Abstract
We report on recent results obtained with a fiber optic hydrophone based on the intensity modulation of the laser light in a FBG (Fiber Bragg Grating) under the influence of the sound pressure. In order to control the behavior of the hydrophone in terms of sensitivity and bandwidth, FBGs have been coated with proper materials, characterized by different elastic modulus and shapes. In particular, new experiments have been carried out using a cylindrical geometry with two different coating, showing that the sensitivity is not influenced by the shape but by the transversal dimension and the material characteristics of the coating.
Highlights
In the last years, fiber Bragg grating (FBG) based sensors have been applied in a growing range of sensing applications, since their response to temperature or strain, or related measurands, is encoded as a linear or near-linear function of wavelength
The laser light intensity modulated by the FBG subjected to the sound pressure is detected by a fast photodiode
We report a series of measurements carried out to evaluate the sensitivity, the linearity and the resolution of the FBG-based hydrophone coated with materials of different geometrical and acousto-mechanical properties and to compare the obtained performances with a reference PZT hydrophone
Summary
Fiber Bragg grating (FBG) based sensors have been applied in a growing range of sensing applications, since their response to temperature or strain, or related measurands, is encoded as a linear or near-linear function of wavelength. For practical use, the low sensitivity to acoustic pressure of the FBG based sensors limit their use in underwater applications, where piezoelectric transducers are widely used, despite their dimensions, complex signal processing and electronic front-end and difficult multiplexing. This limit is essentially due to the high Young module of the optical fiber material (tens of GPa) which converts the effects of a high pressures applied on the grating in weak deformations
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