[Merged] Wireless Power - I am confused...

CardZeus · 23rd July 2009, 06:57 PM

MIT's been developing this for a while and it is featured on the BBC website today http://news.bbc.co.uk/2/hi/technology/8165928.stm

What I 'don't get' is the following:

From the article, it sounds like a loosely coupled resonant transformer. That would be rather inefficient and generate huge problems with the stray fields coupling to everything else (humans, conductors, etc.). Not to mention that this would completely wipe out radio communications at the respective frequencies (and the cited 30 MHz band is smack in the middle of the shortwave region with worldwide ionospheric propagation, being heavily used by e.g. maritime and aeronautic communications).

Keep in mind that electrical energy in ordinary cables is not carried by the wires either, but the electromagnetic field between them. The purpose of the wires is to guide and confine the EM field for very good reasons.

Anyone care to address my comments??

Towlie · 23rd July 2009, 07:24 PM

Actually, the wavelength is 30 meters, which corresponds to a frequency of 10 MHz. Your article mentions that shorter wavelengths (higher frequencies) would not work.

Edit: Wikipedia has more on this "WiTricity^WP":

Quote:

The researchers suggest that the exposure levels will be below the threshold for FCC safety regulations, and the radiated-power levels will also comply with the FCC radio interference regulations.

wackyvorlon · 23rd July 2009, 07:25 PM

It sounds like the work that Tesla was doing. My understanding is that the goal of Tesla's power transmission system was to use ground waves. Mind, the frequencies he was using were much, much lower than 30MHz.

Eggs Ackley · 23rd July 2009, 07:48 PM

It's intended for near-field applications and probably has a very small effective aperture for radiation. The radiation fields might be negligible, while the near fields not. Radiation field power falls off as inverse square while near-field power density falls off as inverse fourth power. That is falling off fast with distance but conversely getting much bigger up close.

The article should say "near-field" where it says "far field".

Towlie · 23rd July 2009, 08:06 PM

Originally Posted by Eggs Ackley

The article should say "near-field" where it says "far field".

Actually, I think it's worse than that. It seems to me that the whole section titled Safety Concerns is garbled:

Quote:

Safety concerns

Mr Giler was keen to stress the safety of the equipment during the demonstration.

"There's nothing going on - I'm OK," he said walking around a television running on wireless power.

The system is able to operate safely because the energy is largely transferred through magnetic fields.

"Humans and the vast majority of objects around us are non-magnetic in nature," Professor Soljacic, one of the inventors of the system, told BBC News during a visit to Witricity earlier this year.

It is able to do this by exploiting an effect that occurs in a region known as the "far field", the region seen at a distance of more than one wavelength from the device.

In this field, a transmitter would emit mixture of magnetic and potentially dangerous electric fields.

But, crucially, at a distance of less than one wavelength - the "near field" - it is almost entirely magnetic.

Hence, Witricity uses low frequency electromagnetic waves, whose waves are about 30m (100ft) long. Shorter wavelengths would not work.

Pantaz · 23rd July 2009, 08:20 PM

Originally Posted by CardZeus

MIT's been developing this for a while and it is featured on the BBC website today http://news.bbc.co.uk/2/hi/technology/8165928.stm

What I 'don't get' is the following:

From the article, it sounds like a loosely coupled resonant transformer. That would be rather inefficient and generate huge problems with the stray fields coupling to everything else (humans, conductors, etc.). Not to mention that this would completely wipe out radio communications at the respective frequencies (and the cited 30 MHz band is smack in the middle of the shortwave region with worldwide ionospheric propagation, being heavily used by e.g. maritime and aeronautic communications).

The BBC piece is typical of science reporting -- it leaves out big chunks of relevant information. The company's website isn't much better. Mostly marketing-speak and techno-babble.

You are basically correct, it is a resonant transformer. Popular Mechanics had a short article about it in 2007, describing a demonstration:

"WiTricity exploits a phenomenon known as magnetically coupled resonance, which allows two objects resonating at the same frequency to exchange energy efficiently. The team was able to wirelessly power a 60-watt light bulb using a pair of 20-in.-dia. copper coils. Drawing power from an electrical outlet, the source coil created a magnetic field, which was 7 ft. in diameter, transmitting at a frequency of 10 MHz. (Many cellphones, by com-parison, operate at 2 GHz.) Seven feet away, a receiving coil was also resonating at 10 MHz, pulling enough energy from the field to power an attached light bulb."

There is also a Wikipedia page.

As for this...

Originally Posted by CardZeus

Keep in mind that electrical energy in ordinary cables is not carried by the wires either, but the electromagnetic field between them. The purpose of the wires is to guide and confine the EM field for very good reasons.

I believe this is only true for high-frequency AC. (It's been a long time since I learned AC theory, but your description doesn't sound right to me.)

technoextreme · 24th July 2009, 05:20 AM

Originally Posted by Pantaz

As for this...

I believe this is only true for high-frequency AC. (It's been a long time since I learned AC theory, but your description doesn't sound right to me.)

Nope. All AC currents travel by EM radiation. The effects don't really become noticable unless you use power lines but he is right.

Careyp74 · 24th July 2009, 05:52 AM

My new toothbrush is recharged this way. If anyone is interested it is a sonicare that I got at Bed Bath and Beyond. It was in the beyond section

Seriously though, it is pretty cool.

Towlie · 24th July 2009, 05:56 AM

Originally Posted by technoextreme

Nope. All AC currents travel by EM radiation. The effects don't really become noticable unless you use power lines but he is right.

If you're implying that alternating current travels by a fundamentally different means than direct current, that can be illustrated to be absurd by imagining that the frequency is gradually reduced. As it falls from 60 Hz to 1 Hz, and then to one cycle per minute, per day, and then per week and per year, it's still technically AC but looks more and more like DC. Tell us then, at what point during the frequency reduction does the energy stop traveling by radiation and begin flowing through the conductors, as it does with direct current?

zerospeaks · 24th July 2009, 10:13 PM

Quote:

Necroloth and other readers sent in the story of Witricity's latest demo at the TED Global conference in Oxford, UK. The company is developing a system that can deliver power to devices without the need for wires. The idea is not new — electrical pioneers Thomas Edison and Nicola Tesla assumed that power would be delivered wirelessly. The BBC quotes the inventor behind Witricity's tech as saying that Tesla and Edison "...couldn't imagine dragging this vast infrastructure of metallic wires across every continent." eWeek Europe notes some hurdles the technology must overcome: "The 2007 experiment it is based on had an efficiency of only around 45 percent, but [Witricity's CEO] promised power delivered wirelessly would start out 15 percent more expensive than wires, and improve on that." Intel has also demonstrated wireless charging.

Story from slashdot!

So now I ask a simple question.
Why are we just now "discovering" wireless power, when Tesla had it working in 1900?

Small Town Jesus · 25th July 2009, 04:38 AM

Originally Posted by zerospeaks

Story from slashdot!

So now I ask a simple question.
Why are we just now "discovering" wireless power, when Tesla had it working in 1900?

I was asking myself the same question as I was reading about this too. As a non scientist a possible answer that came to mind was that maybe the technology to fine tune the resonance has only just been achieved. Good to see Tesla's dream still alive though.

Another link to this story here.

jay.tarnoff · 25th July 2009, 06:01 AM

NPR covered this yesterday with an interview from an individual from Wi-tricity. I was wondering the exact same thing. Is there some difference between their claim for what I think they called "micro magnetic resonance" or something similar and Tesla's original ideas?

bjornart · 25th July 2009, 06:07 AM

The differences are in efficiency and not-making-everything-metal-in-the-vicinity-hot-ency.

ugot2bekidding · 25th July 2009, 11:07 AM

I remember reading somewhere that Tesla's idea was shot down because the electric companies were afraid of the potential for people to receive free electricity.

Pantaz · 25th July 2009, 12:14 PM

There is already a thread on this...
http://forums.randi.org/showthread.php?t=149007

wackyvorlon · 25th July 2009, 02:12 PM

Originally Posted by ugot2bekidding

I remember reading somewhere that Tesla's idea was shot down because the electric companies were afraid of the potential for people to receive free electricity.

There were a couple difficulties. It took time to develop the technology, and Tesla wasn't the best businessman. As I recall, in the end the tower at Wardenclyffe was cut up for scrap to pay off his debts.

Pantaz · 25th July 2009, 03:59 PM

Originally Posted by wackyvorlon

Originally Posted by ugot2bekidding

I remember reading somewhere that Tesla's idea was shot down because the electric companies were afraid of the potential for people to receive free electricity.

There were a couple difficulties. It took time to develop the technology, and Tesla wasn't the best businessman. As I recall, in the end the tower at Wardenclyffe was cut up for scrap to pay off his debts.

... And it's horribly inefficient

BenBurch · 25th July 2009, 05:22 PM

Originally Posted by Towlie

If you're implying that alternating current travels by a fundamentally different means than direct current, that can be illustrated to be absurd by imagining that the frequency is gradually reduced. As it falls from 60 Hz to 1 Hz, and then to one cycle per minute, per day, and then per week and per year, it's still technically AC but looks more and more like DC. Tell us then, at what point during the frequency reduction does the energy stop traveling by radiation and begin flowing through the conductors, as it does with direct current?

Well, now, depends on what frequency you are talking about. Microwaves have different behaviors;

http://www.allaboutcircuits.com/vol_2/chpt_14/8.html

The Man · 25th July 2009, 06:29 PM

Originally Posted by BenBurch

Well, now, depends on what frequency you are talking about. Microwaves have different behaviors;

http://www.allaboutcircuits.com/vol_2/chpt_14/8.html

Indeed transmission lines are inherently practical for AC energy down to zero frequency and thus DC. Waveguides and antennas have practical physical limits relating to half wavelength. For a 60hz power system that works out to be about 155 miles. That’s a big waveguide or antenna. Making transmission lines far more physically practical at frequencies under a few hundred cycles per second. Transmission distance is also an important factor. For a 1GHz signal to be received with a power of 1nW at a distance of 30 miles away, for a transmission line would require a 10¹⁵⁰⁰ nW input (15,000-dB loss), a wave guide would require a 10¹⁵⁰ nW input (1,500-dB loss) and an antenna would require 100 mW input (80-dB loss). The Antenna is clearly the way to go in this case. However if we shorten the distance to just 1500 FT then we have Transmission lines 1 MW (150-dB loss), Waveguide 30 nW (15-dB loss) and Antenna 10 mW (40-dB loss). So at that distance the wave guide is the must efficient.

I had to crack my old text books for this, so credit goes to “Modern Electronic Communication” by Gary M. Miller second edition Copyright 1983, 1978 Prentice-Hall, INC. Englewood Cliffs, N.J. 07632

Chase_the_Bass · 25th July 2009, 07:10 PM

Imagine electric cars that could go cross country without ever having to stop for fuel.

Singularitarian · 25th July 2009, 07:24 PM

Originally Posted by The Man

Indeed transmission lines are inherently practical for AC energy down to zero frequency and thus DC. Waveguides and antennas have practical physical limits relating to half wavelength. For a 60hz power system that works out to be about 155 miles. That’s a big waveguide or antenna. Making transmission lines far more physically practical at frequencies under a few hundred cycles per second. Transmission distance is also an important factor. For a 1GHz signal to be received with a power of 1nW at a distance of 30 miles away, for a transmission line would require a 10¹⁵⁰⁰ nW input (15,000-dB loss), a wave guide would require a 10¹⁵⁰ nW input (1,500-dB loss) and an antenna would require 100 mW input (80-dB loss). The Antenna is clearly the way to go in this case. However if we shorten the distance to just 1500 FT then we have Transmission lines 1 MW (150-dB loss), Waveguide 30 nW (15-dB loss) and Antenna 10 mW (40-dB loss). So at that distance the wave guide is the must efficient.

I had to crack my old text books for this, so credit goes to “Modern Electronic Communication” by Gary M. Miller second edition Copyright 1983, 1978 Prentice-Hall, INC. Englewood Cliffs, N.J. 07632

I must be lacking greatly in this area of physics, since i do not understand this very well.

zerospeaks · 25th July 2009, 07:43 PM

From a telsa website.

Quote:

major breakthrough in 1899 at Colorado Springs by transmitting 100 million volts of high-frequency electric power wirelessly over a distance of 26 miles at which he lit up a bank of 200 light bulbs and ran one electric motor! With this souped up version of his Tesla coil, Tesla claimed that only 5% of the transmitted energy was lost in the process.

Doesn't sound like an efficiency problem to me, we lose more than 5% sending power down wires.

I am not much for conspiracies, but I can't help but think about, what if tesla got it right, and the "powers to be" like the electric companies, don't want us to have it.

ben m · 25th July 2009, 08:15 PM

Originally Posted by Careyp74

My new toothbrush is recharged this way. If anyone is interested it is a sonicare that I got at Bed Bath and Beyond. It was in the beyond section

Seriously though, it is pretty cool.

I suspect your toothbrush is a *non-resonant* transformer, which only works in the very near field; WiTricity can propagate a few wavelengths between the source and reciever.

rjh01 · 26th July 2009, 01:35 AM

Be great to get rid of all the wires in the back of the computer and TV, needed for power. Then add bluetooth for communications and there will be no more wires.

But after reading the thread still no not know if the idea will work. Great if it did.

TjW · 26th July 2009, 07:43 AM

Originally Posted by ben m

I suspect your toothbrush is a *non-resonant* transformer, which only works in the very near field; WiTricity can propagate a few wavelengths between the source and reciever.

Not from standard definitions, it can't.
It's operating "near field", which is significantly less than a wavelength.

The Man · 26th July 2009, 09:27 AM

Originally Posted by Singularitarian

I must be lacking greatly in this area of physics, since i do not understand this very well.

Ok let me see if I can clear up some of the confusion or completely befuddle you. DC requires a build up or transfer of changed particles from the supply to the load and back. Thus requiring conductive paths like transmission lines, in fact, if I recall correctly, the AC power in the US has about a 10 volt DC offset so it does have a DC component. Because a conductive path is required for DC a capacitor (an insulating material between two conductors and thus in the conductive path) acts as an open circuit for DC when charged. For AC the capacitor acts (for the most part) as a short (with some phase shifting) since, as noted by others, AC power is transferred by the electromagnetic fields (by limited motion of charged particles within a conductive loop) and not the direct flow of charged particles (around a conductive loop). The capacitor clearly demonstrates the fundamental differences between how AC and DC power travel as queried by Towlie. With an insulator in the conductive path DC current will not flow (other then leakage) past the insulator, the capacitor will charge, but that is as far as the current will go. If one continues to increase the voltage across the capacitor eventually the dialectic limit of the insulating material will be reached and further increase will result in a dielectric breakdown and sudden discharge (like lightning across an air gap). For AC the capacitor charges some on one part of the cycle then discharges some on the another part of the cycle, the result is the current still flows, but current and voltage peaks become phase shifted. The greater the capacitance (measured in Farads) or the greater the AC frequency the more the capacitor seems like a short. So a capacitor can be used to leach off AC in a DC circuit (like in car radios to get rid of the AC from the ignition system). Fundamentally two antennas and an air gap like two conductors (as in transmission lines) and the air gap or the inner conductor and outer braid separated by an insulator in a coaxial cable are all capacitors. We can receive radio or WiFi signals from one antenna to the other through that air (or insulating gap) only because AC power travels in a fundamentally different way then DC.

So direct conduction is the only way to transfer DC power; however for AC we have some choices. At very low frequencies some of those choices simply become too impractical, you would need a ridiculously large waveguide or antenna so direct transmission (conductor) is the only practical solution. If I remember correctly by placing semi-conductive couplings between the conductors on transmission lines at regular intervals, also used to maintain spacing and dampen vibrations (called spacer dampers), the transmission lines become a rudimentary but effective pseudo waveguide for the AC frequency. It has been a wile though and I have been out of the electrical transmission and distribution industry for almost 15 years (so I’ll have to check my books again when I get home). At extremely high frequencies (such as microwaves) again one is limited as the only way to contain such short cycles (and get the power to where you want to ‘release’ it) is with a waveguide. In the electromagnetic spectrum of light we can use fiber optics which are optical waveguides. In between other factors can play a significant role in the efficiency of the transfer method selected. In the case referenced in the OP they are using a 30meter wavelength or .01 Gigahertz and are using the magnetic (or inductive) aspect as opposed to the electrical (or capacitive) aspect. It is just that the differences in AC and DC are easier to explain from a capacitive stand point since for an inductor in DC some current will flow eventually producing a static magnetic field at which point no motion of charged particles will be induced in a nearby coil stationary in that magnetic field.

marting · 26th July 2009, 10:56 AM

The Tesla 26 mile efficient energy transmission is apocryphal.

Transmission of energy by B fields of two loosely coupled coils at resonance is pretty traditional stuff. The main energy loss is resistive. Both in the coils and currents induced in nearby conductive materials. There is also a loss as energy couples into the far field becoming propagating radio waves. When the coil diameter is less than 1/10 the distance between coils efficiency plummets.

The Man · 27th July 2009, 05:36 AM

Originally Posted by The Man

If I remember correctly by placing semi-conductive couplings between the conductors on transmission lines at regular intervals, also used to maintain spacing and dampen vibrations (called spacer dampers), the transmission lines become a rudimentary but effective pseudo waveguide for the AC frequency. It has been a wile though and I have been out of the electrical transmission and distribution industry for almost 15 years (so I’ll have to check my books again when I get home).

Nope I was wrong about this part, must have just been conflating a couple of things I was remembering, sorry. For a 60 Hz signal a rectangular waveguide would need a 155 mile by 127.5 mile cross section (unless I’m screwing up my math as well).

icerat · 27th July 2009, 06:05 AM

Originally Posted by rjh01

Be great to get rid of all the wires in the back of the computer and TV, needed for power. Then add bluetooth for communications and there will be no more wires.

But after reading the thread still no not know if the idea will work. Great if it did.

eCoupled is doing something like this already over short distances using inductive coupling. Just put your phone or laptop or whatever on the desk and it starts drawing power. It can apparently also be used to send data, so bluetooth could be redundant.

ponderingturtle · 27th July 2009, 09:11 AM

Originally Posted by zerospeaks

From a telsa website.

Doesn't sound like an efficiency problem to me, we lose more than 5% sending power down wires.

I am not much for conspiracies, but I can't help but think about, what if tesla got it right, and the "powers to be" like the electric companies, don't want us to have it.

Did you know he also comunicated with Mars?

The Man · 27th July 2009, 10:03 AM

Originally Posted by marting

The Tesla 26 mile efficient energy transmission is apocryphal.

Transmission of energy by B fields of two loosely coupled coils at resonance is pretty traditional stuff. The main energy loss is resistive. Both in the coils and currents induced in nearby conductive materials. There is also a loss as energy couples into the far field becoming propagating radio waves. When the coil diameter is less than 1/10 the distance between coils efficiency plummets.

We use a non-contact inductive power system for some of our AMHS (Automated Material Handing System) vehicles.

BenBurch · 27th July 2009, 10:13 AM

What Tesla believed was that his power formed a beam spontaneously from the emitter to the receiver. And we can see this is not true by the lack of air ionization along that hypothetical beam.

And even if it did work, the ozone pollution it would cause would be a reason not to use it.

ktesibios · 27th July 2009, 01:25 PM

It would be cool if they retuned the receiver to the 27 MHz band.

That way the next idiot CBer who drives by with an illegal linear in his trunk could be recharging your toothbrush while he stomps all over your radio and TV reception.

BenBurch · 27th July 2009, 03:48 PM

Originally Posted by ktesibios

It would be cool if they retuned the receiver to the 27 MHz band.

That way the next idiot CBer who drives by with an illegal linear in his trunk could be recharging your toothbrush while he stomps all over your radio and TV reception.

Long ago, when I was but a lad, we had a neighbor with a tower and a 5KW linear and it destroyed television for us.

The FCC refused to do anything at all about it.

One night I climbed his tower with some black paint, wire cutters, and a diaper pin. I pushed the pin through his coax, and clipped it flush, and then painted over the ends with paint.

The next day his linear fried itself good.

He had it fixed and the same thing happened.

End of problem.

Not that I would recommend this solution to anybody else.

marting · 27th July 2009, 04:06 PM

Originally Posted by BenBurch

One night I climbed his tower with some black paint, wire cutters, and a diaper pin. I pushed the pin through his coax, and clipped it flush, and then painted over the ends with paint.

The next day his linear fried itself good.
...
Not that I would recommend this solution to anybody else.

Yeah, me either. Especially since cable checking will identify where the short is. I've got one in the closet right now that does CAT 5, CAT 6, and coax. However, I'm surprised his linear fried. Pretty shoddy design. Opens and shorts are way too common for a decent design to fry.

That would piss me off. OTOH, I don't run illegal linears. Still, vandalism often accelerates.

BenBurch · 27th July 2009, 04:20 PM

He wasn't really smart enough to ever think of checking the cable. And he got the cheapest linear he could (or it would not have interfered so badly.)

Giraffe107 · 27th July 2009, 04:34 PM

Originally Posted by zerospeaks

-snip-
I am not much for conspiracies, but I can't help but think about, what if tesla got it right, and the "powers to be" like the electric companies, don't want us to have it.

Going to have to disagree with you there. I work for a regional and rural electricity distribution company. We are mostly funded by government. Since our customers are so far apart, it costs us millions of dollars every year to upgrade our assets (ie poles and wires) to supply them- money which we can never recoup by charging them for electricity. If we could cheaply transmit power to them wirelessly, it would save us and the taxpayer millions. Government would be happy because they could either reduce taxes or the price of electricity (a touchy subject at the moment).

vIQleS · 27th July 2009, 04:54 PM

Bonus if this becomes mainstream: Automatic debunking of magnet therapy...

Downside - New woo: Wireless Power Allergy.

zerospeaks · 27th July 2009, 06:33 PM

Quote:

Did you know he also comunicated with Mars?

Negative, he was picking up a signal from space which at first he believed could have been an intelligent transmission of information. The most likely candidate at the time he thought was mars.

It has been suggested that the signals he was getting was from cosmic background radiation. If true he would have been the discoverer of it. Among many things he discovered that we only figured out after his death. Poor guy needs more credit.

zerospeaks · 27th July 2009, 06:35 PM

Quote:

If we could cheaply transmit power to them wirelessly, it would save us and the taxpayer millions. Government would be happy because they could either reduce taxes or the price of electricity (a touchy subject at the moment).

And how would you meter it?
And how would you stop me from receiving it without a meter?

23rd July 2009, 06:57 PM	#1
CardZeus Scholar Join Date: Jul 2006 Posts: 111	Wireless Power - I am confused... MIT's been developing this for a while and it is featured on the BBC website today http://news.bbc.co.uk/2/hi/technology/8165928.stm What I 'don't get' is the following: From the article, it sounds like a loosely coupled resonant transformer. That would be rather inefficient and generate huge problems with the stray fields coupling to everything else (humans, conductors, etc.). Not to mention that this would completely wipe out radio communications at the respective frequencies (and the cited 30 MHz band is smack in the middle of the shortwave region with worldwide ionospheric propagation, being heavily used by e.g. maritime and aeronautic communications). Keep in mind that electrical energy in ordinary cables is not carried by the wires either, but the electromagnetic field between them. The purpose of the wires is to guide and confine the EM field for very good reasons. Anyone care to address my comments??
CardZeus Scholar Join Date: Jul 2006 Posts: 111

23rd July 2009, 07:24 PM	#2
Towlie ancillary character Join Date: May 2009 Location: Miami, Florida Posts: 1,476	Actually, the wavelength is 30 meters, which corresponds to a frequency of 10 MHz. Your article mentions that shorter wavelengths (higher frequencies) would not work. Edit: Wikipedia has more on this "WiTricity^WP": Quote: The researchers suggest that the exposure levels will be below the threshold for FCC safety regulations, and the radiated-power levels will also comply with the FCC radio interference regulations.
	Last edited by Towlie; 23rd July 2009 at 07:35 PM.

23rd July 2009, 07:25 PM	#3
wackyvorlon Critical Thinker Join Date: Dec 2008 Location: Sarnia, ON, Canada Posts: 333	It sounds like the work that Tesla was doing. My understanding is that the goal of Tesla's power transmission system was to use ground waves. Mind, the frequencies he was using were much, much lower than 30MHz.
	__________________ The universe does not care what we think.

23rd July 2009, 07:48 PM	#4
Eggs Ackley Thinker Join Date: May 2009 Posts: 184	It's intended for near-field applications and probably has a very small effective aperture for radiation. The radiation fields might be negligible, while the near fields not. Radiation field power falls off as inverse square while near-field power density falls off as inverse fourth power. That is falling off fast with distance but conversely getting much bigger up close. The article should say "near-field" where it says "far field".
Eggs Ackley Thinker Join Date: May 2009 Posts: 184

23rd July 2009, 08:20 PM	#6
Pantaz Muse Join Date: Feb 2008 Location: Van Nuys, CA Posts: 896	Originally Posted by CardZeus MIT's been developing this for a while and it is featured on the BBC website today http://news.bbc.co.uk/2/hi/technology/8165928.stm What I 'don't get' is the following: From the article, it sounds like a loosely coupled resonant transformer. That would be rather inefficient and generate huge problems with the stray fields coupling to everything else (humans, conductors, etc.). Not to mention that this would completely wipe out radio communications at the respective frequencies (and the cited 30 MHz band is smack in the middle of the shortwave region with worldwide ionospheric propagation, being heavily used by e.g. maritime and aeronautic communications). The BBC piece is typical of science reporting -- it leaves out big chunks of relevant information. The company's website isn't much better. Mostly marketing-speak and techno-babble. You are basically correct, it is a resonant transformer. Popular Mechanics had a short article about it in 2007, describing a demonstration: "WiTricity exploits a phenomenon known as magnetically coupled resonance, which allows two objects resonating at the same frequency to exchange energy efficiently. The team was able to wirelessly power a 60-watt light bulb using a pair of 20-in.-dia. copper coils. Drawing power from an electrical outlet, the source coil created a magnetic field, which was 7 ft. in diameter, transmitting at a frequency of 10 MHz. (Many cellphones, by com-parison, operate at 2 GHz.) Seven feet away, a receiving coil was also resonating at 10 MHz, pulling enough energy from the field to power an attached light bulb." There is also a Wikipedia page. As for this... Originally Posted by CardZeus Keep in mind that electrical energy in ordinary cables is not carried by the wires either, but the electromagnetic field between them. The purpose of the wires is to guide and confine the EM field for very good reasons. I believe this is only true for high-frequency AC. (It's been a long time since I learned AC theory, but your description doesn't sound right to me.)

23rd July 2009, 08:06 PM	#5
Towlie ancillary character Join Date: May 2009 Location: Miami, Florida Posts: 1,476	Originally Posted by Eggs Ackley The article should say "near-field" where it says "far field". Actually, I think it's worse than that. It seems to me that the whole section titled Safety Concerns is garbled: Quote: Safety concerns Mr Giler was keen to stress the safety of the equipment during the demonstration. "There's nothing going on - I'm OK," he said walking around a television running on wireless power. The system is able to operate safely because the energy is largely transferred through magnetic fields. "Humans and the vast majority of objects around us are non-magnetic in nature," Professor Soljacic, one of the inventors of the system, told BBC News during a visit to Witricity earlier this year. It is able to do this by exploiting an effect that occurs in a region known as the "far field", the region seen at a distance of more than one wavelength from the device. In this field, a transmitter would emit mixture of magnetic and potentially dangerous electric fields. But, crucially, at a distance of less than one wavelength - the "near field" - it is almost entirely magnetic. Hence, Witricity uses low frequency electromagnetic waves, whose waves are about 30m (100ft) long. Shorter wavelengths would not work.

24th July 2009, 05:20 AM	#7
technoextreme Illuminator Join Date: Jun 2007 Posts: 3,786	Originally Posted by Pantaz As for this... I believe this is only true for high-frequency AC. (It's been a long time since I learned AC theory, but your description doesn't sound right to me.) Nope. All AC currents travel by EM radiation. The effects don't really become noticable unless you use power lines but he is right.
	__________________ It's amazing how many of these "paranormal" icons seem to merge together. There always seem to be theories about how they link together in some way. I'm sure someone has a very good explanation as to how Bigfoot killed JFK to help cover Roswell.-Mark Mekes This isn't rocket surgery.-Bill Nye

24th July 2009, 05:52 AM	#8
Careyp74 Illuminator Join Date: Feb 2008 Location: Trevose, PA Posts: 3,407	My new toothbrush is recharged this way. If anyone is interested it is a sonicare that I got at Bed Bath and Beyond. It was in the beyond section Seriously though, it is pretty cool.

24th July 2009, 05:56 AM	#9
Towlie ancillary character Join Date: May 2009 Location: Miami, Florida Posts: 1,476	Originally Posted by technoextreme Nope. All AC currents travel by EM radiation. The effects don't really become noticable unless you use power lines but he is right. If you're implying that alternating current travels by a fundamentally different means than direct current, that can be illustrated to be absurd by imagining that the frequency is gradually reduced. As it falls from 60 Hz to 1 Hz, and then to one cycle per minute, per day, and then per week and per year, it's still technically AC but looks more and more like DC. Tell us then, at what point during the frequency reduction does the energy stop traveling by radiation and begin flowing through the conductors, as it does with direct current?

24th July 2009, 10:13 PM	#10
zerospeaks Metaphysical Naturalist Extraordinaire Join Date: Jul 2009 Posts: 941	Wireless power Quote: Necroloth and other readers sent in the story of Witricity's latest demo at the TED Global conference in Oxford, UK. The company is developing a system that can deliver power to devices without the need for wires. The idea is not new — electrical pioneers Thomas Edison and Nicola Tesla assumed that power would be delivered wirelessly. The BBC quotes the inventor behind Witricity's tech as saying that Tesla and Edison "...couldn't imagine dragging this vast infrastructure of metallic wires across every continent." eWeek Europe notes some hurdles the technology must overcome: "The 2007 experiment it is based on had an efficiency of only around 45 percent, but [Witricity's CEO] promised power delivered wirelessly would start out 15 percent more expensive than wires, and improve on that." Intel has also demonstrated wireless charging. Story from slashdot! So now I ask a simple question. Why are we just now "discovering" wireless power, when Tesla had it working in 1900?

25th July 2009, 04:38 AM	#11
Small Town Jesus Critical Thinker Join Date: May 2003 Location: London Posts: 270	Originally Posted by zerospeaks Story from slashdot! So now I ask a simple question. Why are we just now "discovering" wireless power, when Tesla had it working in 1900? I was asking myself the same question as I was reading about this too. As a non scientist a possible answer that came to mind was that maybe the technology to fine tune the resonance has only just been achieved. Good to see Tesla's dream still alive though. Another link to this story here.
	__________________ 'Can't believe how strange it is to be anything at all' - Jeff Mangum

25th July 2009, 06:01 AM	#12
jay.tarnoff Scholar Join Date: Jul 2009 Location: Philadelphia, PA Posts: 65	NPR covered this yesterday with an interview from an individual from Wi-tricity. I was wondering the exact same thing. Is there some difference between their claim for what I think they called "micro magnetic resonance" or something similar and Tesla's original ideas?

25th July 2009, 06:07 AM	#13
bjornart Master Poster Join Date: Nov 2002 Posts: 2,395	The differences are in efficiency and not-making-everything-metal-in-the-vicinity-hot-ency.
bjornart Master Poster Join Date: Nov 2002 Posts: 2,395	__________________ Well, I DON'T CARE WHAT YOU LIKE TO BELIEVE, GODDAMMIT! I DEAL IN THE FACTS! -Cecil Adams

25th July 2009, 11:07 AM	#14
ugot2bekidding Muse Join Date: Feb 2008 Posts: 765	I remember reading somewhere that Tesla's idea was shot down because the electric companies were afraid of the potential for people to receive free electricity.
ugot2bekidding Muse Join Date: Feb 2008 Posts: 765

25th July 2009, 12:14 PM	#15
Pantaz Muse Join Date: Feb 2008 Location: Van Nuys, CA Posts: 896	There is already a thread on this... http://forums.randi.org/showthread.php?t=149007

25th July 2009, 02:12 PM	#16
wackyvorlon Critical Thinker Join Date: Dec 2008 Location: Sarnia, ON, Canada Posts: 333	Originally Posted by ugot2bekidding I remember reading somewhere that Tesla's idea was shot down because the electric companies were afraid of the potential for people to receive free electricity. There were a couple difficulties. It took time to develop the technology, and Tesla wasn't the best businessman. As I recall, in the end the tower at Wardenclyffe was cut up for scrap to pay off his debts.
	__________________ The universe does not care what we think.

25th July 2009, 03:59 PM	#17
Pantaz Muse Join Date: Feb 2008 Location: Van Nuys, CA Posts: 896	Originally Posted by wackyvorlon Originally Posted by ugot2bekidding I remember reading somewhere that Tesla's idea was shot down because the electric companies were afraid of the potential for people to receive free electricity. There were a couple difficulties. It took time to develop the technology, and Tesla wasn't the best businessman. As I recall, in the end the tower at Wardenclyffe was cut up for scrap to pay off his debts. ... And it's horribly inefficient

25th July 2009, 05:22 PM	#18
BenBurch Gatekeeper of The Left Join Date: Sep 2007 Location: The Universe 35.2 ms ahead of this one. Posts: 32,090	Originally Posted by Towlie If you're implying that alternating current travels by a fundamentally different means than direct current, that can be illustrated to be absurd by imagining that the frequency is gradually reduced. As it falls from 60 Hz to 1 Hz, and then to one cycle per minute, per day, and then per week and per year, it's still technically AC but looks more and more like DC. Tell us then, at what point during the frequency reduction does the energy stop traveling by radiation and begin flowing through the conductors, as it does with direct current? Well, now, depends on what frequency you are talking about. Microwaves have different behaviors; http://www.allaboutcircuits.com/vol_2/chpt_14/8.html
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25th July 2009, 06:29 PM	#19
The Man Scourge, of the supernatural Join Date: Jun 2007 Location: Poughkeepsie, NY Posts: 7,517	Originally Posted by BenBurch Well, now, depends on what frequency you are talking about. Microwaves have different behaviors; http://www.allaboutcircuits.com/vol_2/chpt_14/8.html Indeed transmission lines are inherently practical for AC energy down to zero frequency and thus DC. Waveguides and antennas have practical physical limits relating to half wavelength. For a 60hz power system that works out to be about 155 miles. That’s a big waveguide or antenna. Making transmission lines far more physically practical at frequencies under a few hundred cycles per second. Transmission distance is also an important factor. For a 1GHz signal to be received with a power of 1nW at a distance of 30 miles away, for a transmission line would require a 10¹⁵⁰⁰ nW input (15,000-dB loss), a wave guide would require a 10¹⁵⁰ nW input (1,500-dB loss) and an antenna would require 100 mW input (80-dB loss). The Antenna is clearly the way to go in this case. However if we shorten the distance to just 1500 FT then we have Transmission lines 1 MW (150-dB loss), Waveguide 30 nW (15-dB loss) and Antenna 10 mW (40-dB loss). So at that distance the wave guide is the must efficient. I had to crack my old text books for this, so credit goes to “Modern Electronic Communication” by Gary M. Miller second edition Copyright 1983, 1978 Prentice-Hall, INC. Englewood Cliffs, N.J. 07632
	__________________ "Not a seat but a springboard” (1942 Winston Churchill) "As he who, seeking asses, found a kingdom" (1671 Milton "Paradise Regained") "for it seem'd A void was made in nature, all her bonds Crack'd; and I saw the flaring atom-streams And torrents of her myriad universe, Ruining along the illimitable inane, Fly on to clash together again, and make Another and another frame of things For ever." (1868 Tennyson "Lucretius") Last edited by The Man; 25th July 2009 at 06:39 PM. Reason: typos

25th July 2009, 07:10 PM	#20
Chase_the_Bass Student Join Date: Jul 2009 Posts: 41	Imagine electric cars that could go cross country without ever having to stop for fuel.
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25th July 2009, 07:24 PM	#21
Singularitarian Banned Join Date: Jul 2009 Posts: 1,008	Originally Posted by The Man Indeed transmission lines are inherently practical for AC energy down to zero frequency and thus DC. Waveguides and antennas have practical physical limits relating to half wavelength. For a 60hz power system that works out to be about 155 miles. That’s a big waveguide or antenna. Making transmission lines far more physically practical at frequencies under a few hundred cycles per second. Transmission distance is also an important factor. For a 1GHz signal to be received with a power of 1nW at a distance of 30 miles away, for a transmission line would require a 10¹⁵⁰⁰ nW input (15,000-dB loss), a wave guide would require a 10¹⁵⁰ nW input (1,500-dB loss) and an antenna would require 100 mW input (80-dB loss). The Antenna is clearly the way to go in this case. However if we shorten the distance to just 1500 FT then we have Transmission lines 1 MW (150-dB loss), Waveguide 30 nW (15-dB loss) and Antenna 10 mW (40-dB loss). So at that distance the wave guide is the must efficient. I had to crack my old text books for this, so credit goes to “Modern Electronic Communication” by Gary M. Miller second edition Copyright 1983, 1978 Prentice-Hall, INC. Englewood Cliffs, N.J. 07632 I must be lacking greatly in this area of physics, since i do not understand this very well.
Singularitarian Banned Join Date: Jul 2009 Posts: 1,008

25th July 2009, 07:43 PM	#22
zerospeaks Metaphysical Naturalist Extraordinaire Join Date: Jul 2009 Posts: 941	From a telsa website. Quote: major breakthrough in 1899 at Colorado Springs by transmitting 100 million volts of high-frequency electric power wirelessly over a distance of 26 miles at which he lit up a bank of 200 light bulbs and ran one electric motor! With this souped up version of his Tesla coil, Tesla claimed that only 5% of the transmitted energy was lost in the process. Doesn't sound like an efficiency problem to me, we lose more than 5% sending power down wires. I am not much for conspiracies, but I can't help but think about, what if tesla got it right, and the "powers to be" like the electric companies, don't want us to have it.

25th July 2009, 08:15 PM	#23
ben m Illuminator Join Date: Jul 2006 Posts: 4,639	Originally Posted by Careyp74 My new toothbrush is recharged this way. If anyone is interested it is a sonicare that I got at Bed Bath and Beyond. It was in the beyond section Seriously though, it is pretty cool. I suspect your toothbrush is a non-resonant transformer, which only works in the very near field; WiTricity can propagate a few wavelengths between the source and reciever.
ben m Illuminator Join Date: Jul 2006 Posts: 4,639

26th July 2009, 01:35 AM	#24
rjh01 Gentleman of leisure Tagger Join Date: May 2005 Location: Planet Earth Posts: 17,172	Be great to get rid of all the wires in the back of the computer and TV, needed for power. Then add bluetooth for communications and there will be no more wires. But after reading the thread still no not know if the idea will work. Great if it did.

26th July 2009, 07:43 AM	#25
TjW Philosopher Join Date: Mar 2005 Location: up in the air Posts: 9,969	Originally Posted by ben m I suspect your toothbrush is a non-resonant transformer, which only works in the very near field; WiTricity can propagate a few wavelengths between the source and reciever. Not from standard definitions, it can't. It's operating "near field", which is significantly less than a wavelength.
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26th July 2009, 09:27 AM	#26
The Man Scourge, of the supernatural Join Date: Jun 2007 Location: Poughkeepsie, NY Posts: 7,517	Originally Posted by Singularitarian I must be lacking greatly in this area of physics, since i do not understand this very well. Ok let me see if I can clear up some of the confusion or completely befuddle you. DC requires a build up or transfer of changed particles from the supply to the load and back. Thus requiring conductive paths like transmission lines, in fact, if I recall correctly, the AC power in the US has about a 10 volt DC offset so it does have a DC component. Because a conductive path is required for DC a capacitor (an insulating material between two conductors and thus in the conductive path) acts as an open circuit for DC when charged. For AC the capacitor acts (for the most part) as a short (with some phase shifting) since, as noted by others, AC power is transferred by the electromagnetic fields (by limited motion of charged particles within a conductive loop) and not the direct flow of charged particles (around a conductive loop). The capacitor clearly demonstrates the fundamental differences between how AC and DC power travel as queried by Towlie. With an insulator in the conductive path DC current will not flow (other then leakage) past the insulator, the capacitor will charge, but that is as far as the current will go. If one continues to increase the voltage across the capacitor eventually the dialectic limit of the insulating material will be reached and further increase will result in a dielectric breakdown and sudden discharge (like lightning across an air gap). For AC the capacitor charges some on one part of the cycle then discharges some on the another part of the cycle, the result is the current still flows, but current and voltage peaks become phase shifted. The greater the capacitance (measured in Farads) or the greater the AC frequency the more the capacitor seems like a short. So a capacitor can be used to leach off AC in a DC circuit (like in car radios to get rid of the AC from the ignition system). Fundamentally two antennas and an air gap like two conductors (as in transmission lines) and the air gap or the inner conductor and outer braid separated by an insulator in a coaxial cable are all capacitors. We can receive radio or WiFi signals from one antenna to the other through that air (or insulating gap) only because AC power travels in a fundamentally different way then DC. So direct conduction is the only way to transfer DC power; however for AC we have some choices. At very low frequencies some of those choices simply become too impractical, you would need a ridiculously large waveguide or antenna so direct transmission (conductor) is the only practical solution. If I remember correctly by placing semi-conductive couplings between the conductors on transmission lines at regular intervals, also used to maintain spacing and dampen vibrations (called spacer dampers), the transmission lines become a rudimentary but effective pseudo waveguide for the AC frequency. It has been a wile though and I have been out of the electrical transmission and distribution industry for almost 15 years (so I’ll have to check my books again when I get home). At extremely high frequencies (such as microwaves) again one is limited as the only way to contain such short cycles (and get the power to where you want to ‘release’ it) is with a waveguide. In the electromagnetic spectrum of light we can use fiber optics which are optical waveguides. In between other factors can play a significant role in the efficiency of the transfer method selected. In the case referenced in the OP they are using a 30meter wavelength or .01 Gigahertz and are using the magnetic (or inductive) aspect as opposed to the electrical (or capacitive) aspect. It is just that the differences in AC and DC are easier to explain from a capacitive stand point since for an inductor in DC some current will flow eventually producing a static magnetic field at which point no motion of charged particles will be induced in a nearby coil stationary in that magnetic field.
	__________________ "Not a seat but a springboard” (1942 Winston Churchill) "As he who, seeking asses, found a kingdom" (1671 Milton "Paradise Regained") "for it seem'd A void was made in nature, all her bonds Crack'd; and I saw the flaring atom-streams And torrents of her myriad universe, Ruining along the illimitable inane, Fly on to clash together again, and make Another and another frame of things For ever." (1868 Tennyson "Lucretius")

26th July 2009, 10:56 AM	#27
marting Muse Join Date: Sep 2003 Location: Rancho Santa Fe Posts: 734	The Tesla 26 mile efficient energy transmission is apocryphal. Transmission of energy by B fields of two loosely coupled coils at resonance is pretty traditional stuff. The main energy loss is resistive. Both in the coils and currents induced in nearby conductive materials. There is also a loss as energy couples into the far field becoming propagating radio waves. When the coil diameter is less than 1/10 the distance between coils efficiency plummets.
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27th July 2009, 05:36 AM	#28
The Man Scourge, of the supernatural Join Date: Jun 2007 Location: Poughkeepsie, NY Posts: 7,517	Originally Posted by The Man If I remember correctly by placing semi-conductive couplings between the conductors on transmission lines at regular intervals, also used to maintain spacing and dampen vibrations (called spacer dampers), the transmission lines become a rudimentary but effective pseudo waveguide for the AC frequency. It has been a wile though and I have been out of the electrical transmission and distribution industry for almost 15 years (so I’ll have to check my books again when I get home). Nope I was wrong about this part, must have just been conflating a couple of things I was remembering, sorry. For a 60 Hz signal a rectangular waveguide would need a 155 mile by 127.5 mile cross section (unless I’m screwing up my math as well).
	__________________ "Not a seat but a springboard” (1942 Winston Churchill) "As he who, seeking asses, found a kingdom" (1671 Milton "Paradise Regained") "for it seem'd A void was made in nature, all her bonds Crack'd; and I saw the flaring atom-streams And torrents of her myriad universe, Ruining along the illimitable inane, Fly on to clash together again, and make Another and another frame of things For ever." (1868 Tennyson "Lucretius")

27th July 2009, 06:05 AM	#29
icerat Illuminator Join Date: Apr 2008 Location: sweden Posts: 3,128	Originally Posted by rjh01 Be great to get rid of all the wires in the back of the computer and TV, needed for power. Then add bluetooth for communications and there will be no more wires. But after reading the thread still no not know if the idea will work. Great if it did. eCoupled is doing something like this already over short distances using inductive coupling. Just put your phone or laptop or whatever on the desk and it starts drawing power. It can apparently also be used to send data, so bluetooth could be redundant.
	Last edited by icerat; 27th July 2009 at 06:08 AM.

27th July 2009, 09:11 AM	#30
ponderingturtle Orthogonal Vector Join Date: Jul 2006 Location: Tarrytown, NY Posts: 26,417	Originally Posted by zerospeaks From a telsa website. Doesn't sound like an efficiency problem to me, we lose more than 5% sending power down wires. I am not much for conspiracies, but I can't help but think about, what if tesla got it right, and the "powers to be" like the electric companies, don't want us to have it. Did you know he also comunicated with Mars?
	__________________ Sufficiently advanced Woo is indistinguishable from Parody "There shall be no poofing in science" Paul C. Anagnostopoulos Force ***** on reasons back" Ben Franklin

27th July 2009, 10:03 AM	#31
The Man Scourge, of the supernatural Join Date: Jun 2007 Location: Poughkeepsie, NY Posts: 7,517	Originally Posted by marting The Tesla 26 mile efficient energy transmission is apocryphal. Transmission of energy by B fields of two loosely coupled coils at resonance is pretty traditional stuff. The main energy loss is resistive. Both in the coils and currents induced in nearby conductive materials. There is also a loss as energy couples into the far field becoming propagating radio waves. When the coil diameter is less than 1/10 the distance between coils efficiency plummets. We use a non-contact inductive power system for some of our AMHS (Automated Material Handing System) vehicles.
	__________________ "Not a seat but a springboard” (1942 Winston Churchill) "As he who, seeking asses, found a kingdom" (1671 Milton "Paradise Regained") "for it seem'd A void was made in nature, all her bonds Crack'd; and I saw the flaring atom-streams And torrents of her myriad universe, Ruining along the illimitable inane, Fly on to clash together again, and make Another and another frame of things For ever." (1868 Tennyson "Lucretius")

27th July 2009, 10:13 AM	#32
BenBurch Gatekeeper of The Left Join Date: Sep 2007 Location: The Universe 35.2 ms ahead of this one. Posts: 32,090	What Tesla believed was that his power formed a beam spontaneously from the emitter to the receiver. And we can see this is not true by the lack of air ionization along that hypothetical beam. And even if it did work, the ozone pollution it would cause would be a reason not to use it.
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27th July 2009, 01:25 PM	#33
ktesibios Worthless Aging Hippie Join Date: Feb 2002 Location: Los Angeles Posts: 1,493	It would be cool if they retuned the receiver to the 27 MHz band. That way the next idiot CBer who drives by with an illegal linear in his trunk could be recharging your toothbrush while he stomps all over your radio and TV reception.
	__________________ Ship me somewheres east of Suez, where the best is like the worst, where there ain't no ten commandments and a man can raise a small, bristly mustache.

27th July 2009, 03:48 PM	#34
BenBurch Gatekeeper of The Left Join Date: Sep 2007 Location: The Universe 35.2 ms ahead of this one. Posts: 32,090	Originally Posted by ktesibios It would be cool if they retuned the receiver to the 27 MHz band. That way the next idiot CBer who drives by with an illegal linear in his trunk could be recharging your toothbrush while he stomps all over your radio and TV reception. Long ago, when I was but a lad, we had a neighbor with a tower and a 5KW linear and it destroyed television for us. The FCC refused to do anything at all about it. One night I climbed his tower with some black paint, wire cutters, and a diaper pin. I pushed the pin through his coax, and clipped it flush, and then painted over the ends with paint. The next day his linear fried itself good. He had it fixed and the same thing happened. End of problem. Not that I would recommend this solution to anybody else.
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27th July 2009, 04:06 PM	#35
marting Muse Join Date: Sep 2003 Location: Rancho Santa Fe Posts: 734	Originally Posted by BenBurch One night I climbed his tower with some black paint, wire cutters, and a diaper pin. I pushed the pin through his coax, and clipped it flush, and then painted over the ends with paint. The next day his linear fried itself good. ... Not that I would recommend this solution to anybody else. Yeah, me either. Especially since cable checking will identify where the short is. I've got one in the closet right now that does CAT 5, CAT 6, and coax. However, I'm surprised his linear fried. Pretty shoddy design. Opens and shorts are way too common for a decent design to fry. That would piss me off. OTOH, I don't run illegal linears. Still, vandalism often accelerates.
	__________________ Flying's easy. Walking on water, now that's cool.