1 §6 Applications of fiber optic sensors Strain sensors and temperature sensors Strain sensors and temperature sensors Acoustic sensors, displacement sensors Acoustic sensors, displacement sensors Electric current sensors Electric current sensors Rotation sensors Rotation sensors Chemical sensors Chemical sensors Sensors for mechanical and civil structures Sensors for mechanical and civil structures

2 Three application examples using FBG sensors Sensing mechanism Bragg resonance wavelength: B =2n   B =0.78x10 -6 B . 1   1pm  B =6.7x10 -6 B  T. 1°C  10pm

3 Wavelength detection using passive optical filters ( Melle et al )

4 Wavelength detection using tunable optical filters(Kersey et al) Well suited for WDM Well suited for WDM Resolution demonstrated:  1  and  0.2°C Resolution demonstrated:  1  and  0.2°C Types of TOFs: Fabry-Perot filters, FBG- based filters Types of TOFs: Fabry-Perot filters, FBG- based filters

5 Application 1: Internal strain monitoring of structural materials Application 1: Internal strain monitoring of structural materials Schematic of the test specimen showing the location of the FBG sensors and loading setup

6 Result of strain measurement at position 3 (  ) strain measured by grating, (o) strain measured for a strain gauge attached at the surface

7 Result of strain measurement at position 1 (  ) strain measured by grating, (o) strain measured for a strain gauge attached at the surface

8 Structure under investigation with FBG sensors Optical Interrogation System Wind Tunnel Computer Data Acquisition System Application 2: Measurement of flow-induced vibration Experimental setup THE HONG KONG POLYTECHNIC UNIVERSITY 香港理工大學

9 a) Strain measured from FBG b) Displacement measured from vibrometer c) Wind velocity measured from hot-wire Dependence of the vibration amplitude of the square cylinder on U r : (a) Y rms, (b) X rms. Results THE HONG KONG POLYTECHNIC UNIVERSITY 香港理工大學 See: Zhou Y, Wang ZJ, So RMC, Xu SJ, and Jin W, JOURNAL OF FLUID MECHANICS 443: SEP

10 Application 3: Investigation on Structural Fatigue Problems of the KCR Vehicles Fiber Bragg Gratings Interrogator is used to monitor the strain and stress in the bodyshell of the KCRC compartments in order to identify the possible fatigue problems that may affect the life expectancy. THE HONG KONG POLYTECHNIC UNIVERSITY 香港理工大學

11 Results of static and dynamic load test of the FBG sensors The results from FBG sensors agree well with the electrical strain gauges. THE HONG KONG POLYTECHNIC UNIVERSITY 香港理工大學 See: W. Jin et al., “Structural strain and temperature measurements using FBG sensors,” Chapter in book: Guided wave optical components and devices, B. P. Pal (Eds), Elsevier,Burlington, USA, pp