writes copy 01 Mar 2018

3D Printed Device Developed at UW Allows Laser to Wirelessly Charge a Smartphone

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The wireless charging system. The charging laser and guard lasers are normally invisible to the human eye, but red beams have been inserted in place of the guard beams for demonstration purposes.

As Dr. Evil, and cats everywhere, have conclusively proven, everything is cooler with a laser. What’s definitely not cool is hauling around tangled charging cords or, in my household at least, losing the charging cord or the box more often than James Bond escapes a sticky situation after the villain has explained every detail of her/his vile plan. A team of engineers at the University of Washington may just have solved both my loss of accessories and my lack of cool factor with the development of a laser system that can wirelessly charge smartphones from across the room.

The invention, detailed in a paper in the Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable & Ubiquitous Technologies (IMWUT), allows a laser beam that is emitted to be picked up by a 3D printed power cell attached to the back of the cell phone. This device, which works with invisible laser beams, can charge the phone as quickly as a standard issue USB charger. Also designed into the device is a way of dissipating any excess heat generated by the laser and an automatic shutoff which prevents any damage being done to objects, people, or animals which might accidentally cross the path of the laser beam. This is particularly important as the laser beam itself is invisible to the naked eye. As team member Shyam Gollakota, Associate Professor in the University of Washington’s Paul G. Allen School of Computer Science and Engineering, explained:

“Safety was our focus in designing this system. 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. 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. 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 University of Washington engineers behind the wireless charging system for mobile devices.
Standing (left-to-right): Vikram Iyer, Shyam Gollakota, Elyas Bayati.
Seated (left-to-right): Rajalakshmi Nandakumar, Arka Majumdar.

These guard beams are harmless beams that are transmitted surrounding the actual charging beam and their presence is measured by a series of 3D printed retroreflectors, meaning that before the person actually interrupts the laser beam, the guard beams have been disrupted and sent the shut off signal to the laser’s source. This feature could actually make the laser charger even safer than the regular plug in charger, based solely on the number of times I personally trip over the cord and send my device flying across the room which causes me to nearly have a fatal heart attack – also causing my children to expand their vocabulary in a colorful way.

Illuminated in red is one of the 3-D printed retroreflectors, which reflects the low-power guard beams to diodes on the laser emitter. Interruption of the guard beams triggers a safety system which blocks the charging beam.

The beam produced by the laser charges the phone through contact with a 3D printed power cell attached to the back of the smartphone, delivering 2W of power to a 15-square-inch area from a distance of up to 14 feet. Placing the phone anywhere within that 15-inch range will allow power to be delivered. The laser emitting device detects the specific location of the phone using a series of ‘chirps’ emitted by the phone as a result of a program installed by the engineers. It is also possible to modify the charger to expand the beam’s radius to an area of nearly 40 square inches and to broadcast the beam at a distance of 40 feet.

The system has been designed to function in both commercial and residential settings, after intense safety testing, says paper co-author and team leader Arka Majumdar, Assistant Professor of Physics and Electrical Engineering:

“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. These features give our wireless charging system the robust safety standards needed to apply it to a variety of commercial and home settings.”

The UW team's prototype heatsink assembly, which can be attached to the back of a smartphone, consists of a photovoltaic cell (silver square, top) attached to a thermoelectric generator (in white). The generator is mounted on top of an aluminum heatsink. The entire assembly is only 8mm thick and 40mm wide.

This could be especially useful in households with multiple devices, particularly those who have disagreements about iPhone vs. Android and therefore cannot share USB cords. Instead of an unsightly ma

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