基于石墨烯薄膜的新型声学器件热-振致声机理研究

Graphene, known as the thinnest and hardest nano-material in the world, has excellent mechanical, electrical, optical and thermodynamic characteristic and is considered to be a revolutionary material in the future. This project combines the vibrational vocalization and thermal vocalization of graphene film to exert the advantages of the two sound fields for the first time and then builds a new type of graphene film loudspeaker system.. Based on the nonlocal theory, combined with Kirchhoff piezoelectric thin-plate model, the force-heat-electric coupling dynamics model of graphene thin film / plate is established. The natural frequency and vibration of the film are solved and analyzed, and then the vibrational radiation sound is calculated. The mechanism of thermoacoustic effect of graphene film is revealed, and the thermoacoustic model of the film is established. Additionally, the sound pressure expression of the thermoacoustic effect is derived and verified by experiments. The two sound fields are superposed to derive the total sound pressure expression, which is verified and corrected by experiments. The acoustic characteristics and influential factors of the sound field are analyzed, and then the graphene film loudspeaker devices with excellent performance will be designed and developed. The aim of this project is promoting the application of graphene loudspeakers in the audio industry, intelligent acoustic structure, building sound reinforcement, aviation and defense industry, etc.

石墨烯是已知的世上最薄、最坚硬的纳米材料，具有优异的力学、电学、光学、热学等性能，被认为是一种未来革命性的材料。项目首次将纳米薄膜的振动发声和热致发声结合起来，发挥两种声场的优势，构建新型的石墨烯薄膜扬声器系统。.基于非局部理论，结合基尔霍夫压电薄板模型，建立石墨烯薄膜/板的力-热-电耦合动力学模型，对薄膜的固有频率和振动进行求解和分析，并计算薄膜的振动辐射声;揭示石墨烯薄膜热声效应机理，建立薄膜的热致发声模型，推导石墨烯薄膜热声效应声场的声压表达式，并进行实验验证；将两种声场叠加，推导总的声压表达式，并进行实验验证和修正；分析薄膜声场特性及各因素对声场性能的影响，设计并研制性能优良的石墨烯薄膜扬声器装置，推动此类扬声器在音频行业、智能声学结构、建筑扩声、航空及国防工业领域的崭新应用。

建立了二维石墨烯薄膜和三维石墨烯泡沫的热致发声模型，对它们的声场进行了理论计算；搭建了实验平台，对不同结构石墨烯的声场进行了测试；测试结果与理论计算吻合良好，验证了理论模型的正确性。对石墨烯薄膜进行电-热-声耦合的三维建模计算，计算出薄膜表面的温度振荡和稳态温度分布，建立了热黏性声学和压力声学耦合的声扩散模型，计算出声压的空间分布，结果表明：三维模型数值计算结果与测试结果吻合更好，更好地揭示了薄膜热声效应机理。基于非局部理论，建立了纳米薄膜/板的力-热-电耦合动力学模型，研究了它的固有频率和振动特性。结果表明：固有频率随非局部参数的增加而减小，随轴向拉伸和材料特性尺度的增大而增大，随纳米薄膜/板宽高比的增大而增大。温度变化、材料参数、几何参数和弹性约束对纳米薄膜/板的振动有不同程度的影响。对通电后的不同结构石墨烯进行了激光测振，结果表明：石墨烯泡沫和铜基底石墨烯薄膜在通电后振动，产生了一倍频输出声压，一倍频声压随着输入电压幅度和频率的升高而增大。综合考虑基底热传导、介质参数、薄膜参数、薄膜振动、热渗透深度等影响因素，对石墨烯薄膜扬声器装置进行了优化设计，声压级提高8dB以上。对石墨烯薄膜进行了光声效应研究，建立了光声效应的理论模型，进行了超快脉冲激光下的光声理论计算和实验测试，二者基本吻合。石墨烯薄膜的厚度变化（5nm至15nm）对光声效率影响微弱，基底材料的蓄热系数对光声效率有显著影响，蓄热系数较低的基底材料表现出的声学性能更好；环境气体的密度、热导率和比热对光声效率有较大影响，薄膜产生的声压级与环境气体比热的倒数成正比。建立了氧化铟锡（ITO）导电薄膜磁-热-声效应的理论模型，进行了磁场下的热声理论计算和实验测试，二者基本吻合。薄膜的温度振荡值随频率呈上升趋势，与电-热-声模型相比趋势相反；薄膜声压级随着线圈匝数的增加而增大，随着薄膜与线圈中心距离的增加而减小，随着线圈半径的增加而减小。对银（Ag）和镍（Ni）两种金属薄膜的热声效应进行了理论建模计算和实验测试，研究结果表明：二者均具有良好的热声效应，输出声压高于石墨烯薄膜，尤其是镍薄膜优势更为明显。且镍薄膜无需基底、强度高、透明，应用前景更广阔。