This is a general presentation of fiber optics instrumentation development work being conducted at NASA Dryden for the past 10 years and recent achievements in the field of fiber optics strain sensors

Chan, Patrick Hon Man

Parker, Allen R., Jr.

Richards, W. Lance

NASA Technical Reports Server

Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
https://ntrs.nasa.gov/search.jsp?R=20110000691 2019-08-30T14:03:14+00:00Z
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
Introduc#on:	  	  Why	  Use	  Fiber?	  
•  Immunity to electromagnetic 
interference, radio-frequency 
interference, and radiation. 
•  Compact, lightweight, ruggedized 
device for smart structure 
–  Embedded into structure 
–  Harsh environment (under water) 
•  The ability to be multiplexed.  
(100s of sensors on a single fiber). 
•  Ease of installation and use 
(single fiber vs. multitude of lead 
wires). 
•  Potential low cost as a result of 
high-volume telecommunications 
manufacturing. 
•  WEIGHT SAVING vs Strain gauge 
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
Background:	  	  A	  Piece	  of	  Glass!	  
•  Fiber Bragg Grating (FBG) sensor is that a change in 
strain state will alter the center wavelength (λ) of the light 
reflected from an FBG. 
•  A fiber’s index of refraction (n) depends on the density of 
the dopants it contains. 
•  FBGs are created by redistributing dopants to create 
areas that contain greater or lesser amounts, using a 
technique called laser writing or dopant modulation. 
•  The index of refraction is modulated throughout the length 
of the grating. 
•  This grating reflects a narrow spectrum of light that is 
directly proportional to the period of the index modulation 
(Λ) and the effective index of refraction (n). 
•  The Bragg wavelength (λB), is expressed by λB = 2 n Λ. 
Because change in temperature (ΔT) and strain (Δε) 
directly affect Λ and n, any change in temperature or strain 
directly affects the λB. 
n	  
Λ	

λB	  
Laser	  light	  
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
NASA	  Gra#ng	  Modula#on	  Mul#plexing	  Method	  
•  Multiplex 100s of sensors onto one fiber. 
•  All gratings are written at the same 
wavelength. 
•  A narrowband wavelength tunable laser 
source must be used to interrogate 
sensors. 
•  Sensor size can be from 0.1mm to 
100mm gage lengths. 
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
1548nm	   1552nm	  
Tuning	  Laser	  
Perform	  Windowing	   Filtering	  and	  Centroid	  
S/C	   A/D 
Signal	  Condi#oner	  and	  A/D	  
Centroid	  to	  
Strain	  
Conversion	  
Perform	  FFT	  
Wavelength	  
Domain Length	  
Domain 
Perform	  iFFT	  
Wavelength	  
Domain 
Length	  
Domain 
Processing	  Procedure	  
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
Fiber	  Strain	  Sensors	  in	  Ac#on	  
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
Fiber	  Op#cs	  Wing	  Shape	  Sensing	  System	  (FOWSS)	  for	  Ikhana	  
•  Fiber	  count:	  	   	   	  4	  
•  Max	  Fiber	  length:	  	   	  40	  W	  
•  Max	  sensing	  length:	  	   	  20	  W	  
•  Max	  gages/ﬁber: 	  480	  
•  Total	  gages/system: 	  1920	  
•  Sample	  rate:	  	  	   	  50	  Hz	  @	  2	  ﬁbers	  
	   	   	   	  30	  Hz	  @	  4	  ﬁbers	  
•  Power: 	   	  28Vdc	  @	  4	  Amps	  
•  Weight: 	   	  23	  lbs	  
•  Size: 	   	   	  7.5	  x	  13	  x	  13	  in	  
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
Fiber	  Op#cs	  Instrumenta#on	  Development	  System	  for	  NASA	  
Composite	  Crew	  Module	  
•  Fiber	  count	   	  4	  
•  Max.	  ﬁber	  length 	  40	  W	  
•  Max	  sensing	  length 	  20	  W	  
•  Max.	  sensors	  /	  ﬁber 	  480	  
•  Total	  sensors	  per	  system 	  1920	  
•  Min.	  gra#ng	  spacing 	  0.5	  in	  
•  Sample	  rate	   	  2	  ﬁbers	  @	  50	  sps	  
	  4	  ﬁbers	  @	  24	  sps	  	  
•  Interface	   	  Gigabit	  Ethernet	  
•  Power 	  120	  VAC	  
•  Weight	  	   	  12	  lbs	  
•  Size 	  9	  x	  5	  x	  11	  in	  
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
Fiber	  Op#cs	  Instrumenta#on	  Development	  System	  for	  Global	  Observer	  
•  Fiber	  count:	  	   	   	  8	  
•  Max	  Fiber	  length:	  	   	  80	  W	  
•  Max	  sensing	  length:	  	   	  40	  W	  
•  Max	  gages/ﬁber: 	  1000	  
•  Total	  gages/system: 	  8000	  
•  Sample	  rate:	  	  	   	  0-­‐50	  Hz	  
•  Power: 	   	  28Vdc	  
•  Weight: 	   	  28	  lbs	  
•  Size: 	   	   	  	  7.5	  x	  13	  x	  18	  in	  
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
Recent	  Development	  
Shape	  Sensing	  using	  ﬁber	  strain	  sensors	  
•  From	  collabora#on	  with	  NASA	  
LaRC,	  shape	  sensing	  using	  ﬁber	  
strain	  sensors	  has	  been	  realized	  
–  Ini#al	  research	  focuses	  upon	  3-­‐core	  ﬁber	  
–  This	  speciality	  ﬁber	  can	  be	  replaced	  with	  3	  
conven#onal	  ﬁbers	  superposi#on	  from	  one	  
another	  at	  120o	  
•  From	  knowing	  the	  strain	  value	  of	  
each	  ﬁber,	  the	  3-­‐dimensional	  
posi#on	  of	  the	  ﬁber	  can	  be	  
accuracy	  rendered	  in	  real-­‐#me	  
–  Strain	  	  3D	  Posi#on	  
3	  core	  ﬁber	  
3	  SMFs	  aligned	  in	  120o	  
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
Prototype	  –	  Hexagon	  strain	  rod	  
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
Prototype	  –	  Shape	  sensing	  ﬁber	  
Na#onal	  Aeronau#cs	  and	  Space	  Administra#on	  
Dryden	  Flight	  Research	  Center	  
Conclusion	  
•  NASA	  DFRC	  has	  successfully	  develop	  ﬁber	  op#cs	  strain	  sensors	  technology	  from	  
laboratory	  to	  real-­‐world	  applica#on	  
•  Current	  status	  	  
–  Dryden	  FBG	  system	  are	  installed	  on	  Ikhana	  and	  Global	  Observer	  UAV	  for	  real	  #me	  strain	  sensing	  
–  Real-­‐#me	  ﬁber	  shape	  sensing	  is	  currently	  being	  developed	  
•  Poten#al	  applica#on	  of	  technology	  beyond	  aeronau#cs	  
–  Automo#ve	  Sector	  
–  Energy	  Sector	  
–  Biomedical	  Sector	  
2008	  	  23lbs	  
2002	  	  65lbs	  
2010	  and	  beyond	  
8-­‐channel	  system	  
>100Hz	  
~30lbs	  
2-­‐channel	  system	  
~50Hz	  
~10lbs	  


Fiber Optics Instrumentation Development

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