Design optimization of an optical fiber air-backed concentric hybrid mandrel hydrophone by an iterative design and finite element analysis for submarine passive array applications

The optical fiber hydrophones are well suited for the submarine passive sonar applications taking into consideration of their high sensitivity, fully electrically passive characteristics etc. and are definitely an equivalent replacement for Lead Zirconate and Lead Titanate ceramic hydrophones. In this paper, finite element analysis of several sets of cases of concentric hybrid material-based air-backed OF mandrel hydrophones are analysed and tuned to their geometric dimensions and their mechanical properties for design optimization, suitable for submarine sonar applications. A finite element method is adopted for analysis, strain and sensitivity calculations using ANSYS software. An inverse dependency of the sensitivity and the natural frequency were observed and was overcome by an innovative method where a hybrid inner hollow tube, combining both Aluminium and high-density polyethylene materials, were used, improving both the stiffness property and compliance of the mandrel and thereby improving both the natural frequency and pressure sensitivity. The harmonic analysis was carried out at 5 KHz acoustic pressure, by adding hydrostatic pressures of 2 MPa, 3 MPa and 4 MPa and obtained satisfying results. The acoustic directivity of this OF mandrel hydrophone was estimated, plotted and an omni directional pattern was obtained.