Remember,the 240watt power output of a car audio amp is pretty much a "pretend rating"!
The "steady state"or "average" power output will be lower,probably considerably so,even at audible frequencies.
It is anyone's guess how well it does at ultrasonic frequencies.
That amp is rated at 2 x 50W RMS stereo, with its 3dB point at 30kHz. Lets assume they use a lowish frequency like 30kHz, to minimise the losses. One channel of this amp should still be able to push out 25W, if the impedance of the load is suitable. This is a not inconsiderable amount of power for something which was shown doing nothing more than reading an output voltage into a high impedance. This is, of course, a crude demo without proper beam forming. Hopefully they can do a little better,
I'm sorry to be pedantic,but there is no such thing as "RMS Power".
RMS is a convenient fiction used for ac voltages & currents to allow us to use the standard DC Power formula P=VI.
The product of
Irms x
Vrms or (
Irms)x R is known as Average power.
RMS is a convenient fiction used for ac voltages & currents to allow us to use the standard DC Power formula P=VI.
It isn't just a "convenient fiction" since the power dissipated by a resistive load or wiring fed by an arbitrary waveform is P = R
Tot * I
RMS2 which has tons of non-fictional uses when sizing wiring for motors, transformers, power distribution systems, etc.
Remember,the 240watt power output of a car audio amp is pretty much a "pretend rating"!
The "steady state"or "average" power output will be lower,probably considerably so,even at audible frequencies.
It is anyone's guess how well it does at ultrasonic frequencies.
That amp is rated at 2 x 50W RMS stereo, with its 3dB point at 30kHz. Lets assume they use a lowish frequency like 30kHz, to minimise the losses. One channel of this amp should still be able to push out 25W, if the impedance of the load is suitable. This is a not inconsiderable amount of power for something which was shown doing nothing more than reading an output voltage into a high impedance. This is, of course, a crude demo without proper beam forming. Hopefully they can do a little better,
I'm sorry to be pedantic,but there is no such thing as "RMS Power".
Its really sine wave power, but it usually gets listed as RMS power.
RMS is a convenient fiction used for ac voltages & currents to allow us to use the standard DC Power formula P=VI.
The product of Irms x Vrms or (Irms)x R is known as Average power.
The RMS of a waveform is highly meaningful in many cases, including voltage and current waveforms. However average power is only equal to RMS voltage times RMS current in a very specific case. P=VI, where V and I are RMS values, is not a very useful formula in general, so that is certainly not why RMS voltage and current are interesting.
Some people refer to RMS s continuous or sustained (vs peak). In both cases it's based on some average of abs(v).
The big problem with piezo is impedance matching. MEMS versions of electrostatic speakers would be better.
Even with a phased array of state of the art ultrasonic transducers getting high efficiency is fantasy simply due to transducer losses.
The big problem with piezo is impedance matching. MEMS versions of electrostatic speakers would be better.
What about magnetic transducers like this one, which I wanted to use as energy harversting device
However, those magnetic transducers have below 10kHz resonant frequency and to make sound I drive them directly from MPU using simple transitor based full bridge low power AC amplifier output:
BTW: If u
Beam finds this idea usefull, do not forget donate via Bitcoin my sound energy harversting project too -I don't need any $1M to complete this project, so 0.1% of $1M will be fine
Maybe I will help you make u
Beam investors even more happy-they will get for their $10M free sound energy - no need for bulky high power sound source
The big problem with piezo is impedance matching. MEMS versions of electrostatic speakers would be better.
Even with a phased array of state of the art ultrasonic transducers getting high efficiency is fantasy simply due to transducer losses.
I wouldn't say impedance matching is a big problem. You definitely need a good impedance matching device between a piezo transducer and air, but those exist. Morgan technical ceramics make transducers with good matching, and their name is actually mentioned in ubeam's patent applications. There have been various attempts to make MEMS based ultrasonic transducers, but we still use piezo in almost every case today. Things could change, but so far MEMS has failed to be compelling.
If you send ultrasound between two piezo transducers in water, where the impedance match with the medium is naturally not too bad, you can get pretty good efficiency. The awful efficiency you typically get propagating into air is mostly due to the impedance match. Match the impedance well and you can probably get tolerable efficiency propagating into air. The patent applications from ubeam in 2012 talk about getting 40% efficiency, but I suspect that figure was pulled out of the air.
RMS is a convenient fiction used for ac voltages & currents to allow us to use the standard DC Power formula P=VI.
It isn't just a "convenient fiction" since the power dissipated by a resistive load or wiring fed by an arbitrary waveform is P = RTot * IRMS2 which has tons of non-fictional uses when sizing wiring for motors, transformers, power distribution systems, etc.
Exactly"
RMS allows us to use the DC power formula P=VI & its derivatives in AC circuits.
I don't know if the "Ancients" did the experiment first,then the Maths,or the other way around.
Maybe they just compared how long DC & AC took to boil water,but I think it is more likely that they used a
water cooled resistive load with water flowing through it at a known rate.
They then measured the temperature rise of the water & knowing that & the flow rate,determined the power dissipated in the load.
By adjusting the AC current into the load until the calculated power was the same,they could say that current had the same effect as a DC current which by I^2*R, would produce the same power.
They then either went away, elated that the experimental result matched the Maths ,or went away to see if the Maths agreed with those results.
The RMS of a waveform is highly meaningful in many cases, including voltage and current waveforms. However average power is only equal to RMS voltage times RMS current in a very specific case. P=VI, where V and I are RMS values, is not a very useful formula in general, so that is certainly not why RMS voltage and current are interesting.
OK,things get messy in reactive circuits,but P=VI
was derived from a purely resistive case,& there are many situations where we can assume a resistive load.
P=VI must always apply in a resistive load situation if it applies in any.
Most of the time we use the derived terms,but all of the other power formulae are derived directly from P=VI.
The only reason I used P=VI on my posting was that it is less messy to type.
I did some contract PCB design work for uBeam several years ago. I never thought they would have raised this much money. They can absolutely transmit power over ultrasound (I'm not sure how much), but it seems impractical as many people point out. I'm not sure they deserve some of the vitriol on this thread and it makes me wonder why we engineers have such an aversion to hype. It seems like the general public gobbles it up.
I'm torn. I'm trying to start my own company right now and I'm trying to fight my natural engineer aversion to hype. To sell something, you have to make it sound like it is some revolutionary idea, that only you can carry out this dream. How do we as engineers "cross over?" I don't want to sit in a cubicle for the rest of my life...
I'm not sure they deserve some of the vitriol on this thread and it makes me wonder why we engineers have such an aversion to hype. It seems like the general public gobbles it up.
Most people here tend to just laugh at most impractical ideas. I think the vitriol for ubeam stems from the obnoxious attitude its founder.
The RMS of a waveform is highly meaningful in many cases, including voltage and current waveforms. However average power is only equal to RMS voltage times RMS current in a very specific case. P=VI, where V and I are RMS values, is not a very useful formula in general, so that is certainly not why RMS voltage and current are interesting.
OK,things get messy in reactive circuits,but P=VI was derived from a purely resistive case,& there are many situations where we can assume a resistive load.
P=VI must always apply in a resistive load situation if it applies in any.
Most of the time we use the derived terms,but all of the other power formulae are derived directly from P=VI.
The only reason I used P=VI on my posting was that it is less messy to type.
P=VI is the basic power formula ONLY when V and I are instantaneous values. Nothing is derived from P=Vrms.Irms. That formula gives you apparent power, which is a fairly meaningless quantity for anything but a resistive load. For a pure sine wave source, and a pure linear load you can draw a nice triangle of active power, reactive power and apparent power, but that third side of the triangle doesn't mean much. However, as soon as there is any distortion the whole triangle idea falls apart. A water heater is pretty linear, but try an incandescent light bulb. You'll probably get >10%THD, and things get complex. In reality few loads you meet today looks like the simplistic active, reactive, apparent triangle.
RMS is not some construct for dealing with voltages or currents. It one of the most fundamental statistical measures of varying functions, and crops up all over the place in physics and chemistry.
Sorry,I misunderstood your point.
I also stuffed up with "OK,things get messy in reactive circuits,but P=VI was derived from a purely resistive case,& there are many situations where we can assume a resistive load."
What I should have said was that P=VI was derived from the purely resistive DC case,with P=I^2R,& V^2/R,further derived from that.(those are the "derived" formulae I was referring to)
Irms & Vrms were further determined by calculation & experiment.
And,yes,I am aware of the use of rms in other fields---I used it to find the area under the curve in Mathematics.
RMS current & voltage have been used extensively for over 100years,so they do still have their place.
In the case of a Radio Transmitter,a substantially resistive Test Load is used to determine the RF output power.
This can be,& is,often done using P=I^2R.or V^2R with lower power equipment.
(Larger installations often use a water cooled Test load,with average power determined by flow rate & temperature rise)
A real antenna is then matched to the Transmitter,so that it looks as near to resistive as possible,so the Transmitter can deliver the same power output as to the Test Load.
The incandescent lightbulb case really only applies during the initial warm up period--once it is hot,it is a pretty stable resistance.
My original comments were a bit "dumbed down" to make the point about so-called RMS Power.
I never intended to get into an esoteric "off topic" conversation, so if you don't mind, I'm going to 'bail" on it.
The incandescent lightbulb case really only applies during the initial warm up period--once it is hot,it is a pretty stable resistance.
Try looking at the current waveform for an incandescent lamp with a THD meter. Its 10% to 20% all day long. The temperature really varies that much 100 or 120 times a second.
Why so salty? Its 10x the lab that battaro has...
Problem is it doesn't look like lab where someone is working on something, but... it is rather like for sale exposition with items no longer needed
One monitor in lab might have only pink girl to tweet on facebook-
Engineer will have at least two, three...
She was unlucky, because of by showing this big crap PCBs on this desk, that they still has nothing to show, but completly not ergonomic room corner, because of this can't be called lab-it is nothing there and thay also closed windows, maybe to do not show... private garden with her dog playing with her cat
Basicly, in $10M donated company one might expect more to see, especially when it is showed not in city tabloid, but serious business claims while it looks like a expensive joke
Remember,the 240watt power output of a car audio amp is pretty much a "pretend rating"!
The "steady state"or "average" power output will be lower,probably considerably so,even at audible frequencies.
It is anyone's guess how well it does at ultrasonic frequencies.
Either way, that would be into an appropriate low impedance load like a couple of 4 ohm speakers. I'll bet you that for someone who struggled with the concepts of voltage and power, it's unlikely they'd be capable of developing impedance matching and maximum power transfer.
All that was demonstrated there was a remote control from the 1970s. The amp might've increased the peak-peak voltage across the transducer array, but I doubt there was much more than a watt or so going through those transducers.
Anyway, my guess is this huge funding is only made in virtual cash written only on press webpages, because of I do not believe that rich peaople might be such stupid to invest in something such useless like this else than their time 
What is apparently bizarre is the absence of reasonable due diligence when VCs piss cash into these things. To be fair, the angel investors don't really care too much about the ultimate viablility of an idea, only that there's a reasonable chance they can palm it off to some unsuspecting soul at a later date at a serious profit before the emperor reveals himself in public. If that means the VCs pulling on the resources of a PR firm and using their connections (eg, Tech Crunch) to big up largely empty claims, then so be it. To them it's a numbers game: if you throw enough money at enough ideas, like monkeys and typewriters, surely one or two of them will succeed. As only about 25% of VC investments succeed, you can imagine the amount of ROI subsequent investors will be raping from the few poor sods with the real ideas that are successful to make up for those investments that aren't.
I recently read an article about a day in the life of a VC "investor" (in quotes, because it's not necessarily their own money they're pissing away), the apparently self-assured writer boasted of spending a day in back-to-back meetings with potential startups, with fifteen minutes to half an hour for each, seemingly akin to speed dating. They might also choose to float the idea with their own (self-)appointed buddy "expert in the field" who'll give their view after an equally cursory glance. It seems like that's about it, if it doesn't smell like a Pommie's sock after such an in-depth investigation, they'll call their investor buddies up for a game of golf and the deal is all but done. All that's left is a few well-placed articles in the press bigging up their latest investments for their fan boys.
If the VC investors were so bloody good, they wouldn't be suffering a 75% failure rate: that's not a figure to be proud of IMHO.
What is apparently bizarre is the absence of reasonable due diligence when VCs piss cash into these things. To be fair, the angel investors don't really care too much about the ultimate viablility of an idea, only that there's a reasonable chance they can palm it off to some unsuspecting soul at a later date at a serious profit before the emperor reveals himself in public. If that means the VCs pulling on the resources of a PR firm and using their connections (eg, Tech Crunch) to big up largely empty claims, then so be it. To them it's a numbers game: if you throw enough money at enough ideas, like monkeys and typewriters, surely one or two of them will succeed. As only about 25% of VC investments succeed, you can imagine the amount of ROI subsequent investors will be raping from the few poor sods with the real ideas that are successful to make up for those investments that aren't.
A lot of companies are getting money these days that shouldn't. I think it is down to the same basic cause of the subprime mortgage crisis. With interest rates so low pension funds, endowments, and people with massive wealth need to put their money somewhere to make a decent return. 8 years ago, it was mortgaged-backed securities. The banks needed more mortgages to bundle up and sell to the financial firms so they started granting dodgy mortgages. It's the same thing now but with VCs. VCs need someplace to park the money they get from investors so they can go on and get more investment. While they often put some of their own money in, VCs for the most part are spending other people's money. The more money they have under their control, the bigger their management fees so there is this incentive just to spend spend spend.
The time horizons for lots of these investments are so long that we haven't seen many big failures yet. I'm sure it will happen and I don't think it will drag the whole economy down, but it might be harder to find a tech job for a few years.
Exactly"
RMS allows us to use the DC power formula P=VI & its derivatives in AC circuits.
I don't know if the "Ancients" did the experiment first,then the Maths,or the other way around.
Since integral calculus was discovered long before electricity became an actual science instead of a curiosity or unexplained phenomenon, my guess is that math came first.
I'm torn. I'm trying to start my own company right now and I'm trying to fight my natural engineer aversion to hype. To sell something, you have to make it sound like it is some revolutionary idea, that only you can carry out this dream. How do we as engineers "cross over?" I don't want to sit in a cubicle for the rest of my life...
It shouldn't be about an aversion to hype. Hype is a marketing tool, and if you want to be in business you'd better be good at marketing.
The problem for engineers is when people make exaggerated claims for things that patently can't do what is claimed. It's not the hype that is the problem, it is the bullshit...
Quote from their website: "Ultrasonic energy (energy from ultrasound) is the only type of energy that can safely and reliably transmit energy wirelessly; thus it's the only type of energy that can be used for over-distance wireless power transmission."
http://ubeam.com 
And the hyperbole only gets better from there on..
The problem for engineers is when people make exaggerated claims for things that patently can't do what is claimed. It's not the hype that is the problem, it is the bullshit...
Yes, this. We understand hype, it's part of the game. But BS should not be part of the game. If you make claims, you back them up with demos and data. They have had what, 3 years to demo something tangible, but still nothing.
Looks like there are some figures to work with on the website now:
WHAT IF SOMEONE WERE TO STAND DIRECTLY IN FRONT OF THE BEAM?
uBeam's ultrasound energy will not beam to the skin, and the power levels beamed are more than 50 times lower than the lowest ultrasound imaging exposure limits set by the FDA for medical imaging, making the system inherently safe and within all existing regulatory constraints.
Bingo. If someone can find out what the FDA exposure limits are, then it's 50 times less than that at maximum.
and:
The "holy grail" experience of true wireless power is one where multiple devices can simply charge in the air as they're moving and as they're being used. It's like the experience of Wi-Fi, but for power. In order to achieve this type of experience, you need a system that can achieve the following - simultaneously:
TRANSMIT LARGE AMOUNTS OF POWER SAFELY
(> 1 WATT PER PHONE)...
So presumably the uBeam is at least 1W output? (but under what conditions?)
IKEA lamp in the corner does provide enougth light to serious work? 
