Researchers at the National University of Singapore have demonstrated the use of the human body as a medium for transmitting and harvesting energy to power wearables.

Advancements in wearable technology are reshaping the way people live, work and play, and how healthcare is delivered and received. Wearables that have weaved their way into everyday life include smart watches and wireless earphones, while in the healthcare setting, common devices include wearable injectors, electrocardiogram (ECG) monitoring patches and listening aids.

A major pain point facing the use of these wearables is the issue of keeping these devices properly and conveniently powered. As the number of wearables increases, the need to charge multiple batteries rises in tandem, consuming huge amounts of electricity. Many find it cumbersome to charge numerous devices every day, and inconvenient service disruptions occur when batteries run out.

A research team, led by associate professor Jerald Yoo from the Department of Electrical & Computer Engineering and the N1 Institute for Health at the National University of Singapore (NUS), has developed a solution to these problems.

Their technology enables a single device, such as a mobile phone placed in the pocket, to power wirelessly other wearable devices on a user’s body, using the human body as a medium for power transmission. The system has an added advantage in that it can harvest unused energy from electronics in a typical home or office environment to power the wearables.

The achievement was published in the journal Nature Electronics this month.

To extend battery life and sustain fully autonomous yet wireless operations of wearable devices, power transmission and energy harvesting approaches are required. However, conventional approaches for powering up body area wearables are limited by the distance power can be transmitted, the path the energy can travel without facing obstacles, and the stability of energy movement. As such, none of the current methods have been able to provide sustainable power to wearables placed around the entire human body.

The NUS team decided to turn the tables on these limitations by designing a receiver and transmitter that uses the very obstacle in wireless powering – the human body – as a medium for power transmission and energy harvesting. Each receiver and transmitter pair contains a chip that is used as a springboard to extend coverage over the entire body.

A user needs to place the transmitter on a single power source, such as the smart watch on a user’s wrist, 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 a process termed as 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. Experiments showed that the system allows a single power source that is fully charged to power up to ten wearable devices on the body, for a duration of over ten hours.

The NUS team also looked into harvesting energy from the environment. The research found that typical office and home environments have parasitic electromagnetic (EM) waves that people are exposed to all the time, for instance, from a running laptop. The team’s novel receiver scavenges the EM waves from the ambient environment and, through a process referred to as body-coupled powering, the human body can harvest this energy to power the wearable devices, regardless of their locations around the body.

“Batteries are among the most expensive components in wearable devices, and they add bulk to the design,” said Yoo. “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.”

The team will continue to enhance the powering efficiency of the transmitter-receiver system with hopes that, in future, any given power-transmitting device, be it a user’s mobile phone or smart watch, can satisfy the network power demands of all other wearables on the body, thus enabling a longer battery lifetime.