Alex Boudreau

Active noise control in large circular duct using an error sensors plane

Abstract Active Noise Control (ANC) of higher order modes in a circular duct is studied. To overcome the limitations of a modal approach to locate the error sensors, an alternative strategy, referred to as the error sensor plane concept, is proposed. The basic objective of the error sensor plane concept is to create a quiet cross-section in the duct so that the noise from the primary source cannot propagate over this section. To create this quiet cross-section, a network of error microphones is located in the cross-section of the duct. To determine the required number of error microphones and their location in the quiet cross-section, a model simulating a multi-channel ANC system for a circular duct is developed. Using this model, it was deduced that to achieve good control performance, the maximum distance between adjacent error sensors had to be minimized, as well as the distance between the error sensors and the duct wall. To determine the optimal location of the error sensors, the k mean algorithm is implemented. A scale model was used in a laboratory setup to verify the efficiency of the proposed strategy to control high order modes in a circular duct. The obtained results demonstrate that, for the control to be effective, the maximum distance between each error sensor, and the limit of its zone of influence should be less or equal to 1/3 of the wavelength for the frequency considered, i.e. when D max / λ cf

High-performance digital control system for scanning tunnelling microscopy

This paper describes a flexible, completely digital, scanning tunnelling microscope developed around a fixed-point (TMS320C542) digital signal processor. During the development special attention has been paid to the cost of the instrument, without limiting its performance, and in some regards enhancing it. The instrument has been developed and tested in the air, at room temperature, and atomic resolution has been achieved. Its software provides a maximum of support to the user. The tip approach is completely automated. The control parameters can be adjusted based on an on-line identification and off-line (in simulation) optimization. This technique is completely integrated to the control software. It greatly simplifies the parameter optimization, and completely eliminates the risk of collision between the tip and the sample during the optimization. The scanning of the image and control of the tunnelling current are implemented in software by the DSP. This allows the precise identification and real-time compensation of the capacitive coupling between the scan tube electrodes and the current detector. The image analysis and processing software allows slope compensation, as well as the presentation of differential image, two-dimensional FFT and three-dimensional image.

Actuators positioning for multichannel active control system in circular ducts

Abstract In the particular case of multichannel control, the acoustic power limit of loudspeakers may be an important restriction for active control application when the noise levels are very high. The goal of this paper is to present the different parameters that allow to minimize the power used by the control sources for a multichannel active control system in a circular duct. An experimental study of the longitudinal distribution pressure field for the particular case of higher order modes, as well as some experimentations with active control for different geometric conditions have been done to analyze this problem. The results of these experimentations have allowed us to understand that the most influential phenomenon that determines the control sources optimum position are the reflection from ducts closed end. With this result in mind, a simple and efficient methodology of positioning has been developed. The efficiency of this positioning method has been proved from experimental tests.

Upgrade of a multi-channel active noise control system for an industrial stack

Active Noise Control (ANC) has been studied in the 90s as an innovative way to reduce the noise in specific situations. Some applications are well known today and found commercial success such as noise-cancelling headphones. However, the use of ANC in industrial applications is more complex, thus being an uncommon solution in this field. The use of ANC for industrial stack noise is one of these applications. One of the first large-scale implementation has been set up at the end of the 90s. This system was a 10-Channel ANC system installed on a 1.8 m wide chimney to attenuate a 320 Hz pure tone. At that time an 8 dB noise reduction was achieved at error microphones. In 2011, it has been decided to upgrade the system with the latest generation of Digital Signal Processor (DSP) allowing a real-time optimization and a better tracking speed. This paper describes the overall system and the updated multi-channel controller developed for this application. It also presents the improvements, the achieved noise redu...