Optimal acoustic error sensing for global active control in a harmonically excited enclosure

The performance of an active control system in global control of enclosed sound fields depends largely on the localization of the error sensors, among other factors. In this paper a modified cost function is proposed in order to guarantee the maximum attenuation that can be produced by a set of secondary sources in the case of an harmonically excited sound field. The cost function is modified in order to drive the error signal to the value corresponding to the optimally attenuated sound field, instead of minimizing the squared pressure. To evaluate the performance of the proposed control system, its robustness against unstructured error is also investigated using a set of intensive calculations. Following this approach, the sensors can be located anywhere and the optimal attenuation is reached using an equal number of error sensors and secondary sources. The results also suggest that the greater the number of error sensors than secondary sources the more robust the control system is. This behavior holds for both the usual strategy of minimizing the squared pressure and the approach presented in this paper. However, the latter strategy is more robust than the traditional approach of minimizing the squared pressures and its robustness does not depend on the location of the error sensors. Thus, as a main conclusion, the use of the new cost function leads to a guaranteed efficiency and a more robust control system and gives absolute freedom in selecting the location of the error sensors.     

Error sensing strategy for active acoustic structure based on distributed displacement sensors

The nearfield error sensing approach, which is one of the key problems encountered in the implementation of active acoustic structure, is investigated theoretically. The basic idea involves a limited number of PVDF film pairs be boned to the surface of the primary panel and secondary panels for measuring the total radiated sound power. In this paper, first, a theoretical model associated with the active acoustic structure is established. Second, the formulae for the shape coefficient of the PVDF pairs are derived based on the acoustic radiation modes and a PVDF sensing model. Finally, a number of computer simulations are performed and the shape of the PVDF pairs and corresponding reduction in the radiated sound power are calculated. The results demonstrate the feasibility of the proposed nearfield error sensing strategy.     

分布式位移传感下的有源声学结构误差传感策略

有源声学结构是近年来提出的一种控制结构低频声辐射的有效方案,它是智能结构在噪声控制领域中的具体应用,而实现该结构的关键问题之一是近场误差传感。本文提出将分布式位移传感材料PVDF敷设于有源声学结构初、次级板表面,用有限个PVDF、对测量辐射声功率实现有源声学结构的近场误差传感。论文首先建立了有源声学结构理论模型,然后基于声辐射模态概念和PVDF传感模型,推导了PVDF形状系数理论公式,最后用一系列的计算机仿真实例给出了初、次级板PVDF形状及有源控制效果,证明所提出的方案是有效的。     

Some physical insights for active acoustic structure

Active acoustic structure (AAS) proposed in recent years has been viewed as an encouraging approach to actively control sound radiation from vibrating structures. Much work of AAS has been done on theoretical model, arrangement of the secondary panel and error sensing, and experimental investigation of AAS system, but physical mechanisms is little understanding. In this study, under minimization of the total sound power output, the physical mechanism of noise reduction is investigated by analyzing the sound power output change of primary and secondary structures and the distribution of sound intensity. The results show that there are two kinds of energetic behaviors, which includes the suppression of the sound power radiated by the primary panel and absorption of sound power by the primary and secondary panels.     

用于三层有源隔声结构误差传感的压电传感薄膜阵列及其优化设计

基于平面声源的三层有源隔声结构系统易于实现且具有良好的低频隔声性能,实现该系统需解决的关键问题是误差信号的检测.本文将压电传感薄膜聚偏氟乙烯(polyvinylidene fluoride, PVDF)阵列检测简支梁辐射模态的理论拓展到二维结构, 并应用到三层隔声结构实现误差传感的优化设计.根据三层结构中特殊的能量传输规律, 对误差传感方案中目标函数的选取、PVDF数目确定以及传感系统优化等问题进行深入分析.研究表明, 由于辐射板能量主要集中在有限个振动模态上, 只需将少数经固定系数加权的PVDF薄膜输出电流求和即可获得前三阶辐射模态幅值.辐射模态幅值的检测值与理论值符合良好, 保证传感精度的同时有效简化了系统. 关键词： 三层有源隔声结构 误差传感策略 压电传感薄膜阵列 辐射模态     

有源声学结构降噪的物理机制分析

有源声学结构是近年来提出的降低结构低频声辐射的有效方案,对其降噪中的物理机制进行分析将为系统优化设计、次级源和误差传感器布放及控制目标选取等关键问题提供直接指导。文中在最小辐射声功率条件下,从控制前后初、次级结构的辐射声功率变化以及声场中声强的分布来阐述降噪中的物理机制,研究结果表明:降噪中的能量转换分为能量抑制、能量吸收及能量反吸收三种机制;对于近场声强分布,有源控制效果主要通过声强幅度抑制和声强方向调整两种机制体现,部分区域的声能量在控制前向远场传递,控制后则流向声源。     

用于电流传感的声表面波磁致伸缩效应

利用声表面波(SAW)磁致伸缩效应可以实现一种快速、高灵敏度的电流检测方法,但磁致伸缩薄膜内部矫顽力导致了明显的磁滞误差。磁致伸缩薄膜的栅阵化设计可以减小磁致伸缩时薄膜内部矫顽力,抑制磁滞现象,从而实现高灵敏和低迟滞误差的SAW电流检测。结合有限元和耦合模理论对沉积铁钴(FeCo)薄膜栅阵的声表面波电流传感器中的磁致伸缩效应进行分析,对传感响应进行仿真,确定优化的传感结构参数。为验证理论分析,实验研制了频率为150 MHz的声表面波电流传感器件,并结合差分振荡电路及亥姆霍兹线圈,建立传感器测试系统.实验结果表明,磁致伸缩薄膜的栅阵设计大幅降低了迟滞误差,并显著提升了传感器灵敏度。     

Design and performance analysis of a nanogyroscope based on electrostatic actuation and capacitive sensing

In this paper, a vibrating beam gyroscope with high operational frequencies at mode-matched condition is proposed. The model comprises a micro-cantilever with attached tip mass operating in the flextural–flextural mode. The drive mode is actuated via the electrostatic force, and due to the angular rotation of the base about the longitudinal axis. The secondary sub-nanometric vibration is induced in the sense direction which causes a capacitive change in the sense electrodes. The coupled electro-mechanical equation of motion is derived using the extended Hamilton's principle, and it is solved by direct numerical integration method. The gyroscope performance is investigated through the simulation results, where the device dynamic response, rate sensitivity, resolution, bandwidth, dynamic range, g$g$ sensitivity and shock resistance are studied. The obtained results show that the proposed device may have better performance compared to commercial micro electromechanical gyroscope characteristics.     

A frequency selective acoustic transducer for directional Lamb wave sensing

A frequency selective acoustic transducer (FSAT) is proposed for directional sensing of guided waves. The considered FSAT design is characterized by a spiral configuration in wavenumber domain, which leads to a spatial arrangement of the sensing material producing output signals whose dominant frequency component is uniquely associated with the direction of incoming waves. The resulting spiral FSAT can be employed both for directional sensing and generation of guided waves, without relying on phasing and control of a large number of channels. The analytical expression of the shape of the spiral FSAT is obtained through the theoretical formulation for continuously distributed active material as part of a shaped piezoelectric device. Testing is performed by forming a discrete array through the points of the measurement grid of a scanning laser Doppler vibrometer. The discrete array approximates the continuous spiral FSAT geometry, and provides the flexibility to test several configurations. The experimental results demonstrate the strong frequency dependent directionality of the spiral FSAT and suggest its application for frequency selective acoustic sensors, to be employed for the localization of broadband acoustic events, or for the directional generation of Lamb waves for active interrogation of structural health.     

Vibration analysis of a continuous system subject to generic forms of actuation forces and sensing devices

This work provides a general formulation to solve vibration problems for continuous systems with damping effects, including modal, transient, harmonic and spectrum response analyses. In modal analysis, the system eigenvalues and corresponding eigenfunctions can be determined. The orthogonal relations of eigenfunctions are shown. For transient, harmonic and spectrum analyses, the generic force/actuator functions and response/sensing operators are introduced, respectively, and used to derive the system response. The time domain response is obtained for transient analysis, the frequency response function is derived for harmonic analysis and statistical quantities of response variables due to random excitation are determined in spectrum analysis. The solution for each type of analysis can be formulated and expressed in a concise format in terms of generic force/actuator and response/sensor mode shape functions. In particular, one-dimensional beam and two-dimensional plate vibration analyses are illustrated by following the developed generic formulation. This work provides the complete analytical solutions of four types of vibration analyses for continuous systems and can be applied to other engineering structures as well.     

双水听器传递函数法低频测试及误差分析

在水声声管中用双水听器传递函数法测量水声材料的复反射系数。本文研究了传递函数的特点,提出了等反射系数曲线和等相位角曲线,还研究了传递函数的测量误差和复反射系数的计算误差,得出的结论是:合理选择双水听器位置参数,提高系统信噪比,修正水中声速,并采用交换通道法,在所要求的频率范围内使测量结果达到一定精度。文章还给出测试实例,与经典的驻波法结果一致。     

Decoupling error for the atmospheric correction in ocean color remote sensing algorithms

This paper studies the decoupling error associated with the atmospheric correction procedures in the ocean color remote sensing algorithms. The decoupling error is caused by the lack of proper consideration of multiple scattering between the atmospheric and ocean components. In other words, the atmosphere and ocean are not coupled properly. A vector radiative transfer model for the coupled atmosphere and ocean (CAO) system based on the successive order of scattering (SOS) method is used to study the error. The inherent optical properties (IOPs) of the ocean are provided by the most updated bio-optical models. Two wavelengths are used in the study, 412 and 555 nm. For a detector located just above the ocean interface, the decoupling errors range from 0.3% to 7% at 412 nm; and from 0.3% to 3 % at 555 nm for zenith viewing angles smaller than 70°. The decoupling errors are significantly larger for larger zenith viewing angles for this detector. For a detector at the top of the atmosphere (TOA), it is hard to separate the decoupling error from the error introduced by the diffuse transmittance. If we assume the upwelling radiance is uniform just below the ocean surface when estimating the diffuse transmittance, the decoupling errors are from ?4% to 8% for zenith viewing angles smaller than 70°; and negative decoupling errors show up at mainly large zenith viewing angles.     

Frequency band structure and absorption predictions for multi-periodic acoustic composites

This article introduces a computational framework for studying frequency band structure and absorption behavior in multi-periodic acoustic composite structures. Herein, multi-periodic acoustic composite structures are defined as periodically-layered acoustic media wherein each layer is composed of periodically-repeated fluid unit cells, especially those arising from the study of porous materials. Hence, at least two periodic scales (microscopic and mesoscopic, respectively) comprise the macroscopic acoustic composite media. Exploitation of the multi-periodicity allows for efficient generation of dispersion and absorption curves via the conventional multi-scale asymptotic method (for homogenizing the mesoscale) coupled to the acoustic transfer matrix methods (for the macroscale). The combined computational framework results in a single analysis procedure for evaluating complex dispersion relationships and acoustic absorption. The dispersion curves can be used to reveal frequency stop bands wherein the wave vector is highly imaginary—i.e., plane waves experience rapid attenuation. They can also be used to reinterpret classical absorption curves. The framework is applied to four multi-periodic acoustic composite structures in order to demonstrate the framework's utility and to reveal novel properties, particularly those which can be influenced by design of the mesoscopic unit cell.     

Material and device properties of ZnO-based film bulk acoustic resonator for mass sensing applications

Zinc oxide based film bulk acoustic resonator as mass sensor was fabricated by multi-target magnetron sputtering under optimized deposition condition. Each layer of the device was well crystallized and highly textural observed by transmission electron microscopy and X-ray diffraction measurement. Through piezoelectric test, the device vibrated with significant distance. The influence of top electrode on resonant frequency and the bio-specimen of mass loading effect were investigated. Data show that the device has qualified properties as mass biosensor, with a resonant frequency of 3-4 GHz and a high sensitivity of 8-10 kHz cm²/ng.     

Real-time active suppression of scattered acoustic radiation

Active noise control usually aims at reducing the total acoustic pressure due to a noise source; it may also be used in principle to reduce the scattered acoustic radiation from a reflecting body in order to render it invisible to incident acoustic waves. In this paper, a real-time control strategy is introduced to achieve, with ordinary noise sources and sensors, the effective suppression of the noise scattered by a 3-D surface. Numerical simulations of 2-D and 3-D control are used to illustrate the potential of this control strategy. Preliminary experimental results are also given for the 1-D case of a rigid body inserted into a duct.     

利用声激励控制颤振的实验研究

继声控制颤振的理论研究之后,本文又进行了成功的风洞实验,验证了文献1中所提出的理论,给出了较有价值的实验结果,预示了这一新技术、新思想应用于流致振动领域的前景.     

基于误差修正的传感器阵列水声定位算法

本文分析了海洋环境中定位精度下降的根源,提出了一种基于误差修正的传感器阵列自主定位算法,并进行了计算机仿真和数据分析,结果表明该算法对于提高传感器阵列自主定位精度是有效的。     

分布式无线声传感网加权预测误差语声去混响方法

室内混响会严重降低语声质量,因此在室内语声通信中对混响的抑制显得尤为重要.针对无线声传感网,该文提出一种基于加权预测误差的分布式自适应去混响算法.通过调整传统递归最小二乘算法,所提出的分布式加权预测误差算法仅需利用一路相同的参考信号和其他节点的本地输出而非全部信号,便可实现最优输出,从而大幅度降低节点间传输的通道数与各...