Graphene is showing up in an increasing number of products, including coatings, sports equipment and even light bulbs. Now scientists are one step closer to making graphene audio speakers for mobile devices.

Conventional speakers today rely on many mechanical parts that vibrate to create sound and must be encased in an acoustic cavity. But this approach complicates manufacturing and limits where listeners can put their speakers.

The thermoacoustic loudspeaker consists of an array of 16 three-dimensional graphene aerogels. Image credit: KAIST.Researchers have been pursuing ways around this by turning to a principle conceived of more than a century ago—thermoacoustics—the production of sound by rapidly heating and cooling a material rather than through vibrations. Science has caught up to this concept largely due to the development of graphene, which is highly conductive and durable.

A joint Korea Advanced Institute of Science and Technology research team led by Professors Jung-Woo Choi and Byung Jin Cho, of the School of Electrical Engineering, and Professor Sang Ouk Kim, of the Material Science and Engineering Department, has now devised a relatively simple way to mass-produce ultra-thin graphene thermosacoustic speakers. Using a two-step, template-free fabrication method that involves freeze-drying a solution of graphene oxide flakes and the reduction/doping of oxidized graphene to improve electrical properties, the team produced an N-doped, three-dimensional, reduced graphene oxide aerogel (N-rGOA) with a porous macroscopic structure that permits easy modulation for many potential applications.

Using the 3D graphene aerogel, the team says it was able to fabricate an array of loudspeakers capable of withstanding over 40 watts input power and demonstrating sound-pressure level comparable to those of previously reported 2D and 3D graphene loudspeakers.

The researchers say their fabrication method is practical and could lend itself to mass production for use in mobile devices and other applications. Because the speakers are thin and do not vibrate, they could fit snugly against walls and even curved surfaces.