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."

Comments

The Technology is Not New

[bobbied]

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.

Re:The Technology is Not New

[bobbied]

Getting power from an external RF source is not new. Being able to get it from ambient RF sources is not new either.

The tags I saw where charging whenever RF was available. The tag didn't know or care if the power came from the reader or not. The goal was to keep charged and "ready" for the data burst when the reader asked for it. Any RF source was suitable for charging and that the reader provided power was merely a matter of making sure there was enough power when needed. So for reliability sake you put some RF power out to charge the tag before you need it to transmit the data you want, but they still charged from anything else they picked up.

So what does it matter where the background RF comes from? Capturing energy from RF is certainly not new. Using such power to communicate is not new either.

Re:The Technology is Not New

[adolf]

Actually, passive key cards do store the energy for later use.

"Later" happens to be measured in microseconds or so, but it's still later (much, much later in computer terms).

First, the antenna inside of the card is used with a rectifier and a capacitor to make DC voltage to power an IC from the RF energy radiated by the card reader. Once the voltage is high enough (which cannot occur instantaneously), that IC then uses the energy stored in its capacitor to send its ID string over the same antenna that was part of a power supply a brief moment earlier.

And like anything else RF, distance is largely a function of radiated power and receiver sensitivity. Cards and readers generally only work within a few inches merely because that was one of the design parameters, not because that is the maximum attainable using the technique:

Improve the performance of the card (more capacitance combined with a beefier RF section), and/or increase the sensitivity of the reader (using a higher-gain antenna and/or lower-noise electronics), and functional operating distance is increased accordingly.

Re:The Technology is Not New

[__aaltlg1547]

What's new is they're working with very low power levels. I've never seen a backscatter system that can work with so little incident power.

Re:New???

[bobbied]

Not exactly the same thing, but 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...

it is new... in a way.

[jhfry]

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).

Re:Scientifically, fine, but not good in principal

[Anonymous Coward]

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.

near field is induction, far field is radio

[raymorris]

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.

Re:near field is induction, far field is radio

[adolf]

I'd like to point out that the frequencies involved are most certainly RF.

Inductive coupling is a cute efficiency trick, but it's not necessary -- even in existing systems.

(And if inductive coupling were really the primary means of communication, we'd be calling the radiating elements "inductors" instead of "antennas." I mean: It's not as if these two concepts are not well-understood, even if they are often related.)

Meanwhile, I do not understand your millimeter boojigity as it relates to common practice: If it were only useful within a few millimeters, I would be unable to use my access card from a distance of a few inches (as I routinely do). If the signal were to basically disappear after a few centimeters, then using it at a few inches would be impossible.

And at this point, I'd also like to introduce a car anecdote. As an anti-theft function, my 1995 BMW will not start and run without a properly-coded key in close proximity to the ignition switch. And by close proximity, I mean: There is literally a coil of copper wrapped around the lock cylinder, and it can't "see" the key unless it is within a couple of inches.

But one day, I decided I wanted to add a remote start function to my BMW. I dug into it pretty deep and spent two cold nights standing on my head in the driver's side footwell verifying and splicing wires. And since it requires a key to start and run, I made the two trips to the nearest dealer required to secure a new key (two hours drive time, each trip), and spent $30 on a new key.

This new key was then installed inside of an aftermarket box made for the job. It consisted of physical bits to hold the new key, a coil, a relay, some connectors, and a small PCB to tie it together. Nothing else. The box's purpose was to contain a key, and be hidden in the depths of the dashboard, with the coil to be switched into the RF circuit by the relay which was itself activated by the aftermarket remote start system.

I discovered that while the stock coil would only work within very close proximity, the aftermarket coil would work from a few meters away. Intrigued, I tested it: Factory ignition-switch coil was useable for couple of inches, aftermarket relay-switched coil was about 3 meters.

In either case, the same OEM keys were used. Results were similar no matter if the new-and-shiny key, or the old-and-oxidized key were used.

So either your general theory about inductive coupling is hogwash (likely), or the particular antennas (which may resemble and also function as coils) can dramatically influence the range at which such an RF identification system can operate.