Duke Univ. Device Converts Stray Wireless Energy Into Electricity For Charging 216
Lucas123 writes "Engineers at Duke University say they've constructed a device that can collect stray wireless signals and convert them into energy to charge batteries in devices such as cell phones and tablets. The WiFi collection device, made of cheap copper coils and fiberglass, can even aggregate energy from satellite signals and sound waves (abstract). The researchers created a series of five fiberglass and copper energy conductors on a circuit board, which was able to convert microwaves into 7.3V of electrical energy. By comparison, Universal Serial Bus (USB) chargers for small electronic devices provide about 5V of power. The device, the researchers say, is as efficient as solar cells with an energy conversion rate of 37%."
Units! (Score:5, Funny)
Too bad (Score:5, Funny)
This summary had such potential, too.
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Having just read the "article", the units in the summary are a copy-pasta from the article.
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ooohhh... I was way too slow on this. I just chraged in with a sensible reply. /self-whoosh
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My university (and my former one) has the press office e-mail the article to the researcher for editing, comment and approval. It's not that hard.
Re:Too bad (Score:5, Informative)
Ugh. And the unit we want is missing...
Look at Watt they make you give... (Clive Owen)
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It's not totally missing. Max legal wifi xmit power is 100mW at the source. Conversion at the receiver is ~37% efficient. So if you're directly on top of the xmitter, capturing ALL the (generally omni-radiated) energy, you'd get 37mW of power. USB on newer devices is like ~10W.
And of course if you're not capturing 100% of the signal in all directions, and if you're away from the source (remember friends: inverse square power dropoff), then you'll be lucky to get even a mW.
Re:Too bad (Score:5, Funny)
Re:Too bad (Score:5, Funny)
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Seriously, I'm dyne-ing here. Joule have to come up with a better joke next time.
Re:Too bad (Score:4, Informative)
I'm resisting the urge to cry. TFA on the Duke University web site makes the same mistake.
The whole article smells of bullshit. It's easy to generate 7V from radio waves, I have done it myself, but the amount of current is tiny. I could run a small LCD clock or ultra low power microcontroller, but never charge a phone from it. Even an old Nokia dumbphone needs far more power than this or the small solar panel it is compared to can provide. We are in battery backed solar calculator territory here.
It's s shame because there are genuine uses for this kind of technology. Sensors that need to operate in the dark but are very low power, for example. No-one will be charging their smartphone this way unless they get in the order of 100,000x more efficient though.
Re:Too bad (Score:4, Funny)
At least this headline is current.
Re:Units! (Score:5, Funny)
Smoking pot(entiometer) (Score:2)
If you smoke enough pot
How much current do you have to put through a pot [wikipedia.org] to get it to let out smoke [wikipedia.org]?
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7.3V of energy? USB provides 5V of power? Arggh. I think my head just asploded.
It's a chain reaction! Now my head asploded with 7.32 Volts of energy and 10 coulombs of mass.
They could be dealing in metric electrons.
Re:Units! (Score:4, Funny)
Just relax and drink a few amperes of beer. That'll help.
Re:Units! (Score:5, Funny)
And if I scuff my feet while walking across the room, I can generate TWENTY! THOUSAND! VOLTS! OF! ENERGY! Someone hook me up to the power grid!
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If you say so.
ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ...............poof!
crackle crackle crackle
hisssssssssssssss.....
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I can't find the exact comic, and googling shows that the joke is an old one.. but one of the major comic strips in the past few weeks talked about a "static electricity car" where you rub your feet on the carpet when the battery starts to wear down.
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that would probably take too many volts of time
Light-years of time.
Maybe even parsecs.
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Well, the work was supported by a "Multidisciplinary University Research Initiative from the Army Research Office" and, as they say, military intelligence is a contradiction in terms.
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Re:Units! (Score:5, Funny)
You're not helping.
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You're not helping.
Whoosh.
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Measuring charge by measuring potential (Score:3)
Re:Units! (Score:5, Interesting)
Way back in the 70's (early 80s?) I recall a guy who wrapped his whole house in copper wire making large coils to tap the energy from the overhead power cables. He powered his whole house off this which was a mistake. The authorities charged him with theft.
Re:Units! (Score:5, Funny)
Re:Units! (Score:5, Interesting)
Nope, it didn't, since induction was the key, not resonance. ;)
IIRC, the rig involved the peculiar way the tension lines ran in parallel to his roof peak-line. This allowed him to wrap a shitload of long, large wooden dowels with copper wire, then hang them in his attic, orienting them all parallel to the overhead lines. The results would be captured, cleaned-up, and then presented to his home circuitry as household power (120VAC, 60Hz, etc).
Pretty simple, really - but yeah, I remember his being charged with theft as well (though technically, I think nowadays that wouldn't fly as easily, since there have since been plenty of legal precedents made that allow you to make free use of any and all magnetic and radio energy that falls on your property, even if you get it through induction.)
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The trouble with great schemes like that is people always get greedy. Had he not tried to power the entire house with it, but say maybe just moved the circuits for several rooms as load for the induction coil, so that he still used some power from the grid and paid his bill, i bet he could have got about half his power free and they'd have never caught on.
Re:Units! (Score:4, Interesting)
Exactly. For the win? If he had a few solar panels parked on his roof (even if they were never hooked up), it would easily explain why his usage patterns were screwy at times, explain a battery bank, and even (in states with solar tariff credits) allow him to sell the power company their own juice back.
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Pretty simple, really - but yeah, I remember his being charged with theft as well (though technically, I think nowadays that wouldn't fly as easily, since there have since been plenty of legal precedents made that allow you to make free use of any and all magnetic and radio energy that falls on your property, even if you get it through induction.)
He could have said that the intent in planting the coils in his attic was to filter out the harmful EM energy before it reaches his bedroom and endangers his health in sleep. (Frankly, I don't know what to make of a situation when a residential house can extract energy like this. There must be some hygienic limits, aren't they?)
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Maybe our gadgets need to come with cat cradles.
Professor Norton Nimnul has already beaten you to it.
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Power is the total amount of energy available commonly expressed in watts or joules, sometimes horsepower when not specific to electrical current where as volts is part of the measurement used to calculate power when dealing with electrical currents. Amps is the second component of power in which you multiple the amps by the voltage to get the power in watts.
I don't know if you were playing on the mistakes and I ruined it for you or if you didn't catch the issue (it took me a minute to see it). I hope I did
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The article says 7.3v into 70-80 ohms, which means about 0.7 watts. Or, if you prefer energy, that's 0.7 joules per second.
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I can connect the terminals of a 1.5 V AA battery through a 10 megohm resistor but I don't get millions of watts. If that worked I could just disconnect the circuit entirely and have the most powerful powerplant in the world! Until someone didn't connect the terminals on a 9 volt, that is.
Measuring voltage drop across a resistor can give you a measurement of power, but I seriously doubt that's where that 7.3 V comes from. As another poster pointed out, you can't get more than a few tens of milliwatts fro
Free (Score:3)
Free energy from the ether! Not.
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And by the way, if you want to make a display that uses h
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Thus "solar"-powered wallpaper to re-absorb energy from lightbulbs sounds stupid but makes perfect sense, if it could be produced cheaply enough.
Not everyone wants to wallpaper the interior of their house in black. All that "wasted" light reflecting off the wallpaper is what allows you to see the walls.
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Just think with an efficiency of 25%, which is pretty efficient, the reflectance is now 75%
Solar panels do not work that way! Good night!
Resistor (Score:5, Funny)
Hey, I can get -174 dBm/Hz from a 50 Ohm resistor too. Free energy!
Re:Resistor (Score:5, Informative)
Your joke is too subtle without a reference.
http://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise [wikipedia.org]
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Jokes like that are intended for people who get the joke and shouldn't need explanation. :)
I can tell you got it though
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I got it just fine.
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Are you sure that wasn't just coax gain?
microwaves at what field strength? (Score:4, Insightful)
news flash: any antenna provides voltage. usually in the microvolt range. to get enough voltage like they did, say, enough to blow a FET in the front end of a receiver at basically no current, you have to put the antenna in one hell of a strong RF field. a field strong enough to produce enough current to charge batteries or operate CMOS circuits is a field too strong to stay in, according to FCC emission guidelines. so I see this as a project for a grade, and not a "discovery."
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Forget Wireless or Satellite signals, they are orders of magnitude less power than you can realistically use. You would do be much better off pointing your antenna at that 100KW FM transmitter up on the hill.
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People have grabbed enough power out of the air to power their house, living near power lines and using hidden inductor.
Electromagnetic waves induce current in conductors, and bear eat fish and shits fishy shit in the woods! Story at 10!
7.3V? Psh! (Score:3, Insightful)
Also, sure it might be 37% efficient, but do you realize how SMALL the density of RF energy is? The Friis transmission equation [wikipedia.org] gives you some idea: it decreases by the square of the distance away from the source, due to that power spreading out in a sphere. When you start off with only a couple mW of power and an omnidirectional antenna, there isn't much power left to harvest when these tiny receiving "metamaterial" antennas are even just a few feet from an access point.
For $4, you can read the paper (Score:5, Informative)
Here's the actual paper's paywall. [aip.org] All the paper claims is that "A maximum of 36.8% of the incident power from a 900âMHz signal is experimentally rectified by an array of metamaterial unit cells." So they built a rectenna with a waveguide.
Rectennas [wikipedia.org] have been around for decades, and 82% efficiency [ieee.org] (DC watts out / microwave watts into antenna) has been achieved. So 37% is nothing to be excited about.
If you hook up two long wires or plates to a diode, any RF in the vicinity will produce some DC across the diode. This is the principle behind "crystal radios". The problem is that you need big antennas to get much power from ambient RF.
Re:For $4, you can read the paper (Score:5, Interesting)
Actually, the difference here is that they built a rectenna out of metamaterials, specifically a split-ring resonator (SRR) design. I presume their point here is that they came up with a compact rectenna design that can work fairly well at 900 MHz. The paper you referenced with the 82% efficiency used a dipole antenna for 5.8 GHz. The wavelength at 5.8 GHz is something like 50 mm, and they used a 1/2 wave dipole antenna (their length was around 25 mm). The wavelength at 900 MHz is 333 mm, but their SRR design was only 40 mm on a side (a 1/2 wave dipole would have to be 150 mm or so).
I don't think they were making any claims of new physics here, but probably pointing out a design that would be fairly compact and leverage all the 900 MHz EMI flying around. For what its worth, their max efficiency occurred for a resistive load of 70 Ohms, which is a reasonable load for something that you want to power with an energy harvester.
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The wavelength at 900 MHz is 333 mm, but their SRR design was only 40 mm on a side (a 1/2 wave dipole would have to be 150 mm or so).
Their waveguide/horn [duke.edu] is much bigger than 40mm. More like 150mm x 500mm or so. It looks like a reasonable sized horn for 900MHz. They've been able to reduce the size of the rectenna at the focus, but the whole assembly is still big.
Microwave antenna design is weird. Here's some readable background material [w1ghz.org] if anyone cares. Radio hams are routinely able to build 50% efficient microwave antennas. Above that level it starts to get complicated.
Amps? (Score:2)
How many amps are we talking about?
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Approximately zero.
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Grad students (Score:3)
Cell phones? (Score:5, Interesting)
The FCC limits wireless access point RF power to 1 watt.
From the image, I would guess that the metal thingy is 2 feet square, or about 1/3 square meter. I can't tell from the image whether the capture aperture is the profile or the end of the wedge, but let's give it the benefit of the doubt.
Standing 10 meters from a WAP is a sphere with area 4*M_PI*R^2 = 1256 m^2. A 1/3 meter capture aperture would eclipse 0.3/1256 of this, for about 240 microwatts. At 37% efficiency, that's about 80 microwatts. (Am I doing this right?)
Maybe possibly this could power micropower sensors (note: with a 2-foot square antenna on each one).
But a cell phone?
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What you are looking at in the picture is the waveguide they used to test it. The antenna itself is inside the waveguide
The antenna, in this case, is the open end of the waveguide that interfaces with the external EM field. For example, a horn can have a larger aperture, but at the end of it there is only a small probe. It would be incorrect to call the probe "the antenna."
Or you can say it in a different way. An antenna here is anything that cannot be thrown out without hurting the performance. For ex
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The FCC limits wireless access point RF power to 1 watt.
Maybe possibly this could power micropower sensors (note: with a 2-foot square antenna on each one).
But a cell phone?
The answer is obvious. More access points.
radiation too? (Score:2)
if they can modify this a little bit to absorb nuclear radiation, cosmic rays or universal radiation then they may have invented one of the greatest energy technologies since the solar panel.
- being able to clean up nuclear radiation would be great to avoid a "permanent" wasteland. then again, it brings the option of using nukes back on the table.
- absorbing cosmic rays could make space travel safer and possibly satellites lighter.
- if you can absorb universal radiation then you have a solar panel that alw
Re:radiation too? (Score:4, Insightful)
Nuclear radiation doesn't work that way. We have gizmos that turn nuclear radiation into power; they're called radiothermal generators, and work by absorbing the radiation with some material that heats up, then capturing the thermal energy as it flows across a Peltier junction. We power spacecraft with 'em.
But this doesn't make the plutonium less radioactive any faster. Those plutonium nuclei are still going to take their sweet time decaying.
Nuclear power plants take advantage of this, too; heat in the reactor core is heat in the reactor core, and it doesn't matter whether it comes from fission directly or from secondary decay of fission products. But we can't do anything magic to fission products to make them decay into something stable any faster; eventually they get far enough down the decay chain to something long-lived enough that it's not worth trying to harvest the heat they release any more.
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Actually, we can. Neutron bombardment will usually create particles that are less stable, so they take a faster decay chain down to a stable state. It's a tradeoff: your radioactive waste becomes more radioactive, but for less time.
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Absorbing nuclear radiation and making electricity is a done deal, see your local nuclear power plant or talk to RPG generator manufacturer for a couple different methods.
Cosmic ray to electricity is pretty trivial too, what with a cosmic ray being a charged particle (usually proton) and all....
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- being able to clean up nuclear radiation would be great to avoid a "permanent" wasteland. then again, it brings the option of using nukes back on the table.
Crap my tablet isn't working! Quick get the US to go nuke some pissant country so I can get youtube to show me cute kittens again. Oh wait, aren't we already bombing 2nd-world countries to maintain our flow of cheap oil?
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This signal followed me home - can I keep it? (Score:3, Funny)
Engineers at Duke University say they've constructed a device that can collect stray wireless signals
WTF is a "stray wireless signal"? This is a signal without an owner? Slipped out of its collar?
Does this kill reception of wifi? cell? radio? (Score:2)
Looks to me like a somple Yagi antenna... (Score:2)
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A Yagi will not work inside of a waveguide for a million reasons, starting with the fact that there is no flat wavefront to speak of. Yagi antenna works on the principle that individual elements are hit with the flat wave at a slightly different time, which translates to a phase shift at a given frequency. If you build the antenna just right, these phase shifts are mutually neutralized, but only if the wave comes from there, and on a certain the frequency. Then the signals from multiple elements can be com
Not enough energy, missing the point! (Score:5, Interesting)
This doesn't even pass the common sense logic rules if you understand physics. The issue is there's not much energy in these types of radio waves. A cellphone transmits a maximum of around 1 watts, a wifi router 50 milliwatts if you're lucky. By the time the radio waves have reached you their effective power has already dissipated by the square of the distance. Sure you might get a voltage potential that's in the 7 volt range but how's that useful if there's next to no current to do anything. Short of standing under a high voltage power line or next to some high power transmitter which probably wouldn't be safe for your health, this isn't going to work.
People also misunderstand Tesla's work. Tesla's work wasn't that you could just pop up an antenna and get free power. His plans involved putting up a massive transmission tower that would dump power into the air at an efficient frequency. A coil and antenna could then be used to pick up this power wirelessly. Great idea but the issue then is how exactly would you charge for this power when anyone with some know how could build a receiver to grab the "free" power?
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Tesla's work wasn't that you could just pop up an antenna and get free power. His plans involved putting up a massive transmission tower that would dump power into the air at an efficient frequency. A coil and antenna could then be used to pick up this power wirelessly.
Right. When you read his plans, he's taking about a system where a small town is powered by a massive transmitter, each attic is full of antennas, and each house gets one (1) 40-watt light bulb.
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Great idea but the issue then is how exactly would you charge for this power when anyone with some know how could build a receiver to grab the "free" power?
Doesn't seem to stop them from collecting money in the UK for essentially the same thing: https://en.wikipedia.org/wiki/Television_licensing_in_the_United_Kingdom [wikipedia.org]
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Great idea but the issue then is how exactly would you charge for this power when anyone with some know how could build a receiver to grab the "free" power?
Just encrypt the signal.
Reminds me of the time (Score:2)
We stuck a small TV transformer on the local power companies street level distribution transformer..
This feels like we're... (Score:2)
This feels like we're cleaning the crap out of the air :-) But I already see a way to boost sales: Avoid having to wear tin-foil hats, clean the mind-control signals out of the air before they even reach you!
-Matt
Could be worse (Score:2)
At least it seems that >90% of slashdot readers recognized immediately just how stupid the original article was.
Also, these were STUDENTS. Its actually a nice student project to try to make a RF power receiver. Its quite possible that the students DID use the right units and the person doing the press release didn't understand. (and is currently being crucified by his / her management).
One could even imagine applications for micro-power devices used in an environment where there is some RF background bu
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The guy who invented the theremin apparently made passive bugs like that in the 1940s (http://en.wikipedia.org/wiki/Thing_%28listening_device%29).
How do they know that the waves are stray. (Score:2)
Could be they are cutting down on some peoples signal strength.
Attenuating waves and generating harmonics. (Score:5, Interesting)
This device will also interfere with the radio signals. It will both attenuate them and create harmonics due to the rectifiers.
"Raising ground resistance" by having radio-energy-utilizing devices pull power from the air is a non-trivial issue.
Example: A former colleague had, previously, been a plant manager for a factory in a small African country. The plant was in the country's capital, home to their "voice of the fearless leader" high-powered radio station.
One day, while touring the plant, he found a collection of burned-out fluorescent tubes, and had them hauled away. Shortly after he was contacted by his maintenance head, who asked him not to do it again. It seems there was a black market in burned out fluorescent tubes.
The radio station was so strong that, if you put three feet of wire on each end of a burned-out tube it would light up quite nicely from the radio power. A lot of people couldn't afford electricity and light fixtures. But a burned out tube and six feet of wire was readily available. So much of the town's houses were illuminated this way.
So many were, in fact, that the radio signal would no longer reach the edges of the country. So Fearless Leader would send his troops through town when the attenuation got to be a problem, and they'd confiscate and smash the tubes of all the improvised radio-powered lights they found. After each such raid, the people would be down at the plant to buy more "dead" tubes, creating a profitable side-business for the maintenance guy.
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answer is "yes". legality is "no". damaging gear not your own is "likely yes". getting fined or prosecuted is "possible".
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no, shot down because stupidly inefficient. not to mention the dangerous to those near the transmitter but back then who gave a shit.
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I'm sorry but voltage is not the speed of electrons. It is the difference in potential between two points. You can have voltage with absolutely no current. It is equivalent of pressure, not velocity.
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> voltage is not meaningless. It's the speed at which the electronic (sic) charge passes a given point.
Electric charge, or Coulomb, has dimensions: Amp*Sec
The units on Voltage are: kg*m^2/sec^3/Amp which decomposes to: T^2/S^3
Rewriting voltage in terms of Energy = (kg*m^2/s^2), we are left with:
Voltage = Energy / Coulomb
or even
Voltage = Watts/Amps = J/s/Amp = Amp*J/S
There is NO speed nor velocity in that definition.
If you are being pedantic and going to try to