Experimental investigation of two- and three-dimensional graphene-based thermo-acoustic sound generating devices: Analysis of gap separation effect

Advances in nanomaterials over the last decade have enabled the practical exploration of the “thermophone” concept based on a thermoacoustic (TA) mechanism. By applying an alternating current to thin-film conductive materials that are strong, stiff and of high emissivity, it is possible to rapidly heat and cool the surrounding fluid (air or gas) through resistive heating and convection cooling. The resulting temperature oscillation of the fluid causes it to expand and shrink, which in turn generates acoustic waves with a sound pressure level (SPL) over a wide frequency band. Motivated by two-dimensional (2D) and three-dimensional (3D) graphene thin films possessing the essential characteristics needed for high performance TA, we present herein a comprehensive investigation on the performance of TA sound-generating devices made by mounting 2D and 3D graphene materials on a substrate with a 50-μm gap separation. The effect of the gap, the types of graphene films, and the substrate materials are investigated. Compared with 2D graphene thin films, 3D graphene foams were found to exhibit higher sound generation capability and TA efficiency. In addition, the mechanical properties of the substrate have a small effect on the SPL response of 3D-graphene foam TA devices but strongly affect the SPL response of 2D-graphene thin-film TA devices.