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This paper discusses new work concerned with developing structural sensors and associated signal processing techniques that provide time domain estimates of far-field pressure or structural wave-number information. The sensor arrangement consists of multiple accelerometers whose outputs are passed through an array of linear filters. The impulse response of each filter is constructed from the appropriate Green's function for the elemental source area associated with each sensor. The outputs of the filter array are then summed in order to predict far-field pressure or wave-number information somewhat analogous to the well-known boundary element technique. A major significance of the approach is that it provides time domain information and can thus be efficiently applied to active structural acoustic control approaches.

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The present work gives further developments and experimental testing of a new time domain structural sensing technique for predicting wave-number information and acoustic radiation from vibrating structures. Most structure-borne active sound control approaches now tend to eliminate the use of microphones located in the far field by developing sensors directly mounted on the structure. In order to reduce the control authority and complexity required to minimize sound radiation, these sensors should be designed to provide error information that is solely related to the radiating part of the structural vibrations, e.g., the supersonic wave-number components in the case of planar radiators. The approach discussed in this paper is based on estimating supersonic wave-number components coupled to acoustic radiation in prescribed directions. The spatial wave-number transform is performed in real time using a set of point structural sensors with an array of filters and associated signal processing. The use of the sensing approach is experimentally demonstrated in the time domain LMS active control of broadband sound radiated from a vibrating plate. Comparisons of the control performances obtained with the wave-number sensor and error microphones in the far field show that only a few point sensors are required to provide accurate radiation information over a broad frequency range. The approach demonstrates good broadband global control of sound radiation. ¸

A real time structural acoustic sensor and associated signal processing is developed and applied to the active control of sound radiated by a simply supported beam. The sensor consists of multiple accelerometers mounted on the structure. An array of FIR filters processes the measured structural information to provide an estimate of the structural wave-number component coupled to acoustic radiation in a prescribed direction. This time domain signal is used as the error information in a feedforward adaptive control approach. The single channel filtered-X LMS algorithm is implemented here. Computer simulations in the discrete time domain demonstrate the ability of the sensor to replace the use of error microphones in the far field. The described sensor represents a significant alternative to the use of distributive structural sensors (for example piezoelectric material) by providing accurate radiation information over a broadband frequency range.