Energy without wires. Toward a New World of Wireless Electricity

At the end of the 19th century, the discovery that electricity could be used to make a light bulb glow caused an explosion of research aimed at finding the best way to transmit electricity. At the head of the race was the famous physicist and inventor Nikola Tesla, who developed a grandiose project. Unable to believe in the reality of creating a colossal network of wires covering all cities, streets, buildings and rooms, Tesla came to the conclusion that the only realizable transmission method is wireless. He designed a tower about 57 meters high, which was supposed to transmit energy over a distance of many kilometers, and even began to build it on Long Island. A series of experiments was carried out, but the lack of money did not allow the completion of the tower. The idea of ​​transmitting energy through the air scattered as soon as it turned out


And now, a few years ago, associate professor of the Department of Physics at the Massachusetts Institute of Technology (MIT), Marin Soljačić, was awakened from a sweet dream by the insistent cries of a mobile phone. “The phone didn’t stop, demanding that I set it to charge,” says Soljacic. Tired and not about to get up, he began to dream that the phone, being at home, begin to charge on its own.

Soljacic began research on ways to transfer energy without wires. He abandoned long-range energy transmission projects like the Tesla project and focused on short-range energy transmission methods that would allow charging or even turning on portable devices — mobile phones, PDAs, laptops.

At first, he considered the possibility of using radio waves that transmit information so efficiently at a distance, but found that in this case most of the energy would be dissipated in space. The use of a laser required that the energy source and the rechargeable device be in the field of view of each other without any obstacles between them. In addition, this method was fraught with damage to objects caught in the transmission line. Therefore, Soljacic began to look for a transmission method that would be both effective, that is, capable of transmitting energy without dispersing it, and safe.

In the end, he settled on the phenomenon of resonant coupling, when two objects tuned to the same frequency intensively exchange energy with each other, while only interacting weakly with other objects. A classic illustration of this effect is the experience with several glasses filled with wine each to a different level than the rest. As a result, for each glass there is a unique frequency of sound that causes vibration. If the singer takes a note of the appropriate frequency, one of the glasses can receive such a dose of acoustic energy that it will crumble, while the remaining glasses will remain intact.

Soljacic realized that magnetic resonance is a promising way to transfer electricity. The magnetic field spreads freely in space and, at the right frequencies, is harmless to living things. Working in conjunction with MIT physics professors John Joannopoulos and Peter Fisher and three students, he developed a simple device that lit a 60-watt light bulb wirelessly.

The device consisted of two resonance-tuned copper coils suspended from the ceiling at a distance of about two meters. One coil was connected to an AC source and created a magnetic field. A second coil tuned to the same frequency and connected to the bulb, resonating in a magnetic field, generated a current igniting the bulb. The device worked even when a thin wall was placed between the coils.

The most effective of the devices created by this moment consists of 60-centimeter copper coils and a magnetic field with a frequency of 10 megahertz. It allows you to transmit energy over a distance of two meters with 50 percent efficiency. Research is being conducted with silver and other materials to reduce the size of coils and increase efficiency. Soldacic hopes to achieve 70-80 percent transmission efficiency.



A number of other ways to wirelessly recharge batteries are currently being investigated. Startups such as Powercast, Fulton Innovation, and WildCharge have begun to market adapters that allow wireless charging of mobile phones, MP3 players and other devices at home or in the car. But Soljacic’s approach is different in that it allows automatic charging of devices as soon as they fall into the field of action of a wireless transmitter.

The work of the Soljacic group attracted the attention of companies manufacturing electronic devices, as well as the automotive industry. The research was funded by the U.S. Department of Defense, which was hoping to get wireless automatic battery recharging technology. However, Soldjacic prefers not to spread about the possible industrial application of his technology.

There are so many potential applications in today's battery-driven world where our technology can be used, "he says." It's a very powerful method. "