Active structural acoustic control of sound transmission through a plate

Abstract

This thesis is concerned with the development of systems for active structural acoustic control (ASAC) of sound transmission through a plate.

The theory of plate vibrations and the subsequent sound radiation are described. Plate vibrations are analysed in terms of the conventional structural mode approach, and in terms of radiation modes, which are a set of independently radiating velocity distributions. The first radiation mode is much more efficient than the others at low frequencies and has a shape approximately corresponding to the volume velocity of the plate. This is thus chosen as the variable to be controlled in later parts of the thesis.

A comparison of different actuators and sensors follows. Ideally, a uniform force actuator would be used with a volume velocity sensor. There are inherent problems with using a distributed uniform force actuator with a distributed volume velocity sensor, so in this work piezoceramic actuators are used instead. The placing of the actuators and sensors should be such that the frequency response function between them has as little phase loss as possible for the purposes of feedback control.

Feedback control and a number of related issues are discussed. One control architecture called Internal Model Control (IMC) is analysed in more detail and is then used in a real-time experiment to cancel the output of a volume velocity sensor using piezoceramic actuators.

The distributed volume velocity sensor is then replaced by a number of accelerometers on the plate and several different cost functions are investigated, including summing their integrated outputs to estimate volume velocity, multi-channel cost functions, such as the control of higher order radiation modes and control of the frequency dependent shape of the first radiation mode, and a configuration using multiple local control systems on a structure. A control architecture is also outlined which uses structural reference sensors and acoustic error sensors. This method is then tested in real-time experiments.

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