RELATIVE HUMIDITY DETECTION USING

OPTICAL FIBER TECHNOLOGIES …..

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Motivation

Introduction to Relative Humidity

Field of research

Sensor design using

Fiber Bragg Grating

Humidity Sensor Using

Fiber bend technique

Comparative chemical study

Comsol Multiphysics

Optics implementation using Comsol

Simulation Results

Future Scope

References 2

Table of Contents:2

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OBJECTIVE / MOTIVATION

Fiber is already used in

90% of long distance telephony (Communication).

Most of the LAN(computer networks) connections.

WHY OPTICAL FIBER ??

Economic

Speed

- We transmit signals at Gigabits per second speed.

Very much effective for long distance communications.

Freedom from interference

Security3

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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.

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Our field of research is :

Relative Humidity Sensor using Optical Fiber technologies.

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Application :

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

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FIBER BRAGG GRATING (FBG)…

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• Why FBG ???

Several methods to measure RH including resistive,

capacitive and hygrometric ones.

Drawbacks :

high cost

need for maintenance

inability to use in hazardous and explosive nature

environments ( as electromagnetic inference immunity is

required).

• 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).

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• 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

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• 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

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FIBER BEND BASED

HUMIDITY SENSOR

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A highly sensitive all fiber humidity sensor is demonstrated

Working Principle – Use of hygroscopic material to

modulate light

Bend radius of 10mm-15mm is taken

Advantages -reduces risk of fibre breakage

-high sensitivity with greater

radiusHygroscopic material – polyethylene Oxide(PEO)

Advantages - high range of RI variation wrt

humidity

- high adhesivenessBenefit of using this method – simple structure and low

cost

Sensitivity and time response was studied using an

experiment as shown…

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EXPERIMENTAL SETUP

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GRAPHICAL VARIATION OF THE SETUP12

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GRAPHICAL VARIATION OF THE SETUP

FOR RH VALUE 85%-90%13

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Sensor has very fast response as shown above,

around 785msec(from 70%-90%) 14

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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.

Chemical Comparison2

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PRINCIPLE :

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

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VARIATION OF OUTPUT POWER WITH

RELATIVE HUMIDITY

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COMSOL

MULTIPHYSICS SIMULATIONS

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Engineering simulation software that enables you to

create accurate models .

Why COMSOL?

Conception and Understanding

Enables innovation

Design and Optimization

Achieve the highest possible performance

Testing and Verification

Virtual testing much faster

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OPTICS IMPLEMENTATION

USING COMSOL

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OBJECTIVE

To create a 2-D model to demonstrate the phenomenon of

Refraction and total internal reflection and simulate it.

MATERIALS USED

Air and Glass

The model was designed using electromagnetic waves in

Frequency domain

Boundary conditions were applied on the model as

shown in the next slide..

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glass

air

2-D model of

Air and glass

Applying Boundary

conditions

Way for

EM waves

To enter

boundary

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SIMULATION RESULTS

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Phenomena of

total internal

reflection

Simulated results after exporting the model

Shows variation in wave behavior at different

heights(angles)

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Phenomena of

refraction22

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FUTURE SCOPE

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After a comparative study between

different techniques used in humidity

sensing, we are to use the best

parameters to design a highly efficient

sensor.

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

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REFERENCES

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”,October 2007,www.sensorsportal.com

4. Fiber Optic Communications by Joseph C.Palais,4th Edition

,2002

5. www.comsol.co.in

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