One-dimensional Acoustic Duct Research Articles

Experimental realization of an active non-reciprocal metamaterial using an eigen-structure assignment control strategy.

This paper presents a class of active non-reciprocal metamaterials (ANMMs) in an attempt to control the flow of acoustic waves along a one-dimensional acoustic duct. The proposed method distinguishes itself from the available approaches where the non-reciprocities are generated either actively or passively by various sources of nonlinearities, circulators and gyroscopic/gyrator components, and/or spatiotemporal modulation. The proposed method relies in its operation on a controller that is designed by simultaneous allocation of both the eigenvalues and eigenvectors. In other words, the entire eigen-structure of the closed-loop system is assigned as deemed necessary. Conventionally, the placement of the eigenvalues has been employed to enhance both the damping and response of the system. However, in this study, the focus is placed on adjusting the eigenvectors in a way that enables the spatial control and redistribution of the wave propagation along the acoustic duct in order to produce any desirable non-reciprocal behavior. During this entire process, the system continues to behave in a linear fashion. The theory governing the operation of this proposed approach is introduced, and a comprehensive experimental validation effort is presented to demonstrate the basic features, non-reciprocal behavior, and control characteristics. Generalization of the presented strategies to two-dimensional acoustic systems is a natural extension of the present work.

Active synthesis of a gyroscopic-nonreciprocal acoustic metamaterial

A class of active nonreciprocal metamaterials is developed to control the flow and distribution of energy along periodic dynamical systems. Such a development constitutes a radical departure from the currently available approaches where the non-reciprocities are generated either by utilizing various physical sources of passive nonlinearities, gyroscopic circulators, spatiotemporal modulation, or active control of nonlinear systems. The proposed active Nonreciprocal Gyroscopic Meta-Material (NGMM) cell consists of a one-dimensional acoustic duct provided with linear dynamic control capabilities that virtually synthesize a gyroscopic control action that generates non-reciprocal characteristics of tunable magnitude and direction. The controller is designed in order to enable the spatial control and redistribution of the wave propagation energy flow along the acoustic duct. During this entire process, the system behaves in a linear fashion. Numerical examples are presented to demonstrate the basic features, non-reciprocal behavior, as well as the energy flow characteristics. The presented concept and controller design of the NGMM can be extended to various critical structures to achieve realistic acoustic diode configurations in a simple and programmable manner.

Active nonreciprocal metamaterial using an eigen-structure assignment control strategy.

A class of active nonreciprocal metamaterials (ANMMs) is developed to control the flow and distribution of energy along periodic dynamical systems. Such a development constitutes a radical departure from the currently available approaches where the non-reciprocities are generated either by utilizing various sources of passive nonlinearities, gyroscopic circulators, spatiotemporal modulation, or active control of nonlinear systems. The proposed ANMM cell consists of a one-dimensional acoustic duct provided with linear active control capabilities. The controller is designed by simultaneous assignment of both the eigenvalues and eigenvectors, i.e., the entire eigen-structure, of the closed-loop system. Conventionally, the placement of the eigenvalues has been considered to improve the damping and system's response. However, in this study, the emphasis is placed also on tailoring the eigenvectors in order to enable the spatial control and redistribution of the wave propagation energy flow along the acoustic duct in such a manner that it can introduce non-reciprocity as well as control its direction and reversal. During this entire process, the system remains behaving in a linear fashion. Numerical examples are presented to demonstrate the basic features and non-reciprocal behavior, as well as the energy flow characteristics.

A Sensor Placement Strategy for the Hybrid Adaptive Feedforward Observer

A sensor placement technique is proposed for implementing the hybrid adaptive feedforward observer. The observer is a conventional dynamic observer augmented with an adaptive feedforward component for estimating the effect of persistent, nonstationary disturbances. The placement technique searches for the least possible number of sensors that satisfy two criteria, the observability of the plant, and the lowest condition number of the error dynamic system's state matrix. Demonstration was performed on a one-dimensional acoustic duct. The results show that the proposed technique is an effective guideline for identifying the optimal sensor locations.

MODEL-BASED ACTIVE NOISE CONTROL: A CASE STUDY FOR A HIGH-SPEED CD-ROM SYSTEM

The active attenuation of the airborne noise generated from a high-speed CD-ROM system is investigated using model-based feedback control methods. A mathematical model of the physical system is developed based on a one-dimensional acoustic duct system. The critical system parameter, acoustic terminal impedance, is estimated using the eigenstructure tests through the system identification method. The considered Active Noise Control (ANC) problem is then formulated into a set of standard feedback control design problems. By using standard control methods, a set of simple feedback controllers are developed for the considered system. The simulation and physical test results show a potential to use standard control techniques for a simple, cheap but efficient ANC design and implementation.

A Virtual Sensing Method for Tonal ANVC Systems

Virtual Sensing (VS) is considered to be an extension for feedforward Active Noise and Vibration Control (ANVC) systems when, for example, it is desired to minimize the response at one or more spatial locations where it is either physically impossible or undesirable to place an actual error sensor. In this context, VS is an estimation technique for predicting the appropriate system response using available measurements and a dynamic system model. A hybrid adaptive feedforward observer is proposed which has the ability to overcome the limitations of conventional dynamic observer designs. The hybrid observer utilizes a conventional dynamic observer augmented with an adaptive feedforward element for estimating the effect of the persistent disturbance. For simplicity, we restrict this development to a single tonal disturbance for which a coherent reference is assumed available. It will be appreciated that this technique may be extended to handle disturbances that contain multiple tones as well as broadband noise, as long as suitable reference signals are available. Numerical simulations and real-time experiments were performed on a one-dimensional acoustic duct. The results demonstrate that the hybrid adaptive feedforward observer is an effective method for predicting the virtual sensor response in an ANVC system.

Hybrid Active Noise Control of a One-Dimensional Acoustic Duct

Based on the closed-form solution of a one-dimensional wave equation, the primary, secondary and acoustic feedback paths for the active control of sound in an acoustic duct have been investigated. Accurate models for the condenser microphone and loudspeaker, which include both the electro-mechanical and mechano-acoustical couplings as well as acoustical damping, have been considered. A generalized form of the filtered-x least mean square (FXLMS) algorithm that uses a more general recursive adaptive weight update equation to improve the performance of the FXLMS algorithm has been developed. Computer simulations were carried out to investigate the performance of acoustical feedback and feedback neutralization as well as the effect of boundary conditions on the performance of active noise control (ANC) systems. Comparisons of the simulation results were carried out.

Robust internal model‐based LQG design for active noise control of a one‐dimensional acoustic duct system

A control design method is proposed to design controllers to achieve global sound pressure attenuation for noise of narrow-band frequencies in a one-dimensional acoustic duct system. This method combines a linear-quadratic-gaussian (LQG) theory with an internal model principle to design internal model-based active noise controllers so that noise of a specific (target) frequency in a duct can be reduced. The designed controller is, nevertheless, hyper sensitive to the perturbation of the target noise frequency. A reduced parameter sensitivity technique is further incorporated to improve robustness such that noise of narrow-band frequencies can be attenuated. Computer simulation shows the effectiveness of robustness improvement for the proposed design method. In addition, global sound pressure attenuation along the duct is achieved. Experimental results also demonstrate frequency robustness improvement and global sound pressure attenuation despite the fact that the dynamic effects of the actuator are not considered in the control design. Both simulation and experimental results support the feasibility of the proposed design method. Copyright © 1999 John Wiley & Sons, Ltd.

Robust internal model-based LQG design for active noise control of a one-dimensional acoustic duct system

A control design method is proposed to design controllers to achieve global sound pressure attenuation for noise of narrow-band frequencies in a one-dimensional acoustic duct system. This method combines a linear-quadratic-gaussian (LQG) theory with an internal model principle to design internal model-based active noise controllers so that noise of a specific (target) frequency in a duct can be reduced. The designed controller is, nevertheless, hyper sensitive to the perturbation of the target noise frequency. A reduced parameter sensitivity technique is further incorporated to improve robustness such that noise of narrow-band frequencies can be attenuated. Computer simulation shows the effectiveness of robustness improvement for the proposed design method. In addition, global sound pressure attenuation along the duct is achieved. Experimental results also demonstrate frequency robustness improvement and global sound pressure attenuation despite the fact that the dynamic effects of the actuator are not considered in the control design. Both simulation and experimental results support the feasibility of the proposed design method. Copyright © 1999 John Wiley & Sons, Ltd.

Modeling, identification, and feedback control of noise in an acoustic duct

Although active noise control has been a subject of interest for over 50 years, it has become feasible only with recent technological advances. This paper formulates the problem of noise control in a one-dimensional acoustic duct in a form that lends itself to the application of feedback control theory. In contrast to most of the literature on the subject which uses feedforward techniques, a feedback approach is used. Inconsistencies that appear in previous feedback control models are rectified, controllers are designed using precompensated linear quadratic Gaussian (LQG) synthesis, and experimental verification of the control designs is presented. The experimental results show a reduction of about 5-12 dB over a frequency range from 150-350 Hz.

Development of Wide-Band Active Noise Control System for One-Dimensional Acoustic Duct Using Progressive Wave as Control Signals. 1st Report. Trial Construction of Control System and General Considerations of Noise Reduction Performance.

A new active noise control system for air-conditioning ducts has been presented, together with experimental results. The control system detects the progressive wave component of fluid-borne vibration and then controls the second source feed-forwardly using this detected signal so as to eliminate the progressive wave in its downstream duct by producing cancelling (anti-phase) fluid vibration. The key points of the design of the active noise control system, in which a transfer function-based method is used, are the following : (1) satisfactory noise reduction performance achieved by matching the transfer function of the controller (specifically, the signal processor for control) with the desired (target) characteristics as much as possible, and (2) prevention of howling by increasing the degree of stability. It has been confirmed by both theoretical analysis and tests carried out on a small model apparatus that, when the present control system was operated, pressure pulsation(noise)in a duct down stream of the second source was reduced by aroud 1/10(20 dB) of that in the case where the control system was not operated for almost all harmonics of 40 Hz to 600 Hz, and that the present system had a far higher degree of stability than that of Lueg's system.

Development of Wide-Band Active Noise Control System for One-Dimensional Acoustic Duct Using Progressive Wave as Control Signals. (2nd Report. Trial Construction of Adaptive Control System and Fundamental Experiments).

A new active noise control system forair-conditioning ducts is presented, together with computer simulations and experimental results. The system feed forwardly controls the second source using the signal of the progressive wave conmponent of fluid-borne noise detected upstream of the duct, and has the capability to change system parameters owing to a programmable digital signal processor. The adaptive feed-forward control structure is based on the "filtered-X" LMS algorithm. It is established through testing of a small model apparatus that pressure pulsation (noise) in a duct downstream of the second source can be reduced by at least 20 dB for almost all harmonics of around 40 Hz to 1000 Hz, while maintaining stability, even in the case where uncontrolled system parameters such as acoustic properties and dynamic characteristics of the second source change with time. It is also shown that the computer simulations agree well quantitatively with the experimental results and can be applied successfuly to system design.