In the approach, which features no moving parts, a layer of graphene is rapidly heated and cooled by an alternating current. This causes air to expand and contract, generating sound waves. The Exeter team says it is the first to show that this process allows sound frequencies to be mixed, amplified and equalised within the same device.
Senior lecturer Dr David Horsell explained: “Thermoacoustics has been overlooked because it is regarded as such an inefficient process that it has no practical applications. We looked instead at the way the sound is produced and found that by controlling the electrical current through the graphene, we could not only produce sound but also 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.”
Potential applications for the approach include ultrasound imaging and intelligent bandages that monitor and treat patients. However, because graphene is almost completely transparent, the ability to produce complex sounds without physical movement could lead to new audio-visual technologies, including mobile phone screens that transmit both pictures and sound.
Dr Horsell added: “Frequency mixing is key to new applications. The sound generating mechanism allows us to take two or more sound sources and multiply them together. This leads to the efficient generation of ultrasound (and infrasound). However, the most exciting thing is that is does this trick of multiplication in a remarkably simple and controllable way. This could have a real impact in the telecommunications industry.”