Tesla started it. Intel and Sony are both interested in it. And a Croatian physicist and electrical engineer will likely be the first person to commercialize it. “It” is wireless energy transfer, and I’m betting that it will be commercially deployable in limited form by 2013. This means that the days of having to plug your phone in to charge it are going, going, and almost gone.
This accomplishment will be a holy grail of sorts. Ever since Andre-Marie Ampère codified the laws of nature—dictating that an oscillating magnetic field produces an electric field and that an oscillating electric field produces a magnetic field (Ampère’s circuital law)—history has been littered with theories and attempts to enable the wireless transfer of energy for the purposes of powering lights, objects, and devices.
Amazingly enough, Tesla demonstrated wireless energy transfer almost 120 years ago at the 1893 World Fair in Chicago by providing power to a series of phosphorous light bulbs. In 1904, at the World Fair in St. Louis, a prize was offered for anyone who could successfully transmit enough energy over a distance of 100 feet to power a dirigible. In 1964, William Brown demonstrated a model helicopter that could fly by receiving power via a microwave beam over a distance of one mile.
Nikolas Telsa (left) started the wireless energy transfer revolution almost 120 years ago. In the next few years, Croatian physicist and MIT professor Marin Soljacic (right) will finish it.
More recently, in 2007, a group led by MIT Professor Marin Soljačić (the Croatian physicist mentioned above) wirelessly powered a 60W light bulb from a distance of 2 meters using electrodynamics induction. In 2008, Intel reproduced Tesla’s experiments by wirelessly powering a light bulb. And in 2009, Sony demonstrated a wireless-powered TV at a range of 20 inches.
Fundamentally, there are two different means of wirelessly transferring power. Far-field methods permit long-range power transfers and typically involve beamed power (lasers) or radio and microwave transmissions. However, as Tesla famously espoused, electric currents are also theoretically capable of being transmitted over extremely long distances via the earth’s atmosphere. Near-field transmissions typically involve the use of inductive techniques and magnetic fields to move energy across much shorter distances.
At their core, both methods leverage the principles of electromagnetism and the intrinsic relationship of electric and magnetic fields. Because near-field transmissions are safer and more efficient, most consumer-based development has centered around this method.
The bulk of near-field transmissions function via resonant inductive coupling, which is less complicated than it sounds. A primary coil generates a magnetic field, which induces an alternating electric current in a secondary coil that resides within this field. This magnetic field is then coupled with another magnetic field (which has its own secondary alternating electric current) that is resonating at a similar frequency. The wireless transfer of power is naturally induced between these two fields. The higher the resonance, the lower the loss of power during transmission.
In the last few years, the theories behind near-field transmission have become reality. In 2007, based on the success of his experiments, Marin Soljačić helped start up a company named WiTricity with the stated goal of building a wireless charging apparatus for consumer devices. With the help of the Haier group—a Chinese electronics manufacturer—WiTricity demonstrated this technology at CES by wirelessly powering a 32-inch television at a distance of six feet.
The company’s prototype, which you can see for yourself at www.witricity.com , consists of a transmitter that converts AC power (via a wall socket) into a magnetic field, and then uses the field to transmit this magnetic energy to a capture device. This device then converts the magnetic energy into electricity. The two devices are highly resonant, meaning wireless energy transfer is highly efficient.
Thus far, WiTricity has been extremely quiet about its plans and products, but the company’s web site says that it’s currently working to miniaturize the technology so that it can be embedded directly into devices and systems. This will eliminate the need for the external capture device. By the end of 2013, we should have our first wirelessly charged smartphones.
And, no, you won’t get an electric shock if you step into the energy field.
George Jones is the Editor-in-Chief of
and a dedicated gadget guy.