Retro-Reflective_Fiber_Optic_Displacement_Sensor.pptx

Bhoj Reddy Engineering College For Women
Department of Electronics and Communications Engineering
(Sponsored by Sangam Laxmibai Vidyapeet, approved by AICTE & affiliated to JNTUH)
Seminar Incharge: Internal Guide: Presented By:
G.Srilakshmi Saba Sultana Y.Bhargavi(20325A0401)
Assistant Professor(ECE) Associate Professor(ECE) lV ECE A
Retro-Reflective Fiber Optic Displacement Sensor

Contents
• Introduction
• Fiber optics
• Construction of Fiber optics
• Total internal reflection
• Block diagram of FODS
• Working
• Influence of manufacturing tolerances
on performance
• Various factors and its impact
• Advantages
• Applications
• Conclusion
• References
2
Retro-Reflective Fiber Optics Displacement Sensor

Introduction
3
• Fiber optic displacement sensors will play an increasingly larger role in a broad range of
industrial, military and medical applications.
• Multimode plastic fibers are in a great demand for the transmission and processing of
optical signals in optical fiber communication system.
• They are also widely used in sensing applications because of their better signal coupling,
large core radius, and high numerical aperture as well as able to receive the maximum
reflected light from the target.
• The measurement of displacements is based on the intensity modulation technique.

…..Continuation
• The sensor performance and accuracy
of measurement strongly depend on
the geometrical parameters of the
probe.
• Taguchi method is used for robust
parameter design of retro reflective
fiber optic displacement sensor.
4
Fig-1.Retro-reflective fiber optics displacement sensor

Fiber Optics
• An optical fiber is a glass or plastic fiber that carries light along its length.
• Specially designed fibers are used for a variety of other applications, including sensors
and fiber lasers
• Light Travels through the core by total internal reflection
• Fiber optics materials:
i. Glass
ii. Plastic
iii. Both of them
5

Construction of Fiber Optics
A fiber optic cable consists of five main
components:
• Core
• Cladding
• Coating
• Strength Member
• Cable jacket.
6
Fig-2.Construction of Fiber optics

…..Continuation
• Core: This is the physical medium that transports optical signals from an attached light
source to a receiving device.It is protected by the cladding. The diameter of the core
depends upon the application used.
• Cladding:This is the thin layer that surrounds the fiber core and serves as a boundary that
contains the light waves and causes the refraction, enabling data to travel throughout the
length of the fiber segment.
• Coating:This is a layer of plastic that surrounds the core and cladding to reinforce and
protect the fiber core. Coatings are measured in microns and can range from 250 to 900
microns.
7

…..Continuation
• Strength member: These components
help protect the core against crushing
forces and excessive tension during
installation.
• Cable jacket : This is the outer layer of
any cable. Most fiber optic cables have an
orange jacket, although some types can
have black or yellow jackets.
8
Fig-3. Fiber Cable

Total Internal Reflection
9
Fig-4.Total internal reflection in fiber optics

…..Continuation
• Definition : The phenomenon which occurs when the light rays travel from a more
optically denser medium to a less optically denser medium.
• Following are the two conditions of total internal reflection:
1. The light ray moves from a more dense medium to a less dense medium.
2. The angle of incidence must be greater than the critical angle.
• When light travels from one medium to another it changes speed and is refracted. If the
light rays are travelling for a less dense material to a dense medium they are refracted
towards the normal and if they are travelling from a dense to less dense medium they are
refracted away from the normal.
10

Block diagram of FODS
11
• It consists of a light source, a fiber optic probe and a silicon detector, which is connected
to a lock-in amplifier and computer.
• The fiber probe is a bundled plastic fiber, which consists of one transmitting core and one
or more receiving cores.
• The light source is a He-Ne laser with a peak wavelength of 633nm, which is modulated
externally by chopper with a frequency of 200Hz.
• The modulated light source is used in conjunction with lock-in amplifier to reduce the dc
drift and interference of ambient stray light.

……Continuation
12
Fig-5.Block diagram of FODS

Working of FODS
• The light from a light source enters a transmitting core and then radiates to the target.
• The light reflected from object surface is transmitted through the receiving core to a
photo-detector.
• The amount of light returning to detector depends on the displacement between the end of
the probe and the target being monitored.
• For the displacement a flexible adjusting mechanism using piezoelectric is required.
13

Influence of Manufacturing Tolerances on the
Performance
• Performance of FODS depends on the geometrical and fabrication parameters of FODS.
• Geometry of the FODS affects the target value of the desired performance parameter of
FODS for instance sensitivity in case of FOD.
• Sensor performance also gets affected by these parameters. Thus one has to design a
FODS which is immune to noise factor variations.
• Taguchi technique is used to optimize the FODS design for immunity to noise factors.
14

……Continuation
• This technique is useful in determining the control factors so that the sensitivity of FODS
does not get affected by noise factors and its value will not diverted from the target value.
• A parameter having largest signal to noise ratio is identified as significant contributor for
achieving the best performance characteristic while others having small signal to noise
ratio are considered as insignificant contributors.
• A comprehensive design is suggested for getting the best performance. A range of results
is suggested along with the expected value taking into account the error.
15

Various Factors and its impacts
1. Effect of Variation Is Horizontal Offset(s):
• There is no light entering the receiving fiber for smaller values of distance Z between the
fiber end faces and reflector.
16
Fig-6.Variation Is Horizontal Offset

…..Continuation
• As distance increases the reflected cone starts overlapping the receiving fiber. It shows
linear variation in the amount of light entering the receiving fiber and the distance Z.
• The rate of overlap of reflected cone to the receiving fiber determines the sensitivity of
the sensor.
• The total overlap signifies the maximum intensity collected by the receiving fiber. The
range of distance Z over which this continues is called the operating range of the sensor.
• Thus linear region is important as it decides sensitivity and operating range of the sensor.
17

…..Continuation
2. Effect of Source Fiber Angle (α1) :
• If the source fiber is slightly inclined then the reflected cone gets shifted slightly towards
the receiving fiber.
• This increases the rate of overlap of receiving fiber cone with distance Z. This in turn
increases the sensitivity of the sensor.
18
Fig-7.Source Fiber Angle

…..Continuation
3. Effect of Variation in Core Radius:
• Increase in the core radius of source fiber and receiving fiber causes increase in the
amount of light collected by the receiving fiber.
• Thus for small change in the distance Z between the fiber end face and reflector causes
large change in the amount of light collected by the receiving fiber.
• This means that the rate of overlap of receiving fiber with reflected cone increases.
• This is obvious because of the increase in the core radius of the source as well as
receiving fiber
19

…..Continuation
4. Effect of Variation in h:
• The variation in vertical offset h between the source and receiving fibers does not show
any significant change in the sensitivity of sensor.
• The relative vertical displacement of the two fibers does not cause any variation in the
amount oflight intensity received by the receiving fibers.
• The occurrence of the maximum received intensity takes place at smaller values of Z for
negative offset values and for larger Z values for positive offset values.
20

…..Continuation
5. Effect of Variation in Receiving Fiber Angle (α2):
• The inclination of receiving fiber causes shifting of receiving fiber core centre away from
the source fiber.
• This reduces the overlaparea of the receiving fiber core with the reflected cone.
• The effect of variation in receiving fiber angle does not shown any variation in the
sensitivity.
21
Fig-8. Variation in Receiving Fiber Angle

Advantages
• Immunity to electromagnetic interference
• Small size
• High temperature capability
• Ability to isolate the sensor head from the electronic components by very large distances
• Ability to multiplex number of sensors along single fiber cable
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Applications
• Detecting a hole on the shaft.
• Measuring position of the metal plate.
• Checking type of the parts for automotive
by measuring size.
• Measuring inner diameter of pipe.
• Checking contamination of surface of the
disk brake.
Retro-Reflective Fiber Optics Displacement Sensor 23
Fig-9. Applications

Conclusion
• The reflected light from the mirror is coupled back into a fiber from a reflecting surface
and this power is compared to a portion of thepower emitted by the same light source.
• The beam-through type is based on comparing the transmitted light intensity against that
of the launch light which can provide information on the displacement between the probe
and the target
• Two-fiber retro reflective fiber optic displacement sensor is analyzed for optimized and
robust design for best sensitivity.
• Taguchi method is used for the analysis.
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References
[1] Supriya S. Patil, A. D. Shaligram “Journal of Sensor Technology Vol.10 No.1”,March 31, 2020
[2] Patil, S.S. and Shaligram, A.D. “Modeling and Experimental Studies on Retro-Reflective Fiber Optic
Micro-Displacement Sensor with Variable Geometrical Properties Sensors and
Actuators”,A172,428433.(2011)
[3] M. V. Alfimov and A. M. Zheltikov, “The figure of merit of a photonic-crystal fiber beam delivery and
response-signal collection for nanoparticle-assisted sensor arrays” Laser Phys. Lett. 4 , 363– 367 (2007)
[4] Buchade, P.B. and Shaligram, A.D. (2007) Influence of Fiber Geometry on the Performance of Two-
Fiber Displacement Sensor. Sensors and Actuators, A136, 199-
204.https://doi.org/10.1016/j.sna.2006.11.020
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