uBeam - Still All Sizzle?

An eventful day yesterday on the uBeam front, with Meredith Perry finally giving a demo of uBeam technology and showing it charging a phone at the Upfront Summit - well more precisely showing a big box and then a light on a phone coming on if it was put in front of it. Essentially a slightly more glitzy version of the "All Things D" demo done in 2011, showing what 6 years and $25 million gets you.

Wireless charging of a phone thru the air. Woh. 👏 1st public demo ever @ubeam #UpfrontSummit pic.twitter.com/I6GZx7KDri

— Spencer Rascoff (@spencerrascoff) February 3, 2017

From what we see here, in my opinion, is proof that you can take a non-technical audience and baffle them with bullshit - if you want to know that the phone is charging, you need to do more than turn a screen on. Perhaps there is more not seen here, I'm just going on the info that's public, but you need to show voltage, current (at both transmitter and receiver to get efficiency), and the phone sitting in front of that panel for several minutes and see the actual charge level increase over time. But that isn't what they showed - and if it isn't, please enlighten me and tell me what is the difference between what's shown in that video, and what was shown at All Things D 6 years ago.

It seems at least some are not convinced and there are journalists taking a sceptical view, such as Axios (albeit promoted with a tweet that is more sensational than what was shown and the content of the article, and sadly is all that is quoted by most)

This is a science project that is clearly progressing, but not nearly finished yet.

Pretty faint praise after $25 million. There was also this interesting statement:

we're told Perry picked that particular Android for the demo because of its highly-visible charging icon

Why would that be mentioned so specifically by the company, and why does it make me raise an eyebrow?

Now, let's be clear, no-one ever said that transmitting power via ultrasound is impossible, of course it's possible - but is there a way to do so in a safe, efficient, and cost effective manner? That's the challenge, and in any practical sense it had never been shown publicly. In my opinion, it still hasn't. All that has been shown is a screen lighting up.

I'm sure uBeam now have potential funders lining up outside willing to throw money at them, based on this, even though nothing was really shown. And if I'm wrong about that, tell me what was shown that proves it works. What's the charge rate? How long to charge a phone? What is the efficiency? How does this line up with "4 meters, any angle, multiple devices, faster than a wire" touted before? Is it a safe and legal level? (OSHA now seems to have gone back to a 115 dB limit, not the 145 dB from a few years ago, I certainly hope there's no-one in the way of that beam, or there are any grating lobes giving the audience a facefull.)

Now the fact the phone charge indicator comes on proves they are charging at a minimum of 500mW (around 5 volts at 100 mA) needed on the USB port, which is awesome as that's enough to at least trickle charge a phone over about 10 hours. Or does it? Potentially you could access the Qi chipset on the phone to show the charging light when at <500 mW, or other similar bypassing of standard input methods, but in the end there's no way to know without looking at actual charge rate - which isn't shown in any form. If it works so well, I'm surprised those numbers aren't released - "more than 500mW" is a very straightforward statement to make. Or leave the phone in front of the transmitter and see it gaining battery level during the talk. But that would be too easy.

And at what efficiency? At 30% end-to-end it's incredible, at 1% it's very difficult to justify, at <1% it's ridiculous. We don't know those numbers.

How many devices can this charge at a time? What does the system cost? Can it track the phone? What happens at an angle? Was the beam always on, or did it switch on when it saw the phone? What were the safety measures to stop an always on-beam being pointed at someone accidentally? If this is the best case demo today, why were some people saying they had seen a similar working demo years ago? Weren't they moving to production 18 months ago? All questions still unanswered.

I'm really sad, of course, for the senior staff who just left the company over the last couple of months, and what I guess is the closure of the San Jose office (or that's how it appears if you check the LinkedIn profiles). Amazing they would leave just on the verge of a breakthrough like this, but more fool them I guess, what do they know? Passing by on the billions... 

Overall, with a skeptical eye, there's nothing new here. IMO, no significant new information, nothing to show commercial success or capability, and no path to a realistic product. But it won't stop investors from piling in without doing significant due diligence (investors, feel free to call me and prove me wrong), and it won't convince anyone with one iota of technical capability that there's more there than they thought a week ago. More of the same, move along.

For those of you with a technical bent, I'm including a more detailed analysis from what I saw in that demo below. Anyone non-technical, you may want to stop now.

Taking a technical look at what's there and bearing in mind this is with a lot of assumptions - the video shows an array that seems to be made up of a (approx) 30 by 30 collection of circular transmitters, and given what I see on stage it's about a 30 by 30 cm panel, so each is a 1 cm diameter cylinder. Very much like the Murata MA40S4S used in car parking sensors and available off the shelf at around $3 each in bulk. Of course they couldn't use them because that would be a $2700 transmitter BOM component right there, but let's use them as a starting point.

Assume 40 kHz, and let's say we can drive much harder because why not, something like 6 times more (120 volts p-p, or approx 16 dB in sound pressure) to be generous so that's 120 + 16 = 136 dB sound pressure level. They are circular, so we lose 2 dB from area, that's 134 dB out, across a 0.09 m², and at that level that means a peak pressure of 180 Pa and about 37 W/m² or actual 3.35 W transmitted. Incidentally the capacitance of those devices at 2550 pF means (at P=nCV²f) gives 1.3 kW (900 * 2550e-12 * 120 * 120 * 40e3) so right there is around 0.25% efficient on transmit at best, along with a one bar electric fire (update: this capacitance calculation is not correct, I need to update it). A few million people doing this every day means GW more generation capacity, so I hope I'm wrong or we better start building some power stations. (updated efficiency numbers below - a bit better than here, but still pretty awful).

As a side note, those values of amplitude, if I'm in the right ballpark, may avoid the worst effects of acoustic nonlinearity in the distances shown, but in my opinion (and that of physics), would result in nonlinearity if you tried to increase from there, decreasing efficiency considerably.

Now at 1 to 2 m distance you're probably looking at around 3dB loss in the air (pretty low, yay, but still 50% efficiency), so saying you get all of that power at the phone (about 5 by 10 cm) you'd have an focus gain of around 18 times (25 dB), so now we're at 156 dB (wow, that's loud). Now we convert back to electricity, let's say 30% efficient there (massively higher than the Murata MA40S4S), and around 90% on some awesome conversion electronics, it's about 27% conversion efficiency, and you now get to 450 mW to the battery which is almost enough to charge it. Let's go with that - yay we're charging a phone in about 11 hours. If I'm assuming low numbers, then divide that by about 5 to get a 5% overall rate and 90mW, maybe enough to turn on the charging light (and about 2 days to charge your phone, if you don't move it)

At what efficiency? 0.25% at transmitter (I'm ignoring some losses here, but they're minor in comparison to that capacitive loss), a further 50% in the air, and 27% at the receiver, and you've got 0.034% efficiency. (As noted earlier, not including non-linearity). At 12 c/kWh, that's $2 to charge your phone. Ouch. OK, I'm being mean, let's say it's 10x more efficient, it's 20 cents to charge your phone, only $70 per year done every day, still an ouch. And you can heat your room at the same time with a kW scale transmitter, that costs $7500 because of the high BOM and doesn't make you feel so bad about having spent $1500 on a toaster oven.

As an added note from the original post, I noticed on a Twitter feed that some there indicate that the transmitter seemed to be covered by some form of fabric, which looking again at the video you can see is there. This does not mean that ultrasound can pass through clothing, as was previously claimed, but a thin membrane that is significantly smaller than a wavelength and is of a low enough impedance material will not be 'seen' by the ultrasound, for example a mylar film on the order of 10s microns compared to around 8mm wavelength in air at 40 kHz will likely have a minimal effect. Just as with the membranes or meshes used on car parking sensors like the Murata mentioned above... 

I'll add to this as I have time to do so, and check my calcs for any mistakes. Comments welcome on why I'm wrong, and just a disgruntled former employee :)

Edit: Just an update to some of my numbers here. Looking at the Murata data sheet is seems that SPL was measured at 30cm, not at the source, so some modification needed to the calcs. Using Murata's published factors, a further ~10dB needs applied for the diffraction and absorption (BTW that's quite a good document on how those transducers work), so they could be producing as much as 130 dB at source, so I can reduce the applied voltage by a factor of around 3 to around 40 volts, and does reduce the capacitive loss to around 130 W for 3.35 W acoustic transmitted, meaning 2.5% efficiency in that portion of the calculation, so it's overall 0.34% efficient at best, not 0.034%. Yes, that means the sound field could be of greater intensity and higher power, however that would start to push it into the nonlinear regime, and also you'd then be beaming very high sound levels at that cameraman and of course they totally considered safety in this demo...

Interestingly, this means those Murata's can put out over the 115dB level mandated by OSHA, however I'd note that a) the Murata operate at a duty cycle of about 0.4% or less (20 cycle bursts until return signal at up to around 2 m, another good link on car parking sensors), and b) there is a single transmitter, that is as loud as it will get, and decay rapidly after that - unlike a phased array for power which operates at a 100% duty cycle and uses antenna gain to amplify the sound by a factor of several hundred.