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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.
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.
Approximately zero.
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?
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
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?
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.
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.
"They redundantly repeated themselves over and over again incessantly without end ad infinitum" -- ibid.
If the early nuclear reactors were not built with the dual role of creating bombs in mind, then there would be no wasteland. Pebble bed reactors are one example of clean, failsafe nuclear power. The basic principle in TFA has been know for centuries, I learnt it the 60's as child when dad helped me build a crystal radio. The material with the properties you describe is also well known to electrical engineers, they call it "unobtanium".
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
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.
> 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.
less than 12 with right ship and pilot, is that fast enough for you, old man?
There is no right to feel safe thru security vaudeville at the expense of everyone's freedom, privacy and tax money.
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.
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
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.
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!