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Duke Univ. Device Converts Stray Wireless Energy Into Electricity For Charging
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%."
7.3V of energy? USB provides 5V of power? Arggh. I think my head just asploded.
This summary had such potential, too.
i could make one at 15kV if i want
it'd provide less then 1 pico-amp, but hey. apparently only voltage matters...
Free energy from the ether! Not.
The only thing worse than a Democrat is a Republican.
Hey, I can get -174 dBm/Hz from a 50 Ohm resistor too. Free energy!
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."
if this is supposed to be a new economy, how come they still want my old fashioned money?
I can build up a couple kilovolts by scuffing my shoes on the carpet.
Also, sure it might be 37% efficient, but do you realize how SMALL the density of RF energy is? The Friis transmission equation 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.
Here's the actual paper's paywall. 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 have been around for decades, and 82% efficiency (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.
How many amps are we talking about?
-+-=-+-=-+-=-+-=-+-=-+ *** http://www.mountainfort.com *** +-=-+-=-+-=-+-=-+-=-+-
This is why idiotic grad student posters shouldn't be shown to over enthusiastic marketing types.
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?
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 always has sunlight.
i really hope this tech can be modified. there is a lot of potential for good.
Anons need not reply. Questions end with a question mark.
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?
Wir sind geboren, um frei zu sein - Rio Reiser
Those "stray wireless signals" may well be doing something useful.
Looks to me like a simple Yagi antenna inside of a waveguide. Inside a waveguide, and for an optimum tuned Yagi, the signal would have to be directionally pointed at this setup. Its not like you are going to snag some arbitrary signal that isn't pointed in your general direction. Perhaps if you are eating lunch on a picnic table while standing in front of a microwave repeater, you might be able to charge your cell phone. But then you needed to carry this rig with you while the extra battery option would clearly take less space. Maybe if it cam in an inflatable bubble with mylar deflectors it could be small enough to be practice? If you are not mobile then what is the use case for this?
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?
answer is "yes". legality is "no". damaging gear not your own is "likely yes". getting fined or prosecuted is "possible".
no, shot down because stupidly inefficient. not to mention the dangerous to those near the transmitter but back then who gave a shit.
Voltage is meaningless, and the efficiency number provided is completely beside the point of whether it's USEFUL. The incident radiant energy form the sun is many orders of magnitude more energetic than the output of a WiFi router. I'm glad it's relatively efficient, but efficiently capturing a trivial amount of energy isn't an achievement, it's a hobby.
I'm skeptical this can provide energy to a cell phone even fast enough to keep up with the rate at which standby mode consumes energy.
Er, voltage is not meaningless. It's the speed at which the electronic charge passes a given point. Which means that it can easily provide energy to a cell phone fast enough to keep up -- the problem it that what it doesn't lack in speed, it fails to make up for in volume.
To put it differently, most portable electronics have charging circuits that require 2 amperes of electricity (size of the hose) travelling at 5 volts (rate of travel) for a total of 10 watts (2x5 - amount of actual energy at a given place and point in time), per hour. You're looking at between 3 and 50 watt hours storage in a portable device, and a charging efficiency of around 38%.
From that, you can fill in the variables to see what sort of amperage you need -- for example, a device with a 3 watt-hour battery often uses an average of 1watt/hr; throw in the 38% efficiency rating, and you know how long (rough napkin style) you need to charge during use at an amperage to keep in the positive.
However, ANY amount of charge, as long as it overcomes the inefficiencies, cost of manufacture/parts, and can be stepped up/down as needed, is useful. I'd love to have a collector that could take take in microamp bursts of high voltage (static electricity) and apply those collectively to a charging circuit throughout the day. If it could also absorb radio waves, sound, lightning bolts, direct hits from a kinetic weapon, etc. that'd be great! That means it'd effectively become a radiation "black hole" that I could use to create "walls" and dead spots. Use this material around a room that you want to protect from eavesdropping, while using the directed or reflected energy it absorbs to power whatever's inside. :)
It's even worse considering we're trying to use the reflections to create multiple communication channels, so absorbing all the energy that doesn't go directly to your target might actually impede your communications!
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.
Telsa was undoubtedly a genius but his transmission technique was (and still is) ridiculously inefficient compared to a metal wires. And yes, Edison used propaganda and dirty tricks against Telsa, just like the gas light companies did to Edison, just like the coal miners are doing to the wind/solar farmers right now. It's not a conspiracy, it's just plain old greed.
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
We stuck a small TV transformer on the local power companies street level distribution transformer..
---- Booth was a patriot ----
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
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 but it isn't practical to install your own transmitter. - NSA bugs embedded in building materials for example (thought the power density might be too low even for that). This was supported by the army research office.
> 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 refer to the m/s such as:
V = (N*m) / (Amp*s) = N/Amp * m/s
The N/Amp is NOT equivalent to Coulombs.
Furthermore,
* The units on distance are: S
* The units on velocity are: S/T
* The units on acceleration are: S/T^2
Voltage is the analogous DUAL of acceleration.
Please do some basic dimensional analysis before spouting off such rubbish.
If you smoke enough pot
How much current do you have to put through a pot to get it to let out smoke?
Volts aren't a unit of charge (the proper unit is coulomb or ampere-hour), but potential can be used to estimate charge of a carbon-zinc, alkaline, NiCd, or NiMH battery. The internal resistance of these kinds of batteries varies based on the remaining charge. If a battery has x coulombs of charge left in it, its output potential will be y volts. A more direct relationship between charge and potential can be seen in a capacitor, which puts out a potential roughly proportional to the charge on it.
Could be they are cutting down on some peoples signal strength.
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.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Let's see. The Tesla S battery outputs 375 volts. So if I mount about 50 of these devices on the roof in series can I remove that heavy performance-sapping battery pack?
Oh, wait, I can do a lot better if I just rub a balloon with my cat. Of course, I have to feed the cat, so operation isn't free. And I had to bear the cost of neutering the cat long ago so he wouldn't accelerate unpredictably.
If your cable drop has voltage on it, there's something wrong with your install.
I've got better things to do tonight than die.
37 percent of what?
Let us take a 100 watt transmitter at 900 MHz, the frequency they are speaking about.
Let us assume a dipole antenna on the transmitter. This would be a 2.2 dBi gain
Let us assume this device is placed 100 feet from the transmitter
Let us include ground reflections of the signal for the best case operation
The power at 100 feet will be 0.0037 mW/cm2 (freaky that it came out with 37 in it)
37 percent of that is. around 0.001 mW/cm2
Time has not been entered, don't want to confuse people, just to show there really isn't much power available. Maybe this thing is designed to run in the near field, in which case the whole story is "Big deal". But the idea of you charging our smartphone from available RF energy just hanging around in the air won't be possible or comparable to solar charging until there is as much RF energy hanging around as there is solar insolation.
The shepherds did so well protecting the flock that the sheep no longer believed that wolves existed.
It's just not practical, as the headline and /. imply. I especially like the claim that a device can collect power from orbiting satellites, which of course would be infinitesimally smaller than radiation from the sun or even the moon. Someone forgot the reality check when (and if) they reviewed this article.
Do the antennae on the deKalbs wiggle?
http://en.wikipedia.org/wiki/Waldo_(short_story)
If you'd check the specification sheet that came with your cat. You'd discover the electrical characteristics of fur are not dependent on the observation of its quantum state.
Living or dead. Your cat will perform identically in this application provided your beowulf cluster is designed in a way to minimize hair loss and skin decay.
Unfortunately, Wolfram is unable to give me the weight of a standard cat. But I'd guestimate your feline autostroaker cluster to weigh in similarly to your cars existing battery with the much lower energy density preventing you from driving under any bridges or entering multistory carparks.
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.
Mythbusters tried this and basically got nothing from their rig. Florescent tubes do prove there is a strong static charge produced by high tension lines, but the magnetic field (which is required for induction) is rather weak.
---
DRM is like antifreeze, to the MPAA/RIAA it's sweet, to the consumers it's poison.
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.
It may seem like stray signal until they start stealing your packets!
Unfortunately, Wolfram is unable to give me the weight of a standard cat.
At least you know you can safely assume it to be spherical and of uniform density.
You're overlooking the obvious benefit of the cat-powered car: if it ever rolls over, it will always land on its tires.
Browsing at +1 - no ACs, I ignore their posts. So refreshing!
Reich was targeted ferociously by a government controlled in part by pharmaceutical corporations. True fact. If only those who make our food today were given such scrutiny as Reich, who had his machines and lab destroyed and his papers burned.