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Smart devices could convert motion into electricity

Image credit: Stefanschurr226 | Dreamstime

Scientists have developed small, flexible generators that enable smart devices to charge themselves using energy harnessed from the movements of their user.

The device, developed by scientists from Loughborough University and the University of Surrey, is based on triboelectric nanogenerators (Tengs) and generates electricity from movement similar to how static electricity is produced. The University of Surrey researchers previously proposed a system based on Tengs in 2018.

Previously, using Tengs has been incompatible with many day-to-day electronic devices due to their inability to produce a constant current. However, the researchers have said they found a way to produce a direct current from a unique Teng design, creating a steady flow of electricity and opening up the potential for real-world applications.

“Triboelectric nanogenerators are effectively small-scale, flexible, and sometimes stretchable, energy generators that convert movements in our surroundings such as human motion, machine vibrations, vehicle movements, wind and wave energy into electricity,” said Dr Ishara Dharmasena, of Loughborough’s School of Mechanical, Electrical and Manufacturing Engineering. 

Dharmasena said these generators are versatile and can be constructed in a wide variety of shapes, weights and sizes – from a few mm2 to several m2“Unlike conventional mechanical energy harvesting methods, such as piezoelectric or electromagnetic devices which contain heavy and bulky components, toxic materials and rigid structures, Tengs can be constructed using low cost, lightweight, non-toxic and flexible materials.”

Potential applications of the generators include next-generation wearable and implantable electronics, smart textiles, medical devices, IoT (Internet of Things) and 5G related sensors, smart pavements, smart floors, mobile phones and tablets, the researchers said.

Tengs are made from dielectric materials, such as plastics, which accumulate static charge when they rub against each other. As these charged materials move back and forth, they generate uneven instantaneous alternating electrical current signals. The current is then further processed and stored in a battery or capacitor to be used when needed. Therefore, a typical Teng produces sharp positive and negative current peaks during its operation.

“In our new technology, converting the alternating current into a direct flow involves phase shifting,” Dharmasena said, adding that an assembly of Teng units (poles) are used as a single device, where they are systematically excited to obtain a phase difference among their outputs.

This systematic excitation is obtained through their geometry and spatial arrangement, he explained. The outputs with different phases are then superimposed to obtain the final DC output signal.

In a paper on the research, the team demonstrated the applicability of this technology by continuously lighting a set of LED lights and a photodetector.

Dharmasena said: “This new invention overcomes one of the most critical challenges of Teng technology and will enable countless real-time low-power applications in wearable electronics, such as IoT related applications and smart sensing, getting us one step closer towards a sustainable, autonomous and portable energy source.”

In 2018, South Korean researchers demonstrated that nanogenerators can be used to power battery-free rubber ducks with mechanical vibrations.

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