Two temperature model for thermoacoustic sound generation in thick porous thermophones

Abstract

The thermoacoustic sound generation offers a promising wideband alternative to mechanically driven loudspeakers. Over the past decade, the development of nanomaterials with new physico-chemical properties promoted a wide interest in the thermophones technology. Indeed, several thermophone structures based on suspended nanowires, graphene sheets, highly porous foams or sponges have been investigated. At the same time, theoretical models have been developed to predict the frequency and power spectra of these devices. However, most of models have taken into consideration a solid homogeneous material for representing the thermophone generating layer, and its microstructure was therefore neglected. If this assumption holds for thin dense materials, it is not acceptable for thick and porous thermophone devices. Hence, a model able to describe the behavior of highly porous foam-or sponge-like generating layers is proposed. It is based on a two temperature scheme since the thermal equilibrium is not typically attained between the foam material and the embedded air. To do this, the fluid equations for the air are coupled with the heat equation for the solid foam through boundary conditions mimicking the energy exchange at the contact surface between them. The behavior of the main physical variables within the porous generating layer is explained and comparisons with recent experimental results are thoroughly discussed.

Experimental characterization of three-dimensional Graphene’s thermoacoustic response and its theoretical modelling

“…3D-C with varying parameters were synthesized and the acoustics performance studied and compared to theoretical models and experiments from the literature [7,26,27,38]. Results…”

“…can be evaluated at any position and frequency. More explanations regarding the equations and the development of the model can be found in Guiraud et al 2019 [34,38] and the derivation section in Supporting Information.…”

“…This thermal layer can be estimated from Eq. (A.11) (Supporting Information) assuming weak viscosity as [28,34,38]…”

“…Nevertheless, this backing has to be placed at a controlled distance: close enough for coherent reflections but at least several hundred microns away from the sample in order to avoid undesired losses by thermal conduction. The two temperature model proposed in Guiraud et al 2019 [38] indicated that one method to improve the high frequency radiation of a foam thermophone with a fixed thickness was to increase the number of discretized layers. This would increase the contact surface area between 3D-C and the surrounding air, improving the energy transfer between the two mediums.…”

“…In this study, we investigate the suitability of Guiraud et al's simulation model [38] for describing the acoustic performance of 3D-C. First 3D-C was synthesized in-house and the microstructure and quality of the material tested with the use of a Scanning Electron Microscope (SEM) and Raman spectroscope respectively. Then, acoustic measurements were performed to assess the acoustic performances of 3D-C.…”