Analysis Of Thermoacoustic Characteristics Of Graphene Film Loudspeakers And Its Application

Graphene thermoacoustic loudspeakers,composed of a graphene film on a substrate,generate sound with heat.Improving thermoacoustic efficiency of graphene loudspeakers is the main goal for optimal design.In this work,the acoustic characteristics and temperature pattern of graphene films were studied in terms of thermoacoustic efficiency,and then the graphene film loudspeakers were applied to the active noise control to explore the feasibility of using graphene film loudspeakers for active noise control.The main contents were as follow:(1)The thermoacoustic model of graphene film loudspeakers was established considering the heat dissipation of substrates and the heat capacity of films,and then both near-field and far-field sound pressure formulas were derivated.For analysis of thermoacoustic characteristics,an acoustic platform was built to test acoustic performances of graphene films.It was obvious that the analytical predications agreed well with experimental data verifying the correctness of the thermoacoustic model.(2)Based on the valid model,influential factors on thermoacoustic efficiency of graphene film loudspeakers were studied.It was found that the thickness of graphene films(5nm~15nm)played a trivial role in efficiency,resulting in the sensitivity coefficient less than 0.02.The substrate thermal effusivity,however,had significant effects on efficiency,of which the sensitivity coefficient was around 1.7.For influences of ambient gases,the sensitivity coefficients of density was high up to 2.7;the sensitivity coefficients of thermal conductivity and specific heat were respectively 0.98 and 0.8.(3)In order to analyze the temperature variation and the heat transfer,the heat transfer model of graphene films was constructed considering the heat dissipation of substrates and air natural convection.Additionally,an experimental platform was built to capture thermal signals of graphene films.The transient temperature and steady-state temperature distribution of graphene films were also analyzed.It was found that the surface temperature of graphene films reached the highest in the middle,and decayed to periphery.The temperature oscillation for the thermoacoustic effect was extremely weak,so the thermoacoustic efficiency of the graphene film was low.(4)The graphene film loudspeakers were applied to the active noise control as monopole sound source.The active noise control model was established where graphene film loudspeakers were considered as primary and secondary sound sources respectively.To control the normal sound intensity of total radiation,noise reduction effect versus the distance between graphene films and acoustic frequencies were investigated.It was shown that a smaller value of distance between the two sound sources and a lower value of acoustic frequency resulted in a larger noise reduction.