|Title:||Noise cancellation using piezoelectric actuators as control sources|
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Civil and Structural Engineering|
|Pages:||xxiv,  leaves : ill. (some col.) ; 30 cm|
|Abstract:||Loudspeakers are usually used for generating secondary noise in the active control of the sound in ducts. However, they are bulky, heavy, non-durable and of poor response at low frequencies. Piezoelectric actuators are suggested as an alternative control input in order to overcome some of the captioned disadvantages of the loudspeaker. Piezoelectric sources can reduce the level of acoustic potential energy in the enclosure by altering the vibration of the structure. The objectives of the research in this thesis are to, (1) study the vibration modes of long thin plate excited by the piezoelectric actuators using the nonlinear analysis method; (2) investigate the coupling behaviour of the panel vibration and the sound field in a duct; (3) experimentally study the attenuation of unwanted sound at the low frequency in the duct by using the panel vibration control source excited by piezoelectric actuators. A structural-acoustic coupled system of a long thin plate and a sound field in a duct is discussed. Piezoelectric actuators were used as a secondary (control) source to generate control disturbance to cancel the unwanted sound in the duct. The plate excited by the piezoelectric actuators was analysed by the geometric nonlinear finite element method. A computer program for nonlinear vibration analysis is verified by comparing the theoretical results with the experimental results. The dynamic response of the plate vibration subjected to piezoelectric actuators is small because of the stiffness of membrane structure and the small control forces produced by the piezoelectric actuators. Based on the experimental investigation, the vibration of a long thin plate can be used as the sound absorber at medium frequencies (170-320 Hz). And the plate vibration excited by piezoelectric actuators can be used as the control source to cancel the unwanted sound at low frequencies (60~140 Hz). The piezoelectric sources show the potential for noise cancellation in an enclosed sound field because of its advantages over the loudspeakers. Moreover, the piezoelectric source in this thesis can generate much higher sound pressure levels than the diaphragm piezoelectric actuation device. This thesis introduces a new method for noise cancellation by using plate vibration excited by piezoelectric actuators as an acoustic control source to increase sound absorption instead of the conventional method of reducing sound transmission. It is also found that nonlinear vibration can degrade the performance of piezoelectric actuators as acoustic source but can improve the passive dissipation of noise.|
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