I'm not Keith, but from what I've read about such systems, this isn't a concern: when they hit the Earth's surface, the microwave beam is very large so it wouldn't have a fatal effect on anyone or anything that happened to cross through it, though it might warm you up a bit. Also, the frequency is pretty important; microwave ovens work because they're tuned to the resonant frequency of water, which most of our food is largely composed of, so it excites the water molecules and makes them heat up. If the beam is tuned to something else, it might have very little effect on lifeforms crossing through it (which is probably the intention, since tuning it for water would make it attenuate too much on cloudy days).
... microwave ovens work because they're tuned to the resonant frequency of water...
Bzzt. Microwave ovens use 2.4GHz because there's an ISM band [wikipedia.org] there. There is no resonance at 2.4 GHz for water [flitetest.com]. If there was your food would explode in the oven.
Boy is that a hard myth to dispel. I have no idea how it started but microwaves work on simple induced eddy currents in the "load", ie, your meal.
Anyone who thinks a microwave oven is tuned is encouraged to show me the stabilized power supply and PLL lock to a stable reference... Guess what? The frequency output of a magnetron is all over the place, because it doesn't matter. It would work just as well at 3GHz too.
Yes, very low energy per given area can ensure safety. But that means absolutely huge receivers are required to get a useful power level.
To receive the kind of power levels we're talking about efficiently, you're going to need pretty damned big receivers. Luckily, they don't have to be large single physical structures - you'll have a rectenna array rather than one big one.
It works fine for every other kind of power plant, except they typically have to be sited on waterways, unlike a rectenna field. You're inventing objections which do not exist.
So do solar panels. The difference is a rectenna array generates 300 W/m^2 for 24 hours a day, while solar panels generate about 200 W/m^2 from 4-6 hours a day in most decent locations. In crappy locations for solar (Seattle, Germany), the energy per land area is *way* higher for space beamed power.
' a rectenna array generates 300 W/m^2 for 24 hours a day
That is possible on the high end, but the topic of this thread was doing so with safe energy levels, and to be safe you need to be a lot closer to the 20 W/M^2 range. You can have a setup with higher levels in the center and lower at the edges of the beam, but when beaming from such a great distance it is difficult to manage such an intensity distribution.
For even 80 W/M^2 average, it would take a receiver surface area of about 3 square miles to produce 600 MW ( the size of a medium fossil plant, just fo
UV radiation is the component of sunlight that burns, it is only a slice of the spectrum. That part of the spectrum is not 200 W/m2.
Microwaves interact differently with the human body than UV radiation, so the comparison would not necessarily be telling. My quick searches showed safe levels need to be in the range I specified, I'll admit I don't know the science behind them.
Standing inside the fence of a rectenna array makes as much sense as going inside the furnace of a coal power plant. In other words, no sense at all.
300W/m^2 is the average intensity on the receiving antenna elements. The intensity outside the fence is much much lower. There's a buffer zone between the edge of the antenna and the fence.
Standing inside the fence of a rectenna array makes as much sense as going inside the furnace of a coal power plant. In other words, no sense at all.
300W/m^2 is the average intensity on the receiving antenna elements. The intensity outside the fence is much much lower. There's a buffer zone between the edge of the antenna and the fence.
That is not the configuration that most articles describe, where the antenna covers the full range down to safe levels. And it makes no sense because if you don't you are wasting a lot of energy falling on what is now a unusable zone outside the receiver, not to mention still taking up all that area which was part of the original point.
These space to earth systems are still a paper exercise. To state that "300W/m^2 is the average intensity on the receiving antenna elements." is not based on anything prov
' a rectenna array generates 300 W/m^2 for 24 hours a day
That is possible on the high end, but
Not even possible on the high end. The diffraction-limited beam spread means that you can't focus the beam to a tight spot, without making the space transmitter correspondingly larger. The Glaser sizing of a kilometer-scale transmitter in space beaming to a ten-kilometer scale spot on the ground wasn't picked at random; those are the sizes you need. And the keep-out zone around the ground receiver is much larger; due to the diffraction wings.
Shorter wavelengths make things better... but if you go too sho
Microwaving power to Earth from space (Score:1)
Re:Microwaving power to Earth from space (Score:4, Informative)
I'm not Keith, but from what I've read about such systems, this isn't a concern: when they hit the Earth's surface, the microwave beam is very large so it wouldn't have a fatal effect on anyone or anything that happened to cross through it, though it might warm you up a bit. Also, the frequency is pretty important; microwave ovens work because they're tuned to the resonant frequency of water, which most of our food is largely composed of, so it excites the water molecules and makes them heat up. If the beam is tuned to something else, it might have very little effect on lifeforms crossing through it (which is probably the intention, since tuning it for water would make it attenuate too much on cloudy days).
Re: Microwaving power to Earth from space (Score:0)
There has been a long history of sailors 'cooked' in the radar's path. RF burns are deep and penetrating.
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Of course radar emits all frequency ranges, and therefore applies equally to all forms of RF emission...
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no, there is documented higher incidence of testicular and eye tumors though
the power per unit area is much HIGHER being near ship antenna than these proposed collection systems
Re:Microwaving power to Earth from space (Score:4, Informative)
... microwave ovens work because they're tuned to the resonant frequency of water ...
Bzzt. Microwave ovens use 2.4GHz because there's an ISM band [wikipedia.org] there. There is no resonance at 2.4 GHz for water [flitetest.com]. If there was your food would explode in the oven.
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Boy is that a hard myth to dispel. I have no idea how it started but microwaves work on simple induced eddy currents in the "load", ie, your meal.
Anyone who thinks a microwave oven is tuned is encouraged to show me the stabilized power supply and PLL lock to a stable reference... Guess what? The frequency output of a magnetron is all over the place, because it doesn't matter. It would work just as well at 3GHz too.
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Yes, very low energy per given area can ensure safety. But that means absolutely huge receivers are required to get a useful power level.
To receive the kind of power levels we're talking about efficiently, you're going to need pretty damned big receivers. Luckily, they don't have to be large single physical structures - you'll have a rectenna array rather than one big one.
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A bunch of little ones all together, a smaller number of bigger ones, what does it matter? It still must cover a tremendous area.
It does take up a lot of space, but you can put it someplace crappy that nobody goes anyway and it doesn't look like much of anything.
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Good luck with that.
It works fine for every other kind of power plant, except they typically have to be sited on waterways, unlike a rectenna field. You're inventing objections which do not exist.
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Oh, by the way, are you aware of the scale of area coverage we are talking about?
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Oklahoma?
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So do solar panels. The difference is a rectenna array generates 300 W/m^2 for 24 hours a day, while solar panels generate about 200 W/m^2 from 4-6 hours a day in most decent locations. In crappy locations for solar (Seattle, Germany), the energy per land area is *way* higher for space beamed power.
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' a rectenna array generates 300 W/m^2 for 24 hours a day
That is possible on the high end, but the topic of this thread was doing so with safe energy levels, and to be safe you need to be a lot closer to the 20 W/M^2 range. You can have a setup with higher levels in the center and lower at the edges of the beam, but when beaming from such a great distance it is difficult to manage such an intensity distribution.
For even 80 W/M^2 average, it would take a receiver surface area of about 3 square miles to produce 600 MW ( the size of a medium fossil plant, just fo
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Why do you need 20W/m^2 for safety? The sun beams 200W/m^2 on sunny days and the worst damage it does is sunburn and deterioration of plastics.
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Microwaves interact differently with the human body than UV radiation, so the comparison would not necessarily be telling. My quick searches showed safe levels need to be in the range I specified, I'll admit I don't know the science behind them.
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Standing inside the fence of a rectenna array makes as much sense as going inside the furnace of a coal power plant. In other words, no sense at all.
300W/m^2 is the average intensity on the receiving antenna elements. The intensity outside the fence is much much lower. There's a buffer zone between the edge of the antenna and the fence.
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Standing inside the fence of a rectenna array makes as much sense as going inside the furnace of a coal power plant. In other words, no sense at all.
300W/m^2 is the average intensity on the receiving antenna elements. The intensity outside the fence is much much lower. There's a buffer zone between the edge of the antenna and the fence.
That is not the configuration that most articles describe, where the antenna covers the full range down to safe levels. And it makes no sense because if you don't you are wasting a lot of energy falling on what is now a unusable zone outside the receiver, not to mention still taking up all that area which was part of the original point.
These space to earth systems are still a paper exercise. To state that "300W/m^2 is the average intensity on the receiving antenna elements." is not based on anything prov
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' a rectenna array generates 300 W/m^2 for 24 hours a day
That is possible on the high end, but
Not even possible on the high end. The diffraction-limited beam spread means that you can't focus the beam to a tight spot, without making the space transmitter correspondingly larger. The Glaser sizing of a kilometer-scale transmitter in space beaming to a ten-kilometer scale spot on the ground wasn't picked at random; those are the sizes you need. And the keep-out zone around the ground receiver is much larger; due to the diffraction wings.
Shorter wavelengths make things better... but if you go too sho
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It's not a concern because such "systems", or rather, fantasies, make no sense whatsoever and have precisely zero chance of ever being built.