Scientists use human touch to power electronics

Using the human body as an antenna, the team of researchers has developed a low-cost, innovative way to harvest waste energy from Visible Light Communication (VLC), a wireless version of fibre optics that uses flashes of light to transmit information. 

This waste energy collected can then be recycled to power an array of wearable devices, or even, perhaps, larger electronics.

“VLC is quite simple and interesting,” said Jie Xiong, professor of information and computer sciences at UMass Amherst. “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. Homes, vehicles, streetlights and offices are all lit by LED bulbs, which could also be transmitting data. As such, this new technology could be used to power a huge range of electronics that people interact with daily. 

“Anything with a camera, like our smartphones, tablets or laptops, could be the receiver,” Xiong explained.

In order to make this development, the team built on their own previous research, which had showed that there’s significant ‘leakage’ of energy in VLC systems caused by the fact that 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’s first task was to design an antenna out of coiled copper wire to collect the leaked RF, which they did, but they also noticed that the efficiency of the antenna varied according to what the antenna touched.

The researchers then 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. Then graduate student Minhao Cui decided to test what happened when the coil was in contact with a human body.

The result was a huge success. It immediately 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 to offer the right balance of power harvesting and wearability.

“The design is cheap – less than fifty cents,” the researchers said. “But Bracelet+ can reach up to microwatts, 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.”

“Ultimately,” Xiong added, “we want to be able to harvest waste energy from all sorts of sources in order to power future technology.”