Body-coupled RF charging of wearables

June 14, 2021 // By Nick Flaherty
Body-coupled RF charging of wearables
A single power source can use the human body to power up to 10 wearables on the body for over 10 hours

Researchers in Singapore have developed a technique to charge wearables from an RF source via the human body.

The approach enables a single device, such as a mobile phone placed in the pocket, to wirelessly power other wearable devices on a user's body, using the human body as a medium for power transmission. The system can also tap into ambient RF energy.

The team led by Associate Professor Jerald Yoo from the Department of Electrical and Computer Engineering and the N.1 Institute for Health at the National University of Singapore (NUS) designed a receiver and transmitter system that uses the human body for the power transmission and energy harvesting. Each receiver and transmitter contains a chip that is used as a springboard to extend coverage over the entire body.

A user just needs to place the transmitter on a single power source, such as a smartphone, while multiple receivers can be placed anywhere on the person's body. The system then harnesses energy from the source to power multiple wearables on the user's body via the body-coupled power transmission. In this way, the user will only need to charge one device, and the rest of the gadgets that are worn can simultaneously be powered up from that single source.

The team's experiments showed that their system allows a single power source that is fully charged to power up to 10 wearable devices on the body, for a duration of over 10 hours.

The body-coupled power transmission exhibits a path loss 30- to 70-dB lower than far-field radio frequency transmission in the presence of body shadowing. The system can recover 2 µW at the head from an ~1.2-mW transmitter placed 160 cm away at the ankle.

As a complementary source of power, the NUS team also looked into harvesting energy from the environment. Their research found that typical office and home environments have parasitic RF waves. The receiver scavenges the EM waves from the ambient environment, and through a process referred to as body-coupled powering, the human body is able to harvest this energy to power the wearable devices, regardless of their locations around the body.

This resulted in a power recovery of ~2.2 µW from electromagnetic waves of up to −10-dBm on the body.

“Batteries are among the most expensive components in wearable devices, and they add bulk to the design. Our unique system has the potential to omit the need for batteries, thereby enabling manufacturers to miniaturise the gadgets while reducing production cost significantly. More excitingly, without the constraints of batteries, our development can enable the next generation wearable applications, such as ECG patches, gaming accessories, and remote diagnostics," said Assoc Prof Yoo.

The NUS team will continue to enhance the powering efficiency of their transmitter/receiver system.

www.nus.edu.sg

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Picture: 
Ms Li Jiamin (centre), who has a transmitter on her right wrist and a receiver connected to a smart watch on her left wrist, and Mr Dong Yilong (right) who is holding a panel displaying the technology

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