Practical fiber-optic Bragg grating strain gauge system

Abstract

A fiber-optic strain gauge system for use in structural monitoring and smart-structure applications is described. The strain gauge uses a fiber-optic Bragg grating sensor to measure strain and a passive, wavelength demodulation system to determine the wavelength of the narrow-band, backreflected spectrum from the grating sensor. The fiber-optic strain gauge system permits the measurement of both static and dynamic strains with a noise-limited resolution of 0.44 microstrain/√Hz, a measurement dynamic range of 27.8 dB, and a bandwidth of 250 Hz.

Bragg Grating Corrosion Sensor

“…The Bragg angle Sa is simple half ofthe scatter angle as shown in Eq.ll. This answers the first question that was addressed at the beginning of the section, i.e., What must the Bragg angle and period (SB and AB) be in order to effectively scatter radiation out of the fiber at a desired scattering angle S TBG BAND PASS One of the great advantages of Bragg gratings is that, due to the extreme spectral narrowness of the reflected component [12] (on the order of AA = 0.1 nm), many Bragg gratings can be placed in a single fiber with the ability of being able to interrogating each individual grating individually [7]. This can be done by fabricating each grating in the fiber with a different Bragg period AB and then interrogating the gratings with a broad band signal (BBS).…”

“…In the weak guidance approximation ( 13 ~ knc1) the expression for the spectral width (A A) in terms of the angular spread AS can be obtained by differentiation ofEq. 7 AS AA=A·--tan(~) (12) The angular spread can be calculated by determining the angle at which Eq. 8 has its first zero.…”

Ratiometric wavelength monitor based on singlemode‐multimode‐singlemode fiber structure

“…Alternatively, two edge filters arms with opposite slope spectral responses can be used. The use of two opposite slope edge filters can increase resolution of the ratiometric system [1]. Such a ratiometric wavelength monitor scheme converts the wavelength measurement into a signal intensity measurement.…”

“…Compared with a wavelength-scanning-based active measurement scheme, it has the advantages of a simple configuration, the potential for high-speed measurement and the absence of mechanical movement. The main element of the ratiometric scheme, the edge filter, can be implemented by either a bulk thin filter [1], a fiber grating [2], biconical fiber couplers [3], or a bending fiber [4,5]. An all-fiber edge filter has several advantages by comparison to bulk filters, for example, ease of interconnection, mechanical stability and low polarization sensitivity [6].…”

A method to measure reference strain in FBG strain sensor interrogation system involving actuators

“…Strain measurements based on FBG is a rapidly developing technology which is driven by its performance accuracy and versatility and is being used for structural monitoring and smart structure applications [1,2]. Before using it for different applications, the FBG demodulation system has to be tested in the laboratory.…”