Research on 2D and 3D graphene thermoacoustic loudspeakers

Abstract

To realize a practical graphene thermoacoustic loudspeaker with high efficiency, it is important to minimize heat transfer to the substrate supporting the graphene membrane. We present a graphene thermoacoustic loudspeaker with an extremely thin, mesh-type substrate that maximizes the free-standing area of the graphene membrane exposed to the air, while mini-mizing the heat loss through the substrate. The mesh substrate is fabricated using a fast, cost-effective screen-printing technique. An experiment with substrates of 51% and 77% opening areas show that more than a 15 dB increase in sound pressure level compared to the substrate without any free-standing area. Furthermore, conventional model for the frequency response of a thermoacoustic loudspeaker is modified to be able to reflect the thin (a few hundred nm) and patterned substrate. Through a comparison with the experimental results, it is demonstrated that its sound pressure level can be accurately predicted. In addition, we introduce a ther-moacoustic loudspeaker built on the basis of a 3-dimensional reduced graphene oxide sponge (rGOS). The manufacturing of the rGOS of our speaker requires only a 2-step, non-toxic fabrication process, which includes freeze-drying and thermal reduction. The thermoacoustic loudspeaker shows outstanding performance of sound pressure level (SPL). We carry out experiments to study the SPL of a variety of 3-dimensional thermoacoustic loudspeakers with different structural properties such as area and density and we observe how constructive interference on a substrate causes an increase in the SPL. The investigation on SPLs of thermo-acoustic loudspeakers with different structural properties shows that a rGOS with the lower density and larger area shows a higher level of SPL.