基于压电材料的主动吸声研究

压电材料具有良好的力电耦合性能，被广泛用于诸如传感器，换能器，制动器等的主体材料，可以应用于振动与噪声的控制。基于此，用一片压电材料作为主动吸声系统中的吸声材料，通过等间距布置于压电材料正前方的两个PVDF（Poly Vinylidene Fluoride）传感器检测出平面入射声波声压，利用压电材料的压电性能，在压电材料上加电压，使得反射声波为零，从而达到主动吸声的目的。最后对不同频率入射的平面声波进行了实验，取得了较好的吸声效果。     

基于Cymbal单元的压电复合智能材料设计

本文使用有限元法对Cymbal换能器单元的设计结构进行了仿真分析,并将换能器单元谐振频率与实际测量值进行了比较。将Cymbal换能器单元进行阵列,设计了一种新型的10kHz以下的低频薄板水声智能材料。对两块不同尺寸和结构的Cymbal压电复合智能材料的发射性能进行了测量与标定。并将用Cymbal压电复合智能材料作为主动吸声系统中的吸声材料,在脉冲声管中进行了管道声有源吸声控制实验。研究结果表明,Cymbal压电复合智能材料是一种高效的薄型低频宽带水声材料。     

基于PVDF薄膜的智能材料回声控制实现

提出了用高分子压电材料——PVDF薄膜作为激励声源，将其内嵌于基体材料聚氨酯橡胶中制成具有特殊功能的消声材料。通过声时延的方法，用布置在消声样件前方的两传声器检测出平面入射声波和反射声波，利用压电材料PVDF薄膜的逆压电性能，对其施加具有一定幅值和相位的电压，实现样件材料的声阻抗和介质声阻抗的匹配，以使得反射声波达到最小或零，从而实现回声控制的目的。最后对不同频率的入射声波进行了基于声阻抗管的回声控制实验测试并对结果进行了分析。     

基于压电材料的主动吸声降噪方法研究

提出了用压电材料进行主动吸声的方法。用压电材料作为主动吸声系统中的吸声材料,通过等间距布置于压电材料正前方的两个麦克风传感器,检测出平面入射声波与反射声波,利用压电材料的压电性能,在压电材料上加电压使得反射声波为零,从而达到主动吸声的目的。最后对不同频率入射的声波用matlab语言进行了仿真,仿真结果表明文中所提方法的可行性。     

基于压电材料的主动吸声降噪方法研究

提出了用压电材料进行主动吸声的方法.用压电陶瓷作为主动吸声系统中的吸声材料,通过等间距布置于压电陶瓷正前方的两个麦克风传感器,检测出平面入射声波与反射声波,利用压电陶瓷的压电性能,在压电陶瓷上加电压使得反射声波为零,从而达到主动吸声的目的.最后对不同频率入射的声波用matlab语言进行了仿真,仿真结果表明文中所提方法的可行性.     

采用特性阻抗匹配的半主动组合吸声材料与结构

由于主动吸声在低频声波入射时方有吸声效果,而在中高频声波入射时,吸声效果不明显。鉴此,采用一种新的半主动吸声方法;即由一层吸声材料和可移动的刚性壁组合结构,改变刚性壁移动的速度,使吸声材料的表面声阻抗与空气的阻抗相匹配,从而使吸声材料的吸声系数达到最大。最后,对平面入射声波进行了数值计算与实验,结果表明：在100～2 000 Hz时,吸声系数能达到0.8～1.0,而对于更高频率的入射声波,用此方法进行纯主动吸声的效果改善不明显。     

Alberich型吸声覆盖层的低频吸声机理分析

声波垂直入射Alberich型吸声覆盖层时激起沿厚度方向传播的轴对称波,而决定覆盖层低频性能的最低阶波可等效为“准平面波”,通过共振特性分析了覆盖层的低频吸声机理,指出达到低频有效吸声需要满足的轴对称波相速度的近似条件。低频吸声机理要点包括：（1）吸声覆盖层的共振是粘弹性圆柱腔体的共振;（2）吸声覆盖层的吸声峰值频率对应覆盖层的反共振频率而不是共振频率;（3）绝对软背衬的最低吸声峰频率比绝对硬背衬低一半左右。     

扰流激励下垂尾抖振响应主模态控制风洞试验研究

摘 要：采用压电结构的热弹比拟建模方法,进行了垂尾模型一弯模态和一扭模态响应的压电主动控制仿真。设计制作了一个垂尾气动弹性抖振模型以及两种形式的气流干扰源,用于在风洞中进行垂尾抖振实验及产生扰流对垂尾模型实施抖振激励。采用自主研发的弓形压电作动器,根据垂尾抖振响应控制的主模态控制思想,设计了垂尾模型抖振压电主动控制系统,进行了垂尾模型抖振响应压电主动控制风洞实验。结果表明,采用抖振主模态响应控制思想设计的垂尾抖振压电主动控制系统,可使垂尾模型抖振响应功率谱密度函数峰值降低50%以上。     

斜入射下水中隐身夹芯复合材料附体结构声学设计

摘 要：将隐身夹芯复合材料代替附体结构钢质壳板,建立了斜入射条件下水中隐身夹芯复合材料结构的声学模型;从水声波动方程出发,推导了二维空间声波斜入射时的传递矩阵,及带空腔水附体结构的声反射系数和吸声系数表达式;对带空腔水附体结构模型进行了垂直入射声学试验,试验结果与传递矩阵法数值计算吻合较好;对试验模型进行了斜入射下声学性能数值计算,分析了入射角对反射系数和吸声系数的影响;考虑斜入射下夹芯层厚度、密度、损耗因子、及水层厚度等对隐身附体结构声学性能的影响,应用数值方法对水中隐身夹芯复合材料附体结构进行了声学设计,分析了各层材料参数和几何参数对隐身结构反射系数和吸声系数的影响规律。     

有源吸声尖劈的实验研究

提出了一种利用有源控制改善吸声尖劈低频声吸收的方法。实验研究了正入射下,有源控制系统对吸声尖劈低频段吸声性能的补偿效果;比较了用有源控制分别对吸声尖劈正面和背面声阻抗与空气阻抗进行匹配两种误差策略,发现将误差传声器放置在尖劈前更合理,既能保证较好的低频吸声效果,又能占用较少的空间。实验结果表明,有源控制系统与20cm长的传统尖劈相结合所构成的总长约40cm的有源吸声尖劈,在100-1000Hz频率段,吸声系数可以达到0.98-1.00,和80cm长的传统尖劈的吸声性能相当。     

流场中填充吸声材料夹层板结构的声振耦合特性

采用等效流体模拟吸声材料,建立了外部流场作用下填充吸声材料夹层板结构的声振耦合模型,应用波动分析方法研究结构中声的透射特性,分析了入射声波入射角和方位角、流场流速和流向、夹层结构几何尺寸等参数对填充吸声材料夹层板结构声振耦合特性的影响。仿真计算表明吸声材料提高了双层板结构的隔声性能;隔声性能随着面板厚度和夹层厚度的增加而提高,随着入射角和方位角的增大而减小;在计算频段内(0~5000Hz),逆流入射时传声损失随着马赫数的增大而减小,顺流入射时却随着马赫数的增大而增大。     

采用响度控制改进算法的封闭车厢主动消声

以响度为噪声主动控制目标,提出逆模型结构和延迟补偿结构相结合的LFLMS改进算法。以轿车封闭车厢为载体构建双通道主动消声系统。以发动机噪声为噪声源,用三种控制算法进行试验,结果表明LFLMS改进算法与LFLMS算法的控制效果相近,且收敛速度快;响度控制声压减小不及声压控制,但响度减小量更大,主观听觉效果更好。     

基于数值-解析方法测量静压条件下阻尼材料动态力学参数

建立了一种测量静压条件下阻尼材料动态力学参数的数值-解析方法。首先,分别制作两种空腔半径不同的圆柱空腔覆盖层样品,测量两种样品在静压力下的复反射系数。其次,采用有限元法仿真静压力下的空腔结构变形,在此基础上同样采用有限元法计算复反射系数。以实测复反射系数和计算复反射系数建立二元非线性方程组,利用牛顿迭代法求解方程组可获得复弹性模量和复泊松比等黏弹性动态力学参数。对聚氨酯材料制作的样品进行了复反射系数测量,分析了静压力对聚氨酯材料动态力学参数的影响规律。最后,测量了某不同结构吸声覆盖层静压下的反射系数,并与采用实测材料参数计算的反射系数进行了比较,验证了该方法的正确性。     

低频声有源吸收理论研究

为了吸收低频入射声 ,作者提出了一种有源吸声结构 ,本文从理论上研究了该结构的吸声性能。文章首先建立理论模型 ,然后通过近场方法和求解弹性板 -声腔耦合系统结构响应推导了有源控制前后反射声功率的计算公式 ,然后按声反射功率最小化准则求得最佳有源吸声效果。最后通过一系列算例证明了该吸声结构吸收低频声波的有效性 ,并研究了吸声效果与次级力源位置的关系     

新型智能隔振复合结构的动态特性研究

针对精密机械的微位移隔振问题,设计了一种以PVDF压电薄膜为作动器和传感器的新型智能隔振复合结构。根据压电方程推导出了层叠式PVDF压电薄膜作动器厚度变形量表达式,建立了该智能复合结构的隔振理论模型,采用LMS自适应控制算法,以Matlab和有限元混合建模分析方式对本智能隔振复合结构的动态特性进行研究。有限元模型的分析结果与Matlab计算数据一致,验证了本新型智能隔振复合结构对微位移隔振的有效性,其结论将为精密仪器、微纳米设备的微位移智能主动隔振奠定理论基础。     

Development of a PVDF membrane hydrophone for use in air-coupled ultrasonic transducer calibration

This work describes the use of a polyvinylidene fluoride (PVDF) membrane hydrophone for application in air-coupled transducer calibration. A one-dimensional theoretical analysis is used to demonstrate the potential and performance of PVDF as a hydrophone material over the frequency range 100 kHz to 5 MHz included in the evaluation is the influence of deposited metallic electrode layers on the sensitivity of the material. Experimental validation over the restricted range 400 kHz to 1 MHz is provided by a coplanar 0.028 mm thick membrane hydrophone in conjunction with a custom built 1-3 piezocomposite transmitter. Calibration of the membrane hydrophone is performed by employing a standard hydrophone that has been calibrated to a primary standard in a water medium. Justification for such an approach is presented within the theoretical analysis which provides a close correlation with experimental data. The generation of Lamb waves at critical angles in the PVDF and their subsequent influence on the directional response of membrane hydrophones operating in air is also addressed. A method for partial suppression of the Lamb waves, based around perforation of the membrane (either in whole or in part), is evaluated experimentally with reasonable results.     

Sound shielding by a piezoelectric membrane and a negative capacitor with feedback control

The design and realization of an adaptive sound-shielding system based on a method to control the effective elastic stiffness of piezoelectric materials are presented in this paper. In this system, the sound-shielding effect is achieved by a sound reflection from the piezoelectric curved membrane fixed in rigid frame and connected to an active analog circuit that behaves as a negative capacitor. The acoustic transmission loss through the curved membrane was measured for the incident sound of frequency 1.6 kHz and of acoustic pressure level 80 dB. When the negative capacitor in the system was properly adjusted, the acoustic pressure level of the transmitted sound was reduced from the initial 60 dB to 15 dB by the action of the negative capacitor. Then the system was exposed to naturally changing operational conditions, and their effect on sound-shielding efficiency was studied. It is shown that the acoustic transmission loss of the system dropped by 35 dB within 30 min from the moment of negative capacitor adjustment. Therefore, a self-adjustment of the system has been implemented by appending an additional digital control circuit to the negative capacitor. It is shown that the aforementioned deteriorating effect has been eliminated by the adjusting action of the control circuit. The long-time sustainable value of 60 dB in the acoustic transmission loss of the adaptive sound shielding system has been achieved.     

Design of laminated piezocomposite shell transducers with arbitrary fiber orientation using topology optimization approach

Sensor and actuator based on laminated piezocomposite shells have shown increasing demand in the field of smart structures. The distribution of piezoelectric material within material layers affects the performance of these structures; therefore, its amount, shape, size, placement, and polarization should be simultaneously considered in an optimization problem. In addition, previous works suggest the concept of laminated piezocomposite structure that includes fiber‐reinforced composite layer can increase the performance of these piezoelectric transducers; however, the design optimization of these devices has not been fully explored yet. Thus, this work aims the development of a methodology using topology optimization techniques for static design of laminated piezocomposite shell structures by considering the optimization of piezoelectric material and polarization distributions together with the optimization of the fiber angle of the composite orthotropic layers, which is free to assume different values along the same composite layer. The finite element model is based on the laminated piezoelectric shell theory, using the degenerate three‐dimensional solid approach and first‐order shell theory kinematics that accounts for the transverse shear deformation and rotary inertia effects. The topology optimization formulation is implemented by combining the piezoelectric material with penalization and polarization model and the discrete material optimization, where the design variables describe the amount of piezoelectric material and polarization sign at each finite element, with the fiber angles, respectively. Three different objective functions are formulated for the design of actuators, sensors, and energy harvesters. Results of laminated piezocomposite shell transducers are presented to illustrate the method. Copyright © 2012 John Wiley & Sons, Ltd.