基于碳纳米管薄膜扬声器的结构声辐射有源控制

During past two decades, the research of active control of the sound radiated from the vibrating structure has been a hotspot in noise control field.Generally, for active control of sound transmission, there are two main control strategies which use vibrating of loudspeakers or structure to produce a secondary sound field that interacts destructively with the primary sound field. One involves in adding secondary force input applied directly to the vibrating structure and is called Active Structural Acoustic Control approach. A secondary control strategy is concerned with introducing secondary acoustic sources such as loudspeakers to suppress the unwanted noise and is called Active Noise Control approach. The corresponding control system may be unstable and become overly complicated due to coupling among channels and the large number of computation required which has greatly impeded practical applications. In this project, carbon nanotube thin film loudspeakers are used as secondary sound source to produce an opposite sound field that interacts destructively with the sound radiated from the vibrating structure. The sounds are emitted from carbon Nanotube thin film which could be attributed to a thermoacoustic effect.The acoustic characteristics and mechanism of carbon nanotube film loudspeaker will be researched. The acoustic model of active control system will be established based on near-field error sensing strategies and coupled sound field coming from structural vibrating and thin film's thermoacoustic effect. Physical mechanism of noise reduction will be investigated from several different points of view. Effective rules for secondary sound sources arrangement and near-field error sensing means will be determined and the corresponding adaptive control algorithm should be put out. A set of device and optimal design software for active noise control system will be developed. This new control system has several advantages such as less dependent on external acoustic environments, can be modular assembly, convenient in engineering application, etc.

20多年来，结构声辐射有源（主动）控制一直是噪声控制领域的研究热点。以往采用的各种有源控制系统都是利用次级源驱动扬声器或结构振动，由振动产生反声场来抵消原声场，次级源和传感器布放复杂，系统通用性很差，极大地阻碍了有源控制技术的工程应用。 本项目以碳纳米管薄膜扬声器作为次级声源，利用纳米薄膜的热声效应（非振动）产生反声场，抵消结构振动辐射声场。项目拟对碳纳米管薄膜扬声器的声学特性和机理进行深入研究，基于结构振动辐射声场和薄膜热声效应声场耦合，采用近场误差传感策略，建立有源控制系统的理论模型，揭示降噪的物理机制，确定降噪效果明显、易于实现的薄膜声学作动器布放准则和近场误差传感方式，提出相应的自适应控制算法，研制出一套有源噪声控制系统装置和优化设计软件。这种新的控制系统具有较少依赖外部声学环境、可模块化组装、便于工程应用等优点。

项目主要在碳纳米管和石墨烯薄膜的热声性能、纳米薄膜用于有源噪声控制及纳米结构动力学等方面开展研究。.构建了碳纳米管薄膜扬声器系统，提出添加钳位电路和施加多倍直流偏置电压的方法，较好解决了电-热-声系统的频率失真难题，显著提升了薄膜的声能量。设计了便于应用的可调节并联结构薄膜扬声器，通过智能开关调节扬声器电阻大小。修正了薄膜的近场声压公式，使计算值与测试值吻合良好。基于纳米薄膜的温升理论，测试分析了薄膜温度随电压大小、频率及时间的变化规律，测试了薄膜电阻随温度的变化规律，分析了上述因素对薄膜输出声压的影响。.将碳纳米管薄膜扬声器作为次级声源建立有源消声模型，分别对单极子和平板结构声辐射进行有源控制。针对不同的薄膜扬声器和布放方式，对比有源控制效果，分析主要影响因素，验证了碳纳米管薄膜作为次级声源的可行性和有效性。对水下圆柱壳低频声辐射特性及有源控制策略进行研究，作为碳纳米管和石墨烯薄膜声源的应用领域。.基于热声效应，对石墨烯薄膜发声进行理论研究，推导出石墨烯薄膜热声换能器的声压表达式。将声压测试值与理论计算结果对比，吻合良好，验证了理论模型及声压表达式的正确性。采用实验方法研究了不同基底（PDMS基底、PET基底以及玻璃基底）对石墨烯薄膜发声效率的影响。利用灵敏度分析法系统研究了多层石墨烯薄膜厚度、基底蓄热系数以及周围气体参数对热声效率的影响。探讨了石墨烯薄膜在可穿戴设备领域的应用。.首次提出了碳纳米管等纳米结构非局部行为的多尺度模型，推导了非局部应力场的精确表达；建立了纳米超薄结构的半连续动力学模型，以此分析结构的动力学性能，提出了推导纳米尺度材料弹性模量的新方法。通过非局部场论分析预测了微结构的力学行为，考察了固有频率的尺度依赖特性。基于一种修正的非局部连续理论研究了轴向变速运动黏弹性纳米尺度梁结构的动力学响应，研究了应变梯度非局部理论体系下纳米梁的动力学响应。