[Bored chemist]

I had this same idea a couple years ago. The idea was to constantly charge a battery for small devices like a cell phone, flashlight, ect. A friend and I were brain storming ideas of ways to power spacecraft. Although the fact that power cannot be created or destroyed is as far as we know it true. The world and the universe is filled with it. It has to be otherwise there would be absolutely nothing here. Here on earth there is a barrage of EM waves created from everything from all sorts of things like your automobiles ignition system to the neighbors boys toy car to cell phone's and broadcast signals. We are extremely wasteful creatures. The signals are not just all from us! All you need to do is fire up an old dial type radio and turn the knob and you will find static, buzz and squealing between your channels. Some of this noise is from the universe. The universe is filled with EM radiation from over 4 billion years of stars churning, exploding, planets, stars and black holes singing. This is energy and it is free and will be for the life time of the cosmos. No tax can be placed on it. We live in a soup of energy. All we have to do is pick it up and use it.
Even more simple than a solar cell one could gather radio waves and collect the energy from it. Not just one specific frequency but multiple thousands of them at once.
It is easy to say that power from a tiny radio tower would not be sufficient but how about also including the em waves from the sun and the black hole at the center of our galaxy? Now it gets much more interesting.
So if we constructed a small analog receiver that would search for the strongest thousand bands of static and simply convert that to battery power. It would collect energy continuously for the lifetime of the universe. It would be a small amount of power per frame of time but if collected and used efficiently it would be an indefinite collector of the power of the universe. I am not saying that the construction of the device would be an easy task as portions would need to be constructed in the sub micron scale. But if one could construct such a device that could power even a small processor for short periods of time it would be an innovation.
The trouble with innovating something is the need to imagine and create something that has never been done before. Anything else is just doing things the way we have always done them.                   

essentially, the problem with this is that most of the universe is a long way away, and the inverse square law is a killer.
Here on earth, solar power is a practicaal power source. But only during the day. When the sun isn't visible, the quantity of light we get from all the other zillions of stars is barely enough to see by- perhaps a million times less than sunlight.
Once you are a hundred times further from the sun than we are, even sunlight looks pretty weak and in interstellar terms, that's still very near the sun.

Most of the universe is petty poorly lit.
And the same is true for radio waves etc in just the same way.
The background radiation from the universe looks like a  "glow" that's in a way, very similar to the glow from a candle flame or a red hot piece of metal. The red hot bar isn't as bright as the candle because it's a lot cooler.
but it is the equivalent of the glow from something about 270 degrees below zero.
That's not very bright.
Here on earth, if you built a receiver to pick up the cosmic background radiation, it would produce some power.
but,if you pointed it at the ground, it would produce much more- because the Earth is hotter and thus brighter than the rest of the universe.

[alancalverd]

About 60 years ago, Mullard published an interesting circuit for a single-transistor radio receiver that used the energy rejected by the tuned circuit to power the transistor that amplified the accepted part of the signal. It wasn't much more selective than a crystal set,but was significantly louder.

http://www.oddmix.com/tech/cr_1transistor_crystlset.html

[vhfpmr]

It's nearly three years now, and he hasn't been back to show us his patent. Must be proving more troublesome than he anticipated.  []

[alancalverd]

Apropos extracting significant energy from broadcast transmissions, I now have it on good authority that BBC engineers investigating an occasional "black spot" in the polar diagram for the Wrotham transmitter, found a man in a shed powering his lights and tools from a resonant circuit, a couple of miles from the transmitter.

[alysdexia]

How does arithmètic work?

[teragram]

Pardon me for butting in:-

I understand that the "crystal" in a crystal radio is actually the detector (originally "cat's whisker"). To restate the obvious, radio frequency energy is collected by the aerial, the required frequency is selected by the tuning coil and a capacitor, either of which can be variable to select a particular broadcast. The received signal is of course a sine wave at high frequency, well outside audible frequencies. A broadcast signal carries information by modulation of the sine wave (carrier). The function of the crystal (diode) is purely to rectify the sine wave, as does any single diode, by removing (say) the negative halves. This "demodulation" process allows the signal carried by the sine wave to be heard via a very sensitive earpiece. As far as I know the crystal collects no energy at all, merely rectifies the carrier sine wave.
Any comments correcting the above would be welcomed as attempts to improve my understanding.
Without doubt though, the references to the carbon microphone as an energy collector are misleading, as the device is merely a variable resistor responding to audio sound pressure changes, and must be used in series with a battery or other DC supply. Therefore the energy involved is supplied by the current source, not the microphone.