MIT研究人員成功將電力以無線方式從左方線圈傳送到兩公尺外的右方線圈,點亮了
60W的燈泡。(照片來源:MIT網站,Aristeidis Karalis拍攝)

MIT研究人員近日發表一項無線的輸電技術,並成功透過無線方式讓兩公尺外的60W電
燈泡發亮;這項技術理論上未來可能讓筆記型電腦可以無線充電。

這項被稱為WiTricity的技術是由麻省理工學院(MIT)物理系、電子工程、電腦科學
系,以及軍事奈米技術研究所(Institute for Soldier Nanotechnologies)的研究人員所共同
研發的成果,未來可能會被用在手機、機器人吸塵器、MP3播放裝置、筆記型電腦以及
其他各式可攜式裝置的充電技術。

WiTricity是採用耦合共振物體的概念,透過兩個擁有同樣共振頻率的共振物體進行有效
率的電力交換,這兩個共振物體中受到其他不同共振頻率影響的比例較低,因此,MIT
建置了一個系統,讓兩個耦合電磁共振可以透過同一磁場傳輸電力。

該研究團隊舉了一個容易了解的例子來說明此一概念。例如當一個房間內有一百個同樣
的玻璃杯,但杯子裡裝滿了不同高度的水,讓它們有不同的共振頻率,當一個女高音在
房間內唱出夠大聲的單音符時,擁有同樣共振頻率的玻璃杯就會開始累積能量甚至會碎
裂。

幾個世紀以來,用來作為無線電力傳輸的方式已有很多種,最為人知的就是電磁輻射,
例如無線電波,透過無線電波來交換資訊已有很好的成效,但卻不適合用做電力傳輸
上,最大的問題在於電磁輻射是全方位的散布,這會浪費絕大多數的電力。

還有一種可以指示電磁輻射方向的像是雷射光,這個方法並未被真正落實,而且甚至是
危險的,再加上雷射光與裝置之間必須沒有障礙才能交換能量。

在MIT所建置的系統中包含兩組共振銅線圈,一組是在電源端,另一組則嵌在裝置上,
兩端透過同樣的電磁共振交換電力,這是一個早就為人熟知的物理定律,但之前業界對
這樣的系統並沒有特別強烈的需求。該研究團隊認為,透過這樣的方式,未來的可攜式
裝置甚至可以不用電池。

不過,目前MIT所使用的共振銅線圈直徑長達70公分,而且傳送電力的範圍約為2公尺,
他們希望在未來的幾年內可將銅線圈直接縮小到至少可嵌入筆記型電腦中,同時擴大電
力傳送範疇到5公尺。(編譯/陳曉莉)
Sci-Tech-Prod (Science-Technology-Products) Village: 科學技術產品村: 011
Wireless energy could power consumer, industrial electronics: 跟電線說 bye-bye MIT 研究出無線輸電技術
received from Pi-Twan Huang 黃碧端
http://www.ithome.com.tw/itadm/article.php?c=43823
http://web.mit.edu/newsoffice/2006/wireless.html
文/陳曉莉 (編譯) 2007-06-11

MIT研究人員成功以無線方式點亮了60W的電燈泡,這項被稱為WiTricity的技術未來可
能會被用在手機、機器人吸塵器、MP3播放裝置、筆記型電腦以及其他各式可攜式裝置
的充電技術。
Researchers present a graphic illustrating how magnetism can transmit energy
wirelessly. Marin Soljacic, left, assistant professor of physics, Aristeidis Karalis, G,
and John Joannopoulos, professor of physics, use theoretical calculations and
computer simulations to find ways to recharge electronics wirelessly. Enlarge image

Dead cell phone inspired researcher's innovation
Davide Castelvecchi, American Institute of Physics
November 14, 2006

Recharging your laptop computer, your cell phone and a variety of other gadgets
may one day be as convenient as surfing the web--wirelessly.

Marin Soljacic, an assistant professor in MIT's Department of Physics and
Research Laboratory of Electronics, will describe his and his MIT colleagues'
research on that wireless future on Tuesday, Nov. 14 at the American Institute of
Physics Industrial Physics Forum in San Francisco.

Like many of us, Soljacic (pronounced Soul-ya-CHEECH) often forgets to recharge
his cell phone, and when it is about to die it emits an unpleasant noise. "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?" He began to
wonder if any of the physics principles he knew of could turn into new ways of
transmitting energy.

After all, scientists and engineers have known for nearly two centuries that
transferring electric power does not require wires to be in physical contact. Electric
motors and power transformers contain coils that transmit energy to each other by
the phenomenon of electromagnetic induction. A current running in an emitting coil
induces another current in a receiving coil; the two coils are in close proximity, but
they do not touch.

Later, scientists discovered electromagnetic radiation in the form of radio waves,
and they showed that another form of it--light--is how we get energy from the sun.
But transferring energy from one point to another through ordinary electromagnetic
radiation is typically very inefficient: The waves tend to spread in all directions, so
most of the energy is lost to the environment.

Soljacic realized that the close-range induction taking place inside a transformer--or
something similar to it--could potentially transfer energy over longer distances, say,
from one end of a room to the other. Instead of irradiating the environment with
electromagnetic waves, a power transmitter would fill the space around it with a
"non-radiative" electromagnetic field. Energy would only be picked up by gadgets
specially designed to "resonate" with the field. Most of the energy not picked up by a
receiver would be reabsorbed by the emitter.

In his talk, Soljacic will explain the physics of non-radiative energy transfer and the
possible design of wireless-power systems.

While rooted in well-known laws of physics, non-radiative energy transfer is a novel
application no one seems to have pursued before. "It certainly was not clear or
obvious to us in the beginning how well it could actually work, given the constraints
of available materials, extraneous environmental objects, and so on. It was even
less clear to us which designs would work best," Soljacic said. He and his
colleagues tackled the problem through theoretical calculations and computer
simulations.

With the resulting designs, non-radiative wireless power would have limited range,
and the range would be shorter for smaller-size receivers. But the team calculates
that an object the size of a laptop could be recharged within a few meters of the
power source. Placing one source in each room could provide coverage throughout
your home.

Soljacic is looking forward to a future when laptops and cell phones might never
need any wires at all. Wireless, he said, could also power other household gadgets
that are now becoming more common. "At home, I have one of those robotic
vacuum cleaners that cleans your floors automatically," he said. "It does a fantastic
job but, after it cleans one or two rooms, the battery dies." In addition to consumer
electronics, wireless energy could find industrial applications powering, for
example, freely roaming robots within a factory pavilion.

Soljacic's colleagues in the work are Aristeidis Karalis, a graduate student in the
Department of Electrical Engineering and Computer Science, and John
Joannopoulos, the Francis Wright Davis Professor of Physics. Both are also
affiliated with the Research Laboratory of Electronics. The work is funded in part by
the Materials Research Science and Engineering Center program of the National
Science Foundation.

A version of this article appeared in MIT Tech Talk on November 15, 2006
(download PDF).
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