MEMS Gyroscopes, Smartphones, and Ultrasound

This morning I was reading an article on Ars Technica (great tech website if you don't already read it) about the use of "sonic guns" to disrupt the operation of electronics and gadgets like drones. Here's a simple demonstration video of this happening.

As you can see the toy robot, which balances due to the gryoscopes in it, is quickly confused by the incident sound and ends up moving, then falling over. Why does this happen?

MEMS gyroscopes are Micro-Electrical-Mechanical Systems, essentially a very small structure that's often made by the same processes used to build computer chips, that has combined electrical and mechanical behaviors that are useful to us. In the case of a MEMS gyro, it leads to motion that creates an electrical signal which can be processed to determine rotation. These structures are small enough to be packaged into something smaller than your fingernail, and so can be fitted into compact spaces and consumer goods. Here's a video of a very simple MEMS gyro oscillating.

An image below from UC Davis MEMSLab shows how one small device can detect rotation in all three axes.

You can see that each sensing mode here has at least one "resonant frequency" at which the device naturally oscillates, which means it is very very sensitive to those frequencies. Like finding the right pitch for a glass, you can actually break them by causing them to vibrate at that frequency. Some work here, here, and here shows in more academic detail how the MEMS gyros can be rendered ineffective by ultrasound above around 100 dB. Sound is, after all, just a vibration at a particular frequency - match that sound to the resonant frequency of the gyro and it will play havoc with it.

Here's a drone showing the effect of ultrasound on its behaviour - notice that the transducers used to generate the ultrasound look like Murata devices, very similar in appearance to what uBeam look to be using in their transmitters. (I appreciate the safety precautions this researcher took!)

What this all seems to be pointing to is that high powered ultrasound in the environment can disrupt the activities of more and more of our devices such as drones - what happens if they fly through a high power ultrasound beam? Do they veer off and hit someone? And the smartphones we all use today? Those phones have multiple MEMS sensors in them, and the gyro is what allows you to play games just by tilting your phone. What happens when you direct ultrasound at levels far greater than 100 dB towards a smartphone? The manufacturers know, they spend a lot of time making sure that nothing in the phone vibrates at frequencies that disrupt their operation, but I'm not sure I've seen a study that's been made public.

Those may seem like simple examples, but there are safety considerations. What happens if a safety related system, such as positioning in a vehicle, is disrupted by high power ultrasound? Who is responsible for that? Cars and larger objects can usually shield the gyro to insulate the sound from it, but what about size and weight sensitive devices like smartphones?

If the videos above give an indication, then truly ubiquitous high power ultrasound in the environment is going to be disruptive in more ways than one. Just as well no-one is likely to try to put such loud ultrasound devices out there en-masse.

EEV Blog takes on uBeam

Many readers of this blog will know the name EEVblog, it's a website and online forum for talking about  electronics run by Dave Jones, an Australian engineer. It's host to the uBeam FAQ, which puts together a lot of information on uBeam in one place. In addition to the forum, Dave makes videos where he delves into topics in a pretty entertaining manner, and for his 1000th video, he takes on uBeam.

Gotta say, he does a great job of covering the tech in an entertaining manner, not sure I could have done better myself.

An interesting point he makes is the difference between possible and practical, and it echoes a comment from one of my first posts a year ago that always seems to be missed:

"In theory, it can be done in limited cases, but in practice cost and efficiency issues will likely render it impractical." 

Enjoy the show.

Arguing The Point

Someone on the internet is wrong. You wish to let that person know they are mistaken, as well as inform others to be sure they too do not mistakenly believe this to be true. How do you argue your point in an effective manner, disagreeing with someone, while maintaining civility? There's a good post on How to Disagree by Paul Graham which lays this out, and I'd like to touch on this, especially as it relates to science and engineering discussions.

We're living in a world where we are surrounded by incredibly complicated technology - sometimes the simpler that tech looks on the surface, the more complex it is. There's a large percentage of the population that would have a hard time explaining technology as old as the internal combustion engine in your car, and things get worse from there as you move through things we all use every day but barely know it - encryption and compression get the latest episode of 'House of Cards' onto your TV, but care to lay out how that happens for me? 

More importantly, how do you tell when someone is making false or exaggerated claims about technology? The facetious answer is "study for long enough to become an expert" however even then it's hard - there's a lot of technology out there, and only so many hours in the day. If you don't know the technology, and people are arguing about it, how do you evaluate the arguments they make? One way is to evaluate how they are arguing, even if you don't understand fully what they are saying.

The pyramid in the graphic above is an attempt to lay out Paul Graham's hierarchy (I have no idea where it's from, I'm not taking credit for it, thanks to whoever did it). The pyramid you see here contains the 'best' arguments at the top, the 'worst' at the bottom, and as you can see, it's wider at the base to represent that it's a lot easier to make the worst arguments than the best - 80% of everything, after all, is crap.

At the base it's fairly obvious - if one side is saying "the other guy is a doo-doo head" then they don't have much on their side. Sadly, you don't have to go to far above this for most people to lose critical thinking and an ability to evaluate what's being said. Ad Hominem is actually quite effective in discrediting a party with some audiences - for example saying "they're just a disgruntled former employee with an axe to grind" while ignoring any detailed points that person may have made, or whether they are even justified in being disgruntled. The most common form of argument is often simple Contradiction with no evidence to support it - "My client is innocent, and we're confident that the jury will agree." Frustratingly, we seem to be in a world where there's a media bias to he-said/she-said and placing the weight of argument 50/50, regardless of actual merit of the case.

I've never seen this fake-balance more brilliantly demonstrated than by John Oliver in this Daily Show segment on the Large Hadron Collider, and how there is a "50/50" chance the world would end when it was switched in. The part in question is at around 3:00, but I'd encourage you to watch the whole thing, it's John Oliver comic genius.

Dr Ellis is my hero here. Watch him start at the 'top of the pyramid' and refuse to be dragged down into what we're used to from media. He stays on topic, doesn't get tricked by Oliver (way harder than you might think), sticks to his point, and doesn't let himself be drawn into the arguments from the base of the pyramid. It's a short segment but really highlights how awful the media are in pushing junk science from those with limited understanding compared to those with deep knowledge - but where's the audience in that?

To further illustrate that point, and to show an example of an argument on a technical matter, let's take with this recent statement from uBeam 

uBeam is an innovation that will breed innovation. Ubiquitous wireless power will lead to a world with smaller batteries and thinner, lighter devices. With wires virtually eliminated, TVs can sit in the middle of a room cord-free and light fixtures will become “stick-on” without the need for routed power. uBeam is also a universal standard, making those bulky travel adapters a thing of the past. Imagine charging your phone, laptop or even your hearing aid virtually anywhere, without any effort. This is life powered by uBeam.

I'll take that one bolded point - that TVs can be powered wirelessly with ultrasound in the middle of a room and try and 'refute the central point'.

I'll begin by trying an argument against it:

"They're a bunch of stupid poopy heads" - No, that's bad, that would be Name-Calling

"They're just disgruntled current employees desperate to share their misery with the prospective employee and have no idea of the basics of physics" - No, that's Ad Hominem

"Powering a TV with ultrasound in the middle of a room is not a practical possibility, and is around one hundred times larger a problem than charging a phone in the same manner. While it is theoretically possible, the costs, inefficiency, and safety concerns are staggeringly high, while practical alternatives are low cost, and there is no economic demand to make this happen. Regulatory limits make it difficult in the US, and impossible outside the US." - OK, now we're doing somewhere between Contradiction and Counter Argument.

Let's move this to an argument from the 'top of the pyramid' by Refuting the Central Point

I'll begin by stating my assumptions:

We're talking about a large screen TV, not a small hand held. The TV is in a room you have some control over the infrastructure. The TV does not have a battery and needs a constant supply of power to work that can't be interrupted. From Energy Use Calculator I'm going to take 100 Watts as the power requirement for a 50 inch LED TV. We'll be assuming this is in the USA, and that the pre-2015 OSHA safety regulations are in effect and that in no location is sound over 145 dB used. Outside the USA the 115 dB limit give a transmitter and receiver 1000x area increase requirement. Note this will also apply within the USA should current OSHA limits restrict usage to 115 dB.

I will assume a generous 33% efficiency on receive, with 50% efficiency from transmitter to receiver incorporating both distance and angle of incidence. I will assume there is infinite power available into the transmitter and that efficiency from the wall socket to the ultrasound conversion is also 50%.

I assume each phone case sized receiver, at 5 by 10cm, uses $10 in parts, and we need to sell at 3x BOM to make money.

I'll ignore nonlinearity for the sake of simplicity, even though that's likely to become an issue, and limit the separation of transmitter and receiver to no more than a meter.

Now my calculations:

100 Watts powered means 300 Watts acoustic needs to be received. (100 Watts at 33% efficiency). This compares to around 0.5 Watts requirement for a phone, hence the "hundred times larger" comment. At 145 dB ultrasound is around 300 Watts/m², meaning the receiver will need to be 1 m² in size, that is a square of 1 meter on each side, or equivalent. A 50 inch TV is around 25 by 44 inches in size, (64 by 112cm or 0.72 m²)  so as a meter is around 40 inches, that means the receiver will be around 1.5 times the size of the TV. Ooops, better get to work on that efficiency.

Now a panel that's 1m² is about the size of 200 phone cases, so around $2000 in parts, or $6000 in cost to sell and attach to that 50 inch TV, that costs around $500 right now.

The Transmitter needs to be twice the size of the receiver to take into account that 50% efficiency, so it's 2m², and from the above calculation that means $12,000 for the transmitter.

Note that if the regulatory limit is 115 dB then the area scales by a factor of 1000 and the transmitter and receiver are each larger than the room.

For power supply, going with the efficiencies, the wall socket needs to provide 100 Watts, times 3 for the receiver efficiency, times 2 for the transmit efficiency, times 2 for the conversion efficiency, for a total of 1200 Watts. Fortunately this is (just) what a 110 volt 15 amp circuit can provide at 80% max load regulations allow (1300 Watts).

At 5 hours usage per day, and 12 cents/kWh average power cost in the USA, that's 72 cents per day to run, or $262, of which $22 is the actual TV use, the rest the wireless power system.

The additional 1100 Watts to use the wireless power system will be lost as heat (it's about a one bar electric fire equivalent), so in the winter that will save money, in the summer you'll need AC. I'll call it a wash to simplify this.

Summarizing the Argument:

Given the above, to power a TV wirelessly with ultrasound, it will cost $18,000 in the transmitter and receiver, with an additional $240 per year in running costs. Assuming efficiencies are as high as stated. And that no-one walks into the beam, since any interruption will make the TV switch off. And that you don't mind a receiver that's larger than the TV. And a transmitter that's twice that size and isn't too far from the TV. And that the room gets a bit warm. And that it's in the USA and the OSHA limits don't change to match the rest of the world.

But other than all that, isn't that much more awesome than running a $5 cord to the nearest outlet or paying someone to run a cable under your floorboards?

I think I'm going to call this "impractical".

OK, sarcasm over - I've run my calculations, providing all assumptions, workings, references etc so that anyone who disagrees can say "Your assumptions are faulty, here's what they should be" and then it's simple job to rerun those calculations get the new numbers, and judge from there. If anyone who is an advocate of wireless power would like to argue with these, feel free to correct me, and let's see where it takes the numbers. Or argue that my methodology is incorrect, I'm happy to do so - but like every other time in this blog where I have presented numbers, equations, and physics as core to my argument, I expect I'll be met with silence or more questions as to my motives. The top of the pyramid meeting with a response from the bottom.

My point to most people is this - if you don't understand the physics or details of a technical discussion like this, look to those presenting actual data, references, and their methodology and assumptions. If there is one side doing that, and the other calling names and questioning character, then you should likely consider one side's argument as superior to the other. If both are arguing methodology and data, then you may be watching a genuine scientific debate, which is good and healthy, it's what we want. If both are calling names, they're both idiots.

What Does It Take To Switch a "Phone Charging" Light On? Pt II

Following uBeam's demo, EEV Blog contributor Howard Long made a very interesting video showing how you can turn on a phone charge light with ultrasound. It's about 4 minutes long, with audio commentary, and gives more info in that 4 minutes than in the entirety of uBeam's demo. If this subject interests you at all, I encourage you to watch this.

From his comments (edited for brevity, read the whole thing here):

I could get it to light visibly with about 1mA at a distance of 2cm ... At 2cm distance, I had about 2mW, giving it a 2% efficiency. However, ... perhaps only 15-20% of the transmitted power appears at the rx anyway. So beam forming and reasoanably sized apertures on the receiver are essential facets for this to work.

... That camera thing is an Nvidia Jetson which looks like it's for visual device tracking. ... If it needs visual indication of where the target device is, and the sensors are on the rear of the phone, the phone will have to be used face down for a ceiling arrangement, and you won't be able to hold it in a normal fashion to make a call or use the screen. Even wall mounted, assuming nothing's in the way, you'll have to figure out new ways to hold your phone.

In its current form and key use, as a phone charger, this remains practically speaking a non-starter.

It seems an engineer reproduced a basic version of the uBeam demo in a day with about $20 in parts.

The phone charge indicator lights at 1mA, which implies 5mW (5 Volts supply) and so would take about 1000 hours (~6 weeks) to charge the phone - if it weren't for the pesky fact that a phone requires around 500mW to operate, on average, so it would make no appreciable charge effect at all. 

Now of course there's only a single element here, not a full array which could emit more power, but the key point is that a charging symbol tells you nothing about whether it is practically charging. You need voltage and current to know the actual power, and you need it at both transmitter and receiver to get efficiency (which he's calculating as 2% in this setup, pretty good actually for through air). Those are key numbers you need to have. From Howard's numbers 100 transmitters will get you that 500mW and maintain charge at a constant level, in an ideal world setup - possible but very large and introduce many questions on practicality and cost.

I like the way Howard also brings out a key point in this video - of course you can send power through the air by ultrasound. That's never been doubted or questioned, here or on the EEV Blog. What is questioned is how much power can be received, the efficiency of that, the safety aspect, the cost of transmitter and receiver, and the practicality for the user.

None of those points were addressed by uBeam, other than the emphasis on slow "trickle charging", implying the "faster than a wire" claims of 2015 aren't going to be happening.

Anyway, bravo to Howard Long for showing how to put together a short, clear, technically accurate demo from which you can actually learn something.

What Does It Take To Switch a "Phone Charging" Light On?

A few follow up points on the post from yesterday on the uBeam wireless charging.

I did like seeing this quote from the journalist:

Asked why the battery percentage didn’t appear to increase rapidly, Perry shakes her head.

“You’re thinking about it the wrong way, this is about a paradigm shift,” she says. “If you’re moving from your car to a coffee shop to work and your phone is charging while you’re using it, it’s no long about what percentage you’re at. You could stay at 1% all day.”

So it's an artful dodge of the question (that the journalist didn't press on), and perhaps an admission that the charge rate is not 'faster than a wire' as has been stated before by uBeam. It's more the "trickle charge" route, where you get tiny amounts of power over a long period of time. That "faster than a wire" claim was made at a time when the company was stating 1.5 Watts minimum charging which is much more than "trickle charge", and would fully fill your phone in 3 to 4 hours. Saying you stay at the same charge rate all day implies you are charging at an overall average of around 0.5 Watts, including all the times you are not around any uBeam transmitters, but if the charge rate is much greater than 0.5 Watts, why not say?

I noticed in that article the transmitter and receiver 'prototypes' back then in November 2015 were much smaller as well.

If there is actually a "trickle charge" regime, then the phones need charged as they are in use, and most use is a person standing or sitting holding the phone, fingers around the back, at around 45 degrees. Given line of sight, and assuming the 'bezel free front' of most modern phones, this implies the transmitters will need to be on the floor or base of the wall to get access, but will also likely be cluttered. Fingers on the phone case will prevent charging - unless of course you want to hold your phone by the edges as you use it (unlike in the picture above). I'm not seeing how trickle charge works with a mobile user, you need rapid charge in such circumstances. The practicality here, I'm not seeing. Maybe uBeam can layout the actual use-case scenarios they envision?

Also interesting was the quote from technical adviser Matt O'Donnell:

“When Meredith called me in 2015, I was curious and skeptical as hell, because you just hadn’t seen efficient airborne transducers,” says O’Donnell, dean emeritus at the University of Washington’s college of engineering, who now serves as uBeam’s chief technology advisor. “But holy moly, the leaps they’ve made in the past 18 months have been impressive.”

Hmmm, so all this advancement was made in the last 18 months, they had much, much less back then. But I'm confused because in September 2015 uBeam made this statement (among others):

“We’re at a massive inflection point,” said 26-year old uBeam co-founder and Chief Executive Meredith Perry. “We are about to head into a completely new phase of growth.”...In order to ease the transition into production, uBeam said today it has hired former Cisco Vice President of Supply Chain Management Jeff Devine as chief operating officer...“When we were seeking out an operations candidate we were looking at someone with decades of experience from taking a product from prototype to production,” said Perry. “He’s going to be the one that’s going to help us take this from our small shop to what will become our massive multi-million (unit) production next year.”

So which of those is true? Production ready in September 2015, or not? As with the "faster than a wire" claims from 2015 there are some implications as to 'perception vs reality' over the last few years if what Prof O'Donnell says is accurate. (COO Devine left his role at uBeam earlier this year before 'inflection' happened). For a further point of reference, I left the company at roughly the time these claims were being made.

The current receiver case is pretty interesting too. Looking at it, I'd guess 6 by 11 by 1.5cm which is larger than the phone itself, for around 100 cm^3 of volume. A standard battery for a Galaxy S5 is about 15cm^3 so you could have around 7 of those packed into that volume, giving you around 4 days of continuous use before recharging, and would cost about $70. If uBeam are using Murata (or Murata style) transducers in that case, there's around 60 of them at $3 each, so $180 just in transducers there. I'm not seeing the practicality or economics here.

(For those wondering - Murata are the primary maker of the parking sensors that are used in many cars, using ultrasound as the detection method. They're the small circles you see on bumpers, and individually look like cylinders about 1 cm each in diameter and height. They sell millions of them every years to the auto industry, and are around $3 each in bulk. You can go buy them yourself if you like.)

I did notice they have two different arrays that are used at different times, and I wonder if they are operating in the same manner, or if they are specced to handle different test conditions, and what is seen in these demos can't all be done on the one demo system. It's a little hard to tell from the videos as shown.

Now I could make a few more comments, especially on the posters in the background of the video and what they give away, but that's just going way too detailed even for my blog. 

Last point for now - the above picture shows a Kindle Fire on the right, and if you look in the bottom it's indicating "charging", but what rate is it charging at? 4.62 volts and 10 mAmps - basically  under 50 mW. To give you an idea of what that amount is, a typical phone batter is in the 5 to 6 Wh range, which means at this rate it would take over 100 hours to charge your phone at that rate. That's also assuming the phone is switched off, as it's typically consuming at around 500 mW so without that level of 'charging' it's consuming power faster than it's receiving it. I'm not seeing the practicality if that's the case. (A demo of a charging indicator coming on can be found in a newer post, here)

All this indicates is that the floor to show a device charge light come on is not the same as actually charging it - you need to see something like the screen on the left with voltage and current to know actual charging rate. This floor varies by device (iPhone seems to trigger at a higher floor than Android, and the floor varies with charge level IIRC), it's possible it's charging much faster (faster than a wire even?), but if it is, why not say?

As has been said before - physics doesn't prevent you sending power via ultrasound, or RF like Energous does, but can you send enough power to be useful, safely, efficiently, simply, and cost effectively?

What's In A Picture?

Last Wednesday morning someone emailed me the below picture from uBeam, asking if I was going to be writing about it. A few seconds later, I realized that I probably wasn't, as really there's not much new to say - anyone who understands hardware and business knows what's going on, the rest don't want to be educated or are investors. I also realized a couple of days later that pretty much no-one else cares either - I only had a single journalist call me about it and after giving him my opinion, he basically said that he was just keeping his notes up-to-date and editors weren't at all interested in uBeam. Since then, I've had a few questions from the tech side, and I noticed that the EEV Blog is commenting on it, so given I've a couple of spare hours tonight, here's my take. (For those who have asked, I'm in the middle of a piece about the recent Silicon Valley: A Reality Check blog post that got some attention a couple of weeks ago and will get it up soon, honest - read the original if you haven't already) 

I'm going to split this into three sections - my reaction, the tech, and the business implications so people can skip bits that aren't of interest.

The Reaction
What we have here, I'm going to assume, is a uBeam transmitter (large box with hexagonal tiles up top) and attached to the phone a receiver (the black brick in the bottom right). What was my first thought in seeing this? (After finishing laughing that is) Clearly they aren't any better at handling publicity than they've been over the last couple of years, with the PR firm clearly so asleep at the wheel they don't even know they're being ridiculed. Given they can actually manage to turn a positive article from a journalist into another piece pointing out the ridiculousness of typical day to day life in the company, it's no surprise that this quality a job was done here.

This, I believe, is the first official public unveiling of a setup that's been promised almost every year since 2011 or so, from a company that's raised $25 million. Is there simply no realization of how bad this looks, or is there an absolute lack of shame or care? Your big reveal should amaze and wow, it should scream that you are delivering, at the cutting edge, that you know how to get the details right from the finest detail to the grandest strategy. What this says is "Hey Granny, do you think I'll win the school fair with this?" not "Thanks investors for the $25 million, we're about to change the world!"

How unprofessional does this look? First thing is that they don't seem to be interested in tidying up the lab and staging before taking a picture to send out publicly, with bags of paper, white board, old carpet, and generally an unimpressive setup visible. It's like leaving your dirty underwear on the floor when your partner's parents come round for the first time. It makes me wonder if, like President Trump impulsively sending out Tweets in the early hours while no-one is minding the store, uBeam staff came to work in the morning to see the FB feed and said "we posted what?". If any of that team have been laughing about 'covfefe' then perhaps it's out of sympathy for the Whitehouse staff and what they have to go through every day. I read the goings on with President Trump and his staff and every day I see yet another corollary to working at uBeam - just in that case it's actually about something important.

Allow me to give uBeam some suggestions as to what to do next time. Begin with "decide the image you want to present to the world". Is it "sleek consumer design that Jony Ive would be proud of" or "cutting edge sci-fi level tech", for example, then setup the situation to reflect that aesthetic. For the former, put it in a sleek case that you've built with impeccable industrial design, you know, kinda like the one that was shown at the Upfront Summit last year? Any reason you couldn't use that? Put it in a user setting with happy people pretending to charge their phones, at the office or at the coffee shop. For the sci-fi side, get it in the lab with oscilloscopes and other equipment arranged in an impractical manner that would never actually be used that way but looks really cool to the average Joe. Hey you could even take that last setup to the next step and even show the voltage and current at transmitter and receiver!

Whatever you do, decide on a marketing theme that can sell and take the time to do it justice.

Along with the pics, actually put out a press release that says something. Take a look at Energous, they're perpetually 18 months from product after a few years and yet they put out professional press releases. You've a model to work from - take a look!

And one final suggestion - and it's not like anyone would have ever told you this before - when you're doing wireless power, don't show any wires in pictures of things being powered!

Seriously - I've not worked there since 2015 and I'm embarrassed by this.

The Tech

Now some time was taken to do a little blurring on the pic - you can see over the box that photoshop had a blurring filter applied in a circle over it. Perhaps this is to obscure that it's likely off-the-shelf components from Murata as I noted in a previous blog entry. (It could be an image overlaid to truly obscure and mislead, but I don't think so).  That's a bit strange, as I have pointed out in other posts that there's no issue in putting a mesh over the front to obscure what's behind, those Murata devices have it done to them by default. That mesh would also obscure the screws in the plastic and make it look at least a little more professional.

Blurring aside, the transmitter is now in a hexagonal arrangement, unlike the regular grid seen at the Upfront Summit, with 7 hex panels each around 15 elements across, so 45 or so elements top to bottom. If it is the Murata 40S4S then that's 45 cm top to bottom, and around 1600 or so elements total. At $3 each, there's $5000 of transmitter parts right there, and those are parts that sell in enormous volumes to car manufacturers so there's not a lot of room to lower the prices further. That implies a $15,000 transmitter, minimum (typical 3x markup from COGS to sale price). The box is maybe 3 to 4" deep, and it's positioned so you can't tell if there's a ton of electronics or power supplies sitting behind it - there were a lot of electronics in a large box in the Upfront demo, perhaps they've been downsized and rotated to fit in the box. Regardless, it's a pretty ugly box and nothing like the prototype that we were given a 'sneak peek' of at the 2016 Upfront Summit - what could have happened?

The hex pattern is interesting, and I wonder if it's been setup to beamform along the center line only only, no steering, in an annular array manner (concentric rings). This would really simplify the need for electronics, but if there are bad grating lobes (as you will get in an array where the pitch is larger than the wavelength), you can probably charge off to the side anyway as there's uncontrolled energy going in lots of directions. Basically, it doesn't seem the pitch is improved to allow for better steering and any real control - a big issue for safety in my opinion (beaming energy, you kinda want to control that). It also would not be representative of an array capable of steering in arbitrary directions.

The phone is attached to an enormous receive case that could be described as a 'brick' - it looks to be about 1.5cm thick which would allow for a number of the Murata transducers at about 1cm thick, along with an electronics board. Now an advantage of such a large box is that it will shield the MEMS gyros in the phone from vibrations which can damage them, but I doubt that's what it's there for - it's simply the smallest that can be made with Murata commercial transducers.

It may be that you've heard someone say that'll get better with "Moore's Law for Transducers", implying the transducers get half the size or twice the performance every 18 months. On the face of it is a bit silly as Moore's Law refers to the density of transistors on silicon and has nothing to do with ultrasound, but when you think about it and dig deep it's even sillier when you realise that the performance of ultrasound devices is generally tied through the laws of physics to particular device dimensions. Given those Murata devices were released at least 2 to 3 years ago, shouldn't there have been some major improvements to them by now?

But the phone is charging! Errr, well it shows 100% charge, but not that it's charging, and as before no idea of voltage, current etc that we really need to know the charge rate, nor of the overall efficiency of the system. Also, from memory, at >80% charge level the iPhone still shows charging even when less than 250mW are received.

So what do we learn from this picture? Not much other than there's a rearrangement of the previous demonstration, it's still apparently off the shelf parts, the receiver case is enormous, and there's no-one experienced in charge of publicity at the company to put out good pictures. As before, there can still be power received, even in the low 10's to 100's of mW, but as engineers and physicists have been saying all along, it's not transmitting power via ultrasound that's in question, it's can you do it at a useful amount, safely, in a practical way, at an acceptable efficiency, with hardware at a reasonable price. This still answers none of those.

The Business Side

As noted above, this looks like demo hardware, not even prototype, and still hasn't been shown working or efficiencies given. Can it work in a practical situation like an office or a coffee shop, or under standard use cases? What's the efficiency? Can it steer? How does it know where the phone is and track it? Most importantly, is it proven safe? Is it even legal at the dB level in most countries?

Reaction on Twitter seems pretty muted - in a week there's been a whole 3 replies and ~100 'likes' which is pretty telling. Seems the journalists know their audience...

What's really interesting though is that uBeam have not yet announced a new funding round. It's near 4 months since the Upfront demonstration, enough time to have completed a funding round with such slam-dunk technology. I'm saying 'no funding (yet)' as there are no new job ads, no publicity, and if one of the 'big guys' who a company will already have had come through to price the round were interested, they would not allow pictures of the tech to get out, especially if it's an Apple or a Google. Four or five months into fundraising things are starting to get stale, everyone knows that the first guys you spoke to haven't come up with terms (or acceptable terms), and that holding out will just get the company more eager to deal. Even with reducing burn rate by shedding senior staff and closing offices, runway only buys you so much in this type of situation. It's getting close to summer as well, and VC's are notorious for disappearing for July and August.

I have been expecting it announced soon, since there's no shortage of dumb money to go around these days, as when a 'low toxin butter-coffee' company can raise over $19 million, it seems anything will get funded. Perhaps they're holding out for the best valuation and getting that $100m round on an Energous-beating $400m valuation?

Who knows? And, from the public reaction to this picture, who cares?

Energous' Mid-Sized Watt Up Transmitter - Can It Get FCC Approval?

Reader Lord Stately-Wayne Manor asked me in comments on the last uBeam article:

Would you be willing to give your opinion on whether or not Energous will get FCC approval on their mid range soon? The CEO believes they have a clear path to approval and expects it to happen well before the end of this year. Any thoughts would be appreciated.

In brief - I don't think Energous mid/full range products as stated by the company will be able to be approved by the FCC in any manner, those that could be approved will emit such a low amount of power that they will not charge at any rate practical for consumer devices like phones. Any such approval would require a rewrite of existing regulations, and while I wouldn't put it past the current FCC to do stupid anti-consumer things, the fact that it would simply wreck any current WiFi signals and equipment means there is a massive, entrenched, business interest in making sure that does not happen.

As for the more detailed discussion, including some nerdy stuff since you literally can't analyze the situation without maths/physics/numbers/engineering:

I'll start by saying that the CEO of Energous has made a lot of claims over the years as to outcomes and timelines that are not met - the product promised is always some ways out, on the order of a year. Some call this the "Time to Carrot"(check Seeking Alpha for some good posts, and where I got the above image), which constantly moves forward and you never, ever get the carrot. Here in 2014 is him saying 2015 delivery. You may know of other companies that have promised deliveries of consumer product "by the end of the year" since, say, 2011, that have never materialized.

WATT started with a "full sized transmitter" which was the "~4m, multiple devices, multi-watt" version that no-one could explain with physics without cooking anyone around it. They claimed:

The strength of the charging drops off rapidly with distance; at the moment, 15 feet is the maximum range of the transmitter. At 5 feet, your gadget (actually, four of them at once) can receive a maximum of 4 watts. At 10 feet, it gets 2 watts; at 15 feet, 1 watt.

Which is a "holy crap 20W received we're going to get cooked" statement and had many eyebrows raised in "basic laws of physics" type ways. Quick question - what were uBeam's publicly stated specs before, and after, this announcement by Energous in early 2015?

Eventually Energous announced a 'mini' which at most emitted 300mW when in contact, so basically >10x worse charge rates and less useful than the already available Qi methods, along with a 'soon' medium and full sized which allowed time to carrot to remain at 18 months or so. Such a low charge rate and in-contact requirement, so it could be FCC approved, and allowed claims of "FCC Approval for Energous", but a pointless product.

Now Rizzone stated back in March 2017 he was confident over FCC approval. However - Energous' own filings with the FCC prove they can't get licensed under Part 18, read to the end where they literally say the rules have to change: 

Energous requests OET to interpret its ISM rules to enable WPT AAD conforming devices that satisfy the criteria specified in this Petition to qualify as Part 18 ISM... However, this can only happen if OET adopts a process that enables equipment manufacturers to secure equipment authorization.

How can the CEO argue it's coming when they admit that it can't be approved under current rules? Doesn't make sense to me, so let's dig more.

How about approval under Part 15 instead of Part 18? Part 15 is for "Low Power" so a problem there I think. In these FCC documents you will see that the FCC limit the 5.8GHz band that Energous use to 1W total if spread spectrum - take efficiency etc into account and you are looking at very long charge times (a couple of days to charge your phone if lucky?). If not spread spectrum then it's P=0.3e^2 where E is listed as 0.05 V/m so that's no more than 0.75mW, or to translate to practical implementation - it would take six months or more to charge your phone at 100% efficiency. I can't find the link but I believe Energous state their method is not spread spectrum, so that tells you how useful their method could be under Part 15.

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.

This doesn't even begin to cover the issues of safety or practicality of beamforming to a fine focus with your array is not much bigger than your wavelength. I go into lots of nerdy depth with it here.

One last piece of advice, and it comes from Warren Buffet - Don't invest in companies whose product you can't understand. If the engineers are arguing about the basics of the product working and laws of physics are being called into question, then just run...

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.

Acoustic Nonlinearity

I'm often asked "What is Acoustic Nonlinearity?" (No, really, it's actually surprisingly common. Bet you're jealous.)  Seeing as I have the smartest readers, both of them, I thought I'd do a basic explanation of it here. For something really detailed, I'd suggest these lecture notes, a book like "Nonlinear Acoustics" by Beyer, or "Diagnostic Ultrasound Imaging: Inside Out" by Szabo - I'll be borrowing some images from each of those in this post.

Nonlinearity means "not linear". Obviously. We tend to simplify things and think of them as linear - everything scales together. I kick a ball twice as hard, it travels twice as far - that's linear. I work 40 hours a week I get my salary, I work 80 hours a week and I still get the same salary - that's nonlinear. And stupid. The image below shows how this happens in real physical systems.

Every physical system is nonlinear, but we can often just simplify things and pretend they are linear, right up until they aren't. Once you have to include nonlinearities, things get really complex, really fast. Some smart people spend their lives working on this type of thing. With sound this can happen in a number of ways, some beneficial, and some not.

With acoustic nonlinearity, what happens is this: An acoustic wave travels through a medium - this can be through human tissue for a medical scan, or through air for a sound. You can keep increasing the amplitude of this wave, and as you double the amplitude the wave gets twice the size. At some point, there's enough energy in this wave that at the top half of the cycle it actually compresses (squeezes together) the medium, and at the bottom half it's a rarefaction (pulls it apart). The propagating medium gets denser at the top half, and less dense at the bottom. 

Once this starts to become significant, the density change actually starts to effect the velocity of the acoustic wave - the denser part goes faster, the less dense part slower - and so the wave starts to 'tilt' and one half catches up with the other. That's what you can see happening in the top parts of the image below.

Once the top part of the wave catches up with the bottom part, the middle row of the image, then you get a 'saw tooth' wave. What is happening is that energy that is at the fundamental driving frequency starts moving higher in frequency - for example in a medical ultrasound image if you send out at 1 MHz and nonlinearity happens, you create signal that's 2MHz, 3 MHz etc by 'sucking away' some of the energy at 1 MHz.

If you've had a medical ultrasound scan in the last 15 years you've probably benefited from this. You can use acoustic nonlinearity to get a much better resolution in your scan with that 2 MHz component without some of the difficulties of building a system to transmit at that higher frequency.

The downside to pushing all this energy higher in frequency is that if you need to use it at the lower frequency, well it's gone from there, and more critically the attenuation is almost always higher at higher frequencies. Attenuation is where you lose some of the energy of the acoustic wave over distance, so basically higher frequency waves die off faster. The bottom line of the image above shows the saw tooth wave getting smoothed out by attenuation.

Szabo, Chapter 12, has some more great images.This shows how the wave changes as it travels out, and the graphs on the left show the shift of energy away from the fundamental frequency to the higher harmonics.

How far can a wave go before this occurs? Well, there are some basic equations that can tell you when it does. If you don't like maths, I've put all of that at the bottom and I'll cut to the interesting example right away. For those of you who really like maths, see below, then check out the lecture notes linked to above, or go to Chapter 3 of Beyer's book.

TL;DR. Nonlinear distance gets shorter with:

• Increasing frequency
• Increasing wave amplitude
• Increasing nonlinear properties of the medium

Let's pick a couple of examples and test them. I'm going to take some acoustic numbers from here. Two cases, 45 kHz and 145 dB, and 75 kHz and 155 dB. (dB is a logarithmic way of referring to sound pressure, in this case that's about 500 Pa and 1600 Pa respectively).

For 45,000 Hz and 500 Pa in air, that's about 30 cm when nonlinearity starts.

For 75,000 Hz and 1600 Pa in air, that's about 5 cm when nonlinearity starts.

Wow that's a short distance (it's actually slightly longer than that in reality due to attenuation, but not much). And it doesn't tend to happen slowly - it ramps really quickly and within around 1.6 times that distance (48 and 8cm respectively), huge amounts of the energy are moved to higher frequencies. 

Then the increased attenuation in air removes that acoustic energy entirely, converting it to heat. To give you an idea of the degree of nonlinearity, if you look at the energy available at 1 meter at the fundamental frequency with 155 dB vs 145 dB, then you've driven 10 times harder, but you only get about half as much again (around 95% of the additional energy is lost as heat). Not very efficient. 

This is what's known as saturation - when you keep driving harder and harder, but you just can't get any more energy in. The medium (in this case air) is saturated and can't really absorb any more, most of what you add is lost. There are some basic equations to work this saturation pressure out, one is listed on page 510 of Szabo, it's detailed below. For air, at 45 kHz, at 1 meter, it's about 450 Pa, or 144 dB. Past that value of pressure, at that frequency, you're just running faster and faster to stand still, and getting very hot in the process.

So there you have it, a basic explanation of nonlinear acoustics. Here's a summary:

• Nonlinear acoustics are simple in concept, really complicated to fully understand
• Once you start driving an acoustic wave hard, eventually it becomes nonlinear
• Nonlinear acoustic waves start shifting energy from the fundamental to higher frequencies
• Attenuation converts that energy to heat, sometimes very quickly
• Onset of nonlinearity is sudden, and can happen very close to the source
• Propagating media such as air can saturate when you drive hard, which means it can't take any more energy

Stop reading here if you don't like maths.

Some equations (Beyer page 104):

Nonlinear Distance = 1. / ( Beta * Mach Number * Wavenumber )

Beta (for air) = 1.2
Mach Number = Pressure / ( Acoustic Impedance of Air * Sound Velocity in Air)
Wavenumber = 2 * PI * Frequency / Sound Velocity in Air

The Acoustic Impedance of Air is 410 Rayls, and the Sound Velocity in Air is 343 m/s.

So :
Mach Number = Pressure / 140600
Wavenumber =  Frequency / 56

And

Nonlinear Distance = 1. / (1.2 * ( Pressure/140600) * ( Frequency / 56 ))
Nonlinear Distance = 6500000 / ( Pressure * Frequency )

Finally (Szabo, Page 510)

Saturation Pressure = ( Acoustic Impedance of Air * Sound Velocity in Air ^ 2 ) / ( 2 * Beta * Frequency * Distance )
Saturation Pressure = 20100000 / ( Frequency * Distance )

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.