Estimating acoustic radiation using wavenumber sensors

A number of current problems of interest in active control involve the need to control the acoustic radiation from a vibrating structure. It has been demonstrated that the optimal solution for minimizing the radiation often does not correspond to minimizing the vibration of the structure. As a result, there has been considerable interest in exploiting the radiation mechanisms for a vibrating structure as a means of controlling the acoustic radiation. Several control schemes have been proposed that are based on a model of the acoustic radiation [1,2,3]. An alternative method of minimizing the radiation is to directly estimate the wavenumber spectrum of the vibrating structure, from which the supersonic (radiating) components of the spectrum can be identified and minimized [4]. This method has the advantage of providing a direct measure of the radiation mechanism, which is not based on a model of the system. As a result, if the parameters of the system change, the method would be sensitive to those changes and capable of tracking the changing radiation conditions. This paper outlines a method to obtain an estimate of the structural wavenumber spectrum, from which the radiation can be estimated. The approach is based on the use of an array of distributed sensors, which provides the capability of attenuating the effects of spatial aliasing if there is significant energy in the subsonic (nonradiating) components of the wavenumber spectrum.