Optical Wave Guide Sensor for Structure Health & Damage Assessment

18 June 02

Dr. Everett E. Crisman

Scientist

SNHA

Air Force Research Laboratory

Contributors

Everett E. Crisman & John S. DerovEverett E. Crisman & John S. DerovAir Force Research LaboratoryAir Force Research LaboratoryHanscom AFB, MAHanscom AFB, MA

* Otto J. Gregory & William B. Euler* Otto J. Gregory & William B. EulerUniversity of Rhode Island University of Rhode Island Kingston, RI Kingston, RI

*Supported in part by: *Supported in part by: NSF, Earthquake Hazard Mitigation ProgramNSF, Earthquake Hazard Mitigation Program

BASIC CONCEPTBASIC CONCEPT

reflecting layer

glass capillary wall

CENTER LINE

optically active layers

polyimide

SINGLE LIGHT BEAM/WAVE-GUIDE INTERACTION EVENT

glass capillary wall

CENTER LINE

n0

n1-i

n nn n

1 0

1 0

2

Fresnel’s Law (reflection)

n n1 1 0 0sin sin Snell’s Law (refraction)

Y

y

0eIyI Absorption (

HeNe Laser

Focusing opticsSource Fiber

Detector Fiber

Ref. Beam Detector

Signal Beam Detector

Electronic RatioSignal

Reference

Four Point Bending Apparatus

DisplacementMonitor

Plot of ratio versusdisplacement (~ strain)

Optical Strain Sensor

X inputY input

neutral axisd=0.53R

5.69 cm

0.32 cm

Four Point Bending

tension

compression

2a=2.92cm

d

2

2 2aStrain as a function of

Bend radius as a function of strain: Rd

2

N0

L

R d R d R

1

2 2 2( / )cos ( / ) /

Number of ‘bounces’ as a function of bend radiusFor principal ray, N0:

GI

I 1

0

Gage Factor:

TU

BE

DE

FL

EC

TIO

N,

m

m)

vs Pin Translation0.5 mm ID)

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.00 0.50 1.00 1.50 2.00 2.50 3.00

Plain Glass with Al

Polyimide coated w/o Al

From K. Thomas et al.

INNER PIN TRANSLATION (mm)

0.00

0.20

0.40

0.60

0.80

1.00

0 500 1000 1500 2000 2500 3000

Without Reflector

With Reflector

With ITO & AL

MICRO STRAIN

NO

RM

AL

IZE

D I

NT

EN

SIT

Y R

AT

IO

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

NO

RM

AL

IZE

D I

NT

EN

SIT

Y

Intensity Ratio vs Strain(with ITO layer)

0

0.2

0.4

0.6

0.8

1

0 500 1000 1500

ITO/Al on Polyimide Coated Glass

Linear (ITO/Al on Polyimide CoatedGlass)

From K. Thomas et al.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.000 0.002 0.004 0.006 0.008 0.010

MICROSTRAIN

NO

RM

AL

IZE

D R

ES

PO

NS

EAl onlyAl + 400u SiAl +104nm SiUncoated

0

0.2

0.4

0.6

0.8

1

1.2

0 0.002 0.004 0.006 0.008 0.01

MICROSTRAIN

NO

RM

AL

IZE

D R

ES

PO

NS

E

Al +104nm Si

Sensor Signal Strength (I/I0) Gage Factor Polyimide/Al 8.8x10-2 69.7

6.92Ex10-2 70.44.37x10-2 92.3

Polyimide coated only 4.14x10-4 109.6

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*