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.