throw away the wires
November 15, 2006 5:35 AM Subscribe
wireless electricity is said to be possible by some researchers. the only question is: what will become of this industry?
Interesting BBC link, but whats with the second? Just seems to be a random cable manufacturers website or am I missing something?
posted by lemonfridge at 5:46 AM on November 15, 2006
posted by lemonfridge at 5:46 AM on November 15, 2006
Personally, I am still waiting for pipeless plumbing.
Seriously, though, even when wireless electricity is possible, they aren't going to tear up the utility poles and power houses by a beam of energy. It will be used for stuff like remote controls which never need new batteries, security lights you can hang without running new wire, etc. This isn't because wired power is "good enough," it's because it will always be better. Just ask the guy who went to trade school and makes 40 bucks an hour unwinding wire off a spool and running it through your walls. Also, think of the brain tumors!
posted by sdrawkcab at 6:28 AM on November 15, 2006
Seriously, though, even when wireless electricity is possible, they aren't going to tear up the utility poles and power houses by a beam of energy. It will be used for stuff like remote controls which never need new batteries, security lights you can hang without running new wire, etc. This isn't because wired power is "good enough," it's because it will always be better. Just ask the guy who went to trade school and makes 40 bucks an hour unwinding wire off a spool and running it through your walls. Also, think of the brain tumors!
posted by sdrawkcab at 6:28 AM on November 15, 2006
We'll still use cables and connectors, just as paper's remained in use. There'll always be instances where a connection may require isulation to prevent bleedoff/interference, or high EMF/stray voltage in extreme instances.
posted by Smart Dalek at 6:28 AM on November 15, 2006
posted by Smart Dalek at 6:28 AM on November 15, 2006
It sounds horribly impractical--you'd simply be wasting more energy because you'd have to convert the electricity into motion and then back into electricity via a generator in the actual device, and you always lose copious amounts of energy when you do a conversion. Unless we're actually going to send energy to homes via mechanical vibration, this would simply mean more energy consumption--and that's the very last thing we need.
It would probably be more practical to make everything wind-up.
posted by Citizen Premier at 6:30 AM on November 15, 2006
It would probably be more practical to make everything wind-up.
posted by Citizen Premier at 6:30 AM on November 15, 2006
Also, think of the brain tumors!
I can't--I have a brain tumor.
posted by Citizen Premier at 6:31 AM on November 15, 2006
I can't--I have a brain tumor.
posted by Citizen Premier at 6:31 AM on November 15, 2006
maybe they'll use it to kill an elephant to prove how unsafe it is
posted by kisch mokusch at 6:33 AM on November 15, 2006 [2 favorites]
posted by kisch mokusch at 6:33 AM on November 15, 2006 [2 favorites]
Unfortunately there's such things as the inverse-square law and path loss, which you just can't get away from.
Though it sounds like these '"non-radiative" objects with so-called "long-lived resonances"' can improve the coupling (&, ultimately, the transmission efficiency) quite a bit, ye canna' change the laws of physics...
posted by Pinback at 6:44 AM on November 15, 2006
Though it sounds like these '"non-radiative" objects with so-called "long-lived resonances"' can improve the coupling (&, ultimately, the transmission efficiency) quite a bit, ye canna' change the laws of physics...
posted by Pinback at 6:44 AM on November 15, 2006
The future of power distribution is in local distributed production. It's just not very efficient (except in terms of ownership and administration) to send electricity 100 miles away from production to use.
posted by sonofsamiam at 6:44 AM on November 15, 2006
posted by sonofsamiam at 6:44 AM on November 15, 2006
Bah, I'm so sick of hearing about the tesla myths. His method and this one two are still very inefficient. His big accomplishments like sending power to sea to power ships was either faked or greatly exaggerated. He wasnt the victim of some government conspiracy just impractical engineering. To be fair, he is the victim of a crappy band stealing his name.
This method is a bit more practical commercial-wise. Its a vanity technology that'll recharge a laptop or a remote control but no substitute for wired power around the home. In a time when people are starting to care about energy issues, pollution, and global warming, maybe a wholesale waste of power so you dont have to connect the laptop to the wall isn't such a great idea. Especially when we're still burning coal for power all over the world.
posted by damn dirty ape at 6:54 AM on November 15, 2006
This method is a bit more practical commercial-wise. Its a vanity technology that'll recharge a laptop or a remote control but no substitute for wired power around the home. In a time when people are starting to care about energy issues, pollution, and global warming, maybe a wholesale waste of power so you dont have to connect the laptop to the wall isn't such a great idea. Especially when we're still burning coal for power all over the world.
posted by damn dirty ape at 6:54 AM on November 15, 2006
What Pinback said, re the inverse sqaure law.
However, things will get interesting when small devices like semiconductors become so efficient that they can be powered off of the RF signals from radio or TV stations.
And if you hold a fluorescnet tube light under a power line, it'll glow enough to demonstrate that we are swimming in EM fields, but do get a meaningful amount of power through the air it would involve driving a source transmitter with so much power as to make it inefficient.
Of course, you might as well slap a solar panel on the back of your phone or iPod, because light is EM energy as mcuh as radio is. Those devices may not have enough surface area to provide sufficient current to directly drive the device off solar power, but it would certainly be enough to recharge the battery, at least a little.
Frankly, I'd be happy if they simply made a single connector and wire for all applications. The reason most cables have different plugs and shapes is to prevent you from plugging the wrong thing into the wrong hole.
posted by Pastabagel at 6:55 AM on November 15, 2006
However, things will get interesting when small devices like semiconductors become so efficient that they can be powered off of the RF signals from radio or TV stations.
And if you hold a fluorescnet tube light under a power line, it'll glow enough to demonstrate that we are swimming in EM fields, but do get a meaningful amount of power through the air it would involve driving a source transmitter with so much power as to make it inefficient.
Of course, you might as well slap a solar panel on the back of your phone or iPod, because light is EM energy as mcuh as radio is. Those devices may not have enough surface area to provide sufficient current to directly drive the device off solar power, but it would certainly be enough to recharge the battery, at least a little.
Frankly, I'd be happy if they simply made a single connector and wire for all applications. The reason most cables have different plugs and shapes is to prevent you from plugging the wrong thing into the wrong hole.
posted by Pastabagel at 6:55 AM on November 15, 2006
it seems the best use is a "charging pad" where you just set your numerous devices (mp3 player, camera, phone) on at night and they charge.
No need for 3 different wall worts.
posted by Mick at 6:56 AM on November 15, 2006
No need for 3 different wall worts.
posted by Mick at 6:56 AM on November 15, 2006
The future of power distribution is in local distributed production.
Amen. Not just the future, Germany has it already, which is why they are so far ahead in wind and solar - they are mostly small community owned and operated installations, which all told provide over %20 of the nations power.
posted by stbalbach at 6:58 AM on November 15, 2006
Amen. Not just the future, Germany has it already, which is why they are so far ahead in wind and solar - they are mostly small community owned and operated installations, which all told provide over %20 of the nations power.
posted by stbalbach at 6:58 AM on November 15, 2006
No need for 3 different wall worts.
posted by Mick at 9:56 AM EST on November 15
You only need different ones because the voltage requirements are inconsistent. If electronics companies decided to standardize on something, say 18V 2000mA and lower, then you could build a single adapter with lots of wires, one for each device. The device coulld be built with a switch on each wire to change the polarity and select a voltage(18V, 12V, 9V, 5V, 3V) for that wire.
Frankly, a decent EE could buy a PC power supply and rig this up themselves, but it would be nice if firms standardized on this kind of thing.
The future of power distribution is in local distributed production.
The U.S. is a big country. In places, 100-mile transmission lines would be considered local. And power plants benefit from economies of scale.
What can be practically done now is to get devices like TV's and consumer electronics to shut off completely instead of remaining in a double-digit wattage sleep modes (e.g. a red light on your dvd player means it's "off"), and to provide for solar-generated recharging of lower power DC electronics devices like phones etc. That heat you feel on the wall wort is power wasted in the AC to DC conversion.
Furthermore, the power requirements for computers, and the attendant water or turbofan cooling solutions, is getting a little ridiculous. Something is very wrong in having a video card that needs a 450 W power supply but that also needs a built-in fan to cool it.
posted by Pastabagel at 7:15 AM on November 15, 2006
I wonder if we could use this to put giant solar collectors in space, and then beam the energy back down to earth. I could do it in SimCity 3000 (but not 4000, for some reason).
posted by Afroblanco at 7:15 AM on November 15, 2006
posted by Afroblanco at 7:15 AM on November 15, 2006
"Personally, I am still waiting for pipeless plumbing."
Beam the shit right out of your house!
posted by mr_crash_davis at 7:20 AM on November 15, 2006
Beam the shit right out of your house!
posted by mr_crash_davis at 7:20 AM on November 15, 2006
Beam the shit right out of your house!
posted by mr_crash_davis at 10:20 AM EST on November 15
[+]
[!]
TV has been doing the reverse for years.
posted by Pastabagel at 7:28 AM on November 15, 2006
posted by mr_crash_davis at 10:20 AM EST on November 15
[+]
[!]
TV has been doing the reverse for years.
posted by Pastabagel at 7:28 AM on November 15, 2006
In places, 100-mile transmission lines would be considered local. And power plants benefit from economies of scale.
Most of those places would be primary candidates for home power production. Yeah, power companies benefit from economies of scale, it's the only way they can make up for their inefficient transmission scheme.
The effect of the 'scale' only pays off in dollars, not in total energy efficiency.
posted by sonofsamiam at 7:34 AM on November 15, 2006
Most of those places would be primary candidates for home power production. Yeah, power companies benefit from economies of scale, it's the only way they can make up for their inefficient transmission scheme.
The effect of the 'scale' only pays off in dollars, not in total energy efficiency.
posted by sonofsamiam at 7:34 AM on November 15, 2006
oh snap!
posted by Parannoyed at 7:40 AM on November 15, 2006
posted by Parannoyed at 7:40 AM on November 15, 2006
However, things will get interesting when small devices like semiconductors become so efficient that they can be powered off of the RF signals from radio or TV stations.
.....
Those devices may not have enough surface area to provide sufficient current to directly drive the device off solar power, but it would certainly be enough to recharge the battery, at least a little.
Errr, if a radio can be powered by the RF (crystal radio anyone) how is a solar panel *NOT* going to be enough?
Please show RF powered calculators that outperform the existing CMOS solar powered ones.
posted by rough ashlar at 7:44 AM on November 15, 2006
.....
Those devices may not have enough surface area to provide sufficient current to directly drive the device off solar power, but it would certainly be enough to recharge the battery, at least a little.
Errr, if a radio can be powered by the RF (crystal radio anyone) how is a solar panel *NOT* going to be enough?
Please show RF powered calculators that outperform the existing CMOS solar powered ones.
posted by rough ashlar at 7:44 AM on November 15, 2006
Errr, if a radio can be powered by the RF (crystal radio anyone) how is a solar panel *NOT* going to be enough?
Please show RF powered calculators that outperform the existing CMOS solar powered ones.
posted by rough ashlar at 10:44 AM EST on November 15
Those were two separate thoughts. I was speculating in the future that devices like remotes, etc could store some charage pulled from RF, but was separately wondering why they don't now slap solar panels on existing devices like ipods that could benefit from them.
Your point is a good one - to the extent that I know of no RF-powered calculators that even exist now.
posted by Pastabagel at 7:52 AM on November 15, 2006
Please show RF powered calculators that outperform the existing CMOS solar powered ones.
posted by rough ashlar at 10:44 AM EST on November 15
Those were two separate thoughts. I was speculating in the future that devices like remotes, etc could store some charage pulled from RF, but was separately wondering why they don't now slap solar panels on existing devices like ipods that could benefit from them.
Your point is a good one - to the extent that I know of no RF-powered calculators that even exist now.
posted by Pastabagel at 7:52 AM on November 15, 2006
I attached a baloon to my iPod. People find it annoying when I rub it on their heads but I get to hear my music and that's what counts.
posted by srboisvert at 7:54 AM on November 15, 2006
posted by srboisvert at 7:54 AM on November 15, 2006
Unfortunately there's such things as the inverse-square law and path loss, which you just can't get away from.
Though it sounds like these '"non-radiative" objects with so-called "long-lived resonances"' can improve the coupling (&, ultimately, the transmission efficiency) quite a bit, ye canna' change the laws of physics...
The inverse square law doesn't apply to beams. This technique creates a 'tail' or something, according to the authors. The inverse square law isn't a factor here.
And I think physicists probably know more about the laws of physics then some random mefite...
posted by Paris Hilton at 8:27 AM on November 15, 2006
Though it sounds like these '"non-radiative" objects with so-called "long-lived resonances"' can improve the coupling (&, ultimately, the transmission efficiency) quite a bit, ye canna' change the laws of physics...
The inverse square law doesn't apply to beams. This technique creates a 'tail' or something, according to the authors. The inverse square law isn't a factor here.
And I think physicists probably know more about the laws of physics then some random mefite...
posted by Paris Hilton at 8:27 AM on November 15, 2006
He wasnt the victim of some government conspiracy just impractical engineering
To be fair it should probably be pointed out that you use Teslas impractical engineering every time you plug something into the mains.
posted by Artw at 8:29 AM on November 15, 2006
To be fair it should probably be pointed out that you use Teslas impractical engineering every time you plug something into the mains.
posted by Artw at 8:29 AM on November 15, 2006
The inverse square law appears not to be directly relevant here because (according to the article) the power transmitter is not radiating. Briefly, the inverse square law is relevant for radiation because emitted particles travel in all directions, so a brief pulse would lie on the surface of a sphere. As the sphere expands, the "density" (actually flux) decreases like 1 / (Surface Area) which for a sphere is 1 / (4 pi r^2). However, this transmitter is not radiating. Based on the (admittedly very vague) article, power is not radiated in all directions, but only along "tails"(?) that travel between the transmitter and receiver. I'd like to see a more detailed explanation, but what the scientists are claiming they've done could be efficient (in principle). It's not obviously nonsense to me, as I have seen solutions to electromagnetic wave equations where an oscillating E&M field extends outside an object without radiating. I'm no electrical engineer though.
Also, this oscillation is purely electrical (this is very similar to a transformer) not mechanical, so there's no conversion issue. And semiconductors are a class of materials, not devices.
posted by Humanzee at 8:41 AM on November 15, 2006
Also, this oscillation is purely electrical (this is very similar to a transformer) not mechanical, so there's no conversion issue. And semiconductors are a class of materials, not devices.
posted by Humanzee at 8:41 AM on November 15, 2006
sdrawkcab writes "I am still waiting for pipeless plumbing."
Here ya go.
posted by Mitheral at 8:47 AM on November 15, 2006
Here ya go.
posted by Mitheral at 8:47 AM on November 15, 2006
The future of power distribution is in local distributed production.
How about a residential 'micro-combined-heat-and-power' unit? Pays for itself, and all that.
posted by MetaMonkey at 8:51 AM on November 15, 2006
How about a residential 'micro-combined-heat-and-power' unit? Pays for itself, and all that.
posted by MetaMonkey at 8:51 AM on November 15, 2006
"Bah, I'm so sick of hearing about the tesla myths."
Myths? Does that mean I can't get a Tesla coil for my yard that will incinerate pesky teens on my lawn (you know, like the ones in Command & Conquer)?
It's funny, I just finished reading a book last night (The Prestige) in which Tesla and his inventions were a significant plot point. Actually, Tesla and/or broadcast power have turned up in a couple of books I've read within the last year or so. I guess people love a good conspiracy to keep cheap efficient power from the masses.
posted by MikeMc at 8:57 AM on November 15, 2006
Myths? Does that mean I can't get a Tesla coil for my yard that will incinerate pesky teens on my lawn (you know, like the ones in Command & Conquer)?
It's funny, I just finished reading a book last night (The Prestige) in which Tesla and his inventions were a significant plot point. Actually, Tesla and/or broadcast power have turned up in a couple of books I've read within the last year or so. I guess people love a good conspiracy to keep cheap efficient power from the masses.
posted by MikeMc at 8:57 AM on November 15, 2006
Any energy not diverted into a gadget or appliance is simply reabsorbed.
By any surrounding meatware, no doubt.
posted by ZenMasterThis at 9:21 AM on November 15, 2006
By any surrounding meatware, no doubt.
posted by ZenMasterThis at 9:21 AM on November 15, 2006
A tesla coil could work, for light anyway, unfortunately, they are really really noisy. Maybe if they were buried?
posted by Monkey0nCrack at 10:06 AM on November 15, 2006
posted by Monkey0nCrack at 10:06 AM on November 15, 2006
I guess people love a good conspiracy to keep cheap efficient power from the masses.
Speaking of which, I built a device in my garage that produces infinite energy and offered 10,000 dollars to anyone who could prove it didn't work. But then the government told me I'd be arrested if I turned it on so I had to disassemble it.
posted by Citizen Premier at 10:21 AM on November 15, 2006
Speaking of which, I built a device in my garage that produces infinite energy and offered 10,000 dollars to anyone who could prove it didn't work. But then the government told me I'd be arrested if I turned it on so I had to disassemble it.
posted by Citizen Premier at 10:21 AM on November 15, 2006
what will become of this industry?
Use the factories for arts and stuff!
posted by Anything at 10:32 AM on November 15, 2006
Use the factories for arts and stuff!
posted by Anything at 10:32 AM on November 15, 2006
Tails of power?
That's some of the worst tech writing I've seen.
posted by spazzm at 1:37 PM on November 15, 2006
That's some of the worst tech writing I've seen.
posted by spazzm at 1:37 PM on November 15, 2006
Your favorite energy delivery infrastructure sucks.
posted by CynicalKnight at 2:48 PM on November 15, 2006
posted by CynicalKnight at 2:48 PM on November 15, 2006
The inverse-square law, or something very much like it, applies unless your receiving element captures 100% of the emitted beam-width.
(Yes, I used 'inverse-square law' as shorthand for explaining that. Nobody has disagreed with path loss though, have they?)
It's hard to tell from a pop-sci article like this (WTF does 'non-radiative' mean anyway? If it ain't radiating in a particular domain, you can't remotely detect/use its energy in that same domain!), but to me it looks like what they've found is some very (amazingly?) good method of resonant coupling. Think along the lines of the classical 'lines of electromagnetic force' demonstration using a wire or coil, a sheet of paper, and iron filings - and what happens when you introduce an iron bar into the field. This appears to achieve the same thing without the iron bar, by using extremely well-coupled and low-loss resonators - an effect physics has known since the time of Hertz.
Practical for very short-path power transmission (apart from the inevitable path and conversion losses), and interesting if they really can get practical couplings at metres vs centimetres, but still very short-range stuff. It won't be replacing your power lines, or even your extension cords, though.
Tesla wasn't necessarily a kook, but a lot of his believers are...
posted by Pinback at 4:55 PM on November 15, 2006
(Yes, I used 'inverse-square law' as shorthand for explaining that. Nobody has disagreed with path loss though, have they?)
It's hard to tell from a pop-sci article like this (WTF does 'non-radiative' mean anyway? If it ain't radiating in a particular domain, you can't remotely detect/use its energy in that same domain!), but to me it looks like what they've found is some very (amazingly?) good method of resonant coupling. Think along the lines of the classical 'lines of electromagnetic force' demonstration using a wire or coil, a sheet of paper, and iron filings - and what happens when you introduce an iron bar into the field. This appears to achieve the same thing without the iron bar, by using extremely well-coupled and low-loss resonators - an effect physics has known since the time of Hertz.
Practical for very short-path power transmission (apart from the inevitable path and conversion losses), and interesting if they really can get practical couplings at metres vs centimetres, but still very short-range stuff. It won't be replacing your power lines, or even your extension cords, though.
Tesla wasn't necessarily a kook, but a lot of his believers are...
posted by Pinback at 4:55 PM on November 15, 2006
The professor mentioned in the article, Dr. Marin Soljačić, gave a talk titled "Wireless Non-Radiative Energy Transfer" at the 2006 AIP Industrial Physics Forum in San Francisco. The paper, with the actual technical details, is available here. It's quite readable.
posted by RichardP at 4:58 PM on November 15, 2006
posted by RichardP at 4:58 PM on November 15, 2006
I find the idea of powering something like a laptop without a cord extremely questionable. Laptops take a lot of power. Do you really want to risk accidentally intercepting a 200W stream of electricity going through the air with your head? Sure, it's not going to electrocute you since your body is a poor receptor of radio waves, but they won't simply pass through without effect either.
200W is enough power to make a somewhat underpowered microwave. It's like strapping hundreds of cell phones to your head and operating them under high power all at once. You couldn't find enough power lines to live under to get that kind of flux going through the air. I can't imagine it being a good idea to transmit that kind of juice through the air wantonly. Hell, even if it doesn't cause massive health issues, the EMI would boggle the mind.
posted by Mitrovarr at 5:23 PM on November 15, 2006
200W is enough power to make a somewhat underpowered microwave. It's like strapping hundreds of cell phones to your head and operating them under high power all at once. You couldn't find enough power lines to live under to get that kind of flux going through the air. I can't imagine it being a good idea to transmit that kind of juice through the air wantonly. Hell, even if it doesn't cause massive health issues, the EMI would boggle the mind.
posted by Mitrovarr at 5:23 PM on November 15, 2006
Bingo, RichardP! It's amazingly high Q low loss resonant coupling, taking advantage of near-field capture effects. Somewhat better than 50% efficiency too, if my reading of their examples and some back-of-the-envelope calculations are correct. Practical for short-range convenience, if/where you can stomach the losses.
Mitrovarr: the examples in the paper seem to indicate <1% energy absorption by their theoretical human body. Still more than I'd want to absorb...
posted by Pinback at 5:34 PM on November 15, 2006
Mitrovarr: the examples in the paper seem to indicate <1% energy absorption by their theoretical human body. Still more than I'd want to absorb...
posted by Pinback at 5:34 PM on November 15, 2006
Pinback, they examined two different electromagnetic resonant systems that made use of their scheme. Their first, dielectric disks, uses a predominantly electric field and their second, capacitively-loaded conducting-wire loops, uses a predominantly magnetic field. In their estimates for using dielectric disks, the efficiency was about 10W/15W = 66% and the energy absorption for a "human" extraneous object was about 0.1W/15W = 0.6%. Their second system, using conducting loops, was less efficient, but safer and hence their preferred choice for real-world applications. The efficiency was about 10W/26.5W = 38% and the energy absorption for a human was essentially zero (humans are non-magnetic).
posted by RichardP at 7:25 PM on November 15, 2006
posted by RichardP at 7:25 PM on November 15, 2006
Oh, I just noticed that Jennifer Ouellette, who was at Soljačić's talk, has a nice writeup of the session on the AIP blog.
posted by RichardP at 10:50 PM on November 15, 2006
posted by RichardP at 10:50 PM on November 15, 2006
I'd be interested in seeing new forms of regenerative energy recovery schemes. Think of those watches that generate energy from the wearer's movements, or electric cars that have generators built in to the brakes.
So what about a remote control that has a tiny, super-efficient generator under every button. Or one for every key on your laptop?
posted by tritisan at 10:54 PM on November 15, 2006
So what about a remote control that has a tiny, super-efficient generator under every button. Or one for every key on your laptop?
posted by tritisan at 10:54 PM on November 15, 2006
It should be very, very easy to build and test either the dielectric or the magnetic system. So, lets see it :)
In their estimates for using dielectric disks, the efficiency was about 10W/15W = 66% and the energy absorption for a "human" extraneous object was about 0.1W/15W = 0.6%. Their second system, using conducting loops, was less efficient, but safer and hence their preferred choice for real-world applications. The efficiency was about 10W/26.5W = 38% and the energy absorption for a human was essentially zero (humans are non-magnetic).
It is interesting to look at their field diagrams for the case of two dielectric discs in the presence of a human and a wall. Note how the human and the wall are at least distance D away from the discs? What is holding up the discs? (or, how is a table top different from a wall :P)
The other thought I had.. The characteristics of the load will have to be very tightly controlled, otherwise it would change the coupling efficiency - a lot. With appropriate use of switch mode power conversion, tight control over load characteristics may be possible, but it is a substantial constraint on the system's usefulness. It does go some way to explaining why nobody has bothered pursuing this before.
One final question, forgetting the technical issues, and concentrating on the usefulness. Inductive charging has been used in consumer devices for some time now. The most common example is rechargeable toothbrushes. In practice they seem to require a mechanical mating - a protrusion on the toothbrush base enters an indentation on the toothbrush. The next step is to have a pad, where you drop all the devices that need charging, like this older scheme the BBC article linked. That seems like a substantial improvement, because the mating doesn't have to take place. How much more user friendly is it to have low efficiency energy transmission over ~1m distances though? If it was 100m distances, that would be great, just walk in the door and recharging starts happening, but they don't seem to be proposing that such large distances, with so many interferences, is practical. That isn't anything against the technology, which might turn out to be a better way of doing any of the schemes, but I do wonder what level of wirelessness represents the best trade off (between convenience, efficiency, safety, cost, and whatever else you can think of).
The real problem with chargers, as others have said, is lack of an industry standard. Just look at all those AskMe questions: Why so many AC adapters, Am I using the wrong power adapter, and the sound of silence. In the past, complying with a broad standard would have had a substantial impact on price, that isn't really the case anymore.
I've made a couple of attempts to explain why low voltage can cause problems (older, newer), there are problems with those explanations.
posted by Chuckles at 11:33 PM on November 15, 2006
In their estimates for using dielectric disks, the efficiency was about 10W/15W = 66% and the energy absorption for a "human" extraneous object was about 0.1W/15W = 0.6%. Their second system, using conducting loops, was less efficient, but safer and hence their preferred choice for real-world applications. The efficiency was about 10W/26.5W = 38% and the energy absorption for a human was essentially zero (humans are non-magnetic).
It is interesting to look at their field diagrams for the case of two dielectric discs in the presence of a human and a wall. Note how the human and the wall are at least distance D away from the discs? What is holding up the discs? (or, how is a table top different from a wall :P)
The other thought I had.. The characteristics of the load will have to be very tightly controlled, otherwise it would change the coupling efficiency - a lot. With appropriate use of switch mode power conversion, tight control over load characteristics may be possible, but it is a substantial constraint on the system's usefulness. It does go some way to explaining why nobody has bothered pursuing this before.
One final question, forgetting the technical issues, and concentrating on the usefulness. Inductive charging has been used in consumer devices for some time now. The most common example is rechargeable toothbrushes. In practice they seem to require a mechanical mating - a protrusion on the toothbrush base enters an indentation on the toothbrush. The next step is to have a pad, where you drop all the devices that need charging, like this older scheme the BBC article linked. That seems like a substantial improvement, because the mating doesn't have to take place. How much more user friendly is it to have low efficiency energy transmission over ~1m distances though? If it was 100m distances, that would be great, just walk in the door and recharging starts happening, but they don't seem to be proposing that such large distances, with so many interferences, is practical. That isn't anything against the technology, which might turn out to be a better way of doing any of the schemes, but I do wonder what level of wirelessness represents the best trade off (between convenience, efficiency, safety, cost, and whatever else you can think of).
The real problem with chargers, as others have said, is lack of an industry standard. Just look at all those AskMe questions: Why so many AC adapters, Am I using the wrong power adapter, and the sound of silence. In the past, complying with a broad standard would have had a substantial impact on price, that isn't really the case anymore.
I've made a couple of attempts to explain why low voltage can cause problems (older, newer), there are problems with those explanations.
posted by Chuckles at 11:33 PM on November 15, 2006
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posted by parmanparman at 5:43 AM on November 15, 2006