MIT Wirelessly Powers a Lightbulb

kcurtis writes "According to the Boston Globe, MIT Researchers have powered a light bulb remotely. The successful experiment lit a 60-watt light bulb from a power source two meters away, with no physical connection between the power source and the light bulb. Details about WiTricity, or wireless electricity, are scheduled to be reported today in Science Express, the advance online publication of the journal Science, the Massachusetts Institute of Technology said. 'The team from MIT is not the first group to suggest wireless energy transfer. Nineteenth-century physicist and engineer Nikola Tesla experimented with long-range wireless energy transfer, but his most ambitious attempt - the 29m high aerial known as Wardenclyffe Tower, in New York - failed when he ran out of money. Others have worked on highly directional mechanisms of energy transfer such as lasers. However, unlike the MIT work, these require an uninterrupted line of sight, and are therefore not good for powering objects around the home.'"

Comments

Not the first remotely powered lightbulb

[ksp0704]

This isn't really the first lightbulb to be lit remotely. Flourescents can be lit by an EM field.... so in a microwave, or under highpower lines:
http://www.boxyit.com/r/index.htm

Why this is important.

[Proudrooster]

As a physics student I took an interest in Tesla and if you haven't read the book titled "A Man Out of Time", consider reading it. Tesla was building a tower to transmit power between the US and Europe (across the large ocean). The reason this is important is that is not accomplished by induction, but through some other means. Tesla's other means was probably really, really, high voltage as he was producing with his Tesla coils. Making high voltage is not a mystery, but directly it safely and then dropping it to a safe and usable potential is very difficult.

In short, this is NOT the same as holding a flourescent tube under a high voltage powerline. The MIT method uses controlled power tranmission over larger distances (2m or 6ft). The technique uses resonance frequency but has 40% loss, which is very bad meaning it is only 60% efficient. Many modern PSU (Power Supply Units) are 90%+ efficient. Unless they increase the efficiency, the power industry probably won't be jumping on board anytime soon.

Re:so if cellphone radiation might cause cancer...

[westlake]

MRI uses huge magnetic fields that researchers are exposed to on a daily basis and there is no solid data that it causes biologic harm.

The intense fields generated in MRI present more immediate and sometimes less manageable risks than cancer.

An MRI magnet can pull a stray hairpin across the room at 40 miles per hour. Hemostats, scissors, wheelchairs, patient gurneys, intravenous poles, and defibrillators have all been turned into projectiles capable of severe harm. When nonmedical people enter the magnet room, things can get even worse. In one instance, a police officer's gun discharged as it was sucked out of his grip; in another, a firefighter was trapped and nearly suffocated as he was drawn into the bore when the breathing apparatus strapped to his back became magnetized in the MRI room.

The phenomenon by which metal becomes spontaneously magnetized is ferromagnetism, which affects iron, nickel, cobalt, and many other familiar metals and alloys. Although most implants today are made with titanium or other nonferromagnetic metals, it's common knowledge that MRI systems can affect older angio and cerebral clips, bone pins, dental work, and even some tattoo dyes. That's the key reason patients are screened. What's less recognized is how MRI scanners may interfere with devices such as pacemakers, pulse oximeters, automated defibrillators, cardiac monitors, insulin pumps, cochlear implants, and vagus and other neurological stimulators.

Where a CT installation's lead shielding is designed to keep radiation inside, MRI shielding keeps stray radiowaves out. The focus is on protecting the magnet from interference, not the other way around.

Plate steel is the only physical material that can contain an MRI system's magnetic field. The lines of force penetrate brick, wood, concrete, cement--which means that not only people outside the MRI suite but even people and machines outside the building can be affected. Any steel in the building construction reshapes the magnetic fields in the MRI, and MRI magnetizes the steel in the building. So the levels of complexity are several orders of magnitude greater than a CT, even though they may not look all that different on the floor plan. Current designs using plate shielding, however, usually are not equipped to deal with the newest crop of 3 Tesla (3T) commercially available systems--and even higher-powered research magnets.

MRI magnets have been known to affect gamma cameras, nuclear medicine hot labs, PET/CT scanners, and other equipment--even those sited at what seems a reasonable distance. The extraordinary sensitivity of today's [imaging] systems--the same feature that makes them so valuable--makes them vulnerable to such disruptions. You don't want to expose them to anything significantly above normal. Basically, any magnetic force stronger than the one that makes a compass point north can disrupt or degrade some types of this equipment. MRI Facility Safety -- Understanding the Risks of Powerful Attraction

Re:Induction?

[infaustus]

The summaries really should explain these things, I hate having to RTFA. From TFA: 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."

Re:Wow. 100 years and they finally caught up with.

[FleaPlus]

Personally, I am a bit miffed at the MIT folks for not giving credit where credit is due. This is the second article I have seen in the last month or two on this topic and they hardly even mention the fact that this is a key Tesla invention that was in fact accomplished by him and repeatably demonstrated. To read the articles one would think that the folks at MIT just sat down last week and invented this all by themselves when it is simply not true.

The opening paragraph of their earlier paper:

http://arxiv.org/ftp/physics/papers/0611/0611063.p df

In the early days of electromagnetism, before the electrical-wire grid was deployed, serious interest and effort was devoted (most notably by Nikola Tesla [1]) towards the development of schemes to transport energy over long distances without any carrier medium (e.g. wirelessly). These efforts appear to have met with little success. Radiative modes of omni-directional antennas (which work very well for information transfer) are not suitable for such energy transfer, because a vast majority of energy is wasted into free space. Directed radiation modes, using lasers or highly-directional antennas, can be efficiently used for energy transfer, even for long distances (transfer distance LTRANSLDEV, where LDEV is the characteristic size of the device), but require existence of an uninterruptible line-of-sight and a complicated tracking system in the case of mobile objects. Rapid development of autonomous electronics of recent years (e.g. laptops, cell-phones, house-hold robots, that all typically rely on chemical energy storage) justifies revisiting investigation of this issue. Today, we face a different challenge than Tesla: since the existing electrical-wire grid carries energy almost everywhere, even a medium-range (LTRANS fewLDEV) wireless energy transfer would be quite useful for many applications. There are several currently used schemes, which rely on non-radiative modes (magnetic induction), but they are restricted to very close-range (LTRANSLDEV) or very low-power (~mW) energy transfers [2,3,4,5,6].

Re:Induction?

[QuantumFTL]

A great comment from Wikipedia Talk Page:

: No, neither the BBC article nor the MIT article are correct. It does not at all work like a transformer, despite what they are feeding the public, a transformer like that would not have strong enough magnetic coupling and would waste energy. The actual mechanism behind their 'wireless energy transfer' uses two short circuited resonant radio (although it can work with any light) waveguides. The waveguides produce evanescent waves which do not carry energy, but can affect other nearby waveguides allowing the EM radiation to tunnel from one waveguide to the other (from the base station to the wireless receiver) which can then be rectified into DC electricity. See the wiki article on superlenses, evanescent waves, and evanescent wave coupling (I believe) for more specific information and links to better resources. Note that a negative refractive index material could massively boost the range and coupling for such a system. See the articles for the reason for that as well. --Haplo 24.98.124.237 09:12, 18 December 2006 (UTC)

and the reply:

On the contrary, it works exactly like a transformer. Evanescent fields are the electric and magnetic fields of the nearfield region surrounding any material or substance which interacts with electromagnetism. Evanescent waves are non-propagating in that they are "emitted" during 1/4 cycle by an electric current or a charge-separation, and are then re-absorbed during the next 1/4 cycle, only to be emitted again. Partial reflection can accomplish this, but so can coils or capacitors. If you apply AC to a simple loop inductor, the evanescent wave is the expanding and contracting b-field surrounding the inductor. One simple example of evanescent wave coupling is seen whenever EM energy is transferred between the two plates of a capacitor. Note well that light and radio waves are the same thing. You say that evanescent waves don't apply to transformers? That's exactly the same as saying that Maxwell's Equations apply to transformers but do not apply to the EM fields involved with total internal reflection! When we say that evanescent waves do not carry energy, we actually mean that the EM energy vector is oscillating, with no overall energy flow. The effect is identical to "imaginary power" in AC circuitry. But evanescent waves can easily be made to carry energy. After all, that's what the 2006 MIT paper is all about. But usually such topics are called "capacitive coupling" or "inductive coupling." However, the MIT article contains one difference between simple capacitor/coil coupling versus "wireless power transfer." They are using high-Q resonators. This is identical to a tuned-primary, tuned-secondary transformer. In this type of transformer, the coupling between the coils is proportional to the "Q" of the resonant circuits, and with high Q, even an air-core transformer will exhibit tight coupling. Which high enough "Q", the coupling remains significant even when the primary and secondary are separated by fairly large distance. --Wjbeaty 21:16, 12 January 2007 (UTC)

I haven't really used my physics degree in a while, so I'm hesitant to comment much on the validity of it, but I would tend to agree with Wjbeaty, that this is just another evanescent coupling mode that works at longer ranges than standard transformers. I doubt that it can be used to transform voltage in the same manner that traditional transformers do, however.

Also check out this paper on their technology. Lots of great details, and there's probably even a new one out by now...