BASIC CONCEPT

reflecting layer glass capillary wall CENTER LINE optically active layers polyimide

SINGLE LIGHT BEAM/WAVE-GUIDE INTERACTION EVENT glass capillary wall CENTER LINE

  n0n0 n 1 -i   Fresnel’s Law (reflection) Snell’s Law (refraction) Y Absorption (   

HeNe Laser Focusing optics Source Fiber Detector Fiber Ref. Beam Detector Signal Beam Detector Electronic Ratio Signal  Reference Four Point Bending Apparatus Displacement Monitor Plot of ratio versus displacement (~ strain) Optical Strain Sensor X input Y input

neutral axis d=0.53 R 5.69 cm 0.32 cm  Four Point Bending tension compression 2a=2.92cm

  d    2 22 a Strain as a function of  Bend radius as a function of strain: R d  2   N0N0 L RdRdR   1 222(/)cos(/)/ Number of ‘bounces’ as a function of bend radius For principal ray, N 0 : G I I  1 0   Gage Factor:

TUBE DEFLECTION,  mm)  vs Pin Translation  0.5 mm ID) From K. Thomas et al. INNER PIN TRANSLATION (mm)

MICRO STRAIN NORMALIZED INTENSITY RATIO Intensity Ratio vs Strain (0.5mm ID, Polyimide Coated) K. A. Thomas, E. E. Crisman, W. B. Euler and O. J. Gregory Proceedings: SPIE Smart Structures and Materials 2000: S. C. Liu, ed., SPIE Press, v3988, p429 (2000)

MICROSTRAIN NORMALIZED INTENSITY Intensity Ratio vs Strain (with ITO layer) From K. Thomas et al.

Al only Al + 400u Si Al +104nm Si Uncoated

MICROSTRAIN NORMALIZED RESPONSE Al +104nm Si

Sensor Signal Strength (I/I 0 ) Gage Factor Polyimide/Al8.8x Ex x Polyimide coated only 4.14x Polyimide/Al/40nm Si Polyimide/Al/104nm Si

SUMMARY Large, adjustable gage factors; >100 Reproducible to 8000 micro-strain Easily adaptable to optical fiber data systems Robust Chemically Stable Simple & cheap material and design *Capable of both active and passive strain measurements.* *TEMPERATURE INSENSITIVE*