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Wireless Devices Go Battery-Free With New Communication Technique
melios sends this quote from an University of Washington news release:
"[E]ngineers have created a new wireless communication system that allows devices to interact with each other without relying on batteries or wires for power. The new communication technique, which the researchers call 'ambient backscatter,' takes advantage of the TV and cellular transmissions that already surround us around the clock. Two devices communicate with each other by reflecting the existing signals to exchange information. The researchers built small, battery-free devices with antennas that can detect, harness and reflect a TV signal, which then is picked up by other similar devices."
http://en.wikipedia.org/wiki/Crystal_radio
Dear aunt, let's set so double the killer delete select all
This is not new technology.
Toll Tags and other RF-ID devices have been using "back scatter" techniques to capture energy to transmit with for decades. The reader device provides RF energy that is captured by the tag charging up a capacitor enough to send a short burst of data back to the reader. I saw this being done during a Job interview in Dallas sometime in the 90's and was impressed with the idea. I was even more impressed that it worked well enough to actually be in use on various tolling systems. Still remember the test rig they had with the tags mounted to the ceiling fan blades as being decidedly low tech, but wonderfully effective.
The application might be a bit different, but the technology is NOT new.
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101
Sure backscatter has been done... But it always used known frequencies as the signal source. This will pick up any ambient ref noise and use it to generate a new signal.
Essentially, you could embed a transmitter anywhere without concern for a power source (assuming there are other transmitters around).
Sometimes the best solution is to stop wasting time looking for an easy solution.
http://en.wikipedia.org/wiki/Thing_(listening_device)
I've got no objection to such research scientifically speaking. However, I am staunchly against any form of computation or communication that someone else can simply pull the plug on. Switch off the microwave carrier signals and these systems are dead. Wouldn't that be scary as hell to rely on? Before I used such tech I'd want it made legal to generate my own background radiation at home. That's currently illegal by the way.
Before you say it, yes, as a BBS owner I was against the Internet too, in principal. Not the communication, but the ability to spy on, censor, and pull the plug at will. I use todays technology with gritting teeth because although I have the expertise required to beam my data at high speed between my friends and family nation wide wirelessly with commodity radio gear, use of such systems in that manner are forbidden by the FCC, so I must use the principally corrupt systems.
I remain firmly convinced that large blocks of the air waves, perhaps even in the cellular bands, should belong to the people and if so instead of paying out the ass to support evil "data plans" we'd all be using a decentralized encrypted anonymized high speed hybrid line of sight / self organizing mesh network. You would pay for the hardware once, maintain it, and that's it. Ask a HAMOp about their packet radio "data plans"... If not so restricted by the FCC (and yes some oversight is needed, but not to this degree), we could have cut the cables. Omnivore, Carnivore, ECHELON, and PRISM illustrates why we don't have such technology in place. Before you argue against the feasibility, I would ask if you've actually tried it? If not, then make sure you're not on any (n+2)G network then make a free "long distance" cellular call and tell someone who cares.
I've got no objection to such research scientifically speaking. However, I am staunchly against any form of computation or communication that someone else can simply pull the plug on. Switch off the microwave carrier signals and these systems are dead. Wouldn't that be scary as hell to rely on?
There's degrees of reliance. For a TV remote or PAN application, not scary at all. For a mobile phone that one's life might depend on, somewhat scary.
Before I used such tech I'd want it made legal to generate my own background radiation at home. That's currently illegal by the way.
Sorry, but we have these little thing called the ISM bands, perhaps you've heard of them. (There's one at 2.4GHz, WiFi and bluetooth use it.) You're perfectly allowed to generate RF in these band. You're also allowed to generate unlicensed emissions in many other bands, subject to strict power limits that will still likely be enough (at short ranges) for these devices to work. (I agree with you, at least on a broad view, about what's wrong with the FCC and our current spectrum ownership policies, but you don't help things by overstating the restrictions....)
I'm not saying the eventual commercial implementation of this idea won't be intentionally crippled to rely on frequencies that are more tightly controlled, precisely to provide an off switch, but until/unless they are, your wholesale indictment of the tech is premature. The natural choice for this tech, outside monopolistic/control-freak pressures, is to have it use several options including one of the heavily-used ISM bands, because there's a lot of available energy in them, and (unlike, say, broadcast TV frequencies) they're used even out in the country. (Mobile phone networks are another obvious choice, with better rural penetration than TV, but there's still sufficiently remote places with almost no mobile phone signal, and people in thes places still run WiFi APs connected to their landline internet.)
Also, learn the difference between principle and principal. Botching it as you did makes you look like a moron.
Interesting comments. You mentioned RF power functions. The main function for radio, also called far field, is that power drops with the square of distance.
I'd like to point out card readers do not work using radio waves, not like these devices do. At distances less than about 1 wavelength, the primary effect is what's called "near field", commonly referred to as induction. This is the same way transformers work. Near field power drops at distance to the SIXTH power. That means that while it's very strong within a few millimeters, it basically dissapears within a few centimeters or meters.
The new devices are using RADIO energy from arbitrary far away sources. Card readers use near field induction, a completely different mechanism.
... receiving RF without power has been done for about as long as RF has been received... Actually... Exactly as long as RF has been received. Crystal Radios where how this whole "Let's communicate by radio waves" thing got started...
Not quite. Coherers preceded crystal detectors by a few years.
You are allowed to generate RF at 2.4 GHz, but at a limited power. In the Netherlands you are allowed to put 20 mA into an antenna, more would require a license. In the USA this is a lot higher.
If you choose to dismantle a microwave oven and turn the magnetron radio emitter on without shielding there will probably be consequences, aside from the severe burns if you leave it on to long. And a microwave is in the 2.4 GHz band, so according to you "You're perfectly allowed to generate RF in these band."
I have no idea what intensity of noise these devices need to send their signals, but if it is above the max you can send then the power device may be illegal.
Well, I might have a way, but it only works on a semi spherical planet in a vacuum.
As I mentioned, near field predominates up to about one wavelength, and basically goes away at around four X wavelength. For reference, commercial AM radio in the US is about 1/2 meter wave, commercial FM is about 1/2 centimeter.
So if your key used a wavelength similar to AM radio, the near field would be detectable up to about two meters. In your experiment , you found that it's detectable up to about that distance. It may use a frequency slightly lower than AM radio, meaning a slightly longer wavelength.
You mentioned your key card works to a couple of inches -precisely the limit we'd expect around FM radio frequencies.
"Literally a coil of wire wrapped around the key". There's a name for a coil of wire. A coil of wire is commonly called an "inductor". They are often used for power, and to filter OUT radio interference. You may have noticed radio antennas are normally straight, even when that's inconvenient such ad on a walkie-talkie.
"It's most definitely RF". (Radio Frequency). Yes, as are IDE cables and cable TV. Neither of which use radio waves.