Researchers at the University of Washington (Seattle, WA) have designed and experimentally demonstrated a laser-based line-of-sight wireless power delivery system that could be used, for example, for charging smartphones and other devices.1 The researchers say that the system delivers more than 2 W of power safely over distances of 4.3 and 12.2 m for a smartphone (25 cm2) and tabletop form factor (100 cm2) receiver, respectively.
The system uses a high-power laser-diode source with a 978 nm wavelength, along with two steerable mirrors to aim the beam at the receiver; a photovoltaic cell, heatsink, and retroreflector at the receiver; and a low-power guard laser beam to serve as a safety interlock (using the retroreflector), switching the high-power laser off within 272 µs if the beam is intercepted by a human. The low-power beam is wider than the high-power beam, ensuring switch-off before the high-power beam can contact a person.
"Safety was our focus in designing this system," says Shyam Gollakota, one of the researchers. "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 researchers programmed the experimental smartphone to signal its location by emitting high-frequency acoustic chirps inaudible to human ears.
"The beam delivers charge as quickly as plugging in your smartphone to a USB port," says Elyas Bayati, another researcher. "But instead of plugging your phone in, you simply place it on a table."
Planar metasurface retroreflectors could be used in the future, say the researchers.
Source: http://www.washington.edu/news/2018/02/20/using-a-laser-to-wirelessly-charge-a-smartphone-safely-across-a-room/
REFERENCE:
1. Vikram Iyer et al., Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable & Ubiquitous Technologies (2018); doi: 10.1145/3161163
