一种数字有源降噪耳机控制器设计方法

为了得到一种作用于低频宽带噪声的有源降噪耳机,采用固定系数的数字控制器实施降噪,并提出了一种前反馈混合的控制器设计方法。比较了前馈及混合两种控制模式下对低频宽带噪声的控制效果;进一步提出了一种综合优化方法,改善噪声不同角度入射下的降噪性能。仿真和基于DSP平台的实验表明,提出的方法对多方向入射的20～1500 Hz低频宽带噪声均具有较好控制效果。     

Model independent control of lightly damped noise/vibration systems

Feedforward control is a popular strategy of active noise/vibration control. In well-damped noise/vibration systems, path transfer functions from actuators to sensors can be modeled by finite impulse response (FIR) filters with negligible errors. It is possible to implement noninvasive model independent feedforward control by a recently proposed method called orthogonal adaptation. In lightly damped noise/vibration systems, however, path transfer functions have infinite impulse responses (IIRs) that cause difficulties in design and implementation of broadband feedforward controllers. A major source of difficulties is model error if IIR path transfer functions are approximated by FIR filters. In general, active control performance deteriorates as model error increases. In this study, a new method is proposed to design and implement model independent feedforward controllers for broadband in lightly damped noise/vibration systems. It is shown analytically that the proposed method is able to drive the convergence of a noninvasive model independent feedforward controller to improve broadband control in lightly damped noise/vibration systems. The controller is optimized in the minimum H2 norm sense. Experiment results are presented to verify the analytical results.     

Implementation of the controller for a compound active noise-cancellation earmuff

本文用传递函数描述了复合式有源消声耳罩的系统模型,确定了模拟式消声控制器的合理阶次。对于前馈控制器和反馈控制器,均给出了成熟的电路实现方案。最后,实际设计了复合式有源消声耳罩,并实测了控制器特性和消声效果,验证了本文提出的控制器实现方法的有效性。     

有源消声耳罩控制器的实现

本文用传递函数描述了复合式有源消声耳罩的系统模型,确定了模拟式消声控制器的合理阶次,对于前馈控制器和反馈控制器,均比出了电路实现方案,最后,实际设计了复合式有源消声耳罩,并实测了控制器特性和消声效果,验证了本文提出了的控制器实现方法的有效性。     

Network-based modelling and active control for offshore steel jacket platform with TMD mechanisms

The network-based modelling and active control for an offshore steel jacket platform with an active tuned mass damper mechanism is investigated. A network-based dynamic model of the offshore platform is first established. A network-based state feedback control scheme is developed. Under this scheme, the corresponding closed-loop system is modelled by a system with an artificial interval time-varying delay. Then, a delay-dependent stability criterion for the corresponding closed-loop system is derived. Based on this stability criterion, a sufficient condition on the existence of the network-based controller is obtained. It is found through simulation results that (i) both the oscillation amplitudes of the offshore platform and the required control force under the network-based state feedback controller are smaller than those under the nonlinear controller and the dynamic output feedback controller; (ii) the oscillation amplitudes of the offshore steel jacket platform under the network-based feedback controller are almost the same as the ones under the integral sliding mode controller, while the required control force by the former is smaller than the one by the latter.     

Feedback control of sound transmission through a double glazed window

One way to tackle the control of stochastic noise in three dimensions is to reduce the sound transmission to the zone of interest. In buildings, windows are often the weak link in protecting the interior from outside noise. In particular, double glazed windows have a poor sound insulation at low frequency around the mass-air-mass resonance (double wall resonance). Since passive means for windows are exhausted, an active controller that increases the transmission loss in the low-frequency range is an attractive approach to reduce the noise level in buildings. Previously suggested feedforward controllers need reference microphones to measure the disturbance outside and error microphones for the adaptation somewhere in the room. For a real window this is unpractical or even unfeasible. These limitations can be overcome with the feedback controller presented here, which only uses sensors and actuators in the cavity of the double glazed window. Four different controllers—two feedforward and two feedback strategies—are designed, implemented and compared. With feedback the noise transmission around the mass-air-mass resonance can be reduced by , compared to with a feedforward controller.     

A simplified adaptive feedback active noise control system

In the adaptive feedback active noise control system based on the internal model control (IMC) structure, the reference signal is regenerated by synthesizing the error signal and the secondary signal filtered with the estimation of the secondary path, hence more computation load and extra programming are required. Motivated by the engineering truth that the primary noise cannot be completely cancelled in most practical active noise control applications and the error signal still contains some portions of the primary noise, a simplified adaptive feedback active noise control system is proposed in this paper, which adopts the error signal directly as the reference signal in an adaptive feedforward control system and utilizes the leaky filtered-x LMS algorithm to update the controller. The convergence properties of the proposed system are investigated and its advantages are discussed by comparing with other feedback control systems as well as the weakness. Finally, simulations and experiments are carried out to demonstrate the effectiveness of the proposed system.     

Active control of double-glazed windowsPart I: Feedforward control

This paper describes an experimental investigation of an actively controlled double-glazed window. It is the first part of two companion papers, and it shows the results with a feedforward controller. In the second part about results obtained with adaptive feedback control will be reported. A laboratory version of the window was equipped with loudspeakers and microphones inside the cavity. Various positions of loudspeakers and microphones were tested with band-limited white noise excitation. Different combinations of distributed loudspeakers were realized driving them in parallel by single channels of the controller. Similarly the signals of microphones were summed to realize simple modal filters. Plane mode control as well as control of higher cavity modes were performed with a feedforward controller and the reference signal taken directly from the primary signal. Additionally tests with different traffic noise examples were performed showing the ability of the actively controlled window to enhance protection against traffic noise.     

IMPLEMENTATION OF A BROADBAND DUCT ANC SYSTEM USING ADAPTIVE SPATIALLY FEEDFORWARD STRUCTURE

An adaptive spatially feedforward algorithm is proposed for broadband attenuation of noise in ducts. Acoustic feedback generally exists in this active noise control structure. Munjal and Eriksson (1988 Journal of Acoustical Society of America84, 1086-1093) derived an ideal controller for the spatially feedforward structure. The ideal controller can be partitioned into two parts. The first part represents a repetitive controller that can be implemented by an infinite impulse response (IIR) filter, whereas the second part represents the dynamics of transducer that can be implemented by a finite impulse response (FIR) filter. In the paper, the IIR filter is merged with the original plant. The FIR filter is adaptively updated by the least-mean-square (LMS) algorithm to accommodate perturbations and uncertainties in the system. The proposed algorithm is implemented via a floating point digital signal processor and compared with other commonly used algorithms such as the Filtered-X LMS algorithm, the feedback neutralization algorithm, and the Filtered-U LMS algorithm. Experimental results show that the system has attained 15·7 dB maximal attenuation in the frequency band 200-600 Hz.     

A hybrid active noise controller for finite ducts

A hybrid active noise controller (ANC) is proposed to solve some existing problems, which are related to the non-minimum phase (NMP) path models between uncollocated sensors and actuators in many ANC systems. For hybrid ANC schemes, the NMP path causes design difficulties to both feedforward and feedback control. These problems can be solved effectively by adding an extra actuator in the ANC system. A new design procedure is presented to take the greatest advantage of the extra actuator. Theoretical analysis and experimental results are presented to show the improved performance of the proposed ANC.     

Simulation study on active noise control for a 4-T MRI scanner

The purpose of this work is to study computationally the possibility of the application of a hybrid active noise control technique for magnetic resonance imaging (MRI) acoustic noise reduction. A hybrid control system combined with both feedforward and feedback loops embedded is proposed for potential application on active MRI noise reduction. A set of computational simulation studies were performed. Sets of MRI acoustic noise emissions measured at the patient's left ear location were recorded and used in the simulation study. By comparing three different control systems, namely, the feedback, the feedforward and the hybrid control, our results revealed that the hybrid control system is the most effective. The hybrid control system achieved approximately a 20-dB reduction at the principal frequency component. We concluded that the proposed hybrid active control scheme could have a potential application for MRI scanner noise reduction.     

Control of a unique active vibration isolator with a phase compensation technique and automatic on/off switching

This work examines the characteristics of a unique active vibration isolator and develops a control strategy for it. The proposed active vibration isolator is introduced and its dynamic model is presented. A characterization study is conducted to identify system parameters. It is shown that with a simple proportional feedback the closed-loop system has a very narrow stability margin due to the inherent dynamics of the actuator. To improve the stability of the closed-loop system and enhance the performance of vibration isolation, a phase compensator is incorporated in the control scheme. An optimization problem is formulated to determine the optimum controller parameters by minimizing the 2nd norm of the displacement transmissibility. Both absolute position feedback and relative position feedback are considered. In real time implementation, an automatic on/off switching strategy is devised to take full advantage of both the active isolator and passive isolator. The experimental results show that with the proposed control scheme, the isolator is capable of suppressing base excitations effectively.     

Active control of double-glazed windows. Part II: Feedback control

This paper describes an experimental investigation of an actively controlled double-glazed window. It is the second of two companion papers of which the first treated results obtained employing adaptive feedforward control. Herein, the outcome using adaptive feedback control is presented. This adaptive feedback controller has been tested in different configurations, i.e. fully and partially connected controllers. The differences between fully connected controllers with few filter coefficients and partially connected controllers with many filter coefficients are discussed. Additionally, tests with different traffic noise examples have been performed showing the ability of the actively controlled window to enhance protection against traffic noise.     

Adaptive Laguerre filters for active noise control

Feedforward controllers are used in many active noise control (ANC) systems to generate destructive interference in noise fields. An ideal feedforward ANC controller should have an infinite impulse response (IIR) transfer function, but most available feedforward ANC controllers have finite impulse responses (FIR) instead. The main reason is related to the adaptation algorithms of ANC systems. In general, adaptive FIR filters converge faster with guaranteed stability. In this study, the adaptive Laguerre filter is proposed and tested in an ANC application with positive experimental effects. The new ANC controller is an IIR filter, but its adaptation is similar to that of a FIR filter with fast convergence and guaranteed stability. Detailed explanations and analysis are presented in the main text.     

水下流激孔腔噪声前馈有源控制实验研究

水流流经腔体时引起的自激振荡会形成流激噪声,该文通过仿真和实验研究了水下流激孔腔噪声的主动声场控制。应用有源前馈控制方法,对比了参考信号的选取以及控制器中增加的泄露因子对控制结果的影响,并在水循环管路中对流激孔腔噪声前馈控制效果进行了实验验证。研究结果表明,前馈有源噪声控制方法可有效抑制水下流激孔腔噪声,在误差点和辅助观测点都取得了良好的降噪效果,最大降噪量大于8 dB,并且使用腔内信号作为参考的控制效果优于上游信号作为参考。     

Adaptive variable step-size neural controller for nonlinear feedback active noise control systems

Adaptive filter techniques and the filtered-x least mean square (FxLMS) algorithm have been used in Active Noise Control (ANC) systems. However, their effectiveness may degrade due to the nonlinearities and modeling errors in the system. In this paper, a new feedback ANC system with an adaptive neural controller and variable step-size learning parameters (VSSP) is proposed to improve the performance. A nonlinear adaptive controller with the FxLMS algorithm is first designed to replace the traditional adaptive FIR filter; then, a variable step-size learning method is developed for online updating the controller parameters. The proposed control is implemented without any offline learning phase, while faster convergence and better noise elimination can be achieved. The main contribution is that we show how to analyze the stability of the proposed closed-loop ANC systems, and prove the convergence of the presented adaptations. Moreover, the computational complexities of different methods are compared. Comparative simulation results demonstrate the validity of the proposed methods for attenuating different noise sources transferred via nonlinear paths, and show the improved performance over classical methods.     

Synthesis of a robust broadband duct ANC system using convex programming approach

A robust active controller using spatially feedforward structure is proposed for broadband attenuation of noise in ducts. To meet the requirements of performance and robust stability in the presence of plant uncertainties, an H2 cost function and an H(infinity) constrain are employed in the synthesis of the controller. The design is then converted into a convex programming problem using Q-parametrization and frequency discretization. An optimal controller that satisfies the quadratic cost functions and linear inequality constraints can be found by sequential quadratic programming. The optimal controller was implemented via a digital signal processor (DSP) and verified by experiments. Experiment results showed that the system attained 16.5 dB maximal attenuation and 5.9 dB total attenuation in the frequency band 200-600 Hz.     

存在声反馈的前馈有源噪声控制系统性能分析

在一些应用场合,前馈有源噪声控制系统中次级源产生的声信号会反馈至参考传声器,影响参考信号质量和系统稳定,导致控制性能下降。引入了等效次级路径的概念,并通过等效次级路径与实际路径的相位偏差分析存在声反馈时的收敛性能。若某些频率的相位偏差大于90°,则这些频率附近将较难收敛,降噪性能下降,甚至导致系统不稳定。通过仿真和实验对单指向传声器声学方法、自适应滤波u型最小均方差(FuLMS)算法、反馈中和算法和在线建模算法共4种解决声反馈问题的方法的性能进行了比较。结果表明,4种方法都能提高存在声反馈时的前馈有源噪声控制系统的性能,有效解决声反馈引起的问题,但各有优缺点。单指向传声器方法最为方便,但低频指向性较差。FuLMS算法运算量较低,但不能保证收敛。反馈中和算法性能最好,但当系统时变时鲁棒性较差。在线建模算法不需要额外滤波器,但由于参数调节复杂,降噪性能稍差。      

Robust vibration control based on identified models

In active vibration control, model accuracy of a vibration field is crucial to the stability and performance of closed-loop systems, especially multiple-input–multiple-output feedback control systems. A state-space model is popular for the design of vibration controllers. Its accuracy may be affected by mode truncation, errors in eigenfunctions for a modal model or errors in mass/stiffness coefficients of finite elements for a finite element model. There are few analytical results on controller stability margins with respect to these errors. This paper proposes a controller based on transfer matrices identified from the measurement data, on the ground that the accuracy of transfer matrices is manageable by identification algorithms. The proposed controller is able to introduce active damping to vibration fields. An analytical link is available between the stability margin and identification errors for the proposed controller. These are important features analyzed theoretically and verified numerically and experimentally here.     

Improving temporal stability of stable cavitation activity of circulating microbubbles using a closed-loop controller based on pulse-length regulation

Stable cavitation (SC) has shown great potential for novel therapeutic applications. The spatiotemporal distribution of the SC activity of microbubbles circulating in a target region is not only correlated with the uniformity of treatment, but also with some undesirable effects. Therefore, it is important to achieve controllable and desirable SC activity in target regions for improved therapeutic efficiency and biosafety. This study proposes a closed-loop feedback controller based on pulse length (PL) regulation to improve the temporal stability of SC activity. Microbubbles circulating in a physiological flowing phantom were exposed to a 1 MHz focused transducer. The SC signals produced were initially received by another 7.5 MHz plane transducer, followed by high-speed signal acquisition and real-time processing. Based on the real-time-measured SC intensity excited by the current acoustic pulse, the proposed closed-loop feedback controller used three proportional coefficients to regulate the peak negative pressure (PNP) and PL of the next acoustic pulse during the acceleration and stable stages, respectively. The results show that the rise time and the temporal stability of the SC intensity of the microbubbles circulating in these two stages were improved significantly by the optimized proportional coefficients used in the proposed controller. Importantly, when compared with the traditional closed-loop feedback controller based on PNP regulation, the proposed closed-loop feedback controller based on PL regulation reduced the probability of a transition between stable and inertial cavitation, thus avoiding the risk of disadvantageous bioeffects in practical applications. These results demonstrate the effectiveness of the proposed PL-based closed-loop feedback controller and provide a feasible strategy for realization of controllable cavitation activity in applications.