6 Applications of fiber optic sensors n n

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

Three application examples using FBG sensors Sensing mechanism n n n Bragg resonance wavelength: B=2 n B=0. 78 x 10 -6 B. 1 1 pm B=6. 7 x 10 -6 B T. 1°C 10 pm 2

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

Wavelength detection using tunable optical filters(Kersey et al) n n n Well suited for WDM Resolution demonstrated: 1 and 0. 2°C Types of TOFs: Fabry-Perot filters, FBG- based filters 4

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

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

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

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

Results Dependence of the vibration amplitude of the square cylinder on Ur: (a) Yrms, (b) Xrms. a) Strain measured from FBG b) Displacement measured from vibrometer c) Wind velocity measured from hot-wire See: Zhou Y, Wang ZJ, So RMC, Xu SJ, and Jin W, JOURNAL OF FLUID MECHANICS 443: 197 -229 SEP 25 2001 THE HONG KONG POLYTECHNIC UNIVERSITY 香港理 大學 9

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 大學 10

Results of static and dynamic load test of the FBG sensors • The results from FBG sensors agree well with the electrical strain gauges. 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. 389 -400. 2005 THE HONG KONG POLYTECHNIC UNIVERSITY 香港理 大學 11