Is wireless power possible?

Is it possible for the power source of a device to be transmitted remotely? For instance, to use radio waves to create the current needed to run your electronics, or something.

Tesla Coils
Solar Power Satellites

Possible, yes.

Practical, probably not.

crystal radio converts radio waves to power but very low power levels. Solar pannels also do this. Microwaves have a good shot at transmitting sizable amounts of power wirelessly.

Sure. Like the EZPass transponders at toll booths.

Sure, it can be done. But not safely and efficiently for most applications. Of course, Tesla never acknowledged this, but that’s another story…

I know that NASA has done some actual prototype work of transmitting large amounts of power between satellites using microwaves. But if you are thinking of omni-directional, no line of sight needed, bankrupt Duracell, yes possible, but extremely unlikely.
I mean, good God! We live in a world were people are suing over the infinitesimal amount of power coming out of there cell phones!

Back in 1987 some Canadian scientists (no, it isn’t an oxymoron) used microwaves from an earth station to power an aircraft. Here is a link to it.

thoses transponders have batteries in them and when they die the e-z pass doesn’t work anymore. The e-z pass tag has an expected life of 10yrs but the earlier ones are failing before that.

As mentioned wireless power is possible. In fact, it’s all around you right now in the form of microwaves, radio waves and solar radiation. However, these are all relatively low power and you wouldn’t be able to capture enough to do much of anything useful (you can run a calculator or watch today with nothing but light but not much else).

The problem is most living things wouldn’t tolerate power levels in the ambient environment sufficient to run, say, a car. Enough microwave energy directed at a car sufficient to run it at 60 mph is likely to cook the occupants and anything in between the broadcasting tower and your car.

In addition, wireless power is not a very efficient way to transport energy. Air is a pretty good insulator to electricity. Other forms of radiation tend to attenuate quickly in the atmosphere. If your power is omnidirectional you are beaming a ton of energy to nothing in particular and wasting it (i.e. straight up into space or even horizontally into space). A better method is to focus your energy in something like a laser beam. Again, however, your laser beam will attenuate quickly. If it starts raining or snowing or foggy it gets worse. God help anything that crosses that beam. Lasers are generally invisible and at the very least you are likely to waste a bunch of birds with this method.

By the time you add up the cost of closely spaced receiving towers to continually boost your signal, the amount of power lost both in transmission and in converting energy to laser to energy to laser ad nauseum and you get far more expensive than just stringing power lines and maintaing those. Also consider that you are being more efficient with power lines in your power usage so you don’t dwindle the earth’s finite resources as quickly.

[sub]NOTE: Electricity running along power lines also attenuates albeit not as quickly as it would in air. Superconductors are the hoped for answer to that issue.[/sub]

What about the Mobil Speedpass? Those tags look a bit small to house electronics and mini watch batteries and still last any amount of time. I’ve had one since they offered them a few years back and it’s never failed on me.

Hmm. According to How Stuff Works, you’re right. I always thought that the radio waves induced a current in the EZPass transponder that, in turn, powered (rather than just signaling the battery-run device to start working) the transmission of the vehicle’s ID back to the toll booth’s receiver.

These work without a battery:

can reflect and concentrat sunlight to the earth, where it can be transformed into other types of power.

…Or, if we were feeling spunky, convert two or three continents into smoking craters. I love it! :stuck_out_tongue:

This puzzles me a little. Is the power to the towers to “continually boost your signal” sent by wire?

These devices work at short range. No one doubts that power can be transmitted over any distance within the visible universe (galaxies transmit power in the form of EM waves to us from billions of light years away). But as a way to operate an electric power utility it just won’t do.

I recall a plan to put many electromagnets in roads as a way to recharge electric car batts - just in the thought stage though.

I really don’t know what you have in mind from the OP. If it is far away and in line of sight you could use microwaves (like that canadian plane)- if it’s in the sun you could use solar (like the mars rover pathfinder) - if it’s to power your cellphone w/o batts then I don’t see it happening but I offer this alternative- have shorter range recharge areas (perhaps on trains, offices) much like the electromagnets imbeaded in the roadway. YOu will still need some sort of battery.

I’ve designed RF-ID (Radio Frequency Identification) components into systems. They come in many different flavors. Some are completely beam powered. The incoming RF “beam” charges a capacitor (really just a couple of plates of metal that act kind of like a very small battery in some ways) which then powers the small integrated circuit that sends back the coded pulse stream that the reader then interprets to get the “number” from the tag. I imagine that EZPass and such use the battery powered variant because it responds a little bit faster (you don’t have to wait for the capacitor to charge up) and also because it will work over a longer distance. If you have to rely on beam power then you don’t have as much power available to transmit the codes back to the receiver, which means that the overall functional distance of the thing is less.

The receiving antenna inside an RF tag is usually just some creatively arranged circuit traces on the printed circuit board, not really an external antenna at all. The capacitor can likewise be fabricated into the circuit board. All that’s left is the silicon smarts, which allows the guts of the thing to be made quite small. If you have to add a battery it gets a bit bigger, but it’s still pretty small.

RF ID tags are used in everything from shipping containers to railway cars to cattle. They aren’t just for toll booths. At work we use them for security access cards.

As was previously mentioned, this technique is only good for low power applications.

yes its called a transformer (though only over short distances). The same principle was tried (used?) in pacemakers. The problem is that one doesn’t really want wires coming out of a patient, so an induction coil was fitted indide, powered by a coil outside.

Gotta disagree with one comment up there, which is that wireless transmission is inefficient because of high resistance. Resistance is only really important for DC power transmission, which no one does anyway.

The important feature of wires is that they channel the power along a line from point A to point B. If you transmit without the “guides”, the wires, the power just spreads out from the transmission point, in a spherical wave if you make no effort to focus. Hence point B gets only a small fraction of the total power transmitted.

You can focus, of course, and get the power flowing along (more or less) a straight line, e.g. with a maser or laser, but then the problem is you can’t go around corners. In fact, if we had originally transmitted power by radio, as well as TV, someone would probably have invented “cable” electricity, just like cable TV, and for the same reason: because you can channel the product point-to-point much more efficiently.

Also, the comment about the power flux is a bit of a red herring. Power density alone does not determine the harmfulness of radiation. After all, the Sun dumps of order 300 watts per square meter of radiation on us every day. But of course, it’s visible radiation. If it were X-rays, we’d have a problem. Each photon in really dangerous radiation needs to have enough energy to initiate chemical reactions in the body, i.e. cause tissue damage, and that in essence means the frequency must be high, typically UV (sunburn) to X-ray (radiation poisoning) and up. Radiation with wavelengths in the visible down to microwave are absorbed by the body, and their energy released as heat, so these can cook you at high enough power fluxes. But radiation at longer wavelengths is not absorbed by the body at all. So far as anyone knows, you can stand in front of a huge hydroelectric generator radiating vast amounts of 60 Hz radio waves, and nothing will happen.

However, there’s a catch. You get the best focussability of your radiation at small wavelength, i.e. high frequency. Microwaves are easier to focus then radio, and light better still. So the more you try to focus your radiation, the more you will approach the danger situation where the frequency of radiation would become harmful.

The right solution to your problem (wireless power) is batteries, because you rarely (except in space, maybe) need a permanently wireless power source. Your body, for example, is essentially battery-powered. You top up the chemicals it uses to generate power 3 times a day, typically, with Big Macs and fries. But this last statement makes clear that artificial batteries are very poor batteries qua batteries. There is no comparison between the power storage ability of a lead-acid car battery feeding an electric motor and, say, a hundred pounds of fat feeding the metabolism of a hibernating grizzly all winter long.

Hence I believe the most promising mobile power solutions in the offing are those that crudely duplicate living metabolism, in that they consist of cleverly microengineered cells that run chemical reactions to generate electricity or motive power.