery, and at around 1 to 2 cm probably quite a reduction. Maybe they can use a patch antenna and get the size needed down with a high value dielectric? We'll conveniently forget that patch antenna are highly directional, even more than what is seen in the FCC test. In that case the patch impedance gets high, and the power gathered will drop (power is voltage squared divided by impedance). Here's an online tool for calculating patch antenna sizes and impedances - in this case it fits in a wearable, at around 16 by 24 by 2.0 mm, but at 4.5 kOhms will produce about 1.5% of the power of a standard 70 ohm half wave dipole antenna. Oh dear.

Then we have the orientation issue - this thing is on your wrist or body, right? How do you ensure perfect orientation to get the power needed? Good luck there.

AirPods have a 1.5 Wh battery - standard perfectly at the 50 cm danger-zone limit and if you get the maximum 100 mW they'll charge in 15 hours. Except they won't, you'll get a fraction of that, and if you move the system shuts off.

So no, wearables aren't going to cut it for the huge market either.

Where's the Power Going?

When using a phased array to send power with precision, you ideally want a large grid of transmitters spaced half a wavelength apart, many many wavelengths total on each side, and a target far enough to be in the farfield (many wavelengths away). At 913 MHz, Energous have a line of only 12 antenna, spaced 0.2 of a wavelength apart, about 2.5 by 0.2 wavelengths on each side, and a target barely 2 wavelengths away. It's an awful design if you want to try to control where the beam goes, and you can see that in their own beamplots. The star in the image below is where the power is supposed to be beamed - does this image fill you with confidence as to what's getting powered?

This arrangement might have been enough if they could operate at 5.8 GHz and wavelengths were over 6 times smaller - but the FCC killed that, as no doubt the system wrecked any wWiFi in the vicinity.

Bottom line - this thing sends power everywhere and there is no precision about it. IMO it's a brute force attempt to simply get FCC approval under Part 18 and damn the practicality.

The 2.4GHz Band is for Communications, Not Power

I'm seeing quite a few people refer to the 2.4GHz band Part 15 approval that was granted (in addition to the Part 18 approval for 913 MHz) where maximum power of 0.4 mW (400 millionths of a Watt) is stated. This is not for power transfer, this is Energous getting the communications component of the system approved.

They state they use the 2.4GHz band, Bluetooth LE, for the receiver to communicate to the transmitter that at least 30 mW is being received to continue power. It is not the maximum power transferred - as much as Energous send out tiny amounts of power, this isn't the number to be looking at.

Diminished Expectations

Energous launched with the promise of charging multiple devices, at up to 15 feet, at multiple Watts. Here's part of their January 2015 media blitz:

A new wireless power “router” being shown at CES can charge multiple devices in a 15-foot radius.

The two-tone rectangular box you see mounted on the wall up above is a WattUp transmitter from the wireless power people at Energous. WattUp is capable of delivering .25W to 12 devices or 4W to up to four devices (up to five feet away, dropping to 1W at 15 feet) at the same time, and it’s smart about how it does it.

Inside the “router” there’s a Bluetooth module. It sniffs out compatible devices and helps establish connections to them. Once they’re connected, power is beamed out over frequencies in the 5.7-5.8GHz range, but it doesn’t just constantly blast devices with RF power packets.

Here's the CEO from 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.

5.5 Watts compared to around 100 mW (at best)? Only a factor of 55 to 165 off after a further 2 years of work. Talk about diminished expectations. How can the bulls continue to support Energous after such a letdown? I guess it's better to continue to support than admit you were bamboozled by them.

Did they actually get that amount of power transferred? It's possible, you just have to be damn sure the transmitter is in a Faraday cage or you're a looooong way from it when it's switch on. Put those power numbers into the SAR danger-zone distance and you're looking at 10's of meters, and most likely polluting the surrounding spectrum outside the 902 to 928 MHz range in violation of FCC Part 18.305. I hope their staff weren't exposed to that!

Until the next post, take care, and Happy New Year to all.

Energous - It Just Keeps Getting Worse

Earlier this week wireless power company Energous announced their FCC Part 18 approval, and it sent the shares skyrocketing - after all, surely the sky's the limit now? My two posts, here and here, were quick analyses at the time, and I've had the chance to dig into things a bit more over this holiday weekend, as well as have discussions with other engineers on the topic (thanks to you all for your efforts!). A summary of what I'm going to say below is this:

1) Energous are currently sitting at international safety limits. This is basically as much power as they will ever transmit.

2) Executives in Energous took the opportunity to sell stock for ~$3.5 million.

3) A serious investment research company, Citron Research, are publicly calling Energous deceptive.

4) It's still shocking the Chairman of the FCC publicized this in the way he did. 

Power Limits

What Energous were touting with this approval is that unlike FCC Part 15 that will limit them to mW level transmission (or 1 Watt spread spectrum like Powercast use), Part 18 is in theory "unlimited power". Energous use 12 antenna each at around 0.875W for a total of around 10 Watts output, compared to around 1W from Powercast. So if unlimited, why only 10 Watts? Why not 100 or 1000 Watts? Something else must be limiting them - and that they have a 50 cm "keep out zone" for safety tells you what that is.

SAR is Specific Absorption Rate and is a measure of how much power a human body can absorb when in the vicinity of Radio Frequency (RF) equipment like microwaves, phones, or in this case wireless at a distance power. The FCC has several pages on this, and it's an international limit, though the US and a few other countries actually implement slightly more stringent limits. In the US these two critical limits are Head Localized SAR at 1.6 W/kg and Whole-body Average SAR at 0.08 W/kg - these are maximum values that cannot be exceeded. 

Given manufacturing tolerances and measurement error, any safety conscious company will set the limit well below this number - for example in the medical ultrasound world there is a similar limit called the Mechanical Index (MI) set by the FDA at a value of 1.9. Most companies set the internal limit at 1.3 or 1.4 so that they know even the most widely varying device will never go over. Setting a 30 to 40% margin is pretty reasonable. So what is the value of SAR for the device Energous got approved this week? You can see that here on Page 7:

There you have it, 0.966 W/kg with the 1.6 limit, and 0.043 with the 0.08 W/kg limit. Even under the most lenient of circumstances, and allowing no margin for tolerance or error, Energous could at best double the power out from this system. So they could, at best, charge at 60 mW at 90 cm from the receiver. That is about 10 to 20% of what is needed to maintain charge of a phone in use, and about 1% of the power from a Qi charging pad. Pretty pathetic.

There's really no way around this - any increase in the power to the receiver will up this number, or increase the keep-out-zone significantly (see below). They are tied together, and while you can play games at the margins, you increase one and you increase the other. Basically, there is no way for Energous to increase their charge rate without exceeding the SAR limits at useful distances.

I'm sure they are now on the hunt for an exemption from that limit, or otherwise game the system, and given how friendly the FCC are to Energous perhaps they'll achieve this - but that will be to all our detriment as phones and other equipment will demand the same, and we'll all be living in a slightly more risky world.

Insider Profit Taking

Share price of Energous rocketed after the FCC announcement, shooting from under $10 a share to over $30. Here's the action for this week - see if you can guess where the announcement was made!

In the conference call, the CEO stated it was the beginning of an era of "unlimited power", surely this is a multi-billion dollar comapny and the executives know that their stock is going to the moon an they're going to hold onto the stock knowing what it's worth? Errr, nope. There was a bunch of insider sales this week:

CEO Stephen Rizzone sold about $1.95 million of stock, founder and CTO Michael Leabman sold around $610,000 of stock, Director John Gaulding sold around $750,000 worth, a Senior VP sells a piddling ~$100,000... The SEC data is here, and we'll see in the next 3 days who else sold.

So - simply "taking some money off the table" or is it a sign the executives of Energous know the value is going down? (Thanks Mukticat of SeekingAlpha for noticing this).

Abuse of a Government Position?

It continues to shock me that the FCC Chairman tweeted about the approval and linked to Energous PR materials, while referencing Energous board member Marty Cooper. 

The @FCC has approved the first-ever wireless, "power-at-a-distance" charging technology. @Energous' #WattUp could allow multiple devices to be recharged up to 3 feet away, regardless of manufacturer. https://t.co/6zdj8hxO7R cc @MartyMobile

— Ajit Pai (@AjitPaiFCC) December 27, 2017

It's not even accurate as Powercast had FCC approval a week earlier (Part 15), while there is nothing in the FCC approval data that shows multiple devices or actual recharging levels of power. He then links to a private company press release as well as including his friend Marty Cooper, Energous Director. From the Department of Justice.

This is, in my opinion, a gross abuse of a federal agency position and it's another sign of how far our standards have fallen in this era of Trump. At this point I have to wonder if someone should look if the Chairman himself is profiting from this, given the brazenness of the 'looting' I'm seeing in the public sphere.

Energous and "Deception"

Citron Research posted a bearish take on Energous, stating the company had a history of deception. Citron tend to focus on companies they claim are overvalued or are fraudulent, and often short-sell them (bet on stock price going down, not up).

$WATT Co has a history of deception and the recent FCC info is no different. Tech is not ready for primetime and the loss of Apple for Dialog, death to the rumor. Roth upgrade was as ridic as their defense of Unipixel until BK. Powercast at CES will expose why $WATT to $15

— Citron Research (@CitronResearch) December 29, 2017

From the stock price action yesterday, they may be right - it will be interesting to see what happens on Tuesday.

Regular folks, feel free to stop here, what follows below are more detailed discussions on technical side. Edit: Since I kept adding updates at the end of this post, I wrote a new post to make it a bit more coherent - you can read it here, and covers most of what I say below.

Other nerdy stuff
Page 13 of the test report does not report the field strength at 300m, just states "no non-compliance noted". Pages 18 and 19 do show the results around the transmission frequency, and claim to be in compliance by between 5.5 and 7.3 dB. If this were a limiting factor, they'd push those to 0 - further indication it SAR that's stopping higher power output.

FCC documents show the volume of the transmitter to be 790 x 65 x 235 mm, in a curved C shape, with 6 antenna in each arm evenly spaced. Very roughly, this puts each arm at about 36 cm, so about a 7 cm spacing. Given the wavelength at 913 MHz is 33 cm, it's around 0.2 of a wavelength, while ideal phased array spacing is around 0.5 wavelength. At 2.4GHz it's almost exactly 0.5 wavelength, while at 5.8 GHz it is about 1 wavelength. Previous statements from Energous were that the mid-range would work with the Watt-Up Mini at 5.8GHz, so I wonder if this is the base they expected to use at 5.8GHz with twice the number of transmitters but were denied by the FCC due to WiFi interference, and then tried again at 2.4GHz with the same number, but were also denied?

Table 8 in the evaluation report makes it clear that the field is not smooth - you'd expect that straight ahead from the array along the central axis would be the highest power, yet as you move to the side by 15 or 30 degrees you can see that the field strength often increases slightly. While the coarseness of the sampling makes it difficult to say with certainty, I'd guess that this is still in the nearfield of the system and as such you've got a lot of peaks and troughs. It may also be why the "keep out zone" was set at 50 cm - perhaps closer than that is so variable that you may have hotspots way in excess of the SAR.

This is possibly further evidenced when you look at the field plots in XY - you can see that as they try to focus to given locations where the object under charge is, the field is significantly stronger just about anywhere but the charge point (the star). Not surprising though, given they only have 12 antenna that are so close together. This is what makes the data in Table 7 so confusing - the reported peak number is *not* where the location data would suggest it is, it's much better to look at the YZ data instead. In the above images the star is the supposed target - pretty awful beamforming. Below you can see how the results are so much clearer in YZ.

So using this data, we can see that the peak field strength at around 30cm is about 89V/m (Table 7), then using the other data from Table 8 at 0 degrees, we can see the field strength decay as follows:

Surprisingly close to 1/r for what is near field - it may simply be sampling, but it's the data we've got to work with. If I then assume that they manage to use some dielectrics to squeeze a dipole antenna into an iPhone sized device at 10cm, with an RF to DC conversion efficiency of 60%, and using an impedance of 70 ohms (antenna standard). I get the below values.

The Power column gives around 100 mW at 85cm but Energous state that it's around 30 mW at that distance. The "Scaled Power" basically applies that scaling, and shows you get around 160 mW at 30 cm from source (in the "keep out zone"). It broadly matches the number in the Barron's article that says:

In an email, Energous said that the "transmitter, as published in the certification, is 10 watts of conducted power and greater than 100mw of power received into the receiving device.”

(Notice that is into the receiving device, not the battery, so 60 or 70% of that is actually useful power.)

Assuming this is something fixable in improved tech, you could maybe at best get a factor of 3 more out of the system, but that's highly unlikely. Under ideal circumstances with a perfect system you'd need to be closer that 35 cm or so to charge a phone (in >10 hours at best). It's also 1% efficient at best, as I estimated in my first post. At those close ranges Pi charging should beat them easily. This bit is definitely hand-wavy, lots of assumptions in this bit.

So you've got a system that has to have a safety zone cutoff, barely charges at a fraction of a Watt, single digit efficiencies, sends power almost everywhere but where you're charging, and can't get any more powerful due to international safety rules. Very good.

And to other wireless power companies talking to their investors and customers about Energous and how they are "exaggerating" - don't think I don't know you're using my posts here, they talk to me too. It's amazing how I'm suddenly so useful now... :)

Update later on the 30th December
On the SeekingAlpha forum, contributor CommonSense asked:

Where was this SAR measured? Wasn't it at 50 cm? If so, they can increase the power as much as they want, just increasing the exclusion zone.

My answer (condensed):

Yes, page 42 of the SAR Evaluation Report says the values were taken at 50cm. I don't think there is a way, however, to increase the power to a usable amount without placing everyone in the room in danger. It seems certain increasing the power to any level useful for a phone would mean you could not actually be holding it as it charges. I expect the exclusion zone would expand somewhere between linearly and with the square root of the power increase.

For example linearly, if you increase the power at 1 meter to 100 milliWatts, you've gone up a factor of 3 or so, and if you assume that SAR goes up the same, your exclusion zone is now at 1.5 meters and you can't be holding the chargeable device. If you assume the average room is 3 meters across then you can get to 200 mW at 1 meter charging except you can't be in a room with the charging device.

Going with the square root, which is the worst case, to get to 600 mW which really is a base to charge something like a phone, you've increased your exclusion zone by 20^0.5, so it's now 2.25 meters. There's no way I can see that gets you to a reasonable charge rate without being inside the exclusion zone.

Also, at that point, you also have to start being concerned about the power outside the 902 to 928 MHz range. Right now they have about 5.5dB margin on that before that is an issue. If that increases the same as the output power, they can only increase by a factor of 3 before that becomes an issue. Not sure how linearly they scale together, but at some point that becomes an issue too.

Update on the 31st December
A bullish commentator on SeekingAlpha makes the comment that 100mW at 0.5 meters is fantastic for wearables. I disagree with that for a few reasons:

1) The 100 mW reported will likely be for a half-wave dipole antenna of at least 10cm length. Any wearable will have a patch or smaller antenna which will be a lot less efficient, so you would be unlikely to ever see as much as 100 mW.
2) That 100 mW number was also for perfect orientation - rotate your wrist and you go down even further.
3) That 100 mW number is at 50cm, right on the edge of the "keep-out-zone". Move in a little and power shuts off, step away and it drops even further.
4) At 50 cm, a wire will charge your device faster, more efficiently, and be safer. From the looks of it, so will the Qi based Pi charging product announced recently.
5) Increase the power out so that you get 100 mW (ideal, peak) at 1 meter and you basically extend the unsafe zone to around 1 meter - so you might be able to leave your wearable in the field, but you won't be able to wear it.

So overall, you'd have a wearable that you can't wear to charge at way less than 100 mW, with under 1% efficiency, and is unsafe for pretty much anyone in the room.

Next Update 31st December
I may have to do a new post just to repeat all these updates...

I'm seeing quite a few people refer to the 2.4GHz band Part 15 approval that was granted (in addition to the Part 18 approval for 913 MHz) where maximum power of 0.4 mW (400 millionths of a Watt) is stated. This is not for power transfer, this is Energous getting the communications component of the system approved.

They state they use the 2.4GHz band, Bluetooth LE, for the receiver to communicate to the transmitter that at least 30 mW is being received to continue power. It is not the maximum power transferred - as much as Energous send out tiny amounts of power, this isn't it. Notice this was passed over 6 months ago, back when they were trying for Part 18 approval at 5.8 GHz (and 2.4 GHz?).

Interestingly, it doesn't tie the sending of power to the reception of that same power - only that power is received from somewhere. This means an aberrant other source could be triggering the "I'm charging" response, while the Energous transmitter is happily focused on something else and charging nothing, or someone's head. I do wonder why 30 mW was chosen as the cutoff, will consider.

Finally - isn't it interesting how the bulls are now saying it's great because Energous can charge wearables and it's a huge thing. Apart from wearables charging at a much lower rate, wasn't the entire company built on charging multiple devices at 15 feet at multiple Watts? Here's part of their January 2015 media blitz:

A new wireless power “router” being shown at CES can charge multiple devices in a 15-foot radius.

The two-tone rectangular box you see mounted on the wall up above is a WattUp transmitter from the wireless power people at Energous. WattUp is capable of delivering .25W to 12 devices or 4W to up to four devices (up to five feet away, dropping to 1W at 15 feet) at the same time, and it’s smart about how it does it.

Inside the “router” there’s a Bluetooth module. It sniffs out compatible devices and helps establish connections to them. Once they’re connected, power is beamed out over frequencies in the 5.7-5.8GHz range, but it doesn’t just constantly blast devices with RF power packets.

 Here's the CEO from 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.

5.5 Watts compared to around 100 mW (at best)? Only a factor of 55 off (165x at 1 meter) after a further 2 years of work. Talk about diminished expectations.

I wrote two more posts on Energous in the subsequent 2 days, you can find them here and here.

Further thoughts on Energous

Yesterday's blog post on the Energous FCC Part 18 approval was written quite quickly, so I'll follow on with some additional thoughts here:

1) After the initial kick to stock price, it sat quietly for most of the day and then shot up in the afternoon, ending up 160% or so. This morning it's up a further 25% or so, and is approaching $30. At around $50 they become a billion dollar company. Looking at who is buying and what happens to the shorts once that data is available will be interesting. It reminds me again that this is a stock to stay away from, its volatility is what makes it attractive, and as the average guy that's where you get fleeced. Put your money in if you will, be aware it's a gamble. This is also the time where I preemptively point out that I do not hold any position on WATT stock, and make no money whether it goes up or down.

2) I used the Friis equation to calculate power to various distances - that's only truly valid in the far field, and with distances of 50 cm and wavelengths of 33 cm, that's not really the case. Unfortunately I don't have the details with which to do the near-field modeling, so this is the best approximation I have unless Energous want to give more information. I expect it's there to within a factor of two, but that the geometry of the transmitter strongly increases the gain at around the 50 cm mark at the expense of further out.

3) Powercast, who have had long distance wireless charging by RF available as a product for years, also got FCC approval for their product this week. (FCC approval details here) Unlike Energous, Powercast seem to be very open about their numbers and actually have products you can buy. Why aren't they taking off like Energous did if they already have such a product? Yeah, exactly... 

4) Lots of Energous fans are saying "it's only the beginning, it all takes off from here and they just improve". No, no they don't. There are fundamental laws of physics here that mean you don't just suddenly get to get 10x better. Semiconductor processes, shrinking feature sizes every few years, have conditioned people to think that is possible with everything - it simply isn't. Now if you could shrink the wavelength without changing any other characteristics of the wave or system then sure, you could do it. Or maybe if you reduce how much RF radiation gets absorbed by water. How about being able to get the benefit of focusing the power while broadcasting in all directions? Those would be awesome and make this RF method safe, efficient, and effective, so let's just do that. Except those are impossible - you may as well tell them to invent time-travel. 

Just. Not. Happening.

Where it could transmit more power is if the FCC literally raise the output limits, which has significant implications for safety as well as operation of other equipment. I do have strong concerns about the potential for inappropriate pressure from the FCC chair on the regular FCC employees to revisit output limits to favor Energous at the expense of our safety. Why? Well...

5) The FCC chairman tweeted his congratulations to Energous. We've got used to changing norms over the last year, but a government office promoting a private company is out-of-order. If they do for one, they do for all, so where's his mention of Powercast? Of all the things I see happening with Energous, this is the most disturbing, and yet I see no-one blinking anymore about such an abuse of office. 

6) I continue to be in awe of Energous' genius in playing this game. They have a pair of twos and just keep raking in the cash.

I wrote three more posts on Energous in the subsequent 4 days, you can find them here, here, and here.

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 skeptical of the claim. Yesterday the FCC did approve their mid-range device under Part 18 - the company stock price doubles, doubters are proved wrong, and the sky is the limit for Energous. I was so wrong, I'm here to apologize and beg for everyone's forgiveness as to my stupidity.

Yeah, right, of course I'm not. I'll do a quick analysis below (next day thoughts were added here) as to what has happened but it's essentially this - Energous have done what they did with the Watt-up Mini, which is to have done the bare minimum to get an approval on a essentially pointless and impractical device that doesn't actually charge at a noticeable rate, but that turns the charge light on, and as it's such a technically complex issue very few people understand what it means, see "FCC Approval", and that's it.

Energous press release is here, the conference call is here. (Skip to 19 minutes for Q&A). You can read my many Energous posts here, but the one on FCC approval in particular is here. The key quote was:

So, basically, unless they either get the FCC to change the rules, in opposition to a vast entrenched business interest and wreck WiFi for everyone, or reduce their power output to the point where it is an utterly pointless product, then I just don't see FCC approval for their devices.

And this is what's happened as far as I can see - they've put out a useless device hobbled to meet FCC guidelines for part 18, and it seems most people are dumb enough to fall for this. Part 18 rules can be found here.

While I'm still reading through and analyzing the FCC reports, here's a summary of my opinion of this 'product':

• Fails to charge a phone with a measly 100 mW at best (about 10x lower than needed)
• Unsafe for humans or animals closer than 50cm
• Highly inefficient, around 99% loss
• Weak safety measures to limit unsafe exposure
• Incompatible with previous products as claimed earlier
• Obtrusive impractical transmitter
• Small useful area of operation
• Very limited ability to steer the beam
• Huge "pockets" of energy about 50cm in diameter

The product

Energous have two approvals for the devices in the FCC database, one at 913 MHz and the other at 2.4 GHz. I assume the 2.4GHz approval is because they use the 2.4GHz range for communication with the receiver, not for power transfer. The previous Watt-up Mini operated at 5.8GHz so unless another approval appears soon, there is no interoperability with their previous devices, as they had claimed.

The device itself is a curved bar, certainly not flat and unobtrusive. It would be very hard to place on the wall, or anywhere in a room without becoming an obstacle. Why curved? Well I'd guess it simplifies the beamforming so they can create as tight a focus as possible and maximize the power transfer at the expense of steering. As they have only 12 antenna in the bar, it would be unlikely that they would have fine control over beam steering anyway.

As the transmitter is a bar it's a pretty limited area that can be irradiated - about +/-45 degree up and down, and +/-30 degrees side to side. At the 90 cm mark that means a region about 2 meters up and down, and 1 meter side to side - a pretty small and inconvenient target area, and that's the biggest it gets. Previous claims of charging Internet of Things devices all around your room aren't supported by this arrangement.

Why 913 MHz? I assume the FCC just said no to them putting huge amounts of power out in the wifi range and stopping that from working, so given allowable bands it was that or 24 GHz.

While not stated explicitly, it appears that the system won't charge if there is any movement within 50cm, so it may be that there's a minimum distance over which it will charge. This needs clarification.

The 'pocket'
Energous have always talked of how they create 'pockets' of energy - which is marketing spin as the laws of physics prevent such pockets being arbitrarily small. The larger the transmitter and more elements it has the smaller the focus, down to a limit set by the wavelength of the energy. The power is to be transferred at 913 MHz, which is a 33 cm wavelength, and that's about as low as you would expect - a 'pocket' that is a sphere 30cm in diameter, about the size of your head. This is backed up by their FCC test data, you can see here that the half power points (-3dB) make it about 50cm across.

As you can see in the image below, depending on how the beam is 'steered' you don't get a "pocket" as much as a "smear" - have your phone on one side, but power is definitely going elsewhere. The image below from the FCC

The safety measures
To meet the FCC guidelines, Energous had to implement a number of safety features which prevent the system from working when anyone is in the field of operation. Basically, it appears the amount of power a person would absorb would be illegal and unsafe so there are motion detectors that switch the system off if movement is detected within 50cm of the transmitter - which is, to me, a shockingly weak safety system.

This is one of the frustrations of dealing with amateurs when it comes to safety. You don't build safety systems based solely on common use cases, you think of all the edge cases because customers are annoying that way and will do things you never imagined with your product. Things also change when you aim a product at millions of users - tests on even tens or hundreds of thousands of cases simply won't show up what happens in the field. If you have a product that can't cause harm then there's no issue other than annoyance, but with real health implications like transmitted RF power, there are serious consequences to failures. Quite how their sensing system deals with a sleeping person, pet, or child I'm not sure, I see it as a major flaw. These flaws are easy to see and it's an accident and a lawsuit waiting to happen - another reason I don't ever expect to see this as a real product.

The power
Here we get to the juicy part - how much power will it transmit? Well with around 12 antenna each at around 0.8 W, the total power it can send out is around 10 Watts. Fantastic, right? Well that's not what is received at the target - looking at those numbers and using the Friis equation, (and some estimation, not enough data to be 100% sure) we get around 100 mW at 0.5 meters, and around 30 mW at 0.9m. A phone will need somewhere between 500 mW and 1000 mW to really start charging and be useful, so the power sent is essentially enough to switch the charge light on, and not much more. To even match their rather wimpy Watt-up Mini they'd need to improve it by 10x.

That has to be wrong? It has to send more than that! Well, when asked in the conference call as to the power sent the CEO replied that the power is "not that significant" and dodged the question.

The efficiency
10 Watts transmitted, and 100 mW received gives around 1% efficiency. 99% of the energy is lost as heat, which granted isn't too much, but essentially you've created a very expensive method of mildly warming a small part of your room, and failing to actually charge your phone in the process. This is a generous estimate as well, it does not account for the loss from the wall socket to antenna emission, so that 1% efficiency is a ceiling and goes down from there.

The conference call
The conference call was as expected - very little actual data and dodging of the few limited questions that were asked. The CEO makes clear the power received is minimal and doesn't want to give that number it's so bad. They instead stress that this is an new door that is open and it's all up from here, and give vague comments of partners selling devices in the future. Talk of useful power is deliberately downplayed. Brilliant marketing and bamboozlement of a non-technical audience. Once again, Energous show their genius in extending this run - they'll no doubt be issuing stock or some other form of capital raise to keep paying those executives that ~$5 million a year.

Stock price
The stock price is up near 100% today, back to where it was in early summer - but surprisingly not higher. Shouldn't it be trading above that now it has FCC "approval"? Let's give it time to see.

Conclusions?
Any big name customers? Can we expect Apple to be buying them up? Well, IMHO, Apple isn't dumb, and neither are any other big guy. This is going to be the unsavvy public putting in money again and again on the hopes of a big win. I don't expect to change their mind, at this point it's near a religion to many, and all I'm doing is pointing out the obvious.

The roller coaster ride just keeps going...

I wrote four more posts on Energous in the subsequent 5 days, you can find them here, here, here, and here.