Who Need Wires?

MIT team experimentally demonstrates wireless power transfer, potentially useful for powering laptops, cell phones without cords.

From MIT news - Realizing their recent theoretical prediction, MIt researchers were able to light a 60W light bulb from a power source seven feet (> two meters) away; there was no physical connection between the source and the appliance. The MIT team refers to its concept as "WiTricity" (as in wireless electricity). The work was reported in the June 7 issue of Science Express, the advance online publication of the journal Science.

Shown left-Wireless power transfer over two-meter distance, with approximately 40% efficiency, from the coil on the left to the coil on the right, where it powers a 60W light bulb. Members of the team that performed the experiment are obstructing the direct line of sight between the coils.

WiTricity is based on using coupled resonant objects. Two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with extraneous off-resonant objects. A child on a swing is a good example of this. A swing is a type of mechanical resonance, so only when the child pumps her legs at the natural frequency of the swing is she able to impart substantial energy.

Another example involves acoustic resonances: Imagine a room with 100 identical wine glasses, each filled with wine up to a different level, so they all have different resonant frequencies. If an opera singer sings a sufficiently loud single note inside the room, a glass of the corresponding frequency might accumulate sufficient energy to even explode, while not influencing the other glasses. In any system of coupled resonators there often exists a so-called "strongly coupled" regime of operation. If one ensures to operate in that regime in a given system, the energy transfer can be very efficient.

The team members are Andre Kurs, Aristeidis Karalis, Robert Moffatt, Prof. Peter Fisher, and Prof. John Joannopoulos (Francis Wright Davis Chair and director of ISN), led by Prof. Marin Soljacic.

The MIT team used one particular type of resonance: magnetically coupled resonators. The team explored a system of two electromagnetic resonators coupled mostly through their magnetic fields; they were able to identify the strongly coupled regime in this system, even when the distance between them was several times larger than the sizes of the resonant objects. This way, efficient power transfer was enabled.

Magnetic coupling is particularly suitable for everyday applications because most common materials interact only very weakly with magnetic fields, so interactions with extraneous environmental objects are suppressed even further. "The fact that magnetic fields interact so weakly with biological organisms is also important for safety considerations," Kurs, a graduate student in physics, points out.

The investigated design consists of two copper coils, each a self-resonant system. One of the coils, attached to the power source, is the sending unit. Instead of irradiating the environment with electromagnetic waves, it fills the space around it with a non-radiative magnetic field oscillating at MHz frequencies. The non-radiative field mediates the power exchange with the other coil (the receiving unit), which is specially designed to resonate with the field. The resonant nature of the process ensures the strong interaction between the sending unit and the receiving unit, while the interaction with the rest of the environment is weak.

Moffatt, an MIT undergraduate in physics, explains: "The crucial advantage of using the non-radiative field lies in the fact that most of the power not picked up by the receiving coil remains bound to the vicinity of the sending unit, instead of being radiated into the environment and lost." With such a design, power transfer has a limited range, and the range would be shorter for smaller-size receivers.

Still, for laptop-sized coils, power levels more than sufficient to run a laptop can be transferred over room-sized distances nearly omni-directionally and efficiently, irrespective of the geometry of the surrounding space, even when environmental objects completely obstruct the line-of-sight between the two coils. Fisher points out: "As long as the laptop is in a room equipped with a source of such wireless power, it would charge automatically, without having to be plugged in. In fact, it would not even need a battery to operate inside of such a room." In the long run, this could reduce our society's dependence on batteries, which are currently heavy and expensive.

At first glance, such a power transfer is reminiscent of relatively commonplace magnetic induction, such as is used in power transformers, which contain coils that transmit power to each other over very short distances. An electric current running in a sending coil induces another current in a receiving coil. The two coils are very close, but they do not touch. However, this behavior changes dramatically when the distance between the coils is increased. As Karalis, a graduate student in electrical engineering and computer science, points out, "Here is where the magic of the resonant coupling comes about. The usual non-resonant magnetic induction would be almost 1 million times less efficient in this particular system."

Old physics, new demand

WiTricity is rooted in such well-known laws of physics that it makes one wonder why no one thought of it before. "In the past, there was no great demand for such a system, so people did not have a strong motivation to look into it," points out Joannopoulos, adding, "Over the past several years, portable electronic devices, such as laptops, cell phones, iPods and even household robots have become widespread, all of which require batteries that need to be recharged often."

As for what the future holds, Soljacic adds, "Once, when my son was about three years old, we visited his grandparents' house. They had a 20-year-old phone and my son picked up the handset, asking, 'Dad, why is this phone attached with a cord to the wall?' That is the mindset of a child growing up in a wireless world. My best response was, 'It is strange and awkward, isn't it? Hopefully, we will be getting rid of some more wires, and also batteries, soon.'"

Imagine a future in which wireless power transfer is feasible: cell phones, household robots, mp3 players, laptop computers and other portable electronics capable of charging themselves without ever being plugged in, freeing us from that final, ubiquitous power wire. Some of these devices might not even need their bulky batteries to operate.

Comments

[Engineer-Poet]

An oscillating magnetic field will induce currents in any conductor nearby, resonant or not.  When you consider the health concerns about EMF's lately, it makes me wonder why anyone would push a concept like this.

[Bill Northrup]

Nicoli Tesla did that nearly one hundred years ago!! It was awesome....

[ElectRich]

Tesla claimed nearly no power loss! What did he do different? Wardenclyffe was to be his wireless power grid. It's a shame his funding was pulled and Westinghouse ended up with most of his patents. The guy was way ahead of his time!

[Engineer-Poet]

If the energy field pervades a public space, you are going to have a lot of trouble charging for it.

[Michael Crumpton]

Energy is already dispensed in public places:
Streetlights provide light for all and it is charged to us through taxes.

In any case most mobile apps use relatively small amounts of power: laptops <20watts, Cell phones <5 watts.

It would be a different story if electric cars or scooters could charge while they are waiting at the traffic light, but registration fees can deal with that.

[JimB]

This is very cool but it means using 2.5 times as much energy than if you just plug something in. At 40% efficiency, 60W light bulb consumes 150W.

I'm sure this has some great niche applications, but I would hate to see this catch on just for convenience when we should be thinking about energy conservation. I don't think I have to worry though. Looks like they've got a lot of work to do before it fits in your cell phone or even laptop.

[amazingdrx]

Bees effected by cell phones. Stray voltage from power lines. EMF effects on humans and animals.

A gHG crisis.

And MIT wastes it's time on tesla's flawed dream? What is this country coming to? Ancient Rome repeated.

Please MIT stick to studying renewable energy and plugin vehicle technology. stop the BS.

[amazingdrx]

Recharge of electric vehicles from under roadways with resonant coils of this design ring any bells MIT? Obviously not.

The only application for this waste of resources left out of the article. Is Monica Goodling picking MIT research students now?

[Big Al]

With people being in a state of panic over power line induction, the field strength nessary for power of any sort to recharge batteries etc would be way to high for continuous human exposure

[Ed H.]

Transverse = bad. Longitudinal = good.

100 monkeys just aren't enough, even if they do have MIT degrees.

[amazingdrx]

Facinating challenge here, how to wind power Alaskan villages without diesel backup?

http://gristmill.grist.org/story/2007/6/8/131317/0785/#comment12

Anyway, here's another application for this invention. Stationary parking lot charging for electric cars. park over the sending coil in a parking space. The coils can be almost touching there. For a very efficient, credit card billed automatic recharge of electric cars, no plugging in.

With inches instead of feet between these coils with recharge while you ride from under the road surface the efficiency should be very high, even better than regular induction.

Long haul semis and buses powered by electric with backup generators could ride in the charge lane say half their trip.

Better read this blog MITites. Hehey. (sorry for the "goodling" remark)

[KZ]

Considering that people with pacemakers are warned not to use electric toothbrushes, and that some kid (allegedly) got pacemakers to malfunction when they're too close to a freakin' iPod, I see this as very unrealistic technology from a legal standpoint, much less the increased energy loss, "regular" human exposure, increased airconditioning costs (loss in energy in this case = heat), etc.

Am not against the research per se; remember, the EV1 had a charging paddle that was based upon inductive coupling (over 85% efficient I thought????). The research aspects of this are fine, but expecting it to be used in the proposed manner is, well stupid.

[frank]

"Waldo" c1950, by Robert Silverberg.

[Wow]

I can't believe some of the comments on this post! "Work on renewable energy." Tough if that's not their field. "Waste of resources." Not to whoever funded it! (Maybe you ought to offer your obviously vast knowledge and expertise to the NSF or NIH funding boards?) "No application." Let's cut all fundamental physics research, too, since the hell if string theory is going to help our day-to-day lives anytime soon.

Novel research is novel research, folks. Every dime and every second of effort need not go to EXACTLY what YOU'RE interested in!

[Mike]

I'm not sure of the exact technology used, but I witnessed this exact demonstration at Texas A&M in College Station in 1999.

[Witricity]

News, Experimental Videos And Information:

http://www.witricitynet.com

[Nathan]

This is a new concept and needs time to prove its wothiness.

But, we at Neo Energy Corporation, have invented the world’s first generator, which is run by bullocks and produces energy to power small villages and communities at very negligible cost, when compared to our conventional ways. This is a novel concept of converting animal power to electricity generated from locally available materials. And this energy is clean and green with no carbon emission.

All you need is a small bullock cart, Steel Rotor, variable gear box, Fly wheel Dynamo – able to produce up to 400Watts. This power is sustainable, as the Bullocks are of local breed and can consume fodders, which are available locally. The unit can be housed in a shed with concrete floorings.

We wish to commercialise this product for the welfare of millions of people in Asia and Africa. And we look forward to technocrats and private equity firms to participate in this revolution to make this project a very successful one.

Thanks for providing this platform.

Nathan

[Nathan]

This is a new concept and needs time to prove its wothiness.

But, we at Neo Energy Corporation, have invented the world’s first generator, which is run by bullocks and produces energy to power small villages and communities at very negligible cost, when compared to our conventional ways. This is a novel concept of converting animal power to electricity generated from locally available materials. And this energy is clean and green with no carbon emission.

All you need is a small bullock cart, Steel Rotor, variable gear box, Fly wheel Dynamo – able to produce up to 400Watts. This power is sustainable, as the Bullocks are of local breed and can consume fodders, which are available locally. The unit can be housed in a shed with concrete floorings.

We wish to commercialise this product for the welfare of millions of people in Asia and Africa. And we look forward to technocrats and private equity firms to participate in this revolution to make this project a very successful one.

Thanks for providing this platform.

Nathan

[Nathan]

This is a new concept and needs time to prove its wothiness.

But, we at Neo Energy Corporation, have invented the world’s first generator, which is run by bullocks and produces energy to power small villages and communities at very negligible cost, when compared to our conventional ways. This is a novel concept of converting animal power to electricity generated from locally available materials. And this energy is clean and green with no carbon emission.

All you need is a small bullock cart, Steel Rotor, variable gear box, Fly wheel Dynamo – able to produce up to 400Watts. This power is sustainable, as the Bullocks are of local breed and can consume fodders, which are available locally. The unit can be housed in a shed with concrete floorings.

We wish to commercialise this product for the welfare of millions of people in Asia and Africa. And we look forward to technocrats and private equity firms to participate in this revolution to make this project a very successful one.

Thanks for providing this platform.

Nathan

[wireless cellphone business]

is there anything mit cannot do. These guys are so smart.

[laptops in pakistan]

Nice, and thanks for sharing this info with us.
Good Luck!

[safiq]

super concept...plz help me sir some ideas share about your project

[Electric Coils]

I seriously need more tips from people like you to improve my skills in the field =)