Small graphene speaker

Graphene combines speaker, amplifier and equaliser in fingernail-sized chip

Image credit: David Horsell/University of Exeter

A new method, which produces complex and tuneable sound by heating and cooling graphene, opens up a range of possible applications, including smart bandages and talking smartphone screens.

Speaker technology has barely changed in more than a century. Traditional speakers use a vibrating coil or membrane to push surrounding air back and forth, producing sound waves. A newly developed technique using graphene, however, could eliminate the need for bulky speakers with moving parts.

Graphene, a material composed of an atom-thick film of carbon atoms, is considered a “wonder material” for its extraordinary strength and thermal and electrical conductivity. Its Nobel Prize-winning discovery in 2004 has led to excitement about its possible applications in a range of industries.

As recounted in Scientific Reports, a team of researchers based at the University of Exeter tried rapidly heating and cooling a layer of graphene using an alternating electric current. This thermal variation was transferred to the air, causing the air to expand and contract, and generating sound waves.

While heat has been used before to create sound – this field is known as thermoacoustics – this is the first time the process has been mastered to allow sound to be mixed, amplified and equalised, all within the same cheap, fingernail-sized device.

“Thermoacoustics has been overlooked because it is regarded as such an inefficient process that it has no practical applications,” said Dr David Horsell, study author and a lecturer in the quantum systems and nanomaterials group at the University of Exeter.

“We looked instead at the way the sound is actually produced and found that by controlling the electrical current through the graphene we could not only produce sound but could change its volume and specify how each frequency component is amplified.

“Such amplification and control opens up a range of real-world applications we had not envisaged.”

As graphene is just one atom thick and almost completely transparent, being able to use the material to produce sound without movement opens up the possibility of an entirely new approach to audio technologies. Applications could include smartphone screens, which transmit sound as well as images, or smart bandages, which monitor patients and adapt treatment accordingly.

The research team suggest that the technology could have applications in ultrasound imaging in hospitals and other medical facilities.

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