From Cell Phones to Cars: No More Plugins

Nikola Tesla, who achieved fame more than a century ago for his astonishing experiments, earning him the image of the classic mad genius, would likely have a quick response if he could see today's efforts to transmit electricity wirelessly: "What took you so long?"

Tesla, who was born in Serbia in 1856, patented his invention of the electric motor in 1888, and the vision that made that possible opened new vistas for a very creative mind: If a magnetic field can cause current to flow in a nearby wire, and if current flowing through a wire creates a magnetic field, then electricity could be transferred from one place to another without any direct connection between the field and the current.

That insight has inspired scientists around the world to free us from the need to string wires throughout our homes and our vehicles and our offices and anywhere we are likely to spend much time.

And decades after Tesla's experiments verified his theory, labs around the world are finally making wireless transmission of electricity a reality.

The goals range from having cell phones that recharge themselves without plugging them in, to electric vehicles that are recharged as they roar down the highway. No need to plug in. Just go, any distance, without "refueling."

And it now appears feasible that tiny electronic devices than can monitor a person's entire biological system, and even make sure the heart keeps pumping, can be implanted and recharged without cutting the patient open to replace the battery.

The concept of recharging your vehicle as you drive may seem unlikely, but South Korea has proved it -- with buses, no less.

Since last August, two electric buses have been rolling along the streets of the city of Gumi, and the plan to have 10 more in operation by the end of next year is on schedule, according to a spokesman for the Korea Advanced Institute of Science and Technology.

The buses are recharged from a magnetic field caused by segments of electrical cables buried under the surface of the road. The cables take up only 5 percent to 15 percent of the length of the road, so it isn't necessary to dig up the entire street.

Korean officials say the system operates at 85 percent efficiency, which is an extraordinary high rate of performance.

The cable segment switches on when the bus is passing over it, and off when it leaves, thus improving efficiency, and it doesn't come on when a car passes, although it could if the car was equipped the same way as the buses.

But, of course, some folks might not like the idea of being surrounded by a magnetic field while driving down the highway. No worry, according to researchers at MIT. The cables in the road and the receivers on the vehicle have to operate on precisely the same frequency, so the magnetic field would have no effect on "extraneous materials," including biological systems.

An MIT researcher compared that to an opera singer trying to shatter wine glasses with her voice. Each glass would have a different resonant frequency, depending on the amount of wine in the glass. Only the glass with the resonance that matched the resonance of the singer would break.

That same principle could enable a cell phone to pick up the right frequency from a transmitter in a crowded room, and only that frequency, by using matching coils of wire in the receiver and the sender.

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