ASA 126th Meeting Denver 1993 October 4-8

4aSA11. Development of a new rigid composite for high-frequency sonar window applications.

C. M. Thompson R. Y. Ting

Naval Res. Lab---USRD, P. O. Box 568337, Orlando, FL 32856-8337

L. L. Jenkins C. C. Chiou

Texas Res. Intl., Austin, TX 78733-6201

Successful operation of high-frequency sonar arrays requires an acoustic window that not only has a minimal interference with the acoustical signal but also is sufficiently rigid to protect the electronics from arctic ice penetration. Current designs of the window materials call for composite materials of epoxy containing either glass or Kevlar reinforcements. Those composites have unacceptably high insertion losses and beam pattern distortion. A new window material has therefore been developed based on a bromine-modified epoxy resin. The sound speed and the density of the composite were controlled by the bromine content and by using a soft microballon. The ``Spectra'' reinforcement fibers were used for meeting the strength requirement. Finite-element calculations shows that a three-layer structure of 1:3:2 Spectra/microballon/Spectra composite design should optimize the impact strength of the material while maintaining the acoustical performance. Samples of this new composite were fabricated and their mechanical properties evaluated, including the Izod impact strength. Insertion loss of test panels was measured in the USRD ATFI facility. The results of these tests will be presented for discussion. [Work sponsored by NAVSEA.]