Research On The Characteristics Of The Interferometric Fiber-Optic Hydrophone With A Concentric Mandrel Including An Enhanced Sensitivity Layer

Interferometric optic fiber hydrophone has the highest sensitivity among current underwater acoustic sensors, so it has a high potential of being applied in military uses. Pressure sensitivity, harmonic frequency and directive property are important indexes to characterize its performances. This paper investigates the pressure sensitivity of an interferometric fiber-optic hydrophone element with a concentric mandrel including an enhanced sensitivity layer based on the theory of elastic mechanics and finite element method (FEM) and then investigates its harmonic frequency and vertical directional property using FEM, and verifies all the results derived from theoretic analysis at last.An equivalent model is constructed to study the pressure sensitivity of the interferometric fiber-optic hydrophone element based on the theory of elastic mechanics. The effects of structural parameters and material properties on the pressure sensitivity are analyzed. And the effective means to enhance the sensitivity are obtained. A fiber-optic hydrophone sample is made to verify the theoretic analysis. The results derived from theoretic analysis agree with those observed in experiments.Many approximations are made and some factors are neglected by using the analytical method of elastic mechanics, and the equivalent model can not reflect the free sonic pressure field well. So a more accurate analytical method FEM is put forward to investigate the pressure sensitivity of the element. The results derived from theoretic analysis and those obtained from experiments are less than 0 .2dB, so they agree with each other well.The harmonic frequency and vertical directional property of the hydrophone element are studied using FEM too. The harmonic frequency derived from theoretical analysis is 5283 .7Hz, which agrees with that derived from experiments 5300 Hz. The analytic result derived by studying the vertical directional property shows that, the vertical sensitivity distribution is homogeneous and the fluctuation is 0 dB in theory. The fluctuation observed in experiments is less than 0 .3dB, which agrees well with that in theory.The research on the characteristics of an interferometric fiber-optic hydrophone element with a concentric mandrel including an enhanced sensitivity layer and the results derived from it are propitious to optimize the design and performances of the hydrophone.