Wireless energy to power nano-robots

A team of MIT researchers are developing a wireless power scheme

Imagine coming home after a long day of work; too tired to consider anything besides your favourite sitcom and sleep, you set down your laptop bag by the door, carelessly empty your pockets onto the coffee table, tuck a wirelessly powered LCD TV under your arm and pour yourself into bed, knowing that a wireless power system would have fully recharged your mobile phone, PDA, laptop and MP3 player by morning.

It was a dark, fretful night when wireless energy transfer first presented itself as a research topic for the Massachusetts Institute of Technology's Marin Soljacic. Soljacic had forgotten to recharge his mobile phone and it was complaining in a loud, unpleasant tone as it reached the final moments of its battery life.

"Needless to say, this always happens in the middle of the night," he said. "So, one night, at 3 a.m., it occurred to me: Wouldn't it be great if this thing charged itself?"

Along with colleagues Aristeidis Karalis and John Joannopoulos, Soljacic developed a method of wireless energy transfer that is expected to one day render the need to plug in and power up a thing of the past. The team's research was presented at the 2006 American Institute of Physics Industrial Physics Forum in San Francisco on Tuesday.

Physicists have grappled with the notion of the energy transmission equivalent of wireless data networks for some time, Karalis said, but had no way of overcoming efficiency and range limitations. So instead of using a radiative field as in wireless LANs, TVs and radios, the team has proposed a technique that relies on resonance to transfer energy from one object to another.

In this scheme, energy is radiated from a source at a certain frequency. Just like how a musical tone may shatter one wine glass and not another, the particular frequency of emitted energy is detected only by another object that is resonant at the same level.

A non-radiative wireless power system has many benefits, such as its minimal effect on environmental objects and its efficiency over a theoretical radiative scheme. Once wireless power is commercially developed, Karalis expects such systems to power not only home appliances, but also make possible a range of future technologies.

"The proposed mechanism is promising for many modern applications," the researchers write in a scientific report. "For example, placing a source (connected to the wired electricity network) on the ceiling of a factory room, while devices (robots, vehicles, computers, or similar) are roaming freely within the room. Other possible applications include electric-engine buses, RFIDs, and perhaps even nano-robots."

But it may be years before the team's research comes into fruition. Besides energy inefficiencies to do with the nature of wireless systems, Karalis said, the wireless energy transfer scheme could pose health hazards through the magnetic field it induces around the resonant objects.

"However," he noted, "human beings and most random objects around us are non-magnetic and therefore interfere very little with magnetic field. Considering that the proposed energy transfer scheme generates a much smaller magnetic field than the one produced from Magnetic Resonance Imaging, gives us strong belief that the hazard could be minimised."

"In any case, let's not forget that there are numerous applications that do not entail the presence of humans, [such as] robots in a factory," he said.

The technology is currently undergoing experimental investigation to do with safety and inefficiency issues. Karalis said that it is still too early in the developmental stages for any business plans to be disclosed.

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