Active control of sound radiation from cylinders with piezoelectric actuators and structural acoustic sensing

In this paper, analytical and experimental results of an investigation of active control of sound radiated from cylinders are presented. The aluminium cylinder is 1 m in length, 25 cm in diameter and 24mm in thickness with two rigid end-caps at both ends. The excitation is a band-limited random noise encompassing the first five modes of the cylinder and the control actuators are surface mounted piezoelectric transducers. Since it is desired to integrate the error sensors into the structure, the recently developed Discrete Structural Acoustic Sensing (DSAS) approach is extended to the cylindrical co-ordinates and implemented using 12 accelerometers mounted on the cylinder. The structural acoustic sensor provides times domain estimates of far-field radiated sound at predetermined radiation angles. The controller is a 3 by 3 Filtered-x LMS paradigm implemented on a TMS320C30 DSP. The results show good global control of the radiated sound over the frequency bandwidth of excitation. Most important, the proposed discrete structural acoustic sensor yields similar performances as error microphones located in the far field. The sensor is also shown to improve far-field attenuation over minimization of normal acceleration at discrete locations on the cylinder structure. (C) 1999 Academic Press.