Radio Energy Harvested With Inkjet-Printed Antenna

judgecorp writes "Everlasting green energy for RF tags and other low-power devices could be possible as scientists have harvested energy from ambient radio waves using cheap antennas printed by an ordinary inkjet. The scientists, from Georgia Tech, started at 100MHz but have now produced systems which scavenge power at up to 60GHz, allowing them to draw power from most of today's major radio technologies."

Comments

Re:So they're using background radiation only?

[fuzzyfuzzyfungus]

Because it seems like if you want to power these things, they need to use power from a radio source. Which doesn't make them green at all.

They do, indeed, consume some energy from the RF broadcast(in principle, if you really chaffed the place with them, the reduction in SNR might actually be noticeable by devices trying to communicate...) However, there are two other considerations:

1. Particularly in classic broadcasting(less your fancy 802.11-draft-whatever-with-beamforming-and-a-line-of-sight-yadda-yadda smart antenna nonsense) a substantial amount of broadcast power just floats away into the aether, never to be snagged by any receiver. So long as you are(by making receivers super cheap) just burning through some of this formerly wasted power, the energy counts as "free". Not until your piggybacking requires the towers to start cranking it up is their a cost.

2. If the deployment of some distributed-sensor net widgetry is an inevitability(there are legimitate grounds for question at this point; but we generally don't take advantage of them) it has to be powered somehow. The major contenders are A. Lithium primary cells: unless somebody plans on cleaning the whole thing up a decade from now, the delightsome battery goo is going straight into the environment. B. Photovoltaics(in suitably sunlit locations that are OK with sporadic power): the energy generation itself is clean, the manufacturing and some of the components are rather less so. C. Piezoelectrics: not all of the suitable candidates contain lead; but a lot of the common ones really ought to be collected after use.

In our brutally entropic universe, nothing is truly "green"; but it is quite possible that RF harvesting will prove to be green-er and/or more convenient in some applications.

Re:Big numbers

[Fordiman]

I wonder what the nominal ambient flux actually is (i.e., W/m^3), and how much of it they're actually capturing.

FCC says?

[HTH NE1]

Which reduces the quality of the radio signal for anyone downwave from the power harvesting site. It effectively steals power from the transmitter intended to provide service to those more distant than you from the transmitter.

Permissible is interception for purpose of reception of the signal, such as a crystal radio, at a small scale. Not permissible is powering your lights, robots, or anything else that does not simply turn the signal back into its intended form.

It may be permissible to leech power from a WiFi signal in order to power a device that will use the data in the stream if you could be sure you're stealing power from signals intended for you and no one else.

But AFAIK the rules are to protect man-made signals, unless the scientific community have petitioned to protect their ability to study background radiation by preventing the same harvesting of power from natural radio sources, else they'll have to do their studies elsewhere.

Re:FCC says?

[Kral_Blbec]

Incorrect. It doesn't reduce the signal quality for anyone downwave from the transmitter. It only reduces signal quality for those in the direct path of travel in a line intersecting the transmitter and this power harvesting antenna. It can only interact with waves that travel directly through it already. It doesn't alter the path of travel of nearby waves to suck them in. In this it is just like any other receiving device, meaning it wouldn't effect signal quality any more than having an equal number of radios/TVs.
Considering the height of radio/TV towers, the direct path of travel is mostly going to be into the ground anyway. The energy this would pick up would be wasted anyway.

Re:dumb question

[bradgoodman]

I keep equating it to the story about standing next to a transformer at an electrical substation - or high-power line with a coil, and trying to leach power from it. (I'm botching/simplifying the idea here)

One might argue "I'm not stealing power, because I'm just letting the EM field that the line/substation/coil is already sending through the air - go through my coil).

However, the field's emitter does have to work harder to generate the power which the consumer is using. If this wasn't the case, a power generator on one side of a transformer would be uneffected by (and see no load presented by) a load connected to the other coil on the "load" side of the transformer.

So - I would imagine it working the same here - the transmitter *would* have to "push harder" to accommodate people leaching power from it in this way.

Did I just make any sense? :(