Finally a reasonable and informative comment. Also a retrodirective transmitting array can be used to stay targeted automatically using a pilot signal. Additionally the beam can be defocused if the pilot signal is lost.
Here is an analogy. If a I have a flashlight that puts out a million watts, it would burn you if you stood a foot in front of it right? Now what if you were standing a mile away, you would be receiving much less power and you would be perfectly safe. But the light energy doesn't just disappear, it is spread across a large area. Now, if you build a large collector several miles wide you would absorb all that light. Assuming nothing in between the flashlight and the receiver to block/absorb energy, then you just transmitted 1 million watts a distance of 1 mile to a receiver and it is perfectly safe to stand in the beam because the energy density is so low.
This SPS works the same way. The receiving power density would be less the limits set by the government for exposure to electromagnetic radiation. A large rectenna would collect all that energy over a wide area at >85% efficiency. Walking in the low power density beam is harmless.
Exposure limits: http://www.astrosurf.com/luxorion/Radio/table-power-field.gif Notice the limit is lower at about the point that a half wavelength is about the same height as a human...
You answered your own question. It cant produce a narrow beam, which is the same reason why it cant cook anybody. You have a large diameter beam (kilometers in diameter) at a low power density (similar to the energy density of sunlight) and a huge rectenna array (say, covering many farmers fields by being upheld on stilts). Yes, this works. I have studied it. Smarter people than you or I have studied it. I swear to god NOBODY on slashdot understands power density. Every frikin time this subject comes up its always "its a weapon!"
Now economic viability and possible electronic interference you can go and argue all you want.
Just to clarify, Jimmy Carter created the Department of Energy and the Department of Education in 1977 and 1979 respectively. So the Dept. of Education has been around for only 29 years. Most voters are probably older than that, so it makes me wonder if when people hear that Ron Paul wants to get rid of these departments that these people are all thinking that our education and energy research will all die? Why would they, our education was fine before. Schools are funded by local taxes anyways, run by locally elected people. I can understand the Fed. government wanting some small bit of uniformity in the quality of education, but they shoud for the most part stay out of it like they have done for decades and decades before. Amazingly there are people who think our school systems would end without the Dept. of Education!
Another thing that bothers me are single issue voters. People who might agree with Ron Paul on 70 or 80 or even 90% of the issues but refuse to vote for him because of one thing. It is totally illogical. Now don't get me wrong, I understand that some issues have more weight than others. But its not like the second he is (hypothetically) elected that his positions will be irrevocably etched into diamond or something. I am pro-choice but I agree with Ron Paul on so many other issues, it would be stupid to ignore the parts we do agree on. Another thing is that the President is not king! Electing someone like Paul will not make everything he says law, it will just push us into the right direction (in my opinion). He will still have to argue out his positions with congress and democrats etc...
This is very interesting considering I just heard about http://gnupdf.org/Goals_and_Motivations today. As I understand this project will allow editing of pdfs, a feature which is lacking in current FOSS pdf tools.
These antennas sound interesting, reconfigurable and all that, but I am guessing that their noise performance must be awful. And I mean electrical noise not audio noise for those out there who are confused. Usually in an RF system you want as little noise up front as possible, and noise goes up with temperature. So this is an antenna made of very hot plasma as the very first element in the receiver system.
The solar power satellite was conceived by Peter Glaser around 1968. Its not that the idea was copied, or re-floated, its that the basic research has been ongoing (on and off) all these years. So what would he be laughing about? The fact that basic research that helps Peter Glaser's original idea has continued for almost 40 years? You think this is the first time our government has a taken a look at this? Other governments (especially Japan) have been studying this too.
Disclaimer: I have been doing research for a small automatically pointing microwave wireless power transmission system (60 Watts)
I always wondered, does the car make that whiny transmission noise and exhaust rumble like in the BTTF movies, or was that just movie sound effects? For some reason I always liked that whiny noise:)
I was so dreading seeing this article because I feel I have to stop the spreading of all this miss-information. I always hate to see the first "death ray" type response. I'm sorry it doesn't work like that, complete FUD. You do realize that noon-time sunshine has a power density of about 1000 Watts per meter squared right? Oh noes! Your body could be absorbing a kilowatt of energy! But all you do is feel warmth. With wireless power transmission the power density of the beam would be low, below safety standards set by the IEEE. This means a larger beam requiring square miles of receiving antenna, but it would be harmless to walk through. Certainly no more destructive than sunshine is. As for keeping the beam on target, you could use a retrodirective transmitting array which is a type of phased array that stays locked onto a pilot signal. The geometry of the array does not affect the return beam under this configuration, meaning the array can bend and flex in space but will not deviate from the target. As an added bonus, since the return beam follows the exact same path as the pilot signal, any atmospheric scintillation that the pilot experiences will be undone on the transmitted beam. Add in a defocussing mechanism in case the pilot signal fails, and the whole thing is safe. The biggest problem is constructing a very large array that can output such a high power.
(By the way I am studying retrodirective arrays and have done wireless power transmission over about 15 feet in the lab)
Not really. You can only collect power that falls on the aperture of your receiving antenna, and the aperature is proprtional to the antenna size. Anything not falling on your or anyone else's antenna is absorbed or reflected away. That would mean transmitting a huge amount of power to only receive very little of it. You can either have a very concentrated beam (high power density) and smaller antenna, or a low power density beam and a very large antenna to capture it, or don't capture all of it and the rest is wasted.
Just want to say that things are not as bleak as they seem, recent advances in solar cell technology have pushed efficiencies up to 43%. Solar power density in space is greater than on the surface because of atmospheric attenuation. And end to end microwave power transmission (read DC to DC) was greater than 50% 30 years ago (see my youtube link in a post above). Now rectenna efficiencies (the part that converts RF to DC) are greater than 85% for lower power densities. Unfortunately RF generation is not nearly as efficient.
Uh, farmers do have the ability to buy untaxed fuel. The fuel is dyed so that it can be checked if used on public roads. In fact that is probably what the checkpoint from TFA was for.
This is so incredibly wrong that it makes my brain hurt thinking about it. In fact no one should be able to discuss these types of threads without an EE degree, and even then mosts EE's don't bother to study electromagnetics because its hard, or boring or whatever.
Ok, first off here is a discalimer: I do research in microwave wireless power transmission. AKA we send power (about 40-60 Watts) in a beam of 5.8GHz microwaves to a receiving antenna that converts it back to DC. And guess what, at the receiver you can stand in front of the beam because the power DENSITY (key word) is under the IEEE standard limit for safety. Your calculation above is completely wrong because you forgot a few key things.
1. WiFi will use a lower power if it can, so its not always 100mW 2. Its not always transmitting, the signal is modulated so the average power is lower. 3. And this is the most important, its 100mW delivered to the antenna! Which assuming its isotropic will radiate in all directictions. So as the spherical "shell" of power is radiated the power DENSITY goes down with the square of the distance.
power density = (Power to the antenna)/(4*pi*r^2) (assuming isotropic, AKA in all directions) so for 100mW that is 2.65mW per meter squared at 3 meters away (10 ft away)
For a comparison, noontime sunshine has a power density of about 1000 WATTS per meter squared. (http://en.wikipedia.org/wiki/Solar_power)
So the WiFi is 370,000 times less powerful than daylight when standing 10ft away.
They call them millimeter waves because thats what they are. I work in a microwave lab, and we call them millimeter waves. wavelength (in meters) = speed of light / frequency. So 3x10^8 (m/s) / 30 GHz = 1 mm. So anything above 30 GHz are millimeter waves. Anything above 300 MHz are also called microwaves. So as far as terminology goes, millimeter waves are microwaves, just higher than 30 GHz. Just to clear things up, generally, higher frequencies penetrate LESS into the body (skin effect), EM radiation is NON-ionizing, metal screens to effectively block this should have apertures less than the wavelength of the signal (so less than 1 mm holes, thats pretty small). I don't know what frequency they are using, but I would guess 80-90 GHz. -Brandon
Skin effect
Also microwave ovens operate at 2.45 GHz, This thing probably operates closer to 100 GHz which causes the skin effect to be greater. Also also, 2.45 GHz is specifcally used to vibrate hydrogen bonds in water so a different frequency may not cause so much heating.
The point is not skull penetration, its heating of the fluid in the eyes which I beleive someone else pointed out causes cataracts. Using a wire mesh similar to the screen on the doors of microwave ovens is sufficient to protect as long as the holes in the mesh are much smaller than a wavelength. Also partially conducive material attenuate microwaves, so any comming from the back of the head would be dissipated as heat before reaching the eyes.
Slashdot Mirror
Finally a reasonable and informative comment. Also a retrodirective transmitting array can be used to stay targeted automatically using a pilot signal. Additionally the beam can be defocused if the pilot signal is lost.
Here is an analogy.
If a I have a flashlight that puts out a million watts, it would burn you if you stood a foot in front of it right? Now what if you were standing a mile away, you would be receiving much less power and you would be perfectly safe. But the light energy doesn't just disappear, it is spread across a large area. Now, if you build a large collector several miles wide you would absorb all that light. Assuming nothing in between the flashlight and the receiver to block/absorb energy, then you just transmitted 1 million watts a distance of 1 mile to a receiver and it is perfectly safe to stand in the beam because the energy density is so low.
This SPS works the same way. The receiving power density would be less the limits set by the government for exposure to electromagnetic radiation. A large rectenna would collect all that energy over a wide area at >85% efficiency. Walking in the low power density beam is harmless.
Exposure limits: http://www.astrosurf.com/luxorion/Radio/table-power-field.gif
Notice the limit is lower at about the point that a half wavelength is about the same height as a human...
You answered your own question. It cant produce a narrow beam, which is the same reason why it cant cook anybody. You have a large diameter beam (kilometers in diameter) at a low power density (similar to the energy density of sunlight) and a huge rectenna array (say, covering many farmers fields by being upheld on stilts). Yes, this works. I have studied it. Smarter people than you or I have studied it. I swear to god NOBODY on slashdot understands power density. Every frikin time this subject comes up its always "its a weapon!"
Now economic viability and possible electronic interference you can go and argue all you want.
I put my vote on the neutronium and antineutronium pieces from The Forge of God.
Ok I tried it:
for i in xrange(2000000000):
if (i%1000000) == 0: print i
Its slow, and I stopped it after about 200 Million, but I don't see the problem.
-Brandon
Just to clarify, Jimmy Carter created the Department of Energy and the Department of Education in 1977 and 1979 respectively. So the Dept. of Education has been around for only 29 years. Most voters are probably older than that, so it makes me wonder if when people hear that Ron Paul wants to get rid of these departments that these people are all thinking that our education and energy research will all die? Why would they, our education was fine before. Schools are funded by local taxes anyways, run by locally elected people. I can understand the Fed. government wanting some small bit of uniformity in the quality of education, but they shoud for the most part stay out of it like they have done for decades and decades before. Amazingly there are people who think our school systems would end without the Dept. of Education!
Another thing that bothers me are single issue voters. People who might agree with Ron Paul on 70 or 80 or even 90% of the issues but refuse to vote for him because of one thing. It is totally illogical. Now don't get me wrong, I understand that some issues have more weight than others. But its not like the second he is (hypothetically) elected that his positions will be irrevocably etched into diamond or something. I am pro-choice but I agree with Ron Paul on so many other issues, it would be stupid to ignore the parts we do agree on. Another thing is that the President is not king! Electing someone like Paul will not make everything he says law, it will just push us into the right direction (in my opinion). He will still have to argue out his positions with congress and democrats etc...
This is very interesting considering I just heard about http://gnupdf.org/Goals_and_Motivations today. As I understand this project will allow editing of pdfs, a feature which is lacking in current FOSS pdf tools.
-Brandon
Actually if you don't use quicktime you are immune.
-Brandon
These antennas sound interesting, reconfigurable and all that, but I am guessing that their noise performance must be awful. And I mean electrical noise not audio noise for those out there who are confused. Usually in an RF system you want as little noise up front as possible, and noise goes up with temperature. So this is an antenna made of very hot plasma as the very first element in the receiver system.
I could be wrong, I didnt RTFA.
-Brandon
http://en.wikipedia.org/wiki/Inotify
And before that, now obsolete...
http://en.wikipedia.org/wiki/Dnotify
-Brandon
The solar power satellite was conceived by Peter Glaser around 1968. Its not that the idea was copied, or re-floated, its that the basic research has been ongoing (on and off) all these years. So what would he be laughing about? The fact that basic research that helps Peter Glaser's original idea has continued for almost 40 years? You think this is the first time our government has a taken a look at this? Other governments (especially Japan) have been studying this too.
Disclaimer: I have been doing research for a small automatically pointing microwave wireless power transmission system (60 Watts)
I always wondered, does the car make that whiny transmission noise and exhaust rumble like in the BTTF movies, or was that just movie sound effects? For some reason I always liked that whiny noise :)
-Brandon
I was so dreading seeing this article because I feel I have to stop the spreading of all this miss-information. I always hate to see the first "death ray" type response. I'm sorry it doesn't work like that, complete FUD. You do realize that noon-time sunshine has a power density of about 1000 Watts per meter squared right? Oh noes! Your body could be absorbing a kilowatt of energy! But all you do is feel warmth. With wireless power transmission the power density of the beam would be low, below safety standards set by the IEEE. This means a larger beam requiring square miles of receiving antenna, but it would be harmless to walk through. Certainly no more destructive than sunshine is. As for keeping the beam on target, you could use a retrodirective transmitting array which is a type of phased array that stays locked onto a pilot signal. The geometry of the array does not affect the return beam under this configuration, meaning the array can bend and flex in space but will not deviate from the target. As an added bonus, since the return beam follows the exact same path as the pilot signal, any atmospheric scintillation that the pilot experiences will be undone on the transmitted beam. Add in a defocussing mechanism in case the pilot signal fails, and the whole thing is safe. The biggest problem is constructing a very large array that can output such a high power.
(By the way I am studying retrodirective arrays and have done wireless power transmission over about 15 feet in the lab)
-Brandon
Not really. You can only collect power that falls on the aperture of your receiving antenna, and the aperature is proprtional to the antenna size. Anything not falling on your or anyone else's antenna is absorbed or reflected away. That would mean transmitting a huge amount of power to only receive very little of it. You can either have a very concentrated beam (high power density) and smaller antenna, or a low power density beam and a very large antenna to capture it, or don't capture all of it and the rest is wasted.
-Brandon
Just want to say that things are not as bleak as they seem, recent advances in solar cell technology have pushed efficiencies up to 43%. Solar power density in space is greater than on the surface because of atmospheric attenuation. And end to end microwave power transmission (read DC to DC) was greater than 50% 30 years ago (see my youtube link in a post above). Now rectenna efficiencies (the part that converts RF to DC) are greater than 85% for lower power densities. Unfortunately RF generation is not nearly as efficient.
-Brandon
How about this?
http://www.youtube.com/watch?v=IkVlkSnoGNM
-Brandon
Uh, farmers do have the ability to buy untaxed fuel. The fuel is dyed so that it can be checked if used on public roads. In fact that is probably what the checkpoint from TFA was for.
-Brandon
Hmm, I screwed up my own math... I forgot to square the distance of 3 meters.
That should have been 0.884mW per meter squared at 10ft away.
Which makes it 1,130,973 times less powerful than daylight.
-Brandon
The U.S. legal limit of leaking radiation is 1 mW/cm at 5 cm (about 2 inches) from a new oven.
Quoted from wikipedia.
-Brandon
This is so incredibly wrong that it makes my brain hurt thinking about it. In fact no one should be able to discuss these types of threads without an EE degree, and even then mosts EE's don't bother to study electromagnetics because its hard, or boring or whatever.
Ok, first off here is a discalimer: I do research in microwave wireless power transmission. AKA we send power (about 40-60 Watts) in a beam of 5.8GHz microwaves to a receiving antenna that converts it back to DC. And guess what, at the receiver you can stand in front of the beam because the power DENSITY (key word) is under the IEEE standard limit for safety. Your calculation above is completely wrong because you forgot a few key things.
1. WiFi will use a lower power if it can, so its not always 100mW
2. Its not always transmitting, the signal is modulated so the average power is lower.
3. And this is the most important, its 100mW delivered to the antenna! Which assuming its isotropic will radiate in all directictions. So as the spherical "shell" of power is radiated the power DENSITY goes down with the square of the distance.
power density = (Power to the antenna)/(4*pi*r^2) (assuming isotropic, AKA in all directions)
so for 100mW that is 2.65mW per meter squared at 3 meters away (10 ft away)
For a comparison, noontime sunshine has a power density of about 1000 WATTS per meter squared. (http://en.wikipedia.org/wiki/Solar_power)
So the WiFi is 370,000 times less powerful than daylight when standing 10ft away.
They call them millimeter waves because thats what they are. I work in a microwave lab, and we call them millimeter waves.
wavelength (in meters) = speed of light / frequency. So 3x10^8 (m/s) / 30 GHz = 1 mm. So anything above 30 GHz are millimeter waves. Anything above 300 MHz are also called microwaves. So as far as terminology goes, millimeter waves are microwaves, just higher than 30 GHz. Just to clear things up, generally, higher frequencies penetrate LESS into the body (skin effect), EM radiation is NON-ionizing, metal screens to effectively block this should have apertures less than the wavelength of the signal (so less than 1 mm holes, thats pretty small). I don't know what frequency they are using, but I would guess 80-90 GHz.
-Brandon
Skin effect
Also microwave ovens operate at 2.45 GHz, This thing probably operates closer to 100 GHz which causes the skin effect to be greater. Also also, 2.45 GHz is specifcally used to vibrate hydrogen bonds in water so a different frequency may not cause so much heating.
The point is not skull penetration, its heating of the fluid in the eyes which I beleive someone else pointed out causes cataracts. Using a wire mesh similar to the screen on the doors of microwave ovens is sufficient to protect as long as the holes in the mesh are much smaller than a wavelength. Also partially conducive material attenuate microwaves, so any comming from the back of the head would be dissipated as heat before reaching the eyes.
Whoops, that should be microwaves from 300MHz to 30GHz, and then milimeter waves from 30GHz to 300GHz.
Microwaves occupy the range from 300MHz to 300GHz. After 300GHz they are called millimeter waves.