An inverse method for the identification of the radiation resistance matrix from measurable acoustic and structural responses

The control of structurally radiated noise is becoming more important as vehicles and machinery must become lighter and quieter. Provided that the radiated sound field is known, an Active Structural Acoustic Control (ASAC) system can be implemented to reduce the level of radiated noise when there is a low weight requirement. However, it is often not possible to measure the radiated sound field directly with acoustic sensors and so indirect sensing of the radiated sound power is required. Previously, the radiation resistance matrix, which can be used to estimate the radiated sound power from structural variables alone, has been calculated theoretically for simple structures such as a flat plate in an infinite baffle. However, it is not straightforward to calculate this matrix for more complex practical structures due to the difficulty in obtaining accurate models. To overcome this limitation, a method that is able to estimate the radiation resistance matrix from measurable responses on practical structures is required. In this paper, a method to calculate the radiation resistance matrix using measurable structural and acoustic responses is presented. The presented method requires a series of measurements to be taken on the structure and in the radiated sound field when the structure is excited by different force distributions and these responses are then used to formulate an inverse problem. The accuracy of the solution to this inverse problem is investigated via comparison with the theoretical radiation resistance matrix for a flat plate in an infinite baffle. Through this comparison it has been shown that the accuracy of the solution to the inverse problem depends on the number of structural and acoustic sensors and structural forces used in the identification process.