Wireless technology has changed our world, with more and more objects in the physical world connected to the Internet. While you may just be starting to take advantage of 5G wireless technology, researchers around the world are already working on the future: 6G. Visible light communication (VLC) is widely regarded as a promising technology for future 6G networks.
However, recent research has shown that VLC transmitters not only emit visible light signals, but also leak RF signals during transmission.
Now, a team of researchers at the University of Massachusetts Amherst has invented a low-cost, innovative way to harvest waste energy from VLCs by using the human body as an antenna. This waste energy could be recovered to power a range of wearable devices and even larger electronics.
“VLC is very simple and fun,” Jie Xiong, a professor of information and computer science at UMass Amherst and the paper’s senior author, said. “Instead of using radio signals to send information wirelessly, it uses light from LEDs that can be turned on and off, up to a million times a second.”
Part of the appeal of VLC is that the infrastructure is already ubiquitous — our homes, vehicles, street lights, and offices are lit by LED bulbs that can also transmit data. “Anything with a camera, like our smartphone, tablet or laptop, can be a receiver,” Xiong said.
In their previous research, Xiong and first author Minhao Cui showed that there is a significant energy leak in the VLC system because the LEDs also emit side-channel radio frequency signals, or radio waves. If the leaked RF energy can be harvested, it can be put to use.
To get around this, the team first designed an antenna made of coiled copper wire to pick up leaking radio frequencies. To maximize energy harvesting, they experimented with various design details, from the thickness of the wires to the number of times they are coiled. The researchers also noticed that the antenna’s efficiency varies depending on what the antenna is in contact with.
They experimented with placing the coils on plastic, cardboard, wood and steel, and touching them to walls of varying thicknesses, phones and laptops that are switched on and off. Cui then had an idea to see what happens when the coils come into contact with the human body. It is clear that the human body is the best medium to amplify the coil’s ability to collect leaked RF energy by a factor of ten over a bare coil alone.
Based on the observations, the team came up with a system called “Bracelet+,” which incorporates the human body into the harvesting system to increase the energy harvested. After carefully analyzing the influence of the human body on harvested power, they prototyped the coil antenna as a bracelet, achieving both high harvested power and wearing convenience. The design is suitable for wearing as a ring, belt, anklet or necklace.
In tests, the new device collected radio frequency energy at an average power ten times that of conventional coil antennas without causing any disruption to the VLC system’s communications. In the scenarios tested by the team, the harvested power can reach microwatts. Harvesting energy at such a microwatt level has the potential to power ultra-low-power sensors such as temperature sensors and glucose sensors.
“finally,” Bear said, “We hope to be able to harvest waste energy from various sources to power future technologies.”