Team leader Dr Walid Daoud, of university’s School of Energy and Environment, says the device could be incorporated into athletic leisure wear or the sole of a running shoe.

“It means less recharging and it encourages more physical exercise,” says Daoud.

And it’s not just for the athletic. The energy spent in normal daily activities, such as walking to the MTR or typing on a computer keyboard, will no longer be wasted, but converted to electrical energy for powering up a cellphone, smartwatch or tablet, he says.

“Even the very unfit and obese can benefit from the device because the extra forces exerted by their weight will produce more energy,” Daoud says, explaining that the device combines two key technologies which could potentially provide 10 per cent to 25 per cent of a smartwatch’s power.

The piezoelectric element requires the compression of a sandwich of materials to produce polarisation charges, ideal for the sole of a running shoe. The second is triboelectric, using a principle similar to a balloon being rubbed on a person’s hair to produce electrostatic charges. It requires the materials to be close, better suited to form part of clothing.

“We wanted to create a device that needs physical contact (piezoelectric) and close proximity (triboelectric), and the challenge was getting them to work in harmony using the same materials,” says Daoud.

He says the larger the surface area of the sandwich, the more energy produced, but if the device needs to be part of a smart electronic device, his team can expand the area vertically, using microscopic materials known as nanostructures.

Similar systems have been invented but the City University team’s breakthrough, recently published in the journal Advanced Functional Materials, was to isolate the effect of the two key technologies and identify which was producing the best outcomes.

“It’s our ability to separate the two effects and determine their individual transduction that allows us to design a nanogenerator for different daily activities,” says Daoud.

His team also modified the surface area with nanostructures that significantly improved efficiency.

“We found that the energy output can be increased by 50 to 60 per cent owing to the zinc oxide nanorods,” he says. Previously, this type of device could only offer 5-10 per cent of a smartwatch’s typical power needs, and was not considered commercially viable unless contributing about 25 per cent and significantly prolonging battery life.

Daoud also thinks batteries eventually could be obsolete. Not only would charging be a thing of the past, but the body motion power devices could be designed for different lifestyles and applications.

If not built into the smartphone or smartwatch itself, the device could be larger and manufactured as part of the lining of a jacket, with a charging pocket allowing the wearer’s phone or tablet to be charged wirelessly when not being used. Or the device could form the sole of a running shoe and wirelessly charge the smartwatch worn elsewhere. Daoud says wireless charging of electric cars is now being tested using induction techniques, so why not phones?

“By virtue of its simple design and the wide range of materials it can be used with, the device is highly practical and the manufacturing cost is expected to be low,” he adds.

Daoud estimates the first of these devices could be seen in shops within two years. Not surprisingly, commercial technology companies are making inquiries.

“We have been approached by a well-known electronics manufacturer from China, which wants to explore our energy technology ideas,” he says.