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Watch: Laser Beam Developed to Charge Your Phone Across a Room Without Wires or Charging Pads

22 February 2018

Wireless charging is the next step for consumer electronics. There are already a few smartphones on the market that can be charged wirelessly. Even though they boast wireless charging, these phones still need to be touching the charging pad to actually gain a charge. Researchers are trying to develop a way to charge electronics without wires or charging pads. Engineers from the University of Washington say they have developed a method to charge a phone with a laser. No wires or charging pads required!

The wireless charging system created by University of Washington engineers. Source: Mark Stone/University of WashingtonThe wireless charging system created by University of Washington engineers. Source: Mark Stone/University of Washington

The researchers developed a narrow and invisible laser beam that delivers a charge to a smartphone sitting across a room. They say that this tiny laser beam could potentially charge a smartphone just as quickly as a standard USB cable.

A power cell was placed on the back of a smartphone. This power cell is the part that actually charges the smartphone through the laser. The team also developed custom-designed safety features like a metal flat-plate heatsink on the smartphone to eliminate heat from the laser and a reflector that shuts off the laser if a person stands in front of the beam.

"Safety was our focus in designing this system," said co-author Shyam Gollakota, an associate professor in the UW's Paul G. Allen School of Computer Science & Engineering. "We have designed, constructed and tested this laser-based charging system with a rapid-response safety mechanism, which ensures that the laser emitter will terminate the charging beam before a person comes into the path of the laser."

"In addition to the safety mechanism that quickly terminates the charging beam, our platform includes a heatsink to dissipate excess heat generated by the charging beam," said Arka Majumdar, UW assistant professor of physics. "These features give our wireless charging system the robust safety standards needed to apply it to a variety of commercial and home settings."

The beam is generated by a laser emitter that comes from a focused beam that is in the near-infrared spectrum. Because safety is so important to the team, they implemented a safety system to make sure that the laser doesn’t affect humans. The system shuts off the charging beam by using low-power, harmless laser “guard beams” that are emitted from a different laser area. These low-power beams surround the charging beams so if a person steps in front of the beam, the charging beam is automatically shut off.

"The guard beams are able to act faster than our quickest motions because those beams are reflected back to the emitter at the speed of light," said Gollakota. "As a result, when the guard beam is interrupted by the movement of a person, the emitter detects this within a fraction of a second and deploys a shutter to block the charging beam before the person can come in contact with it."

The charging beam charges electronics and smartphones through a power cell on the back of the phone. The beam has a 2W of power to 15 square-inch area from up to 4.3 meters (14 feet). The charging beam’s radius can be expanded to up to 100 square centimeters from 12 meters away (40 feet). The radius extension means the beam may be able to charge larger electronics with larger surface areas, like laptops.

The smartphones the researchers used were programmed to send out small, high-frequency “chirps” that humans can’t hear, but the laser microphones can pick them up. This allows the laser to find the smartphone no matter where it is in a room and switch on once it finds the smartphone.

"This acoustic localization system ensures that the emitter can detect when a user has set the smartphone on the charging surface, which can be an ordinary location like a table across the room," said co-lead author Vikram Iyer, a UW doctoral student in electrical engineering.

Overheating is another worry that crossed the researchers' minds. They implemented thin aluminum strips on the back of the smartphone surrounding the cell. The strips dissipate and absorb the heat from the laser beam, eliminating worries about overheating the phones. They are further developing the strips to use the heat to help further charge the cell phones.

The paper on this research was published in the Proceedings of the Association for Computing Machinery on Interactive.

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