Sound is the result of a pressure wave in the air. A regular speaker creates this wave by physically moving back and forth, regardless of whether it’s a magnetic coil-driven speaker or a membrane-based one. Thermo-acoustic sound generation is different. It causes the necessary pressure wave not by physically moving a component, but by periodically varying the temperature of the air next to it.
To achieve this, a material is required that’s able to heat up and cool down very rapidly, at a rate comparable to the frequency of the generated sound. That rules out a lot of metals because, although they conduct heat quickly, they turn out to be too good at storing heat over a long period of time.
The answer? According to a new piece of research coming out of the U.K.’s University of Exeter, it could be to use all-around wonder material graphene to create a non-moving solid-state audio device that may one day replace your existing bulk sound system.
“Graphene is great at conducting heat but, as it is just a single sheet of atoms, it has really poor capacity to store heat,” Dr. David Horsell, a professor of physics who worked on the project, told Digital Trends. “As a result, it can heat and cool at a very high rate indeed – enough to generate sound at audible frequencies and at much higher, ultrasonic frequencies.”
There are several possible applications for the work of Horsell and his colleagues, which go beyond merely acting as a replacement for regular hi-fi systems. One is to incorporate the tech into ultra-thin touchscreen technologies, which would no longer need separate speakers as a result, since the screen could be made to produce sound on its own — courtesy of a thin, invisible layer of graphene.
Another possible use-case concerns ultrasonic imaging or treatments in healthcare, since being small and potentially able to be produced on flexible substrates could allow a host of new medical techniques to be realized down to very small scales.
“There are two key aspects of the work we want to explore next,” Horsell continued. “The first is an issue with efficiency: Can we increase it enough to make graphene-based speakers compete with current, established loudspeaker technologies? For this, we need to look at exactly how the power we put into the graphene is dissipated. The other aspect we had not expected is that if you ‘listen’ closely to the graphene, it can start to reveal secrets of its inner workings. We have already seen that small nonlinearities in the conduction in graphene [are] translated into a specific frequency of sound output. We want to explore this further to see what other details we can discover just by listening to graphene when we question it with different electrical signals.”
An article describing how the researchers were able to combine speaker, amplifier, and graphic equalizer into a chip the size of a human thumbnail was published in the journal Scientific Reports.
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