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I have a car charger for my phone, but I frequently forget to use it. I end up with a dead cell phone and annoyed loved ones. I wanted to come up with an idea that would PASSIVELY charge my phone while driving and without having to remember to remove it from my pocket.
Have you ever built a diode
radio? It powers the ear piece entirely with the power extracted from the radio waves. Have you also seen the early un-tuned radio experiments involving large coils of wire mounted on walls?
I propose a receiver built into a cell phone tuned very precisely to a currently unused radio band. (It wouldn't matter if the band gets interference; it would actually be desired at times.) Mounted within the consumer's vehicle, a matching transmitter would be mounted broadcasting on said frequency in order to charge the consumer's cellular telephone.
The first obvious criticism may be of health concern, but a proper radio frequency may be chosen to alleviate such concerns. This idea need not use radio waves; pure magnetic fields might also prove useful albeit harmful to credit cards.
The second obvious criticism may be that such a device would be inefficient, but with the lower power consumption of cell phones, I believe an efficiency of 5% would be perfectly acceptable. The device could perhaps locate the phone's position within the car (via triangulation of the receiver's heterodyne) and focus the energy toward it.
This is for cordless or mobile phones, as in this idea [neelandan, Jul 02 2008]
||This isn't a new idea and actually a present popular topic as it made last months Popular Mechanics. What they call it is wireless power transmission first publicized by Nicola Tesla around the turn of the century, so you are traveling with a good crowd.
||Your worries about health concerns are probably valid if you travel along the path described. If you transmit power into an enclosed vehicle and only 5% gets where you want it, that means 95% is going somewhere else. Most of the conductive pieces in the car will reflect the EM waves so most of the "lost" energy will be absorbed by the occupants or leave thru a window. The amount that is absorbed by the occupants depends on focus and the ability of the body to absorb the frequencies you are using.
||As a starting point assume people can be 2M tall so will act as a 2M long antenna wire. The shortest non-ballasted antenna is ¼ wave, so as long as you use a frequency whose wavelength is longer than 8 meters (~37.5 MHz) you should be OK. Id suggest Citizen Band in US which is around 11 meter should be fine. Broadcasting at the 5W legal limit on an antenna near the center of the car should reach a coil antenna on the phone with only a passable power loss.
||MisterQED, - actually, Tesla promoted this idea not as recently as you say. It was more like a hundred years prior to that.