Pre-test analysis to reproduce random pressure fields with multi-channel acoustic control

Multichannel feedforward active noise control system combined with noise source separation by microphone arrays

The convergence speed of multichannel adaptive active noise control algorithms can be improved by pre-whitening the reference signals and reducing their cross-correlations. When considering nonstationary processes, like road noise, it proves advantageous to use a short time-based cross-correlation estimation of the reference signal, which can be obtained as part of the bin-normalised frequency domain least-means-squares algorithm. However, the regularisation of such an algorithm is crucial to its success and can further improve the convergence rate. In addition, virtual sensors can be employed by using the additional filter method, which provides targets for the measured error signals to follow, generated from the reference signals. Still, the performance of this virtual sensing is known to be degraded if the properties of the reference signals change, so special consideration should be taken when the reference signals are nonstationary.

Actuators positioning for multichannel active control system in circular ducts

Acoustic Black Holes (ABHs) can be realised as tapered structural features that focus and absorb vibrational energy. In a plate, the damping effect of ABHs can be used to reduce the radiation efficiency, particularly above the critical frequency of the plate. However, at lower frequencies, there is still significant radiation due to the low order modes of the plate. It has previously been shown that the combination of active control and ABHs can result in an effective broadband control solution with lower computational and power requirements compared to a standalone active configuration. This paper presents an investigation into how two different active control strategies affect structural response and radiated sound power of a plate with active ABHs (AABHs). It is shown, through an active vibration control strategy and an active noise control strategy, that the AABHs can be used to successfully control either the global structural response of the plate or the radiated sound power. However, it is also shown that controlling either response can lead to an enhancement in the other.

The convergence speed of multichannel adaptive active noise control algorithms can be improved if the reference signals are preconditioned, so it is advantageous to whiten them and reduce their cross-correlations. However, this preconditioning depends on the properties of the reference signals, which will generally change over time. It may still be possible to approximate the properties of the measured reference signals using a limited number of exemplar cases. By classifying the measured reference signals into the closest of these cases, the most appropriate preconditioning can be selected for the adaptive algorithm at any one particular time. Also, one method of implementing virtual sensors is to use the additional filter method, which provides targets for the measured error signals to follow, generated from the reference signals. The performance of this virtual sensing is known to be degraded if the properties of the reference signals change, so this classification method could also be used to select the most appropriate additional filter.

The acoustic impedance at the diaphragm of an electroacoustic transducer can be varied using a range of basic electrical control strategies, amongst which are electrical shunt circuits. These passive shunt techniques are compared to active acoustic feedback techniques for controlling the acoustic impedance of an electroacoustic transducer. The formulation of feedback-based acoustic impedance control reveals formal analogies with shunt strategies, and highlights an original method for synthesizing electric networks ("shunts") with positive or negative components, bridging the gap between passive and active acoustic impedance control. This paper describes the theory unifying all these passive and active acoustic impedance control strategies, introducing the concept of electroacoustic absorbers. The equivalence between shunts and active control is first formalized through the introduction of a one-degree-of-freedom acoustic resonator accounting for both electric shunts and acoustic feedbacks. Conversely, electric networks mimicking the performances of active feedback techniques are introduced, identifying shunts with active impedance control. Simulated acoustic performances are presented, with an emphasis on formal analogies between the different control techniques. Examples of electric shunts are proposed for active sound absorption. Experimental assessments are then presented, and the paper concludes with a general discussion on the concept and potential improvements.

Accurate model of secondary paths is very crucial for the multi-channel filtered-X least mean square algorithm applied in adaptive active noise control system. The auxiliary random noise technique is popular for online secondary path modeling during adaptive active noise control operation. This paper proposes a simplified variable step-size strategy and an effective auxiliary noise power scheduling strategy for the multi-channel filtered-X least mean square algorithm. Through a defined indirect error signal, the proposed method can guarantee every online secondary path modeling filter has its own exclusive variable step-size strategy to update their coefficients, and every injected noise has its own exclusive scheduling strategy considering all of the corresponding online secondary path modeling filters. The proposed method can improve the adaptive performance and simplifies the complexity of multi-channel adaptive active noise control system. Computer simulations show that the proposed method gives much better noise reduction and secondary path modeling accuracy at a somewhat faster convergence rate comparing with the competing methods.

The presence of acoustic noise in audio recordings is an ongoing issue that plagues many applications. This ambient background noise is difficult to reduce due to its unpredictable nature. Many single channel noise reduction techniques exist but are limited in that they may distort the desired speech signal due to overlapping spectral content of the speech and noise. It is therefore of interest to investigate the use of multichannel noise reduction algorithms to further attenuate noise while attempting to preserve the speech signal of interest. Specifically, this thesis looks to investigate the use of microphone arrays in conjunction with multichannel noise reduction algorithms to aid aiding in speaker identification. Recording a speaker in the presence of acoustic background noise ultimately limits the performance and confidence of speaker identification algorithms. In situations where it is impossible to control the noise environment where the speech sample is taken, noise reduction algorithms must be developed and applied to clean the speech signal in order to give speaker identification software a chance at a positive identification. Due to the limitations of single channel techniques, it is of interest to see if spatial information provided by microphone arrays can be exploited to aid in speaker identification. This thesis provides an exploration of several time domain multichannel noise reduction techniques including delay sum beamforming, multi-channel Wiener filtering, and Spatial-Temporal Prediction filtering. Each algorithm is prototyped and filter performance is evaluated using various simulations and experiments. A three-dimensional noise model is developed to simulate and compare the performance of the above methods and experimental results of three data collections are presented and analyzed. The algorithms are compared and recommendations are given for the use of each technique. Finally, ideas for future work are discussed to improve performance and implementation of these multichannel algorithms. Possible applications for this technology include audio surveillance, identity verification, video chatting, conference calling and sound source localization.

This paper describes a comprehensive off-line system level test strategy developed for several complex high speed, telecom chips. These chips feature a large number of clocks, mixed analog and digital logic and large high speed RAMs. The test strategy was based on the principles of hierarchical test, DFT reuse, BIST and at-speed test, and was implemented using DFT solutions provided by Logic Vision. The paper further specifies the requirements for integration of the DFT solutions within the ASIC vendor's flow. The final DFT implementation which includes scan, at-speed Logic BIST, RAM BIST, PLL BIST, user-defined IEEE 1149.1 TAP and Boundary Scan with fault insertion capability, is presented The system level test architecture focusing on an in-house developed TAP Master is given. Motivation from a cost saving perspective in system SW development and improved system quality monitoring are highlighted as major driving forces in support of this strategy. Finally, some practical issues for consideration when planning system test based on BIST are presented.

To explore the addressed issue of closed-loop vibration control using semi-active magneto-rheological (MR) fluid damper, an innovative control algorithm based on feedback of acceleration response at several points along stay cable for active/semi-active control of stay cables is firstly proposed in the present paper. Theoretical analysis, laboratory investigation, and in-situ tests are conducted in this study to verify the proposed control algorithm. Moreover, this paper presents the negative stiffness characteristic of the combined stay cable/semi-active MR damper system. These investigations indicate that the semi-active MR damper can achieve much better mitigation efficacy than the other passive MR dampers and the proposed control algorithm is proved to be practical. The effect of the negative stiffness on response reduction is demonstrated by the improved energy dissipation ability of the damper due to the enhanced displacement of the stay cable at the location attached with the damper. Introduction In the past few decades, many control methods have been proposed and some have been implemented to mitigate the unaccepted stay cable vibration (Johnson, 2003). At present, semi-active dampers have been proven to be effective in many applications and can potentially achieve performance levels that are almost the same as comparable active devices. For stay cables vibration control incorporated with semi-active dampers, most of the existing control strategies are based on full-state feedback of generalized coordinates. However, the generalized displacements and velocities of the stay cable cannot be measured directly. Since accelerometers can readily provide reliable and inexpensive measurements of the stay cable accelerations at strategic points on a stay cable, development of control method based on acceleration feedback at limited locations along stay cable is an ideal solution to solve the addressed practical problem. Moreover, even though the characteristic of negative stiffness of active control of stay cable vibration has been observed by some researchers(Johnson, 2003), the effects of negative stiffness on the stay cable vibration control using active/semi-active dampers 2 has not been fully researched in the present literatures. In this paper, a control algorithm based on feedback of acceleration response at several points for active and semi-active control of mass-distributed dynamic systems, e.g. stay cables is firstly proposed. Using the proposed control algorithm, the vibration control for the stay cable model attached with one MR damper and a series of field tests are carried out to investigate the control efficacy achieved by different control strategies. These investigations address that the semi-active MR damper can achieve much better mitigation efficacy than other passive MR dampers and the proposed control algorithm is proved to be practicable and available. Moreover, the effect of the negative stiffness provided by semi-active MR dampers on response reduction of cables is theoretically and numerically demonstrated by the improved energy dissipation ability of the damper due to the enhanced displacement of the cable at the location attached with the damper. Control Algorithm Based on Acceleration Feedback at Several Locations Governing equation of the combined stay cable/MR damper system shown in Figure 1 is given as (Irvine, 1981) ) ( ) ( ) , ( ) , ( ) , ( ) , ( d s x x t u t x f t x v c t x v T t x v m − + = + ′ ′ − δ & & & (1) with the boundary conditions v(0,t)=v(l,t)=0 for all t .where v(x,t) is the transverse deflection of the cable, l is the length of the cable, T is the cable tension, m and c are the cable mass and viscous damping per unit length, respectively, xd is the distance of the installed MR damper position from the left end, us(t) is the transverse control force provided by the MR damper at location x= xd, f(x,t) is the distributed load along the cable. δ(.) is the Dirac delta function. Figure1. Combined stay cable/MR damper system The transverse deflection could be approximated using a finite series ) ( ) ( ) , ( ∑ = = r j j j x t q t x v 1 φ (2) where the φj(x) is a set of shape modal functions and continuous with piecewise continuous slope to satisfy the geometric boundary conditionsφj(0)= φj(l)=0. Utilizing the approximate series solution and a standard Galerkin approach, the motion equation of the cable-MR damper system in matrix form is written as ) ( ) ( f Kq q C q M q t u x s d φ + = + + & & & (3)

Active sound transmission control using a piezoelectric sensor and actuator on a thin plate is investigated experimentally. The plate made of aluminium covers the opening of an acoustic enclosure where a sound source is located. The exterior acoustic field is measured by a microphone array, which scans a hemispherical surface. The isolation performance of the passive plate is poor at its resonance frequencies. Sound transmission through the plate is actively controlled at the resonance frequencies. A one-sensor one-actuator control system minimizes the sensor output by applying a proper electric voltage to the actuator. Global sound reduction of 15-22 dB is achieved at the first three resonance frequencies by using the same sensor and actuator. Using a sensor at a different location, a reduction of 9 dB is obtained at a higher frequency. The relation between control performance and the coincidence of the responses of the transmitted sound and the sensor is briefly discussed based on the mode decomposition theory.

Human postural sway during stance arises from coordinated multi-joint movements. Thus, a sway trajectory represented by a time-varying postural vector in the multiple-joint-angle-space tends to be constrained to a low-dimensional subspace. It has been proposed that the subspace corresponds to a manifold defined by a kinematic constraint, such that the position of the center of mass (CoM) of the whole body is constant in time, referred to as the kinematic uncontrolled manifold (kinematic-UCM). A control strategy related to this hypothesis (CoM-control-strategy) claims that the central nervous system (CNS) aims to keep the posture close to the kinematic-UCM using a continuous feedback controller, leading to sway patterns that mostly occur within the kinematic-UCM, where no corrective control is exerted. An alternative strategy proposed by the authors (intermittent control-strategy) claims that the CNS stabilizes posture by intermittently suspending the active feedback controller, in such a way to allow the CNS to exploit a stable manifold of the saddle-type upright equilibrium in the state-space of the system, referred to as the dynamic-UCM, when the state point is on or near the manifold. Although the mathematical definitions of the kinematic- and dynamic-UCM are completely different, both UCMs play similar roles in the stabilization of multi-joint upright posture. The purpose of this study was to compare the dynamic performance of the two control strategies. In particular, we considered a double-inverted-pendulum-model of postural control, and analyzed the two UCMs defined above. We first showed that the geometric configurations of the two UCMs are almost identical. We then investigated whether the UCM-component of experimental sway could be considered as passive dynamics with no active control, and showed that such UCM-component mainly consists of high frequency oscillations above 1 Hz, corresponding to anti-phase coordination between the ankle and hip. We also showed that this result can be better characterized by an eigenfrequency associated with the dynamic-UCM. In summary, our analysis highlights the close relationship between the two control strategies, namely their ability to simultaneously establish small CoM variations and postural stability, but also make it clear that the intermittent control hypothesis better explains the spectral characteristics of sway.

High noise in infant incubators results in numerous adverse health effects which have lifelong consequences for neonatal intensive care unit (NICU) graduates. This paper presents multi-channel hybrid active noise control (ANC) systems for infant incubators. A hybrid ANC algorithm is an integration of a feedforward algorithm (to cancel noise generated from sources outside the incubator) and a feedback algorithm (to reduce the predictable noise inside the incubator). Computer simulation and real-time experiment results show that the proposed hybrid algorithms are effective in cancelling both outside and inside noises of infant incubators in real NICU environment.

The container automated guided vehicle (AGV) is gaining prominence owing to its efficient operation. This paper presents an electro-hydraulic proportional steering system and cascade proportional-integral-derivative control strategy suitable for container AGVs. Mathematical models of key components and mechanical mechanisms were constructed, and parameters affecting response speed and stability were analyzed. A linear active disturbance rejection control (LADRC) strategy was proposed to improve the anti-jamming capability of the system. The effects of the two control strategies were compared based on multi-software co-equivalent simulation. Results show that in the 12 s period sinusoidal tracking experiment, LADRC improved tracking accuracy by 53.85% and reduced deviation amplitude by 85%, and the anti-interference ability was stronger. The proposed system and control strategy were tested on a bench and prototype vehicle. The passing ability and operational efficiency of the container AGV under complex road conditions were improved by the proposed method.

In the microgrid with high penetration rate of renewable energy, multiple distributed generations operate in parallel. To ensure stable operation of the microgrid, research for multi-inverter coordination control is necessary. Master-slave control can realize various functions with the combination of different control strategies. Voltage and active power control strategy can provide voltage support for the grid and reduce the voltage fluctuation in the point of common coupling. Previous voltagesupporting methods are usually based on constant droop coefficient, where the control curve is linear. When the voltage fluctuation is too large, the change of the distributed generations power is too small to support the gird voltage. This paper presented an improved master-slave voltage and active power control strategy for multiple photovoltaic inverters. The master inverter operates under maximum power point tracking control strategy as the sample. The slave inverter adopts nonlinear voltage and active power control. When the voltage is too high, increase the droop coefficient to accelerate the power reduction. Conversely, when the voltage is much below the rated value, the distributed power supply will output its maximum power. Finally, the effectiveness of the proposed control strategy is verified by simulation.