Prediction and Measurement of Acoustic Transmission Loss of Acoustic Window with Composite Sandwich Structure.

Sensors for underwater acoustic detection are mounted on outside of the submarine. The acoustic window for protecting these sensors must be structurally robust and at the same time minimize deterioration of the sensor sound detection performance. In order to simultaneously satisfy these two conditions, composite materials are widely used with acoustic window materials. However, since the composite material is manufactured by laminating fibers, there is a probability that delamination occurs in which an air layer is formed inside due to process errors. Delamination inside of the acoustic window degrades the acoustic performance of the sensor and results in a failure of military operations. In case of composites composed of sandwich structures located in the center part, the possibility of internal delamination is higher than that of a single composite material. Therefore, it is very important to discriminate the presence or absence of internal delamination after producing the acoustic window. In this paper, numerical and analytical methods were used to determine the internal delamination of the acoustic window fabricated with sandwich structure. In addition, the results were compared and analyzed through ultrasonic measurement and acoustic transmission loss test.