It's called a lightning rod, although a clock tower and a sufficient length of cable will work in a pinch. Figuring out how to get lightning to strike a DeLorian while traveling at 88mph is left as an exercise for the reader.
What, I must have cheated when I watch this documentary about time travel several years ago.
That's odd, I wasn't going to start producing any documentary until next year. I guess it works. Uh, will work. Will have worked? Damnit, I have a hard enough time trying to get regular-flow grammar right, and now I'm going to have to lear it all over again.
Another great example as to how Tesla has shaped our future. Truly ahead of his time by leaps and bounds.
I know Tesla is a posterboy for the Slashdot community, but I think you mean http://en.wikipedia.org/wiki/Heinrich_Hertz [wikipedia.org]. Hertz was responsible for the discovery that you could generate and detect radio waves.
That lead to the use of radio for communications, which is why such a modern device as the article describes. Tesla envisioned pumping energy into the air via dedicated stations. I don't think he envisioned a situation where we would be pumping so much energy into the air for communications, that there would be usable power as a byproduct.
I find it frightening, not "cool", that such a device is possible, given that my body relies on faint electrical signals.
It's more an electrochemical signal, though, not really anything to do with the energy of radio waves. It's electrical in the sense that it's charged (ions), not in the sense that there's an actual stream of electrons moving along like wires.
So? What does it matter whether it's "an actual stream of electrons moving along like wires"? Electrical signals in biological systems get generated and transmitted by tiny local movements of ions across membranes in order to change local electrical fields, fields that then change the shape of charged molecules slightly. The process is very sensitive to electrical fields, and it can be affected by radio waves.
No, Mahlon Loomis may have invented a kind of long wave radio with his kites, but he had the theory behind it wrong. He was theorezing about layers in the atmosphere that carry a current, while Heinrich Hertz was correctly pointing out that it was electromagnetic waves he was demonstrating. Of course, Heinrich Hertz had the big advantage of knowing James Clerk Maxwell's Theory of Electromagnetism (1879), and he was indeed looking for an experiment that could test if radio waves have the same characteristics
Hertz came up with the math for (transverse) electromagnetic waves.
Tesla was into broadcast power - which he apparently visualized as using capacitive coupling to the ionosphere at high impedance and low frequency) along with conduction in it and the ground below it as the transport medium. That's just electric fields and conduction (or longitudinal waves in the ionosphere's plasma) rather than electromagnetic waves.
It happens that his systems would also generate electromagnetic radiation and propagate power with it. But it's apparently not the particular mechanism he had in mind. (It's also not as efficient as the one he envisioned, since EM waves radiate in all directions and falls off as inverse square, while Tesla's system would essentially pump energy into a resonant cavity and contain it between the ground and the ionosphere until it was dissipated by loads or parasitic resistances).
Now the devices in question in TFA are designed around Hertz's EM radiation rather than Tesla's "elevated capacitance" system. But it was Tesla, not Hertz, who was the big cheerleader for broadcast power using electric and magnetic phenomena (if not precisely Hertizan waves).
They also reduce the power of the signal for everyone else further away from the transmitter, reducing the range of the signals. If deployed widespread into cellphones, this could result in a non-trivial reduction in signal range for broadcasters in the harvested frequency range.
But if they sequester a range of frequencies specifically for wireless power usages....
But if they sequester a range of frequencies specifically for wireless power usages....
No one would use them for broadcast, and thus, no "free" energy to suck up.
Someone would: the people using it for power for their wireless communication devices. They could just have it broadcast dead air (silence) or white noise, though they'd likely figure out a suitable signal that maximizes the power that can be harnessed most efficiently.
Someone would: the people using it for power for their wireless communication devices. They could just have it broadcast dead air (silence) or white noise, though they'd likely figure out a suitable signal that maximizes the power that can be harnessed most efficiently.
Well at that point, you'd just use a conventional charger. I think the point is "free" power - if you have to broadcast it yourself it would be even more expensive than a normal charger.
I'm sorry but that has got to be one of the dumbest ideas I've seen in a while. The lack of power efficiency of this would make a fleet of Hummers look green in comparison.
What you suggest is deliberately sending out EM energy for these devices to pick up and recharge. The EM waves don't travel directly to phones; they travel in all directions from the tower. I don't know the exact equations, but for a cell phone a couple of miles from a tower you can count the zeros in the efficiency numbers. Tesla experimented with this idea, but found that the efficiency made it not feasible over any worthwhile distance.
To respond to grandparent's post, there is the possibility it could result in a non-trivial reduction in signal strength. However, I'll bet our use of aluminum and steel in large quantities for buildings, roads, and bridges have a larger effect today (as one constraint is the size of the device).
What do you think they're going to do, block the entire airways between the buildings with cellphones? Most of the radiation is going to miss the phones *and* the buildings.
"They also reduce the power of the signal for everyone else further away from the transmitter" seems impossible to achieve specifically.
Signal strength varies at 1/square of the distance of the transmitter, there is no possible border defined by "for everyone else further further away from the transmitter" where the signal strength could suddenly drop compared to everyone on the other side of that theoretical border.
I might have missed something although. If so, please clarify how they "reduce the power of
Not really. Cellphones, along with cars, buildings, trees, people, and nearly everything else will already weaken the signal. That's why devices can easily transmit 10 billion* times more power than would be needed by the receiver in a lossless environment. We might as well grab some of that power back out of the air and put it to good use, instead of just letting it turn to heat.
* 10 billion == 100 dB, which is an entirely reasonable attenuation from transmitter to receiver, but the actual multiplier va
6 microwatts from a 1MW antenna - so a "mere" 166000 phones charging off just one transmitter would sink a massive 1W, or one millionth of that transmission power... that sounds trivial to me.
Oh sorry, I was confused 50 milliwatts = Nokia's claim, 6 microwatts = Intel. Hmm.. that implies just 20 cellphones could draw 1W from a 1MW antenna? Still small, but I suppose if hundreds of thousands of users did this in a built-up area it might make a tiny dent. Densely populated areas though tend to be more flooded with multiple antennae transmissions; I still doubt it would make a big difference, considering that cellphones are tiny, and the maximum absorption is the size of a cellphone... you don't
"In some circumstances, florescent light bulbs can draw enough power from a nearby power source to light up." In that case, the nearby power is huge.
From the Slashdot summary: "A team from Intel previously developed a compact sensor capable of drawing 6 microwatts from a 1.0-megawatt TV antenna 4.1 kilometers away." Six microwatts from 1 megawatt is about right.
The estimate of "50 milliwatts" from ambient radiation to charge a cell phone is not. Remember that cell phones are generally inside buildings
Presumably, they're relying on the fact that you're very rarely within range of just ONE transmitter. I'm going to assume that the following maths are bad, but if 1Megawatt gives you 6miliwatts from 4.1Km away, then is it unreasonable to assume that if you're 2.05Km from that same transmitter, you could get 12millwatts? And getting back to the first point, what if there's more than one transmitter nearby? Cellphone stations, radio towers, TV transmitters and so on - it's bound to all add up in some way. No d
Are you all forgetting that this is supposed to be wideband and pull from essentially any/all available frequencies between 500mhz and 10 ghz rather than try to rape a single source for all it's worth?
Yeah, I wonder how much energy passes through the human body in an average developed area. We are transparent to radio waves, but I'd love to see how many micro/milliwatts pass through our skin. I wouldn't be surprised if you add up all man made signal types (ignoring EMF from electricity lines, appliances, and the like) would be less than 1 milliwatt if you're not really near a tower. Sure you could run a long line antenna along your roof to suck up that power, but why bother? You'd probably have to keep i
There was this guy I heard about who lived next door to an AM radio transmitter. The transmitter site was encircled by a cyclone wire fence which made a complete loop with the gates closed. Being an enterprising sort of chap he immediately saw the potential of this arrangement and went to work with power diodes and an inverter. Eventually he got found out because they weren't getting the range they expected and techs were sent in to find out why.
As a very young geek I spent many a night tucked in bed listening to my crystal (actually geranium) radio. But I had a couple of metres of hookup wire for an antenna. This article talks about short wavelength stuff, but I still think you would need a lot of metal to collect a significant amount of power. MY cellphone charger supplies (I think) 300mA.
There is indeed quite a bit of power available at close range since the strength varies at 1/square of the distance.
The local TV station had a desperate guy jumping the fences and climbing on top of the transmitter tower with the intention of jumping. They immediately shutdown the transmitter while police were dealing with him. They finally got him down after 4 or 5 hours although he was exposed for a brief period of time.
Apparently, the guy would have cooked in a microwave like fashion had they left the tr
I did an amateur radio course when I was 16. At one point we did a field trip to the Radio Australia transmitting station in Shepparton. They had old transmitters on display which were just like a normal valve radio, scaled up to the size of a small room. It even had an air gapped tuning gang in the middle with a steering wheel on top. Amazing stuff.
One of their operational transmitters had a gauge showing two kilowatts of reflected power from the antenna. We asked, but the staff wouldn't let us take it home, even though they weren't using it for anything.
You have to extract the dye from the geranium flowers, then use it to build a continuous dye laser which you modulate with the incoming RF signal. The beam is aimed at a very fast response bolometer which provides rectification. Just amplify the signal from a small current through the bolometer to get audio output.
This is an easy project for a 16 year old provided mummy or daddy is a full professor of physics at Stanford.
For a short time, I lived within a couple of kilometres of an AM transmission tower. A pair of vintage high-impedence headphones, a high-power rectifier diode and an earth were all I needed to listen. I was toying with the idea of home-made detectors (galena, iron pyrites, rusty razor blades and a piece of lead etc), but moved before I got around to it.
"Harvesting" is cool and all, but what I've been wondering is why manufacturers haven't been putting solar panels in phones. Such as my Casio G-Shock watch I bought 3 years ago...it has solar panels built into the watch face and a rechargeable battery, and works fantastic. I was looking at the iPhone the other day and thinking they could probably do the same thing with the large surface area of the "face" of the phone. Seems like a logical, relatively easy addition if you ask me.
Well yeah, I thought of that. But if my battery was low and I didn't have a charger, simply leaving it in a windowsill or something would be a pretty handy feature.
Um, I guess that I am technically putting it in a place where the sun doesn't shine. Are you saying that I shouldn't be doing that if I want to take advantage of your proposed solar wonder?
Interesting...the holsters disappeared from here long time ago. They were only somewhat popular at the very beginning of cellphone availability...mostly as a pseudo status symbol.
Mine broke. I bought a cheap replacement, it broke. I don't bother anymore and also keep it in my pocket or on a nearby surface (usually nowhere new sunlight, put possibly under indoor lighting).
Exactly my point, that's why "pseudo". I don't want to see them back, I don't want to be reminded by another thing how many people around me can be described as "douche".
If we take for granted that women then keep their cell at 6 inches from their body and that men keep theirs at 1/4 of an inch from theirs, it means that women get square 6/1*4 = 576 less exposure !!!
My pocket holds my phone at a safe distance already.
Women tend to put them in their hip pocket (when they have one), btw. Men use the front pockets. Not much difference except for the risk of butt-dialing.
I don't know where people are putting smartphones, though. They don't look like they'd be very comfortable in either pocket unless you didn't walk around much.
Wouldn't this draw energy out of the radio signal, thus making it weaker? If this becomes popular in Los Angeles, will a radio station's not be able to broadcast as far because a million people are leeching power off it's transmitting power?
Maybe in the immediate area (size of antenna plus 1 to 2 wavelengths) there will be some signal disruption. But it won't have any affect at a distance. It isn't going to overload the transmitter.
Some numbers for my own comparison... KPWR [radio-locator.com] (A popular Hip Hop radio station in Los Angeles) transmitts 25,000 watts of power. This article claims that it can pull 50 milliwatts. If this technology became standard on all cell phones, 1 million cell phones in Los Angeles would be able to pull a collective 50,000 watts out of the air.
the 1 million cell phones might have to form a contiguous dyson sphere to capture all of the energy from that 25,000 watt power supply. Its a good thing that there's more than just KPWR in this world though, otherwise this nokia guy's idea might never get off the ground.
no more so than a bunch of radios tuning in. If an antenna or chunk of metal is between you and a signal, your signal quality will be degraded. If not, you have a virtual line of sight (or LOS via reflections from the ground, buildings, etc) and can receive like normal. Its like worrying about your lawn receiving less light because your neighbor has solar panels on his roof. If the panels were between you and your lawn, it wouldn't matter if they were generating power, or just made of plywood, your lawn would be in the shade, but since they're not, your grass will be just as green. Its not like these antennas suck up the power, it won't bend the radio waves towards it like a magnetic pole would affect magnetic fields.
Its not like these antennas suck up the power, it won't bend the radio waves towards it like a magnetic pole would affect magnetic fields.
Well, actually they do. It's not at all significant in the grand scheme of things, but antennas do affect (reduce) the signal in the area near them. Antenna designers refer to an antenna's "aperture", the effective area in space from which it can "suck" signal. This is a very abstracted view, but is a useful analogy to understand how antennas affect electromagnetic waves passing near them. It is as if your power-sucking cell phone device creates a radio shadow a couple feet in diameter, instead of only the size of the antenna. Fortunately, the effect only extends a few wavelengths from the antenna at most (the so-called near field region) and has absolutely no impact on receivers outside that space.
Shouldn't be too hard to harvest energy from changes of momentum and orientation, similar to how many mechanical watches have for years been able to wind themselves.
Yeah, that seems more practical when you're in the wild. Especially since the tech is already there - not only mechanical watches are able to wind themselves up, there were also some quartz ones obtaining their power that way.
In the meantime - carrying a phone like Nokia 1208 (ubercheap, standby mode of almost 2 weeks, with the biggest compatible batter probably 3) isn't a big problem when you want to be sure it's working...
See, that's precisely what I thought when I read the title. I thought a wireless power-harvesting phone was a wireless phone capable of power-harvesting, most likely from motion or heat.
Shouldn't be too hard to harvest energy from changes of momentum and orientation, similar to how many mechanical watches have for years been able to wind themselves.
When I was in college in the early 80s we built inductive loops to draw power from the local radio station. We drew enough power to light an incandescent bulb. The only problem was the radio station had remote power meters across their broadcast footprint, and we dropped their power levels significantly for the station to call the college. The funny thing was the college knew exactly what professor to call for this was done repeatedly through the semesters, and the radio station could get a pretty good reading on where the actual drop was coming from per their power readings.
This is useful knowledge to have. Imagine being lost and in need of rescue. If you could create a device that siphoned sufficient power from radio signals to reduce their range, not only would you have power for a beacon but also the FCC would take care of tracking down your location so that you'd stop doing it.
by Anonymous Coward writes:
on Wednesday June 10, 2009 @07:55PM (#28287265)
I call BS on the phone call. I think your prof may have been pulling your legs. For one thing, 60 watts is a drop in the bucket compared to megawatt transmitters, for another, radio waves behave like light waves, there isn't a return loop or any sort of return transmission involved in radio waves.
Agreed. They could put little radio receivers all over the place to measure the signals, but they wouldn't be able to notice the signal drop unless his receiver was practically on top of the other.
Neat story. It would take a ton of wire to get that much power, and the phone call is a total fabrication.
... figure out a way to force people to pay them money for this ambient background radio power? And how are they going to keep freeloaders from stealing it?
What made me think of this was the digital watch I had back in the late seventies that used radioactive tritium for a backlight. It was bright enough on a dark night to use as a flashlight. The only downside was that there was no way to shut it off, a disadvantage when going out to a movie. (Oh, and my left arm fell off. Not really.)
The significant advance since the times of Tesla is that devices take much less power to operate, which is, I think, the real reason broadcast power has become interesting again.
During recent years, there's been significant advances in atomic batteries. So, given that, why not atomic? If a device is typically replaced every three years (or one year if from Apple), I wonder if a tritium betavoltaic (for instance) of sufficient capacity could be made small enough to reside in the device, either powering it directly or charging a conventional battery during periods of unuse.
I'm thinking, watches, almost certainly. Solid state personal music players, possibly. Phones... maybe?
You'll have to select a power company and only get power from them. They'll find some way to track your usage (probably an electric chip on the device which... requires power).
Now to keep power sorted out right, each company will get their own frequency. It will be against the SDMCAaPDA (Super-DMCA and Puppy Disbursement Act) to explain to anyone the concept of an antenna or a diode, as those could be used to steal power.
If it's not coaxial then you just make use of the fact that the moving electric current induces a strong magnetic field outside the cable. Forgot my vector calculus but by placing wires/inductors in the correct configuration it would leech power off the power lines through the magnetic field.
There are two ways to transfer energy wirelessly. Either you couple the receiver to the transmitter using the near field (inductive coupling), or you obtain the energy from the radiated energy in the far field (electromagnetic radiation).
http://en.wikipedia.org/wiki/Wireless_energy_transfer [wikipedia.org]
The power doesn't actually flow IN the wires. It flows in the fields AROUND the wires. It falls off pretty fast. But there's a LOT of power in a high-line so there's a non-trivial amount at ground level outside the right-of-way.
Back in the '60s at EE school I heard a story (from the prof). Seems a farmer who had the local power company eminent-domain a right-of-way through his land to put in a high-line, but still wanted tens of thousands to run a service drop to his farm. This guy got ticked. So he s
Well, if (1) the TV antenna will be pouring out 1MW whether there's phones charging off it or not, and (2) charging your phone from the TV station eliminates one or more permanently plugged-in wall warts per cell phone, then, yes, I would think that's environmentally friendly.
Even if eliminating a couple of wall warts really doesn't help with pollution or anything, I would still like to have this sort of charger in my phone just for the convenience of not having to plug it in as often.
The rule on staying alive as a forecaster is to give 'em a number or
give 'em a date, but never give 'em both at once.
-- Jane Bryant Quinn
Need More (Score:4, Funny)
Wake me up when it can harvest 1.21 gigawatts
Re:Need More (Score:5, Funny)
Re: (Score:3, Insightful)
is left as an exercise for the reader.
What, I must have cheated when I watch this documentary about time travel several years ago.
Re: (Score:3, Funny)
is left as an exercise for the reader.
What, I must have cheated when I watch this documentary about time travel several years ago.
That's odd, I wasn't going to start producing any documentary until next year. I guess it works. Uh, will work. Will have worked? Damnit, I have a hard enough time trying to get regular-flow grammar right, and now I'm going to have to lear it all over again.
Re: (Score:3, Funny)
Crazy Idea - during his time... (Score:3, Insightful)
Another great example as to how Tesla has shaped our future. Truly ahead of his time by leaps and bounds.
Re: (Score:2)
Tesla invented radio?
Re: (Score:2)
Yes?
Re: (Score:3, Funny)
Macaroni?
Re:Crazy Idea - during his time... (Score:5, Funny)
They are asking about radio, not noodles.
Re: (Score:3, Informative)
Whoosh?
http://en.wikipedia.org/wiki/Guglielmo_Marconi [wikipedia.org]
Re: (Score:3, Funny)
Your own reply points out the joke victim made.
Macaroni vs. Marconi
Re: (Score:2)
I made that joke.
Re: (Score:2, Funny)
Re:Crazy Idea - during his time... (Score:4, Informative)
No.
Mahlon Loomis used radio for wireless transmissions in 1868. about 25 years before Tesla.
Tesla created a circuit for doing it, but he wasn't the first and it isn't the only way.
Cool boat, tho'.
Henrich Hertz (Score:5, Interesting)
Another great example as to how Tesla has shaped our future. Truly ahead of his time by leaps and bounds.
I know Tesla is a posterboy for the Slashdot community, but I think you mean http://en.wikipedia.org/wiki/Heinrich_Hertz [wikipedia.org]. Hertz was responsible for the discovery that you could generate and detect radio waves.
That lead to the use of radio for communications, which is why such a modern device as the article describes. Tesla envisioned pumping energy into the air via dedicated stations. I don't think he envisioned a situation where we would be pumping so much energy into the air for communications, that there would be usable power as a byproduct.
I find it frightening, not "cool", that such a device is possible, given that my body relies on faint electrical signals.
Re:Henrich Hertz (Score:5, Informative)
Re: (Score:3)
wrong (Score:3, Insightful)
So? What does it matter whether it's "an actual stream of electrons moving along like wires"? Electrical signals in biological systems get generated and transmitted by tiny local movements of ions across membranes in order to change local electrical fields, fields that then change the shape of charged molecules slightly. The process is very sensitive to electrical fields, and it can be affected by radio waves.
Re: (Score:2)
try Mahlon Loomis
Re: (Score:3, Informative)
No, Mahlon Loomis may have invented a kind of long wave radio with his kites, but he had the theory behind it wrong. He was theorezing about layers in the atmosphere that carry a current, while Heinrich Hertz was correctly pointing out that it was electromagnetic waves he was demonstrating. Of course, Heinrich Hertz had the big advantage of knowing James Clerk Maxwell's Theory of Electromagnetism (1879), and he was indeed looking for an experiment that could test if radio waves have the same characteristics
Re:Henrich Hertz (Score:5, Informative)
Hertz came up with the math for (transverse) electromagnetic waves.
Tesla was into broadcast power - which he apparently visualized as using capacitive coupling to the ionosphere at high impedance and low frequency) along with conduction in it and the ground below it as the transport medium. That's just electric fields and conduction (or longitudinal waves in the ionosphere's plasma) rather than electromagnetic waves.
It happens that his systems would also generate electromagnetic radiation and propagate power with it. But it's apparently not the particular mechanism he had in mind. (It's also not as efficient as the one he envisioned, since EM waves radiate in all directions and falls off as inverse square, while Tesla's system would essentially pump energy into a resonant cavity and contain it between the ground and the ionosphere until it was dissipated by loads or parasitic resistances).
Now the devices in question in TFA are designed around Hertz's EM radiation rather than Tesla's "elevated capacitance" system. But it was Tesla, not Hertz, who was the big cheerleader for broadcast power using electric and magnetic phenomena (if not precisely Hertizan waves).
Crystal radio (Score:5, Informative)
Crystal radio sets [wikipedia.org] harvested enough power to drive an earphone-sized speaker.
In some circumstances, florescent light bulbs can draw enough power from a nearby power source to light up.
Re: (Score:3, Insightful)
They also reduce the power of the signal for everyone else further away from the transmitter, reducing the range of the signals. If deployed widespread into cellphones, this could result in a non-trivial reduction in signal range for broadcasters in the harvested frequency range.
But if they sequester a range of frequencies specifically for wireless power usages....
Re: (Score:3, Insightful)
But if they sequester a range of frequencies specifically for wireless power usages....
No one would use them for broadcast, and thus, no "free" energy to suck up.
Re: (Score:3, Insightful)
But if they sequester a range of frequencies specifically for wireless power usages....
No one would use them for broadcast, and thus, no "free" energy to suck up.
Someone would: the people using it for power for their wireless communication devices. They could just have it broadcast dead air (silence) or white noise, though they'd likely figure out a suitable signal that maximizes the power that can be harnessed most efficiently.
Re: (Score:2)
Someone would: the people using it for power for their wireless communication devices. They could just have it broadcast dead air (silence) or white noise, though they'd likely figure out a suitable signal that maximizes the power that can be harnessed most efficiently.
Well at that point, you'd just use a conventional charger. I think the point is "free" power - if you have to broadcast it yourself it would be even more expensive than a normal charger.
Re:Crystal radio (Score:4, Insightful)
Do you know how incredibly inefficient a power broadcast system would be?
Do you know the rate at which said power broadcast would drop off with regards to range?
Simple physics.
Re: (Score:2, Funny)
Re:Crystal radio (Score:5, Funny)
Re:Crystal radio (Score:4, Insightful)
What you suggest is deliberately sending out EM energy for these devices to pick up and recharge. The EM waves don't travel directly to phones; they travel in all directions from the tower. I don't know the exact equations, but for a cell phone a couple of miles from a tower you can count the zeros in the efficiency numbers. Tesla experimented with this idea, but found that the efficiency made it not feasible over any worthwhile distance.
To respond to grandparent's post, there is the possibility it could result in a non-trivial reduction in signal strength. However, I'll bet our use of aluminum and steel in large quantities for buildings, roads, and bridges have a larger effect today (as one constraint is the size of the device).
Re: (Score:3, Informative)
Well it was a few mW received from a 1 MW transmitter. So.... 12 zeros...
Huh? (Score:4, Informative)
Most of that power would be absorbed by some material, nearby concrete, or ground.
Re: (Score:2)
Precisely, a lot is lost to buildings etc. And now they're talking about harvesting the rest, between the buildings, where people with phones are.
Re:Huh? (Score:4, Insightful)
That's insane.
What do you think they're going to do, block the entire airways between the buildings with cellphones? Most of the radiation is going to miss the phones *and* the buildings.
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How about home and car low range transmissions?
Distribute it.
Re: (Score:2)
So do buildings, mountains, vegetation and people. All of these are going to be absorbing electromagnetic radiation.
Re: (Score:2)
"They also reduce the power of the signal for everyone else further away from the transmitter" seems impossible to achieve specifically.
Signal strength varies at 1/square of the distance of the transmitter, there is no possible border defined by "for everyone else further further away from the transmitter" where the signal strength could suddenly drop compared to everyone on the other side of that theoretical border.
I might have missed something although. If so, please clarify how they "reduce the power of
Re: (Score:3, Interesting)
Not really. Cellphones, along with cars, buildings, trees, people, and nearly everything else will already weaken the signal. That's why devices can easily transmit 10 billion* times more power than would be needed by the receiver in a lossless environment. We might as well grab some of that power back out of the air and put it to good use, instead of just letting it turn to heat.
* 10 billion == 100 dB, which is an entirely reasonable attenuation from transmitter to receiver, but the actual multiplier va
Re:Crystal radio (Score:4, Informative)
this could result in a non-trivial reduction
6 microwatts from a 1MW antenna - so a "mere" 166000 phones charging off just one transmitter would sink a massive 1W, or one millionth of that transmission power ... that sounds trivial to me.
Re: (Score:2)
Oh sorry, I was confused 50 milliwatts = Nokia's claim, 6 microwatts = Intel. Hmm .. that implies just 20 cellphones could draw 1W from a 1MW antenna? Still small, but I suppose if hundreds of thousands of users did this in a built-up area it might make a tiny dent. Densely populated areas though tend to be more flooded with multiple antennae transmissions; I still doubt it would make a big difference, considering that cellphones are tiny, and the maximum absorption is the size of a cellphone ... you don't
Re:Crystal radio (Score:5, Interesting)
What is the CEO of Nokia doing? (Score:2)
From the Slashdot summary: "A team from Intel previously developed a compact sensor capable of drawing 6 microwatts from a 1.0-megawatt TV antenna 4.1 kilometers away." Six microwatts from 1 megawatt is about right.
The estimate of "50 milliwatts" from ambient radiation to charge a cell phone is not. Remember that cell phones are generally inside buildings
Re: (Score:3, Insightful)
Presumably, they're relying on the fact that you're very rarely within range of just ONE transmitter. I'm going to assume that the following maths are bad, but if 1Megawatt gives you 6miliwatts from 4.1Km away, then is it unreasonable to assume that if you're 2.05Km from that same transmitter, you could get 12millwatts?
And getting back to the first point, what if there's more than one transmitter nearby? Cellphone stations, radio towers, TV transmitters and so on - it's bound to all add up in some way. No d
Microwatts, not milliwatts (Score:4, Insightful)
The Nokia press release says they are expecting almost 10,000 times 6 microwatts, all received inside a tiny cell phone that is covered with metal.
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The body is more than 60% water. (Score:2)
The human body is mostly water [madsci.org] mixed with salt, which is conductive and therefore opaque to radio waves.
I agree with you. The total amount of energy is tiny, especially when tiny antennas are used.
Re:Crystal radio (Score:4, Interesting)
As a very young geek I spent many a night tucked in bed listening to my crystal (actually geranium) radio. But I had a couple of metres of hookup wire for an antenna. This article talks about short wavelength stuff, but I still think you would need a lot of metal to collect a significant amount of power. MY cellphone charger supplies (I think) 300mA.
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There is indeed quite a bit of power available at close range since the strength varies at 1/square of the distance.
The local TV station had a desperate guy jumping the fences and climbing on top of the transmitter tower with the intention of jumping. They immediately shutdown the transmitter while police were dealing with him. They finally got him down after 4 or 5 hours although he was exposed for a brief period of time.
Apparently, the guy would have cooked in a microwave like fashion had they left the tr
Re:Crystal radio (Score:4, Interesting)
One of their operational transmitters had a gauge showing two kilowatts of reflected power from the antenna. We asked, but the staff wouldn't let us take it home, even though they weren't using it for anything.
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This would be plain crazy, they usually shut down the transmitter during maintenance. Are they still doing it today ?
I wouldn't like being kept warm in a microwave oven, would you?
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Geranium powered radios (Score:5, Funny)
This is an easy project for a 16 year old provided mummy or daddy is a full professor of physics at Stanford.
Once lived *really* close to AM transmitter... (Score:2)
Why not solar? (Score:3, Interesting)
Re:Why not solar? (Score:5, Insightful)
Where do you put your mobile phone when not in use?
Exactly.
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In Africa, we are used to carry things on our heads on a daily basis, other places do it too ;-)
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Re:Why not solar? (Score:5, Insightful)
I'll stop putting my phone in my pocket the moment someone proves that this "possible harm" is anything more than luddite hysteria.
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Interesting...the holsters disappeared from here long time ago. They were only somewhat popular at the very beginning of cellphone availability...mostly as a pseudo status symbol.
I don't miss them at all.
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Mine broke. I bought a cheap replacement, it broke. I don't bother anymore and also keep it in my pocket or on a nearby surface (usually nowhere new sunlight, put possibly under indoor lighting).
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Exactly my point, that's why "pseudo". I don't want to see them back, I don't want to be reminded by another thing how many people around me can be described as "douche".
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If we take for granted that women then keep their cell at 6 inches from their body and that men keep theirs at 1/4 of an inch from theirs, it means that women get square 6/1*4 = 576 less exposure !!!
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My pocket holds my phone at a safe distance already.
Women tend to put them in their hip pocket (when they have one), btw. Men use the front pockets. Not much difference except for the risk of butt-dialing.
I don't know where people are putting smartphones, though. They don't look like they'd be very comfortable in either pocket unless you didn't walk around much.
TV Antenna = Compact sensor (Score:2)
> A team from Intel previously developed a compact sensor capable of drawing 6 microwatts from a 1.0-megawatt TV antenna 4.1 kilometers away.
Oh..... You mean the high def TV antenna.....
http://www.techonline.com/learning/techpaper/212902041
I do have to say the WISP project sounds neat. They're essentially RFID powered sensors.
http://www.seattle.intel-research.net/wisp/
Question. Won't this weaken the RF signal? (Score:3, Interesting)
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Maybe in the immediate area (size of antenna plus 1 to 2 wavelengths) there will be some signal disruption. But it won't have any affect at a distance. It isn't going to overload the transmitter.
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Re:Question. Won't this weaken the RF signal? (Score:5, Informative)
Re:Question. Won't this weaken the RF signal? (Score:5, Informative)
Its not like these antennas suck up the power, it won't bend the radio waves towards it like a magnetic pole would affect magnetic fields.
Well, actually they do. It's not at all significant in the grand scheme of things, but antennas do affect (reduce) the signal in the area near them. Antenna designers refer to an antenna's "aperture", the effective area in space from which it can "suck" signal. This is a very abstracted view, but is a useful analogy to understand how antennas affect electromagnetic waves passing near them. It is as if your power-sucking cell phone device creates a radio shadow a couple feet in diameter, instead of only the size of the antenna. Fortunately, the effect only extends a few wavelengths from the antenna at most (the so-called near field region) and has absolutely no impact on receivers outside that space.
This is vaguely reminding me... (Score:2)
Of the novella Waldo, by Robert Heinlein.
Harvest motion energy as well (Score:5, Interesting)
Shouldn't be too hard to harvest energy from changes of momentum and orientation, similar to how many mechanical watches have for years been able to wind themselves.
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Yeah, that seems more practical when you're in the wild. Especially since the tech is already there - not only mechanical watches are able to wind themselves up, there were also some quartz ones obtaining their power that way.
In the meantime - carrying a phone like Nokia 1208 (ubercheap, standby mode of almost 2 weeks, with the biggest compatible batter probably 3) isn't a big problem when you want to be sure it's working...
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Shouldn't be too hard to harvest energy from changes of momentum and orientation, similar to how many mechanical watches have for years been able to wind themselves.
Like these guys. [cnet.com]
College experiments (Score:3, Interesting)
Re:College experiments (Score:5, Funny)
This is useful knowledge to have. Imagine being lost and in need of rescue. If you could create a device that siphoned sufficient power from radio signals to reduce their range, not only would you have power for a beacon but also the FCC would take care of tracking down your location so that you'd stop doing it.
Re:College experiments (Score:5, Informative)
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Agreed. They could put little radio receivers all over the place to measure the signals, but they wouldn't be able to notice the signal drop unless his receiver was practically on top of the other.
Neat story. It would take a ton of wire to get that much power, and the phone call is a total fabrication.
Charge it in the microwave oven (Score:4, Funny)
So when are those corporate CEOs going to ... (Score:2)
... figure out a way to force people to pay them money for this ambient background radio power? And how are they going to keep freeloaders from stealing it?
Why not atomic? (Score:3, Interesting)
Why not atomic?
What made me think of this was the digital watch I had back in the late seventies that used radioactive tritium for a backlight. It was bright enough on a dark night to use as a flashlight. The only downside was that there was no way to shut it off, a disadvantage when going out to a movie. (Oh, and my left arm fell off. Not really.)
The significant advance since the times of Tesla is that devices take much less power to operate, which is, I think, the real reason broadcast power has become interesting again.
During recent years, there's been significant advances in atomic batteries. So, given that, why not atomic? If a device is typically replaced every three years (or one year if from Apple), I wonder if a tritium betavoltaic (for instance) of sufficient capacity could be made small enough to reside in the device, either powering it directly or charging a conventional battery during periods of unuse.
I'm thinking, watches, almost certainly. Solid state personal music players, possibly. Phones... maybe?
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Solar cell (Score:4, Insightful)
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They all work, they just don't cure the kind of cancer you have.
Sorry.
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Which leads to more power to harvest.
Which leads to more devices developed to harvest it.
Which leads to more powerful signals.
Which leads to Tesla's dream of sufficient power being broadcast wirelessly to run all of our electric devices. For free! Woohoo!
(Well, either that, or the amount it takes from the signal is so tiny as to not make any practical difference...)
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Don't be ridiculous. This is America.
You'll have to select a power company and only get power from them. They'll find some way to track your usage (probably an electric chip on the device which... requires power).
Now to keep power sorted out right, each company will get their own frequency. It will be against the SDMCAaPDA (Super-DMCA and Puppy Disbursement Act) to explain to anyone the concept of an antenna or a diode, as those could be used to steal power.
But don't worry, they'll make the power broadcast
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If it's not coaxial then you just make use of the fact that the moving electric current induces a strong magnetic field outside the cable. Forgot my vector calculus but by placing wires/inductors in the correct configuration it would leech power off the power lines through the magnetic field.
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And playing Star Wars lightsaber battles using florescent light tubes at night under high power lines.
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Hmmm.. Not sure those people were actually steeling, I open the question for debate.
Can a device like the ones we are discussing actually "pull" more power from the source if present ?
Or would a device like this impact be limited to depraving downstream users from the energy they catch ?
Thanks in advance for answers ! ;-)
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Can a device like the ones we are discussing actually "pull" more power from the source if present ?
Yes, the process uses inductive coupling and works just like a transformer. http://en.wikipedia.org/wiki/Inductive_coupling [wikipedia.org]
There are two ways to transfer energy wirelessly. Either you couple the receiver to the transmitter using the near field (inductive coupling), or you obtain the energy from the radiated energy in the far field (electromagnetic radiation). http://en.wikipedia.org/wiki/Wireless_energy_transfer [wikipedia.org]
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The power doesn't actually flow IN the wires. It flows in the fields AROUND the wires. It falls off pretty fast. But there's a LOT of power in a high-line so there's a non-trivial amount at ground level outside the right-of-way.
Back in the '60s at EE school I heard a story (from the prof). Seems a farmer who had the local power company eminent-domain a right-of-way through his land to put in a high-line, but still wanted tens of thousands to run a service drop to his farm. This guy got ticked. So he s
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Yes, I'm sure it could only power a single device *rolls eyes*
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There's not a limit of one per world. My guess is multiple devices could use it.
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Well, if (1) the TV antenna will be pouring out 1MW whether there's phones charging off it or not, and (2) charging your phone from the TV station eliminates one or more permanently plugged-in wall warts per cell phone, then, yes, I would think that's environmentally friendly.
Even if eliminating a couple of wall warts really doesn't help with pollution or anything, I would still like to have this sort of charger in my phone just for the convenience of not having to plug it in as often.