Fiber Optic Health Monitoring Research Articles

Fiber optic health monitoring and temperature behavior of bridge in cold region

The objectives of this research are (a) to establish a structural health monitoring system for bridge safety evaluation that is suitable for cold, remote regions and (b) to identify the bridge responses under variations in temperature. To achieve this, fiber optic sensors with temperature compensation were selected that were suitable for cold regions. This technique allows monitoring equipment to operate far from the sensor installation site, which avoids exposing much of the equipment to extremely cold temperatures and makes a power supply more accessible. The bridge temperature behavior is studied based on the real-time field measurement data, and the relationship between the thermal loading and the bridge response is presented.

Development of a fiber optic health monitoring system for aerospace applications

This paper describes our research activity involved in the identification, development and test of a prototype SHM system constituted by optical sensing nodes to measure both temperature and strain on ultra high temperature ceramics (UHTC) materials up to 1000 °C. Commercially available optic devices can operate up to 550 °C. To raise temperature limit up to 1000 °C, custom devices, mainly under development for scientific applications, have been identified. A prototype SHM system has been developed adopting a FBG sensor for temperature measurement and an EFPI sensor in sapphire fiber for strain measurement. The preliminary findings from thermo-mechanical tests indicate that former SHM system is capable of accurately measuring strain at elevated temperatures on UHTC materials.

Optical fiber sensor systems for simultaneous monitoring of strain and fractures incomposites

In this paper, a fiber optic health monitoring system was proposed and applied to thesensing of strain and fracture behaviors of composites. In order to detect strain andfracture signals simultaneously, we combined a white light interferometer with an intensitydemodulator in an EFPI (extrinsic Fabry–Perot interferometer) sensor. Both abroadband light source and a narrowband filter such as an FBG (fiber Bragg grating)and a Fabry–Perot filter were coupled in an EFPI sensor imbedded in compositespecimens. This paper compares the performance of two fracture sensing units withdiffering intensity demodulating filters and describes the implementation of thetime–frequency analysis of STFT (short time Fourier transform) for the detection of thefracture signals like matrix cracking. From the test of tensile load monitoring usingthe optical fiber sensor system, the measured strain agreed with the value of anelectric strain gage, and the fracture sensing unit could detect matrix crackingwith high sensitivity to recognize the onset of the micro-crack fracture signals.

Fiber optic health monitoring of civil structures using long gage and acousticsensors

Structural health monitoring with optical fibers provides practical sensing capabilities inmany applications including in aeronautics and mechanical structures. A variety of opticalfiber sensors have been used including Bragg gratings, intensity or amplitude sensors, andFabry–Perot ones. Civil structures pose further challenges in monitoring mainly due totheir large dimensions, diversity as well as heterogeneity of materials involved, and hostileconstruction environment. Monitoring of strains, deformations, and deflections providesclues essential for evaluation of design parameters and behavior under service loads. Longgage distributed or multiplexed sensors are excellent candidates for such applications. Onthe other hand, detection of structural damage and anomalies such as cracking in concrete,splintering of fibers in composites, and fracturing of welds and connections are bestaccomplished by acoustic sensors. This paper describes principles involved in serialmultiplexing of two kinds of optical fibers, namely long gage and acoustic sensors.Both sensor types offer promise in structural health monitoring of large civilstructural systems. Representative examples are introduced and described in detail.

Comparison between Non-Destructive Evaluation Techniques and Integrated Fiber Optic Health Monitoring Systems for Composite Sandwich Structures

Non-Destructive Evaluation (NDE) methods have been adapted to composite sandwich structures in order to detect damage, in particular impact induced damage. Using three coupons representative of radome structures, several techniques were tested: ultrasonics, the Electromagnetic/InfraRed method (EMIR), stimulated shearography and stimulated infrared thermography. The extension of the measured damaged area was taken as a criterion, showing that stimulated shearography and ultrasound are the most sensitive methods. Moreover, two integrated Health Monitoring Systems (HMS) were tested, based on the one hand on microbending sensitive fibres and Optical Time Domain Reflectometry (OTDR), and on the other hand on Fibre Bragg Grating (FBG) sensors. The experiments demonstrated that HMS can detect damage with sensitivity comparable to that of the external NDE techniques.

Comparison between Non-Destructive Evaluation Techniques and Integrated Fiber Optic Health Monitoring Systems for Composite Sandwich Structures

Comparison between Non-Destructive Evaluation Techniques and Integrated Fiber Optic Health Monitoring Systems for Composite Sandwich Structures