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Introduction to Relative Humidity
Field of research
Sensor design using
Fiber Bragg Grating
Humidity Sensor Using
Fiber bend technique
Comparative chemical study
Optics implementation using Comsol
Table of Contents:
OBJECTIVE / MOTIVATION
Fiber is already used in
90% of long distance telephony (Communication).
Most of the LAN(computer networks) connections.
WHY OPTICAL FIBER ??
- We transmit signals at Gigabits per second speed.
Very much effective for long distance communications.
Freedom from interference
What is Relative Humidity ??
- It is nothing but the amount of water vapor present in air
expressed as percentage.
• MATHEMATICALLY :
Relative Humidity = Pw / P*w
A HYGROMETER is a device used
for measuring the humidity of air.
Our field of research is :
Relative Humidity Sensor using Optical Fiber technologies.
Forecasting Applications of Relative Humidity
Used as human breath rate monitor in medical fields
Structure health monitoring test mostly by
using concrete blocks
Humidity control in textile application
FIBER BRAGG GRATING (FBG)…
• Why FBG ???
Several methods to measure RH including resistive,
capacitive and hygrometric ones.
need for maintenance
inability to use in hazardous and explosive nature
environments ( as electromagnetic inference immunity is
• Optical Fiber Sensors overcomes these disadvantages.
• Also has possibility of multiplexing a large number of
different sensors (temperature, displacement, pressure, pH
value, humidity, high magnetic field and acceleration).
• Transducer layer used for RH : organo-silica based material.
• strong adhesion to the optical fiber that swells in the presence of
distinct RH levels.
• Di-Ureasil Layer and Sensor Setup…
• Di-Ureasil is formed by poly ether chains with average molecular
weight of 600mol inv. Covalently linked to a siliceous inorganic
skeleton by urea bridges .
• It is also can be written as d-U(600).
• d-U(600) layers were deposited on FBG using a homemade dip-
coating system at room temperature by immersing the FBG
vertically in d-U(600) solution at a velocity of 1.4mm per sec.
• Then kept in oven and kept at 50 degrees. For 40hrs.
As a result the coating reveals a strong adhesion to the
optical fiber and mechanical stability.
• Then the sensors are identified as
• The sensors response is temperature dependant due to
thermal expansion of fiber and coating .
• So it is compulsory the compensation
Were encapsulated and being inserted into a stainless steel
tube 15cm long with internal diameter of 2mm.
• The tube has been punctured in the area of the coated
optical fiber to allow the sensitive materials to be exposed
to the ambient humidity
FIBER BEND BASED
A highly sensitive all fiber humidity sensor is demonstrated
Working Principle – Use of hygroscopic material to
Bend radius of 10mm-15mm is taken
Advantages -reduces risk of fibre breakage
-high sensitivity with greater
Hygroscopic material – polyethylene Oxide(PEO)
Advantages - high range of RI variation wrt
- high adhesiveness
Benefit of using this method – simple structure and low
Sensitivity and time response was studied using an
experiment as shown…
GRAPHICAL VARIATION OF THE SETUP
FOR RH VALUE 85%-90%
Sensor has very fast response as shown above,
around 785msec(from 70%-90%) 14
CHITOSAN & AGAROSE
Chitosan derived from Chitin.
Source of Chitin
Deacetylation of Chitin gives Chitosan and soluble in
dilute acidic solutions below pH 6.0
Thin films fabricated from solutions of chitosan and
acetic acid have refractive indices approximately 1.45
and there is nearly no absorption (300 to 2700) nm.
Agarose,a polysaccharide obtained from the cell walls of
some species of red algae or seaweed.
Agarose, made up of subunits of the sugar galactose.
The materials used as the functional cladding layer in the sensing
region are Chitosan and Agarose, which swells in the presence of
water without dissolving at room temperature. The variation in the
refractive index (n) of these swelling polymers with respect to
humidity (H) is obtained from Lorenz-Lorenz relation as
VARIATION OF OUTPUT POWER WITH
Engineering simulation software that enables you to
create accurate models .
Conception and Understanding
Design and Optimization
Achieve the highest possible performance
Testing and Verification
Virtual testing much faster
To create a 2-D model to demonstrate the phenomenon of
Refraction and total internal reflection and simulate it.
Air and Glass
The model was designed using electromagnetic waves in
Boundary conditions were applied on the model as
shown in the next slide..
2-D model of
Air and glass
Simulated results after exporting the model
Shows variation in wave behavior at different
After a comparative study between
different techniques used in humidity
sensing, we are to use the best
parameters to design a highly efficient
Determine the right hygroscopic
material to be used
From the simulated model ,we can
implement it to demonstrate the effect of
light travelling through the core
1. Sandra F. H. Correia,Paulo Antunes,Edison
Pecoraro,Patricia P. Lima,Humberto Varum,Luis D.
Carlos,Rute A. S. Ferreira and Paulo S. Andree,” Optical
Fiber Relative Humidity Sensor Based on a FBG with a Di-
Ureasil Coating”,June 2012,www.mdpi.com
2. Jinesh Mathew,Yuliya Semenova,Ginu Rajan, Pengfei
Wang, Gerald Farrell ,” Improving the sensitivity of a
humidity sensor based on fiber bend coated with a
hygroscopic coating ”, April 2011 www.elsevier.com
3. Jinesh Mathew, K. J. Thomas, V. P. N. Nampoori and P.
Radhakrishnan,” A Comparative Study of Fiber Optic
Humidity Sensors Based on Chitosan and Agarose”,
4. Fiber Optic Communications by Joseph C.Palais,4th Edition