While 6G wireless networks are still some way off, Visible Light Communication (VLC) is seen as a possible alternative to using the radio spectrum.
VLC is like a wireless version of fibre optics, using flashes of light to transmit information.
Researchers at the University of Massachusetts Amherst have invented a low-cost, innovative way to harvest the waste energy from VLC by using the human body as an antenna.
This waste energy can be recycled to power an array of wearable devices, or potentially even larger electronics.
"VLC is quite simple and interesting," said Jie Xiong, a professor at UMass Amherst and the paper's senior author.
"Instead of using radio signals to send information wirelessly, it uses the light from LEDs that can turn on and off, up to one million times per second."
Part of the appeal of VLC is that the infrastructure is already everywhere – our homes, vehicles, streetlights and offices are all lit by LED bulbs, which could also be transmitting data.
"Anything with a camera, like our smartphones, tablets or laptops, could be the receiver," Xiong added.
The researchers have previously showed that there's significant "leakage" of energy in VLC systems, because the LEDs also emit "side-channel RF signals," or radio waves. If this leaked RF energy could be harvested, then it could be put to use.
The team initially designed an antenna out of coiled copper wire to collect the leaked RF and experimented with various designs, from the thickness of the wire to the number of times it was coiled.
They noticed that the efficiency of the antenna varied according to what the antenna touched. They tried resting the coil on plastic, cardboard, wood and steel, as well as touching it to walls of different thicknesses, phones powered on and off, and laptops.
But it became apparent that a human body is the best medium for amplifying the coil's ability to collect leaked RF energy, up to ten times more than the bare coil alone.
After much experimentation, the team came up with Bracelet+, a simple coil of copper wire worn as a bracelet on the upper forearm. While the design can be adapted for wearing as a ring, belt, anklet or necklace, the bracelet seemed to offer the right balance of power harvesting and wearability.
"The design is cheap – less than fifty cents," note the authors. "But Bracelet+ can reach up to micro-watts, enough to support many sensors such as on-body health-monitoring sensors that require little power to work owing to their low sampling frequency and long sleep-mode duration."
Xiong said: "We want to be able to harvest waste energy from all sorts of sources in order to power future technology."
