Forgive me if I'm off the deep end or stuck on stupid, but science isn't my forte and I'm not sure how this kind of thing works, but...

If an incoming radio signal can be sent down your car antenna and somehow transformed into music, voices, etc., is there a way to use that same sort of signal to electronic pulse transformation to send a charge into a battery? I was driving around today and was just thinking that it would be neat to take the radio signals, cellphone signals, etc., and sort of pirate part of the signal into a battery or series of batteries to power a car, thus making it independent of fueling stations altogether and reliant only on anyplace there's a signal available. (Juice could be stored in batteries for those wonderful dead areas we always seem to find in the middle of a good joke, crucial moment in a game, important sounding traffic report, etc.)

Feasible, or allergy-induced delusion? I'm holding a dunce cap right now just in case I'm really way off course.

as far as im aware it would take more energy to convert radio waves to electricity than you would be able to harness by doing so.

It would be possible using conventional radio technology but terribly inefficient.

Forgive me if I'm off the deep end or stuck on stupid, but science isn't my forte and I'm not sure how this kind of thing works, but...

If an incoming radio signal can be sent down your car antenna and somehow transformed into music, voices, etc., is there a way to use that same sort of signal to electronic pulse transformation to send a charge into a battery? I was driving around today and was just thinking that it would be neat to take the radio signals, cellphone signals, etc., and sort of pirate part of the signal into a battery or series of batteries to power a car, thus making it independent of fueling stations altogether and reliant only on anyplace there's a signal available. (Juice could be stored in batteries for those wonderful dead areas we always seem to find in the middle of a good joke, crucial moment in a game, important sounding traffic report, etc.)

Feasible, or allergy-induced delusion? I'm holding a dunce cap right now just in case I'm really way off course.

Actually, it's not only possible but doable. There's plenty of RF floating around everywhere so all it would require is a wide-band (in other words not selectively tuned) crystal receiver, a few diodes to build a bridge rectifier and a good, rechargeable battery like lithium - the kind used for laptops and other portable electronics. It wouldn't produce/store a great amount in any give moment but if left connected 24/7 it night well be practical.

Although it work fine, keep in mind that charging such a battery could be done much easier and more efficiently with just a cheap solar cell array.

Incidently, back in the 1950s, it was quite the rage for electronics hobbyists to build such radios that required no external power at all. They consisted of three sections - first a normal crystal detector/turner, second the broadband receiver I just described and the third took power from that to run a single-tube amplifier. Worked great.

The concept of using current radio technology to provide power to run a car has some immediately obvious problems.

Since electromagnetic field strength drops off at the inverse square of the distance from the source, a strong field at the transmitting antenna becomes very weak at some distance away. And the power must be radiated in every direction so that a car at any location can get a charge: it is easy to see that 99 percent of the transmitters power would just fly off into places without a car. That means that the idea might be doable, but would be terribly inefficient.

Well, part of my thought was that radio waves and electromagnetic fields rae given off by pretty much everything in a city, at least. I don't know about deep rural areas. Radio stations, cell phones, cell phone towers, even the boxes that control the traffic lights, not to mention the power lines strung up overhead. They're all over the place. an omnidirectional receiver would rake it in from everywhere. Even when a cop pastes you with a radar gun, it'd throw a charge into your car. You could drive along harvesting all that free energy.

Oh, good grief!!! I totally misread the question. I took it to be asking about powering a radio. I guess it was the part about a critical point in a game, etc. that caught me. Also, I was talking about capturing existing RF, not about trying to transmit power al la Tesla-style.

Perhaps I should be more careful when answering a technical question in the wee hours of the morning when I really should be sleeping. Aaug!

Actually, I read a little while ago about a technology something like this. It's a battery charger that charges with EM waves. That way you can recharge a battery wirelessly. However, as far as I know, it's a low power device. However, some day what you're talking about might become feasible.

I just did a google search. If you're interested in this technology, check this out.
http://money.cnn.com/magazines/business2/business2_archive/2007/04/01/8403349/index.htm

As for using regular energy waves floating around in our atmosphere for powering our cars, I don't think there's nearly enough energy for that to be possible.

Thank god theres not enough energy waves for this purpose or we would all be toast.

Tesla technology.... could do it.

It would set up a standing wave which has a potential in the millions of volts, which would allow machines to be operated by tuning recievers to resonance with the source wave energy.

... however... that tech has not been built.


the existing radiowaves... simply do not carry enough power.

althought... you could possibly, store it up... OVER TIME.

BUT THE charge time for such a system would be to long to run a car with any real use.


the idea is doable... but not for cars...

unless we built massive collection stations, to draw in the energy of radio, light and heat... and then used its massive storage capacity to then charge up cars.... but still.. the power levels are low, and the charge time very long.


-MT

The total power transmitted by the biggest radio stations in America is 50,000 watts. Draw a sphere one mile away from that antenna, its surface area is 4 pi r squared, roughly one hundred million square feet. If you've got a receiving grid three feet square, only one mile away from the source, you have access to about one ten millionth of the energy, roughly five milliwatts. Even if we assume 100% conversion efficiency, which of course is science fiction, there's not much you can do with five milliwatts. As other people have noted, you can power a fairly small radio, not even a boom box, and sound reproduction is a very very low-energy technology.

People have designed, in theory, directional transmitters that have a tight beam and don't dissipate the energy in a spherical pattern. The idea is to put giant solar panels in orbit and beam the electricity they generate, point-to-point, to ground stations. Once we build the space elevator first (see that thread), so the cost of raising objects into orbit becomes affordable, this idea may turn out to be practical. However, whether it would make a serious dent in the world's energy consumption, without casting huge shadows depends on a lot of factors I can't calculate. But hey, China just destroyed an entire ecosystem and a big chunk of its archeology to build a stupid dam that only supplies something like two percent of its electricity--at today's rate of usage, not tomorrow's.

There's no limit to the ill-conceived gigantic projects human beings will undertake just to get into the record books.

Oh wait, if we shade the earth from some of the sun's radiation, it would be a way to combat global warming! :)

I read somewhere about how they would use similar technology to beam electricity to UAVs that loiter in particular areas. The power would not be omni directionally transmitted, but would be beamed either with a parabolic dish or a phased-array toward the UAV, with wavelengths in the high radio, low microwave range, which I belive is still pretty harmless to most people and electronics (microwave ovens run on higher frequencies, closer to infared). The reciever would be a panel of rectifiers, antanae designed to convert electromagnetic energy on a design-specific frequency into DC electrical power. This technology has been succesfully tested with fairly good efficiencies around and beyond 75% from what I remember (read this a few years ago, don't have the sources, sry!).

What I think would be many, many times more practical however, is to forget the beaming of power, and take the rectifier part of the setup to new limits. Rectifiers have elements in them that are sized dependent on the wavelength of EM radiation they are to recieve. For radio and low microwave, wave lengths range from meters to millimeters, and can thus be fairly workable without microscopic componentry. However, if one made a rectifier for visible light, it would need to accomidate wavelengths of nanometer scale. Enter nanotech! If nano-scale rectifiers were to become feasible and workable, we could potentially have solar panels that are not 10-15% efficient, but ballparking 85% efficient!!! One square meter of solar paneling on a car would do the work of about six square meters of traditional panel, probably providing more than enough power to charge batteries and do daily driving. Also, the rectifier-solar-panel would not degrade like current chemical panels, it could theoretically run as long as you wanted, because it's not a chemically dependent system, it's just an array of very small antanaes!

Yeah, pie-in-the-sky, but more likely to happen than a car that runs off residual radio-waves in the air.

....the rectifier-solar-panel would not degrade like current chemical panels, it could theoretically run as long as you wanted, because it's not a chemically dependent system, it's just an array of very small antanaes! ...It is its smallness, combined with the small heat disipated inside that causes the "rectena" to degrade via atomic diffusion.

I do not know what you are speaking of when you imply a conventional solar is a chemical process. As many expect technology to improve the efficiency of silicon solar cells I will briefly explain why they will always (unless using multiple materials with different band gaps) convert at least 80% of the solar energy into heat; (This to also show you it is not a chemical process.)

Sunlight is a set of photons each with different energies. Pure silicon has most electrons in it bound to a particular location in the crystal. Those with the highest energy are in the "valance" band. A few thermally excited ones will have significantly higher energy and are in the "conduction band." Neglecting the effect of "lattice defects" there is a "band gap" between these two bands with electrons. I for get the values but roughly the energy gap between is about 1.2 ev. (In germanium it is less than 1ev as I recall.)

If only photons with 1.2 ev energy fell on the silicon photo cell it could be essentially 100% efficient, but much of sunlight has less than 1.2ev so lacks the energy to non-thermally excite (lift) a valance band electron to the conduction band and can not be used. Also the solar photon with 1.5ev will excite a valence band electron to 0.3ev above the bottom of the conduction band. It will very rapidly "fall" to the bottom of the conduction band, producing heat as it does so. Silicon and to some extent germanium are the two materials best match to the solar distribution of photons, but unless you are converting from a colder source than the sun, silicon is more efficient. When averaged over the solar distribution, silicon can capture (theoretically) 22% of sunlight, but in practice, only about half that has been achieved and then only with very expensive carefully grown / made cells. When the most over all economical cells are made (cheaper to make but less than max efficiency). I think the most economical (over all) cell's conversion efficiency is in the 5 to 7% range, but this from memory and more than 15 years old information. None the less it is never going to be significantly wrong information (because of the physics of the process) and there is no chemistry in the process of converting sunlight to DC energy via solar cells.

Radio cars will never be attractive. Radio is an EM wave as is sunlight. The intensity in the radio spectrum, except very close the radio transmission antenna, is many orders of magnitude lower that that of noon sunlight striking the day side of the Earth. Someone here commuted that one mile from a 50,000 W radio source you have 0.005W/ m^2. (I did not check but it seems about right to me.) The noon sun on cloud less day provides more than 500w/m^2. I.e. a factor of 100,000 times more power per unit area.

Even if one collected sun light for only one hour each 24, the sun provides 4000 times more energy EVERYWHERE ON EARTH (even including all night) than the radio car one mile from the antenna! Thus to match the sunlight energy falling on car's roof top square meter, the radio car's antenna would need to be a square 20* meters on and edge! As the typical residential street is about 6 meters wide, one would need to more than triple all such streets or widen them by factor of 6 if they are not all made one-way only. As economic is very important, anyone who even slightly understands this should agree with the first sentence.

I will not go into many details, but if one wants to drive "city cars" with energy supplied to them externally, a small battery, inductively recharged at stoplights may be practical. Many stoplights already have sensors to detect the presence or absence of a stationary car, waiting to go thru the red light for more efficient control of traffic flow. In contrast to idiocy of the "radio car," which would radiate much more than 100,000W continuously, from each of a set of transmitters located approximately one in every city block even if no car were driving in its zone, the stoplight would have modest losses and only when a car was being recharged. (The coupling between the driven loop and the car's pickup loop could be reasonbly high as these coils could easily be less than 0.1 of their "diameter" (rectangular coils no doubt) apart.

*Later correction: Radio car's antenna should be square about 65meters on an edge. Streets would need to be so wide that 90+% of all houses would need to be destroyed! Thus the radio car has gone from extremely silly idea to an absolutely insane one.

Billy T, my mistake for screwing up the mechanics of solar cells, I never knew much about their actual function, but I hear commercial models usually only last about 10-15 years or so, right? I'd think a nano-rectena array might fair better, but then again, in the nano-scale, quantum physics might have a way of screwing things up. Heck, who knows, but thanks for the synopsis!

That's a cool idea, induction-recharge at stoplights, but then again, for city travel, wouldn't it just be cheaper to plug the car up at a destination? After all, in a city, you're not doing cross-country durations of driving before stoping somewhere. Actually, maybe more practical, rig parking lots with inductors, either under parking spots or on guard-rails directly adjacent to parking spot pavement (for inductors to be mounted on front and/or rear of a vehicle). A car will spend more time in a parking spot than on the street usually with exception to work vehicles like taxis, delivery trucks, etc. which would be a couple battery packs away from better performance, maybe even make the packs interchangable so after a few hours of driving, the taxi driver goes to the garage, slides the near-depleated batt-pack out from the trunk/hood, drops in a freshly-charged one, and is on his way.

Then again, that's free power for anyone in a parking lot, some might be clever enough to put, say, an electrolysis system in a van, park it in such a spot, go home and use the hydrogen to power their house for a few days. Guess a parking meter could control the current... hmm...

Artificial porphyrins are coming out that will make it possible to refill solar cells with the active ingredient.