Design of a Reflective Intensity Optical Fibre Bundle Displacement Sensor

Optical fibre sensor has the advantages of small size,light weight,anti⁃electromagnetic interference,and high measurement accuracy,which has important applications in research and industrial production.To design an optical fibre displacement sensor(OFBDS)with simple structure and high measurement accuracy,the unified model of the commonly used OFBDS structures was proposed and the feasibility of the intensity⁃modulation of multi⁃structural optical fibre bundles was analysed based on the arrangement characteristics of the fibre bundle end⁃face.The intensity⁃modulation characteristic of different fibre bundles was analysed,and the single coil coaxial fibre bundle was chosen as the fibre probe in this study.The sensor hardware system was designed.Lastly,the calibration experiment,temperature interference experiment,changes of measured plane surface area,and the dynamic experiment were conducted.Results showed that the sensor linear measurement range was about 3 mm,and the sensor system had excellent static and dynamic characteristics.

Fibre Optic Protection System for Concrete Structures

The design concepts, modelling and implementation of various fibre optic sensor protection systems for development in concrete structures were investigated. Design concepts and on-site requirements for surface-mounted and embedded optical fibre sensor in concrete were addressed. Finite element （FE） modelling of selected sensor protection systems in strain-transfer efficiency from the structure to the sensing region was also studied. And experimental validation of specified sensor protection system was reported. Results obtained indicate that the protection system for the sensors performs adequately in concrete environment and there is very good correlation between results obtained by the protected fibre optic sensors and conventional electrical resistance strain gauges.

Ultrahigh-speed distributed Brillouin reflectometry

Optical fibre sensors based on Brillouin scattering have been vigorously studied in the context of structural health monitoring on account of their capacity for distributed strain and temperature measurements.However,real-time distributed strain measurement has been achieved only for two-end-access systems;such systems reduce the degree of freedom in embedding the sensors into structures,and furthermore render the measurement no longer feasible when extremely high loss or breakage occurs at a point along the sensing fibre.Here,we demonstrate real-time distributed measurement with an intrinsically one-end-access reflectometry configuration by using a correlation-domain technique.In this method,the Brillouin gain spectrum is obtained at high speed using a voltage-controlled oscillator,and the Brillouin frequency shift is converted into a phase delay of a synchronous sinusoidal waveform;the phase delay is subsequently converted into a voltage,which can be directly measured.When a single-point measurement is performed at an arbitrary position,a strain sampling rate of up to 100 kHz is experimentally verified by detecting locally applied dynamic strain at 1 kHz.When distributed measurements are performed at 100 points with 10 times averaging,a repetition rate of 100 Hz is verified by tracking a mechanical wave propagating along the fibre.Some drawbacks of this ultrahigh-speed configuration,including the reduced measurement accuracy,lowered spatial resolution and limited strain dynamic range,are also discussed.