[EMAIL PROTECTED] wrote:
We don't know all of the "laws" of physics because we have not
explored them all, nor do we BOTHER to do so until we are pushed.
Radio or sound waves AS WE KNOW THEM NOW may not be suitable, but
certain frequencies MAY BE.... People who developed carburation
achieved a breakthrough in fuel delivery, but they probaly never
envisioned using electric fuel injection. People who developed radio
probably were so amazed that it likely took a while to realize that
television was possible.
I've been kindof ignoring this thread for a while, but this is just too
much. As a radio engineer, it amuses me considerably.
The current IEEE personal safe exposure limit for E-field energy between
30-300 MHz in an "uncontrolled environment" (ie: areas which
non-engineers can access) is 0.2mW/cm^2 . In other words, this is the
strongest electromagnetic field that you may produce within that range,
which not coincidentally is where all of FM and VHF falls. Translated
into plain English, an antenna with an active area of 1 square
centimeter would be able to produce 0.2 milliwatts of electricity,
assuming 100% conversion efficiency. But let's think bigger. Assume an
antenna measuring one square meter (that's 3.28 feet square). At the
maximum safe exposure limit, that antenna would be able to drive a load
with a whopping two watts of power. In other words, it might be able to
make one of the lights on your dashboard glow dimly, assuming you car
was parked just outside the fence surrounding the tower.
And don't say "well, antenna technology will improve" because these are
already theoretical maximum values.
It doesn't take a genius to figure this stuff out. Just look at the
power going into the system.
A typical high-power FM transmitter will generally produce between
25-50Kw of RF output power, and through the magic of focused antennas we
can boost this to an effective horizontal radiation of 100Kw maximum.
That's 100Kw right at the "effective center of radiation". Now, ever
heard of the inverse square law? Basically, each time you double your
distance away from a point-source, the energy which previously was
falling upon a surface with the size X is now spread out over a surface
with the size X^2 .
So, build an imaginary sphere with a radius of 1m around a point-source
antenna spitting out 100Kw. The sphere has a surface area of 12.56m^2 ,
so each square meter is receiving 7.96Kw of power. Now, move 1 meter
further away, and the power drops to 1.99 Kw. Move another meter away,
and the power drops to 884 watts. Move 1 more meter away, and the power
is down to 497 watts. And bear in mind, we're only 13 feet down an 800
foot tower.
Now, I'd consider a 150cc scooter to be just about the minimally
practical motorized vehicle for in-town commuting. Depending upon
exactly which manufacturer's spec you believe, such engines generally
produce somewhere in the vicinity of eight HP. That's 6Kw.
So, assuming you are always operating in an area where you are
continuously exposed to the maximum permissible RF radiation at all
times (ie: your commute to work takes you past a hundred full-power FM
and VHF transmitters) you could power your scooter by mounting an
antenna on the back with an area of three square kilometers.
Who volunteers to go first?
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