????尼古拉?特斯拉是19世紀末20世紀初與托馬斯?愛迪生相媲美的發明家。1901年，他從億萬富翁J.P.摩根那里獲得資助，在紐約長島修建了一座高達187英尺的無線電能傳輸塔——沃登克里弗塔。可惜項目最終失敗，特斯拉本人也宣告破產。（特斯拉之前曾在科羅拉多州做過類似的實驗，成功地將25英里之外的200盞燈點亮。不過據現場目擊者稱，他們能感到電流從地面穿過腳底，甚至當地居民在打開水龍頭時，都能看到水流在嘩嘩放電……）

????一個多世紀過去了，無線電能傳輸技術已取得了一些進展。一百多家公司正在研究這項技術，其中既有WiTricity和ProxybyPower等新創公司，又有豐田（Toyota）、英特爾（Intel）、三星（Samsung）和富士康（Foxconn）等跨國企業。目前的挑戰在于：按照功率方程原理，讓電能從通過電纜傳輸變成通過磁場傳輸。

????電能在空氣中傳播時會轉變為電磁場。所以我們可以非常安全地給手機等設備無線充電。現在普遍使用的無線充電式電動牙刷就是這個原理——電能通過磁場從電源傳輸給牙刷。市面上還有不少無線充電板，只要接通電源，再把手機放到上面就能無線充電。不過這種充電板有不少缺點：手機必須放得恰到好處，而且充電時間也很長。新西蘭一家叫PowerbyProxy的公司發明了一套新系統，用戶可以同時把多部手機擺放在充電板上的任何位置，充電速度很快，時間與傳統方式相當。三星公司上個月宣布向PowerbyProxy投資400萬美元。

????下一個目標：無需充電板也能無線充電。位于馬薩諸塞沃特敦的WiTricity公司在這個領域頗有作為。這家公司利用電磁諧振技術在空氣中傳輸電能，意味著電能有望實現遠距離無線傳輸。這項技術的基礎是麻省理工學院（MIT）的研究成果，WiTricity持有獨家專利。它的具體原理如下：如果兩個諧振物體具有相同的頻率，那么電能將非常精確地從一方傳輸到另一方。只要把諧振器插入插座，在另一邊的電動汽車或手機里安裝上對應的設備，它們就能接收到電能，開始充電。WiTricity稱目前已能傳輸高達3300瓦特電能而損耗極小，這已經足夠給一輛電動汽車充電了。WiTricity首席執行官埃里克?吉爾說：“我們都熱愛電能，愿意不惜一切代價獲得它。電能也許是我們最后一個希望無線化的東西，而這個目標必將實現。”

????這個過程是否安全？吉爾稱因為電能以電磁波的形式通過空氣傳輸，這和地球的電磁場類似，所以對人類不會造成危害。美國聯邦通訊委員會（FCC）對電磁場技術有不少規定，WiTricity自稱它的設備都符合FCC的要求。不過，整個工業界仍面臨巨大的挑戰，需要在教育和宣傳上不斷努力，以打消廣大消費者的顧慮。

????英特爾和鴻海/富士康集團將無線充電技術視為筆記本和手機等電子設備的殺手級應用。它們在幾周前投資了WiTricity公司。石油巨頭斯倫貝謝（Schlumberger）是WiTricity的早期投資者，它希望新技術能減少自己油田里的電線數量，以節約維護成本。豐田公司也參與了投資，有消息稱它計劃測試一種用于插電式電動車的無線充電站。

????Backed by the financier J.P. Morgan, Nikola Tesla, the inventor and rival to Thomas Edison, built in the early 1900s the Wardenclyffe Tower, a 187-foot-high structure on Long Island, which he said could transmit electricity wirelessly. The project failed, and Tesla ended up broke. (In an earlier experiment in Colorado, Tesla had wirelessly lit up 200 lamps over a distance of 25 miles, but pedestrians witnessed sparks jumping between their feet and the ground, and electricity flowed from faucets when turned on. Oops.)

????Fast-forward over a century, and wireless electricity is finally gaining some traction. More than one hundred companies including startups such as WiTricity and ProxybyPower and giants such as Toyota (TM), Intel (INTC), Samsung, and Foxconn are investing in the technology. The challenge: to take the wires out of the power equation by transmitting electricity through magnetic fields.

????When in the atmosphere, electricity exists as a magnetic field. The trick is to capture it safely to recharge devices. Today's electric toothbrushes charge wirelessly -- as power is transmitted through a magnetic field from the charger to the brush. You can already buy wireless recharging pads: Place your cellphone on a pad that's plugged into the wall, and it will recharge. These pads, however, have their limitations -- the cellphone has to be in the right position, and it can take a long time. A New Zealand company called PowerbyProxy has demonstrated a system where you can put multiple cellphones on a pad in any position, and it will charge the devices as fast as a traditional charger. Samsung last month invested $4 million in the company.

????The next step: charging without being so tied to a pad. That's the technology a Watertown, Mass., company named WiTricity is developing. Based on work done at MIT, the technology -- on which the company holds exclusive patents -- uses magnetic resonance to move power through the air -- which means electricity can be moved farther distances without a wire. The way it works: Two devices resonate at the same frequency so that the magnetic waves can travel very precisely from one point to another. Plug a resonator into a wall outlet, and a device installed on a cellphone or an electric car receives the power and starts recharging. WiTricity says its system can move an impressive 3,300 watts -- enough to charge an electric car -- with little efficiency loss. Says Eric Giler, the CEO of WiTricity: "We all love electricity and are willing to do almost anything to get it. It will be the last thing to go wireless, but it will go wireless."

????Is the process safe? Because electricity moves through the air as magnetic waves that are similar to the earth's magnetic waves, it poses no harm to humans, says Giler. The FCC has set limits for magnetic fields, and WiTricity claims its devices fall well below that threshold. The industry, however, will still face a tough time educating and persuading consumers that these devices are safe.

????In recent weeks, Intel and Hon Hai/Foxconn, seeing wireless charging as a possible killer app for electronic devices such as laptops and cellphones, invested in WiTricity. Schlumberger, which is interested in cutting the number of wires in its oil rigs to save maintenance costs, was an early investor, as was Toyota, which is reported to have plans to test a wireless charging station for plug-in cars.????