Wireless Power For Laptops, Cellphones?
Battery technology has come a long way; more power from cells that are smaller and lighter. But what about devices like laptops, cellphones and Roombas that have no batteries, never need to be plugged in, but still work?
If you've read science fiction or know about the early history of electric power, you've heard this story before. Before the American landscape was covered with wires, inventors like Nikola Tesla thought it might be possible to beam energy through the air. The largest Tesla coil ever built could generate 300,000 watts of power, creating bolts of lightning 130 feet long. Tesla actually managed to successfully transmit about 30 to 50 thousand watts of power without wires using the coil.
However, this kind of power transmission typically required uninterrupted line-of-sight; the beam was usually focused on the object needing power, which means that some method of tracking objects was also needed.
Marin Soljacic, Aristeidis Karalis and J.D.Joannopoulos recently published a paper on Wireless Non-Radiative Energy Transfer, in which they describe several ways of using energy-transfer methods over short distances (like within a room or office cubicle). Rather than filling a space with electromagnetic radiation; the transmitting side of the device would provide a "non-radiative" field that would provide energy only to devices designed to resonate with the field. Unused energy would be (for the most part) reabsorbed by the emitting device.
Researchers worked with two well-known electromagnetic resonant systems: dielectric disks and capacitively-loaded
conducting-wire loops. In their study, both showed acceptable performance.
the proposed mechanism
is promising for many modern applications. For example, in the macroscopic world, this scheme
could be used to deliver power to robots and/or computers in a factory room, or electric buses on
a highway (source-cavity would in this case be a “pipe” running above the highway). In the
microscopic world, where much smaller wavelengths would be used and smaller powers are
needed, one could use it to implement optical inter-connects for CMOS electronics, or to transfer
energy to autonomous nano-objects (e.g. MEMS or nano-robots) without worrying much about
the relative alignment between the sources and the devices.
My favorite science fiction story dealing with radiant power is Robert Heinlein's Waldo, published in 1942. In reading the story, you need to remember that radiant power transmission was all the rage in the 'Teens and 'Twenties.
He had seen radiant power grow up. He had seen the great transmission lines removed from the sky - mined for their copper.
(Read more about radiant power)
Update 04-Nov-2006: As it happens, E.E. "Doc" Smith mentions something very much like this charging scheme in his 1930 novel Skylark Three:
"No wiring — tight beam transmission. The Fenachrone do it with two matched-frequency separable units."
(Read more about Matched-Frequency Separable Units)
Take a look at some other power alternatives:
Read the Soljacic, Karalis and Joannopoulos paper Wireless Non-Radiative Energy Transfer. And thanks to Winchell Chung for the update.
Scroll down for more stories in the same category. (Story submitted 11/16/2006)
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