Active noise reduction by structural control using piezo-electric actuators

A common source of noise is operational excitations of mechanical devices, which cause vibrations and thus sound radiation from their surfaces. Plate and shell structures in automotive, aviation and space applications vibrating in resonance show particularly high noise levels. Classical methods of noise reduction such as passive damping or anti-noise are not efficient enough in certain cases. Therefore, the use of structural control for reduction of sound radiation is presented here. Control forces are generated by piezo-electric actuators directly attached to the panel surface. The Finite Element Method supplies a numerical description of the noise radiating structure and the effects of the attached piezo actuators. Technical expenditures are kept low by minimizing the number of sensors and actuators used in the control system. To achieve a high control performance, a method is derived to find suitable locations for these elements. The rapid development of the capability of digital signal processors opens the possibility to use structural control with complete state feedback as a method for active noise control of plate structures. The instantaneous state of vibration is measured and these signals are transmitted to a real-time computer. Control outputs are computed on the basis of a modal state observer considering 10 modes in connection with a linear quadratic controller. The developed active noise control achieves good results for the reduction of the sound pressure levels at resonance frequencies. In a frequency range of 0-650 Hz attenuations up to 17 dB have been measured. Through the use of commercially available components such as digital signal processors and piezo-electric actuators a wide spectrum of future applications is opened. (C) 2000 Elsevier Science Ltd. All rights reserved.