A genetic algorithm for active noise control actuator positioning

Active noise control systems (ANCS) have been used extensively in several diverse applications in order to reduce the sound levels within a confined space. Several control schemes have been proposed, all of which rely on the same basic idea, namely that of introducing an artificial secondary sound field in order to partially cancel the primary sound field. This secondary field is created by using a number of actuators (usually speakers), placed in several locations within the space of interest. In our particular case of interest, the ANCS under consideration is an interior one. The overall ANCS comprises a set of sensors, a control system, and the actuators. Clearly, the optimal design of all three components needs to be addressed when designing an ANCS. In this paper, the problem of deciding to which specific locations (out of several possible ones) the actuators will be located for optimal performance of the ANCS is addressed. Specifically, a genetic algorithm is designed for this problem. The algorithm was implemented and tested against a simple greedy approach. Results indicate the efficiency of the Genetic Algorithm for the problem at hand.     

基于响度控制的封闭腔有源噪声控制

传统有源噪声控制（ANC）通常是控制声压平方和最小，但声压与人耳对声音强弱的主观感觉并不完全一致。为了考虑人的主观听觉作用，在传统ANC系统中加入若干个响度滤波器，使其控制目标从声压转变为响度。从心理声学出发，建立了用于ANC的人耳听觉响度模型，给出了矩形封闭腔响度ANC模型以及基于FLMS算法的响度控制算法。仿真结果表明，与声压控制相比，基于响度控制的ANC系统的声压下降量稍小，但响度的减小量更大，具有更好的主观听觉效果。     

Acoustic-based modal filtering of orthogonal radiating functions for global error sensing: Part I theory and simulation

This is the first of two companion papers which summarise the theoretical and experimental work aimed at developing a generalised, acoustic-based sensing strategy for free and semi free field problems. The aim of the work is the design of practical acoustic sensing systems for active noise control of large complex noise sources, based on data fusion of a large number of sensor signals. A wide breath of literature illustrates several practical advantages to pursuing a sensing system which measures orthogonal functions with respect to a global error, and how a large number of point sensors are required in the filtering process. For this reason we examine modal filtering of orthogonal functions for two-dimensional noise sources and highlight the practicalities of sensing systems which measure the associated constituents. We compare three variations of orthogonally radiating shapes based on structural modes, structural elements and combinations of in-/out-of-phase acoustic monopoles. Comparisons are made based on the number of constituents required to estimate 90% of radiated power; the modal filtering weights frequency dependence; and simulated decompositions of a sound pressure field to radiated power. Of the sensing strategies which are structural specific, we extend them to facilitate the use of acoustic sensors to measure the orthogonal “structural” patterns.     

Electromechanical system frequency response equilization using three different methods

The frequency response of different electromechanical systems like sensors and actuators is in many cases the most important parameter for their evaluation. In some cases, when a short time delay does not play an important role and the flatness of frequency response is more important, an approximate of inverse system for frequency response compensation can be used. We equalized the frequency response of a non-minimum phase linear time-invariant electromechanical system using a digital finite impulse response (FIR) filter. Three different deconvolution methods for determination of the approximate of inverse filter impulse response were used and the results of the compensation using three different inverse filters are compared. The first method is based on the solution of the system of linear equations, while the second method is based on a simple direct inverse Fourier transformation. The third method uses an active noise control algorithm based on a least mean square adaptive algorithm. The results of all three methods can be applied in a FIR filter realized on DSP boards to perform real time compensation. The theoretical simulations are compared with experiments. Compensation of arbitrary systems is an interesting subject and it can be applied in numerous different fields from sensors and actuators to measurement and acoustics.     

一种含次级通道在线辨识的窄带主动噪声控制系统

分析了噪声危害设备产生的谐波噪声,特别是以500 Hz或600 Hz以下的低频成分为对象,介绍了主动噪声控制(ANC)技术的原理、意义及发展现状。在实际声学场所,由于控制系统易受初级噪声功率、残余噪声幅值等因素影响而不稳定。在分析控制系统收敛条件的基础上,通过对系统误差引入一个比例因子从而改进系统模型,并以一维管道为实验平台,基于高速数字信号处理器(DSP)设计了含次级通道在线辨识的主动噪声控制器。实验结果表明,在250 Hz左右的频段上能够达到16 dB的降噪效果。     

一种低复杂度快速收敛的窄带主动噪声控制系统

传统窄带主动噪声控制( ANC)系统的计算负荷与窄带噪声频带数量正相关,而且其收敛速度和降噪效果存在此消彼 长的关系。 为解决以上问题,首先基于滤波误差技术简化窄带 ANC 模型,使系统计算量与窄带噪声频带数量相互独立。 然后 通过自适应混合参数将两个简化的窄带 ANC 系统进行并行凸组合,其中一个系统拥有最快的收敛速度,另一个系统拥有较低 的稳态误差。 提出的系统不仅降低了传统窄带 ANC 系统的计算复杂度,而且在不牺牲降噪性能的情况下提升了系统收敛速 度。 实验结果表明,提出系统在不牺牲稳态误差的基础上,收敛时间缩短了 78% ,有效提升了系统收敛性能。     

管道复合主动噪声控制系统及其实现

为了提高管道噪声主动控制系统的性能,设计出基于TI公司的TMS320C30芯片作为控制器的实时管道复合噪声主动控制系统(简称ANC系统)。针对前馈ANC可实现较宽的降噪频带,但在实际复杂系统中不能完全满足参考传感器信号和噪声声源要紧密相关要求;而反馈ANC系统中,降噪效果不依赖于声场的相关性,但其降噪频带较窄的特点,设计出复合FXLMSANC系统。在某风机、通风管路系统上进行ANC试验的结果表明,应用复合FXLMSANC方法,能获得比单独使用前馈FXLMSANC算法或反馈FXLMSANC算法更好的降噪效果。     

Improved numerical integration method for flowrate of ultrasonic flowmeter based on Gauss quadrature for non-ideal flow fields

Multipath ultrasonic flowmeters with large diameter are widely used in industry. And their measurement performances are sensitive to velocity profiles in conduits. Gauss–Jacobi and Optimized Weighted Integration for Circular Sections (OWICS) method are commonly applied in flow measurement of multipath ultrasonic flowmeters, both of which assume ideal flow in pipes. They are not proper for non-ideal flow measurement. Therefore, an improved numerical integration method for flowrate based on Gauss quadrature is proposed. With this method, optimum relative path heights and corresponding weights are determined according to specific disturbed flows. By comparison Gauss–Jacobi, OWICS with the improved method, the validity of the proposed method is verified for typical disturbed flows based on both theoretical analysis and experiments, and measurement performances of ultrasonic flowmeters are improved significantly.     

基于残差信息的汽车液压主动悬架故障诊断与隔离研究

为提高汽车液压主动悬架控制性能,提出一种针对液压作动器、车身垂向加速度传感器的故障诊断与隔离方法。建立四自由度汽车液压主动悬架动力学模型,并考虑液压作动器和传感器常见故障,建立悬架故障模型。采用极点配置方法设计故障检测滤波器,利用输出残差信息对作动器卡死和增益故障、传感器增益故障进行诊断。在此基础上,为准确诊断故障发生部位,利用相关系数和故障向量径长值对故障进行隔离。在MATLAB/Simulink环境下对故障悬架进行大量仿真计算,结果表明:残差波动超过一定阈值时可敏感地诊断出作动器或传感器故障;汽车液压主动悬架作动器故障采用最大相关系数准确隔离,车身垂向加速度传感器故障采用最大相关系数和最小故障向量径长值准确隔离。     

Analysis of the optimal sampling rate for state estimation in sensor networks with delays

When addressing the problem of state estimation in sensor networks, the effects of communications on estimator performance are often neglected. High accuracy requires a high sampling rate, but this leads to higher channel load and longer delays, which in turn worsens estimation performance. This paper studies the problem of determining the optimal sampling rate for state estimation in sensor networks from a theoretical perspective that takes into account traffic generation, a model of network behaviour and the effect of delays. Some theoretical results about Riccati and Lyapunov equations applied to sampled systems are derived, and a solution was obtained for the ideal case of perfect sensor information. This result is also interesting for non-ideal sensors, as in some cases it works as an upper bound of the optimisation solution.     

齿轮传动振动噪声计算的Kato方法

建立了齿轮传动的时变动力学模型，分析了啮合刚度，传动误差对振动响应的影响，在此基础上，将齿轮传动啮合分成单齿啮合区，采用Kato方法对振动产生的噪声进行了定量计算，得出了双齿啮合区内辐射噪声大于单齿啮合区，并给出了每一啮合时刻辐射噪声大小，研究表明该方法可以较好地对齿轮振动所产生的噪声进行定量计算，为齿轮系统的降噪设计奠定了基础。     

平面十字磁梯度张量系统的两步线性校正

磁梯度张量系统的测量精度受限于磁传感器的零漂、灵敏度差异和三轴非正交性等系统误差以及各传感器轴系间的非对准误差。构建了平面十字磁梯度张量系统的误差参数线性模型,提出了两步线性校正法。利用两个非线性变量转换构建单磁传感器系统误差的线性方程组,对误差参数进行最小二乘估计,将传感器实际输出校正为各自理想正交输出;利用旋转矩阵构建各传感器理想正交轴间非对准误差的线性方程组并求出最小二乘解,将各传感器输出校正到参考平台框架正交坐标系上。两步校正过程均无数学简化。仿真与实验表明,相比忽略二阶及以上高阶小量的常规线性校正,提出的张量系统两步线性校正法更为精确,误差参数仿真估计准确率高于93%,实测校正后总场强度均方根误差小于13 n T,张量分量均方根误差小于90 n T/m。     

Optimal placement of sensors and actuators using measures of modal controllability and observability in a balanced coordinate

In this paper, a method for optimal placement of sensors and actuators is presented by using new measures of modal controllability and observability defined in a balanced coordinate system. The proposed new measures are shown to have a great advantage in practical use when they are used as criteria for selecting the locations of sensors and actuators, since the most controllable and observable locations can be obtained to be identical. In addition, they are more accurate than the measures of Hamdan and Nayfeh in that the effects of the eigenvector norm are considered into the magnitude of measures. In simulations, to verify the effectiveness of the proposed measures and optimal placement method, the closed-loop response of a simply supported flexible beam, in which the number and locations of actuators are determined by using the proposed measures and optimal placement method, has been examined and compared with the case of Hamdan and Nayfeh’s measures.     

Active noise control using a distributed mode flat panel loudspeaker

A flat panel distributed mode loudspeaker (DML) has many advantages over traditional cone speakers in terms of its weight, size, and durability. However, its frequency response is uneven and complex, thus bringing its suitability for active noise control (ANC) under question. This paper presents experimental results demonstrating the effective use of panel DML speakers in an ANC application. Both feedback and feedforward control techniques are considered. Effective feedback control with a flat panel speaker could open up a whole range of new noise control applications and has many advantages over feedforward control. The paper develops a new control algorithm to attenuate tonal noise of a known frequency by feedback control. However, due to the uneven response of the speakers, feedback control is found to be only moderately effective even for this narrow-band application. Feedforward control proves to be most capable for the flat panel speaker. Using feedforward control, the sound pressure level can be significantly reduced in close proximity to an error microphone. The paper demonstrates an interesting application of the flat panel in which the panel is placed in the path of sound and effectively used to block sound transmission using feedforward control. This is a new approach to active noise control enabled by the use of flat panels and can be used to prevent sound from entering into an enclosure in the first place rather than the traditional approach of attempting to cancel sound after it enters the enclosure.     

A local active noise control system based on a virtual-microphone technique for railway sleeping vehicle applications

Low-frequency broadband noise generated on a railway vehicle by the wheel–rail interaction could be a big annoyance for passengers in sleeping cars. Low-frequency acoustic radiation is extremely difficult to attenuate by using passive devices. In this article, an active noise control (ANC) technique has been proposed for this purpose. A three-dimensional cabin was built in the laboratory to carry out the experiments. The proposed scheme is based on a Filtered-X Least Mean Square (FXLMS) control algorithm, particularised for a virtual-microphone technique. Control algorithms were designed with the Matlab-Simulink tool, and the Real Time Windows Target toolbox of Matlab was used to run in real time the ANC system. Referring to the results, different simulations and experimental performances were analysed to enlarge the silence zone around the passenger's ear zone and along the bed headboard. Attenuations of up to 20 and 15 dB(A) (re:20 μPa) were achieved at the passenger's ear in simulations and in experimental results, respectively.     

Adaptive frequency tuner for active narrowband noise control systems

The reference frequency error can significantly degrade the performance of the narrowband active noise control (ANC) system. This paper investigates the relationship between the reference frequency error and the performance of the narrowband ANC system, and presents an adaptive frequency tuner which can reduce the reference frequency error and improve the performance of the system. Effectiveness of the adaptive frequency tuner is validated by simulation results using experimental transfer functions.     

Magnetostatic detection using magnetoresistive sensors with vertical motion flux modulation

Recently, the flux modulation has been presented to deal with the 1/f noise of magnetoresistive (MR) sensors. However, the efficiency of most flux modulation schemes with simple micro- electromechanical-system (MEMS) actuators is not satisfying yet. In this paper, the vertical motion flux modulation (VMFM) is proposed to improve the modulation efficiency. In VMFM, the soft magnetic film driven by a MEMS actuator vibrates vertically above the MR sensors with a pair of flux concentrators. Consequently, the detected magnetostatic field is modulated to the higher frequency where the 1/f noise is much lower. A VMFM prototype based on AA002 (multi-layered giant magnetoresistive sensors) was fabricated and its flux modulation efficiency can reach 18.7%, which exceeds most achieved efficiency with other schemes. Also, the magnetostatic detection ability is improved to 530 pT/√Hz.     

Parameter estimation of integrating and time delay processes using single relay feedback test

Autotuning using relay feedback is widely used to identify low order integrating plus dead time (IPDT) systems as the method is simple and is operated in closed-loop without interrupting the production process. Oscillatory responses from the process due to ideal relay input are collected to calculate ultimate properties of the system that in turn are used to model the responses as functions of system model parameters. These theoretical models of relay response are validated. After adjusting the phase shift, input and output responses are used to find land mark points that are used to formulate algorithms for parameter estimation of the process model. The method is even applicable to distorted relay responses due to load disturbance or measurement noise. Closed-loop simulations are carried out using model based control strategy and performances are calculated.     

压电振子及流体对泵近场噪声的影响

研究了压电振子的弯曲振动形变及振动辐射噪声.首先建立压电泵压电振子振动方程,导出弯曲振动形变函数;提出用微平面活塞振动理论简化压电振子振动模型,推导了近场声压理论计算方程及泵内流体对泵噪声贡献量方程;最后把理论计算结果与试验结果进行比较分析,分别得出在不同频率下压电振子及泵内流体对泵噪声贡献的大小.在输入频率为50 Hz时,泵噪声的理论值为45 dB,实际值为37 dB,泵内流体对泵噪声的影响较大,实际值与理论值的相对误差为21.6%;在输入频率为120 Hz时,泵噪声的理论值为61 dB,实际值为62 dB,泵内流体对泵噪声的影响较小,实际值与理论值的相对误差为1.6%,证明了本研究所提出理论的正确性.     

非规则结构表面多声源近场声全息方法

为了提高非规则结构表面多声源声场的全息精度,提出基于目标深度识别与球面波叠加逼近的非规则表面多声源近场声全息方法。该方法使用声源空间深度识别理论,确定结构体上各声源的空间位置,在各声源处分别使用球面波的叠加描述空间声场分布,然后结合现有单原点球面波叠加近场声全息法重构声场。为了验证方法的可行性,首先使用所述方法和现有单原点球面波叠加声全息法,分别对径向脉动球与横向振动球组成的不同声场进行全息重构。结果表明,当声源集聚分布时,所述方法与现有方法均能有效全息重构声压分布,重构误差在5%以下;当声源离散分布时,现有方法失效,所述方法能够较准确地给出重构面的声压分布,主要频段内的全息重构误差小于20%。进一步的对比实验表明,在全息重构多扬声器非规则空间分布声场时,使用所述全息方法的重构误差平均下降14.08%,显著提升了多声源非规则空间分布声场的全息精度。