1. 광섬유 센서를 이용한 변형 측정 김대현 2000. 3. 25

2. - 1 - Department of Aerospace Engineering Smart Structures and Composites Laboratory Optical Fiber Jacket (  = 300  m ) Cladding (  = 125  m ) Core (  = 5~10  m )

3. - 2 - Department of Aerospace Engineering Smart Structures and Composites Laboratory Fiber Optic Sensors I Advantages of fiber optic sensors –nonelectrical and remotable –allow access into normally inaccessible areas with electrical sensors –no EMI (dielectric material) –easy to embed in composites –flexibility of the sensor size (  m ~ km) –wide temperature range (-200 o C ~ 1500 o C) –capability of multiplexing –non-corrosion in the various environments

4. - 3 - Department of Aerospace Engineering Smart Structures and Composites Laboratory Fiber Optic Sensors II Sensor systems with optical fiber –intensity based fiber optic sensor systems –fiber optic sensor systems using interferometer –fiber optic sensor systems using polarization –FBG(fiber Bragg grating) sensor systems Advantages of FBG sensor systems –fiber optic advantage –absolute measurement –small size –multiplexing

5. - 4 - Department of Aerospace Engineering Smart Structures and Composites Laboratory Fabry-Perot Sensor Merits excellent strain resolution fast response time Demerits difficulty in signal processing difficulty in multiplexing Bragg Grating Sensor Merits absolute measurements minimal strength degradation multiplexed Demerits Strain resolution may be limited with broadband light source

6. - 5 - Department of Aerospace Engineering Smart Structures and Composites Laboratory Literature Survey I - Fabrication History of FBG K. O. Hill et al. (Appl. Phys. Lett., 1993, Vol. 62) –phase mask method –a simpler and mass production technique

7. - 6 - Department of Aerospace Engineering Smart Structures and Composites Laboratory Grating fabrication method using a phase mask

8. - 7 - Department of Aerospace Engineering Smart Structures and Composites Laboratory Fiber Bragg Grating Optical Fiber 1mm to 20mm Reflected Signal Signal In Fiber Core Index Grating Signal Out L nene Index of Refraction of Fiber Core   n 10 -5 to 10 -3 z1z1 z2z2 z

9. - 8 - Department of Aerospace Engineering Smart Structures and Composites Laboratory FBG sensor wavelength-encoding operation Broadband source Wavelength Detection Input Signal Reflected Siganl Transmitted Signal  I Input spectrum Transmitted Signal I  I  Reflected signal

10. - 9 - Department of Aerospace Engineering Smart Structures and Composites Laboratory Theory Bragg wavelength by Bragg condition Center wavelength shift by external interference The relationship between strain and center wavelength shift only when  T=0 : Effective refractive index : grating period

11. - 10 - Department of Aerospace Engineering Smart Structures and Composites Laboratory V FP scanning waveform Filter Controller FBG Sensor system by WSFL Wavelength-division-based multiplexed FBG sensor system WSFL     I I I I     I Input spectrum Wavelength encoded returns source profile I       swept range output

12. - 11 - Department of Aerospace Engineering Smart Structures and Composites Laboratory Wavelength Swept Fiber Laser - Broadband Source

13. - 12 - Department of Aerospace Engineering Smart Structures and Composites Laboratory Peak-hold optical spectrum by OSA

14. - 13 - Department of Aerospace Engineering Smart Structures and Composites Laboratory EFPI 센서의 측정원리 s I I o I1I1 I2I2 Gauge Length I nor = A ( 1 + B cos2ks )

15. - 14 - Department of Aerospace Engineering Smart Structures and Composites Laboratory EFPI signal