Assessment of an extrinsic polymer-based optical fibre sensor for structural health monitoring

Abstract

Plastic optical fibre sensors offer remarkable ease of handling, and recent research has shown their potential as a low-cost sensor for damage detection and structural health monitoring applications. This paper presents details of a novel extrinsic polymer-based optical fibre sensor and the results of a series of mechanical tests conducted to assess its potential for structural health monitoring. The intensity-based optical fibre sensor proposed in this study relies on the modulation of light intensity as a function of a physical parameter (typically strain) as a means to monitor the response of the host structure to an applied load. Initially, the paper will reveal the design of the sensor and provide an outline of the sensor fabrication procedure followed by a brief description of its basic measurement principle. Two types of sensor design (fluid type and air type) will be evaluated in terms of their strain sensitivity, linearity and signal repeatability. Results from a series of quasi-static tensile tests conducted on an aluminium specimen with four surface-attached optical fibre sensors showed that these sensors offer excellent linear strain response over the range of the applied load. A comparison of the strain response of these sensors highlights the significant improvement in strain sensitivity of the liquid-filled-type sensor over the air-filled-type sensor. The specimens were also loaded repeatedly over a number of cycles and the findings exhibited a high degree of repeatability in all the sensors. Free vibration tests based on a cantilever beam configuration (where the optical fibre sensor was surface bonded) were also conducted to assess the dynamic response of the sensor. The results demonstrate excellent agreement with electrical strain gauge readings. An impulse-type loading test was also performed to assess the ability of the POF sensor to detect the various modes of vibration. The results of the sensor were compared and validated by a collocated piezofilm sensor highlighting the potential of the POF sensor in detecting the various eigen-frequencies of the vibration. Finally, preliminary results of a loading-unloading test of the same sensor design encased within a metal tube will be presented. The results obtained were encouraging offering the possibilities of employing the proposed device as an embedded sensor for damage detection in concrete beams.

Multiparameter Optical Monitoring of Madeira Wine

“…The developed optical platform for the pilot scale facility is based on a multi-wavelength detection scheme with four measurements cells each dedicated to one selected wavelength and centered wavelengths at 470 nm, 530 nm, 660 nm and 870 nm [5][6][7]. The sensor head is designed to be at a position that will always be submersed in the wine, considering that small samples are periodically removed from the tanks for physicochemical analysis.…”

Sensing Applications for Plastic Optical Fibres in Civil Engineering

“…This example provides further evidence of the cost-effectiveness of the intensity-based approach in meeting the sensing needs of an important area in civil engineering. Another significant design based on intensity sensing technique relies on the principle that a change in the gap between two cleaved POF surfaces resulting from an applied strain will leads to a corresponding chance in the light intensity of the sensor [14]. The operating principle of the POF sensor is straightforward-the sensor relies on the monitoring of the optical power transmitted through an air-gap between two cleaved optical fibre surfaces.…”

“…11. Photos showing (a) the damage of the electrical strain gauge due to an intersecting crack (b) the relatively better survivability of the four POF sensors (no visible damage) even under severe crack (after [14]). …”

Recent development and applications of polymer optical fiber sensors for strain measurement

“…Kuang et al [10] investigated a surface-mounted, extrinsic POF sensor used to monitor static, dynamic and impulse-type loading conditions. The sensor, which resembled an extrinsic Fabry-Perot sensor, consisted of two cleaved step-index multi-mode POFs enclosed in a specially designed housing comprising two polytetrafluoroethylene (PTFE) sleeves and a PTFE outer tube.…”