Nanomaterials have been responsible for all sorts of innovation of audio speaker designs. We’ve seen magnetic nanoparticles used to eliminate the need for a magnet in speakers. Carbon nanotubes have also been demonstrated to produce sound with heat. While these designs have been innovative, they were developed to demonstrate the capabilities of nanomaterials rather than to produce a piece of audio equipment.
Now, researchers at Korea Advanced Institute of Science and Technology (KAIST) have developed a new speaker design specifically targeted for the mobile audio market that draws its capabilities from nanomaterials. The KAIST researchers have used graphene to produce a speaker that does not require an acoustic box to produce sound.
In research described in the journal ACS Applied Materials & Interfaces, the researchers used graphene in a relatively simple process that yielded the long-elusive thermoacoustic speaker. Thermoacoustics is based on the century-old idea that sound can be produced by the rapid heating and cooling of a material instead of through vibrations.
While graphene has previously been shown to enable thermoacoustics (and carbon nanotubes have even been used previously to create thermoacoustic speakers), what sets the KAIST researchers’ work apart is the ease with which the graphene-based speakers are fabricated. The simple, two-step process, they say, will make commercial applications more likely.
They started by first freeze-drying a solution of graphene oxide flakes. They then reduced and doped the oxidized graphene to improve its electrical properties. (The process does not require any templates to complete the fabrication.) The end result: an N-doped, three-dimensional, reduced graphene oxide aerogel (N-rGOA) that is freestanding.
The final aerogel sound element has a porous macroscopic structure can be easily modulated. The speaker the KAIST researchers produced consists of an array of 16 of the aerogels; it operates on 40 watts of power and produce a sound quality comparable to that of other graphene-based sound systems.
The researchers believe that because of the simplicity of their fabrication method, speakers can be mass-produced for use in mobile devices and other applications. As you can see in the video below, the fact that speakers are flat and don’t vibrate means that can be placed against walls and even curved surfaces.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.