Composite fiber optic flexural disk hydrophones.

Abstract

Fiber optic flexural disk hydrophones made from castable epoxy have previously been reported. These Michelson interferometric hydrophones produced excellent sensitivity and reasonable depth tolerance. They were designed in the shape of closed cylinders with fiber coils mounted on both sides of each end cap in a push–pull configuration. The current work seeks to increase the depth tolerance without sacrificing the sensitivity by constructing the end caps from composite materials. The present sensors were configured as Mach–Zehnder interferometers and terminated with 3×3 couplers. Three different composite materials were tested. The first was a quasi-isotropic lay-up of unidirectional E-glass in a thermoplastic matrix. The second was a 0°/45° lay-up of woven E-glass in a thermoplastic matrix. The third composite tested was a random orientation of E-glass fibers in a vinyl ester matrix. The theoretical sensitivity and depth tolerance of each composite sensor were calculated using the experimentally determined values of the dynamic Young’s modulus, static flexural rigidity, and tensile strength and compared to measured results. [Work supported by NAVSEA.] a)Lt., USN.