Graphene-Based Thermoacoustic Sound Source

Abstract

Thermoacoustic (TA) effect has been discovered for more than 130 years. However, limited by the material characteristics, the performance of a TA sound source could not be compared with magnetoelectric and piezoelectric loudspeakers. Recently, graphene, a two-dimensional material with the lowest heat capacity per unit area, was discovered to have a good TA performance. Compared with a traditional sound source, graphene TA sound sources (GTASSs) have many advantages, such as small volume, no diaphragm vibration, wide frequency range, high transparency, good flexibility, and high sound pressure level (SPL). Therefore, graphene has a great potential as a next-generation sound source. Photoacoustic (PA) imaging can also be applied to the diagnosis and treatment of diseases using the photothermo-acoustic (PTA) effect. Therefore, in this review, we will introduce the history of TA devices. Then, the theory and simulation model of TA will be analyzed in detail. After that, we will talk about the graphene synthesis method. To improve the performance of GTASSs, many strategies such as lowering the thickness and using porous or suspended structures will be introduced. With a good PTA effect and large specific area, graphene PA imaging and drug delivery is a promising prospect in cancer treatment. Finally, the challenges and prospects of GTASSs will be discussed.

Research on Frequency Doubling Effect of Thermoacoustic Speaker Based on Graphene Film

“…In 2020, Ahn et al extracted carbon nanotube sheets from a vertically grown carbon nanotube forest, and found that the electrical performance of carbon nanotube sheet speakers and the heat spreading into the surrounding medium are closely related to the sound pressure levels [12]. Among them, graphene-based materials stand out for their thin thickness, low HCPUA and large thermal conductivity, becoming the preferred conductive thin film material for thermoacoustic speakers [13][14][15].…”

Application of three-dimensional graphene in sound generation via thermoacoustics

“…Generally, a good material used for thermoacoustic sound generation needs to have a high thermal conductivity (κ) and low specific heat capacity (Cp). High thermal conductivity is required for efficient dissipation of the induced thermal energy into its surrounding medium, while a low specific heat capacity is needed to decrease the amount of thermal energy required to increase the material temperature [14,15]. Low thickness is also desired to minimize the heat capacitance per unit area (HCPUA) of the material [14,15].…”

“…High thermal conductivity is required for efficient dissipation of the induced thermal energy into its surrounding medium, while a low specific heat capacity is needed to decrease the amount of thermal energy required to increase the material temperature [14,15]. Low thickness is also desired to minimize the heat capacitance per unit area (HCPUA) of the material [14,15]. Among the various materials, metals are a class of materials, which possess the required thermal properties (κ = 10.7 -418 W•m -1 •K -1 , Cp = 0.015 -1.885 [16]) for thermoacoustic sound generation, have been used as an initial proof of concept of thermoacoustic sound generation in the early 1900s.…”

“…The patterns of these rapid movements follow that of the temperature gradient, which was induced by the programmed AC input. This vibration couples into the surrounding medium as longitudinal waves and hence the generation of sound [13,14,19,76,77].…”

“…The large decrease in electro-thermoacoustic sound performance in Sample L is attributed by an increased strut thickness brought about by increased material density. For optimal electro-thermoacoustic sound generation to occur, a material is required to have a low heat capacity per unit area (HCPUA) [14,15]. A low HCPUA means that when heat is induced in the material, most of the induced heat along its contact surface is dissipated into its surroundings instead of being stored within the material.…”