Kris Henrioulle

Design of an active noise control system using a distributed actuator

A distributed acoustic actuator for active noise control, consisting of a piezoelectric PVDF film, bonded at each side of a carrier structure, is simulated and built. The piezoelements are driven in anti-phase, resulting in a bending motion of the actuator, and thus in the necessary out-of-plane displacement for sound radiation.An analytical model for the acoustic actuator is derived, relating the actuators displacement to the applied voltage, taking into account the influence of the piezoelectric film on the actuators stiffness. The model is used to optimise the specifications for the piezoelectric film and the carrier structure, resulting in the highest sound power output in a frequency range from 30–500 Hz.An analytical model for the behaviour of a double panel partition is derived. The analytical model is combined with the model for the acoustic actuator, describing an actively controlled double panel partition with a distributed acoustic actuator integrated in the cavity. A controller is added to the system to control the sound power transmitted through the double panel partition. Simulation results show that a substantial increase of transmission loss can be achieved in the low frequency region (30–500 Hz) with this configuration.

Model-Based Feedback Control of Acoustic Radiation from Vibrating Structures by Means of Structural Control

In this work, it is investigated how classical techniques of linear feedback control design can be applied to the problem of the reduction of acoustic radiation from vibrating structures for cases where the disturbance is broadband and where no reference is available. Much of the work carried out to date in the field of active noise and vibration control has concentrated on applications where either the disturbance to be cancelled is periodic (propeller noise in aircraft,...) or a reference signal, highly correlated with the disturbance, is available (air conditioning duct noise,...) such that a feedforward control approach can be used. When the disturbance is broadband and where no reference is available, feedforward control cannot be used and feedback control must instead be used. Feedback control theory is well established and a vast amount of analytical tools are available to the feedback control designer. However, due to the inherent delays associated with the propagation of sound waves, feedback control of acoustic fields is prone to being unstable.In this paper, a controller is presented which feeds back a measure of the structural response (vibration) of the system in order to determine the control force that needs to be applied to the vibrating structure in order to reduce the total acoustic energy radiated by the vibrating structure.

Experiments on the active increase of sound transmission loss using distributed actuators

A series of experiments have been performed to improve actively the sound transmission loss through a single‐panel partition in the low‐frequency range. Two types of flat acoustic actuators, designed in the framework of the European project DAFNOR (distributed active foils for noise reduction), are tested. The first acoustic actuator is based on PVDF piezoelectric material, which induces a bending motion in the actuator. The second acoustic actuator is based on the electrostatic principle. The experimental setup consists of a single steel panel of size 300×400×1 mm which is subject to a plane‐wave acoustic excitation. The control system consists of the distributed acoustic actuator, which is placed near the steel panel. Various control strategies, which were previously simulated, are tested. The control actuator is driven by a controller which aims at reducing the acoustic energy at the radiating side. [The work reported herein was related to the EC Brite/Euram Research Project ‘‘DAFNOR’’ (under contract BRPR‐CT96‐0154). The project is supported by the Directorate‐General for Science, Research and Development of the CEC.]