DEPARTMENT OF PHYSICS

ENGINEERING PHYSICS - PH2101

ULTRASONICS

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 SYLLABUS

UNIT-I ULTRASONICS 9

Generation of Ultrasonic Waves –Magnetostriction Generator – Piezoelectric Generator -

Detection of Ultrasonic Waves - Properties – Cavitation - Velocity Measurement –
Acoustic Grating - Industrial Applications: SONAR - Non Destructive Testing - A,B and
C – Scan Displays.
UNIT-II LASER AND FIBER OPTICS 9
Lasers: Population of Energy Levels, Einstein’s A and B Coefficients– Semiconductor
Lasers: Homojunction and heterojunction.
Fiber Optics: Principle, Numerical Aperture and Acceptance Angle - Types of Optical
Fibre (Material, Refractive index Profile and Number of Modes) – Sensors: Pressure and
Displacement, Optical Fiber Communication System, Endoscope.
UNIT-III THERMAL PHYSICS 9
Thermal Conductivity – Forbe’s and Lee’s Disc Method- Conduction through Compound
Media (Series and Parallel) - T hermal Expansion of Solids and Liquids – Thermal
Insulation- Applications: Heat Exchangers, Refrigerators, Ovens and Solar Water Heater.
UNIT-IV QUANTUM PHYSICS 9
Postulates of Quantum Mechanics - Black body Radiation – Planck‘s theory (Derivation)
- Wave Particle Duality – Electron Diffraction – Degenerate and Non-degenerate States –
Physical Significance of Wavefunction- Schrödinger’s Wave Equation – Time
Independent and Time Dependent Wave Equations – Particle in a One-Dimensional Box
- Scanning Tunneling Microscope.
UNIT-V CRYSTAL PHYSICS 9
Crystalline and Non-Crystalline Solids - Unit Cell, Crystal Systems, Bravais Lattices,
Directions and Planes in a Crystal, Miller Indices – Interplanar Distances - Coordination
Number and Packing Factor for SC, BCC, FCC and HCP - Crystal Defects: Point Defect
and Line Defect - Role of Imperfections in Plastic Deformation - Bridgman and
Czochralski Crystal Growth Techniques.

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 UNIT-I

ULTRASONICS
INTRODUCTION

 The human ear can hear the sound waves having frequencies in between 20
Hz to 20 kHz. These frequencies are known as audible frequencies. The
sound waves having frequencies less than 20 Hz are known as infrasonic
waves
 The sound waves having frequencies greater than 20 kHz are known as
ultrasonic waves.
 The wavelength of ultrasonic waves are very much less than the wavelengths
of audible sound waves.
 So they applications in non-destructive testing of materials, medical
diagnostics, military and marine.
 Ultrasonic method is widely used in industries to find the size, shape, and
location of flaws such as cracks, voids, laminations, and inclusions of
foreign materials, walls thickness of produced pipes and vessels. The wall
thickness measurements are very important in corrosion studies.

PROPERTIES OF ULTRASONIC WAVES

 Ultrasonic waves are high frequency and high energetic sound waves.
 Ultrasonic wave travels longer distances without any energy loss.
 The speed of propagation of ultrasonic waves increases with the frequency
of the waves.
 Ultrasonic waves produce cavitation effects in liquids.
 Ultrasonic waves produce acoustic diffraction in liquids.

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 Ultrasonic waves cannot travel through the vacuum.
 Ultrasonic waves travel with speed of sound in a given medium.
 Ultrasonic waves require one material medium for its propagation.
 Ultrasonic waves produce heat effect when they pass through the medium.
 Ultrasonic waves obey reflection, refraction, and absorption properties
similar to sound waves.
 Ultrasonic waves produce stationary wave pattern in the liquid while passing
through it.
 When the ultrasonic wave is absorbed by a medium, it generates heat. They
are able to drill and cut thin metals.

PRODUCTION OF ULTRASONIC WAVES

There are three methods for producing ultrasonic waves.
1. Mechanical generator or Galton’s whistle
2. Magnetostriction generator
3. Piezoelectric Generator

MAGNETOSTRICTION GENERATOR

Magnetostriction effect is the principle of producing ultrasonic waves.

Magnetostriction Effect: When a rod of ferromagnetic material like nickel is

magnetized. Then the rod is thrown into longitudinal vibrations, thereby
producing ultrasonic waves by resonance. This is called Magnetostriction
effect.

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Construction:
The circuit diagram of magnetostriction ultrasonic generator is as shown in the
figure.

A short permanently magnetized ferromagnetic rod is clamped at the centre of

the rod AB. The two ends of the rod is wound by the coils L1 and L2.
The coil L1 is connected to the collector of the transistor and the coil is L 2
connected to the base of the transistor. The frequency of the oscillatory circuit
can be adjusted by a condenser (C1) and the current can be noted by the

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milliammeter, connected across the coil L1. The battery connected between
emitter and collector provides necessary biasing, i.e, emitter is forward biased
and collector is reverse biased for the npn transistor. Hence, current can be
produced by applying necessary biasing to the transistor with the help of the
battery.
Working
When the battery is switched on, current is produced by the transistor. The
current is passed through the coil L1, which causes a corresponding change in
the magnetization of the rod. Now the rod starts vibrating due to
magnetostriction effect, due to this an emf is induced in the coil L2.
The induced emf is fed to the base of the transistor, which acts as a feedback
continuously. In this way, the current in the transistor is built up and the
vibration of the rod is maintained. The developed alternating current frequency
can be tuned with the natural frequency of the rod by adjusting the capacitor. At
resonance, the rod vibrates longitudinally with larger amplitude producing
ultrasonic waves.
Condition for Resonance:

Frequency of the oscillatory circuit = Frequency of the vibrating rod

Where
‘l’ is the length of the rod
‘E’ is the Young’s modulus of the rod
‘ρ’ is the density of the material of the rod.

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Advantages:
1. It is mechanically versatile
2. Cost is low
3. It can produce large acoustical power with high efficiency.

Limitations
1. It can produce frequencies up to 3MHz only.
2. It is not possible to get a constant single frequency, because it depends on
the temperature and the degree of magnetization.
3. Frequency is inversely proportional to the length of the rod, to increase the
frequency, the length of the rod should be decreased which is practically
impossible.

Piezoelectric Crystals
The crystals which produce piezoelectric effect and converse Piezoelectric
effect are termed as Piezoelectric crystal.
Example: Quartz, Tourmaline, Rochelle Salts etc.
At typical example or a piezoelectric crystal (Quartz) is as shown in the figure.
It has an hexagonal shape with pyramids attached at both ends. It consists of 3
axes. Viz.,
(i) Optic Z axis, which joins the edges of the
pyramid
(ii) Electrical axis (X axis), which joins the corners
of the hexagon and
(iii) Mechanical axis, which joins the center or
sides of the hexagon as shown in figure.

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X-cut and Y cut crystals
X-Cut crystal:
When the crystal is cut perpendicular to the X-axis, it is called X-crystal.
Generally X-cut crystals are used to produce longitudinal ultrasonic waves.
Y-Cut Crystal:
When the crystal is cut perpendicular to the Y-axis, it is called Y-cut crystal.
Generally, Y-Cut crystal produces transverse ultrasonic waves.
Piezoelectric Effect
When a mechanical stress is applied to the mechanical axis with respect to
optical axis, a potential difference is developed across the electrical axis with
respect to optic axis. This is known as Piezoelectric effect.
Inverse Piezoelectric Effect:
When an alternating electric field is applied to electrical axis with respect to
optical axis, expansion or contraction takes place in the mechanical axis with
respect to optical axis. This is known as Inverse Piezoelectric effect.

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PIEZOELECTRIC GENERATOR
Principle
This is based on the Inverse piezoelectric effect. When a quartz crystal is
subjected to an alternating potential difference along the electric axis, the
crystal is set into elastic vibrations along its mechanical axis. If the frequency of
electric oscillations coincides with the natural frequency of the crystal, the
vibrations will be of large amplitude. If the frequency of the electric field is in
the ultrasonic frequency range, the crystal produces ultrasonic waves.

Construction
The circuit diagram is shown in the figure. The piezoelectric generator consists
of primary and secondary circuits. The primary circuit is arranged with coils L1
and L2. The coil L1 is connected to the base of the transistor and coil L2 is
connected to the collector of the transistor. The capacitor C1 is used to vary the
frequency of the oscillatory circuit [L1C1]. The coil L2 is inductively coupled to
the secondary circuit, which comprises of the coil L3 and two metal plates A
and B as shown in figure. The crystal is kept in between the plates A and B for
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the production of ultrasonics. Emitter is forward biased and collector is reverse
biased.
Working
The battery is switched on and hence the current is produced by the transistor in
the circuit. The current is passed through the coil L1 and L2 of the primary
circuit. The current is transferred to the coil L3 in the secondary circuit due to
transformer action and is fed to the plates A and B. Now the crystal starts
vibrating along the mechanical axis of the crystal. The frequency of the
oscillatory circuit is adjusted, when this frequency is equal to the frequency of
the vibrating crystal, resonance occurs and ultrasonic waves are produced on
both sides of the crystal.

Condition for Resonance

Frequency of the oscillatory circuit = Frequency of the vibrating crystal

Where ‘l’ is the length o the rod

‘E’ is the Young’s modulus o the rod
‘ρ’ is the density of the material of the rod.
‘P’ = 1,2,3 …. etc for fundamental, first overtone, second overtone etc
respectively
Advantages:
1. It can produce frequency up to 500MHz.
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 2. It can produce longitudinal as well as transverse ultrasonic waves by properly
cutting and shaping the crystal with respect to the optic axis.
4. Independent of temperature. So we can get a stable and constant frequency
of ultrasonic waves.

Disadvantages
1. The cost of the quartz crystal is very high.
2. Cutting and shaping the crystal is quite complex.

DETECTION OF ULTRASONIC WAVES

Ultrasonic waves propagated through a medium can be detected in a number

of ways. Some of the methods employed are as follows:

(1) Kundt’s tube method

Ultrasonic waves can be detected with the help of Kundt’s tube. At the nodes,
lycopodium powder collects in the form of heaps. The average distance between
two adjacent heaps is equal to half the wavelength. This method cannot be used if
the wavelength of ultrasonic waves is very small i.e., less than few mm. In the case
of a liquid medium, instead of lycopodium powder, powdered coke is used to
detect the position of nodes.

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(2) Sensitive flame method
A narrow sensitive flame is moved along the medium. At the positions of
antinodes, the flame is steady. At the positions of nodes, the flame flickers because
there is a change in pressure. In this way, positions of nodes and antinodes can be
found out in the medium. The average distance between the two adjacent nodes is
equal to half the wavelength. If the value of the frequency of ultrasonic wave is
known, the velocity of ultrasonic wave propagated through the medium can be
calculated.

(3) Thermal detectors

This is the most commonly used method of detection of ultrasonic waves. In this
method, a fine platinum wire is used. This wire is moved through the medium. At
the position of nodes, due to alternate compressions ad rarefactions, adiabatic
changes in temperature takes place. The resistance of the platinum wire changes
with respect to time. This can be detected with the help of Callendar and
Garrifith’s bridge arrangement. At the position of the antinodes, the temperature
remains constant. This will be indicated by the undisturbed balanced position of
the bridge.

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(4) Piezoelectric Detector
Piezoelectric crystals have the ability to develop an electric potential when a stress
is applied across certain faces of the crystal. This phenomenon can be used to
detect ultrasonic waves. One pair of faces of a quartz crystal (piezoelectric
material) is subjected to ultrasonic waves as shown in Figure. An alternating
potential then develops across the perpendicular faces. This potential can be
amplified and measured to detect the presence of ultrasonic waves.

CAVITATION
Microscopic bubbles with diameters in the range of 10–9 to 10–8 m are
generally present in a liquid. A reduction of pressure in regions around these
bubbles leads to evaporation and thus results in the growth of the bubbles. This
growth, however, is not unlimited. Ultimately, it leads to the collapse of the
bubbles. All this happens within a very short span of time, just a few milliseconds.
The process of collapse of the bubbles results in the generation of shock waves and
the temperature increases manifold in the region of the collapse.

Ultrasonic waves passing through a liquid induce alternate regions of rarefaction

and compression. Rarefaction regions are local negative pressure regions and result
in the process of bubble growth and collapse. This phenomenon is called

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 cavitation. The collapse of bubbles can result in local pressures reaching thousands
of atmospheres and local temperatures increasing by as much as 10,000°C. The
phenomenon of cavitation can be used for the following applications:
(i) ultrasonic cleaning
(ii) exploration of minerals and oil deposits
(iii) speeding up chemical reactions
(iv) emulsification
(v) formation of stoichiometric alloys and compounds.

VELOCITY MEASUREMENT USING ACOUSTIC GRATING

Principle
When ultrasonic waves travel through a transparent liquid, due to alternate
compression and rarefaction, longitudinal stationary waves are produced. If
monochromatic light is passed through the liquid perpendicular to these waves, the
liquid behaves as diffraction grating. Such a grating is known as Acoustic Grating.

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Here the lines of compression and rarefaction act as transparent light waves. It is
used to find wavelength and velocity (v) of ultrasonic waves in the liquid.
Construction
It is consists of a glass tank, filled with the liquid. A piezoelectric (Quartz) is fixed
at the top of the glass tank and is connected with piezoelectric oscillatory circuit as
shown in the figure.

An incandescent lamp is used as a monochromatic source (S) and a telescope

arrangement is used to view the diffraction pattern. A collimator consisting of two
lenses L1 and L2 is used to focus the light effectively in the glass tank.

Working

(i) When the piezoelectric crystal is kept at rest

Initially the piezoelectric crystal is kept at rest and the monochromatic light
is switched ON. When the light is focused in the glass tank filled with the liquid, a

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single image or a vertical peak is observed in telescope, which shows that there is
no diffraction.

(ii) When the piezoelectric crystal is set into vibrations

Now the crystal is set into vibrations using piezoelectric oscillatory circuit.
At Resonance, Ultrasonic waves are produced and are passed through the liquid.
These Ultrasonic waves are reflected by the walls of the glass tank and form a
stationary wave pattern with nodes and antinodes in the liquid.
At nodes the density of the liquid becomes more and at antinodes the density
of the liquid becomes less. Thus, the liquid behaves as a directing element called
acoustical grating element.
Now when the monochromatic light is passed through the acoustical grating, the
light gets diffracted and a diffraction pattern consisting of central maxima (Cm) and
principle maxima(Pm) on either side is viewed through the telescope as shown in
figures.

Calculation of Ultrasonic Velocity

The velocity of Ultrasonic waves can be determined using the condition.
Thus, this method is useful in measuring the wavelength and velocity of ultrasonic
waves in liquids and gases at various temperatures.
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If λu is the wavelength of Ultrasonics,

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SOUND NAVIGATION AND RANGING (SONAR)
Principle
It is based on the principle of Echo – Sounding. When the Ultrasonic waves are
transmitted through water, it is reflected by the objects in the water and will
produce an echo signal. The change in frequency of the echo signal, due to
Doppler Effect helps us in determining the velocity and direction of the object.

Description
It consists of timing section which triggers the electric pulse from the pulse
generator. This pulse generator is connected to the transducer so that ultra sonic
can be produced. The transducer is further connected with the CRO for display.
The timing section is also connected to the CRO display or reference of the timing
at which the pulse is transmitted as shown in the block diagram.
Working
The transducer is mounted on the ship’s hull without any air gap between them as
shown. The timing at which the pulse generated is recorded at the CRO or
reference and this electrical pulse triggers the transducer which is kept in hull of

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 the ship to produce ultrasonic waves due to the principle of inverse piezoelectric
effect.
These ultrasonic waves are transmitted through the water in sea. On striking the
object the ultrasonic waves (echo pulses) are reflected in all directions as shown in
the figure.

INDUSTRIAL APPLICATIONS
Ultrasonic waves can be used in a variety of industrial applications.
1) Drilling
Ultrasonics can be used to drill holes in hard materials like glass and diamond.
Schematic diagram of an ultrasonic drilling system is shown in Figure.

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The system consists of a tool bit connected to an ultrasonic generator. The tool bit
carries out a vertical up–down motion due to the generated ultrasonic waves.
Slurry (thin paste of corborundum powder and water) flows in the region between
the plate of the material to be drilled and the tool bit. As the tool bit undergoes the
vertical motion, the slurry removes material from the plate. Holes with a very good
control of dimensions can be obtained using this technique.

2) Welding
Welding is the process of joining metals. Ultrasonics can be used to carry out welding.
A schematic representation of an ultrasonic welding system is shown in the figure.

The set-up consists of a hammer connected to an ultrasonic generator. M 1 and

M2 represent two metal sheets that are to be welded together. The ultrasonic
generator makes the hammer vibrate vertically at ultrasonic frequencies,
generating pressure on the metal surfaces and causing the molecules of the
metals to diffuse into each other. This results in welding of the two metal parts
without the need for heating the plates to high temperatures. This process of
welding is, therefore, also called cold welding.

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3) Soldering
Aluminium has diverse industrial applications. However, using the
conventional soldering technique, aluminium cannot be soldered without the
use of fluxes. Ultrasonic soldering is extremely effective under such conditions.

The set-up consists of an ultrasonic soldering iron with a soldering tip at the end.
Provision exists for heating the soldering tip. The heated tip melts the solder placed
on aluminium and the ultrasonic vibrations of the tip remove the aluminium oxide
layer. This results in excellent adhesion of the solder to the aluminium.

4) Ultrasonic Cleaning
Ultrasonic waves possess high energy and this energy can be used to clean
ultensils, clothes, machine parts, etc. Ultrasonic cleaning is an important step in the
processing of semiconductor wafers to realize integrated circuits and devices. A
schematic diagram of a typical ultrasonic cleaning system is shown in Figure. The
set-up consists of a transducer that converts electrical energy to mechanical energy.
The ultrasonic waves so generated are coupled to the container vessel. This vessel
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contains the component requiring cleaning, in a suitable cleaning solution. The
high energy of the ultrasonic waves acts on the contaminants to loosen them and
thus clean the component.

ULTRASONIC NON DESTRUCTIVE TESTING

The basic principle behind the ultrasonic inspection is the transmission of the
Ultrasound with the medium and the reflection or scattering at any surface or
internal discontinuity in the medium due to the change in the acoustic impedance.
The Discontinuity means the existence of the flaw, cracks or hole in the material.
The reflected or scattered sound waves are received and amplified and hence, the
defects in the specimen are suitably characterized.

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ULTRASONIC FLAW DETECTOR
Principle
Whenever there is a change in the medium, then the Ultrasonic waves will be
reflected. This is the principle used in Ultrasonic flaw detector. Thus, from the
intensity of the reflected echoes, the flaws are detected without destroying the
material and hence this method is known as a Non Destructive method.

Working
 The pulse generator generates high frequency waves and is applied to the
Piezoelectric transducer and the same is recorded in the CRO.
 The piezoelectric crystals are resonated to produce Ultrasonic waves.
 These Ultrasonic waves are transmitted through the given specimen.
 These waves travel through the specimen and is reflected back by the other
end.
 The reflected Ultrasonic are received by the transducer and is converted into
electric signals. These reflected signals are amplified and is recorded in the
CRO.
 If the reflected pulse is same as that of the transmitted pulse, then it indicates
that there is no defect in the specimen.
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 On the other hand, if there is any defect on the specimen like a small hole or
pores, then the Ultrasonic will be reflected by the holes (i.e.) defects due to
change in the medium.
 From the time delay between the transmitted and received pulses, the
position of the hole can be found.
 From the height o the pulse received the depth of the hole can also be
determined.

ULTRASONIC SCANING METHODS - A, B AND C SCAN DISPLAYS

In the Ultrasonic scanning methods, the principle, construction and working
is the same as that of the Ultrasonic law detector. Here, it is based on the
position o the transducer and the output displayed in the CRO screen, we can
classify the scanning methods into three types

1. A-scan
2. B-scan
3. T-M scan or C-scan
All these three modes of scanning are obtained with respect to the pulses of
Ultrasound transmitted into and received from the specimen. The three modes
are explained below.
1) A-Scan or Amplitude mode display
Amplitude mode display gives only one-dimensional information about the
given specimen. In this, a single transducer is used to transmit and receive the
pulses from the specimen.
The received or the reflected echo signals from the specimen is given to the
Y-Plate and time base is connected to the X-Plate of the CRO, so that they are
displayed as vertical spikes along horizontal base line as shown in the figure.
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 The height of the vertical spikes corresponds to the strength of the echo from
the specimen. The position of the vertical spike from left to right along the X-
axis corresponds to the depth of penetration i.e, it gives the total time taken by
the Ultrasonic sound to travel from transmitter to the specimen and from the
specimen to the receiver.

Thus by passing Ultrasonic waves o known velocity and by noting the time
delay, we can find the distance at which detect or flaws are present, by using the
formula.
Distance = Velocity × time
In ultrasonic flaw detector, A-scan method is used to detect the position and
size of the flaws.
2) B-Scan or Brightness Mode Scan
B-scan or Brightness mode display gives a two dimensional image. The
principle of the B-Scan is same as that of A-Scan except with a small
difference. Here in the B-Scan the transducer can be moved rather than keeping
in a fixed position. As a result each echo’s are displayed as dots on the screen as
shown in the figure.
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3) T.M Scan or Time –Motion Mode or C-Scan display
This method is used to obtain the information about the moving object.
This combines the features of both A-Scan as well as B-Scan. In this the
transducer is held stationary as in A-scan and echoes appear as dots in the B-

scan. Here, the X-axis indicates the dots at the relevant location and Y-axis
indicates the movement of the object. Therefore when the object moves, the dot
also moves at a low speed. Thus an object with the oscillatory movement will
appear as a trace as shown in the figure.

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TWO MARK QUESTIONS

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 UNIT-II
LASER AND FIBER OPTICS
FIBER OPTIC COMMUNICATION SYSTEM

The major components of an optical fiber communication system are

i. Transmitter
ii. Optical fiber
iii. Receiver

Principle

A fiber optic system converts an electrical signal to an infrared light signal.

This signal is transmitted through an optical fiber. At the end of the optical fiber, it
is reconverted into an electric signal.

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Working

1. Encoder encodes the information in the binary sequence zeros and ones.

Encoder is an electric circuit where in the information is encoded into binary

sequences of zeros and one. In the light wave transmitter each ‘one’
corresponds to an electrical pulse and ‘zero’ corresponds to an absence of a
pulse. These electrical pulses are used to turn a light source on and off very
rapidly. The driver converts the incoming electrical signal into a form that
will operate with the light source. These electrical pulses are used to turn a
light source on and off rapidly.

2. The optical fiber acts as a wave guide and transmits the optical pulses
towards the receiver, by the principle of total internal reflection.
3. The light detector receives the optical pulses and converts them into
electrical pulses. These signals are amplified by the amplifier.
4. The amplified signals are decoded by the decoder.

Advantages

1. Extremely wide bandwidth

Optical frequencies are very large (1015 Hz) as compared to radio

frequencies (106 Hz) and microwave frequencies (1010 Hz). The rate at
which information can be transmitted is directly related to signal
frequency. Therefore, a transmission system that operates at the
frequency of light can theoretically transmit information at a higher rate
than systems that operate at radio frequencies or microwave frequencies.

2. Lack of cross talk between parallel fibers

There is virtually no signal leakage from fibers. Hence, cross-talks

between neighboring fibers are almost absent. This is quite frequent in
conventional metallic system.

3. Immunity to inductive interference

Since optical fibers are not metallic, they do not pick up electromagnetic
waves. The result is noise free transmission i.e., fiber optic cables are

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 immune to interference caused by lighting or other electromagnetic
equipment.

4. Smaller diameter and light weight cable

Optical fibers, because of their light weight and flexibility, can be handled
more easily than copper cables.

5. Signal Security

The transmitted signal through the fibers does not radiate. Further the
signal cannot be tapped from a fiber in an easy manner. Therefore,
optical fiber communication provides a hundred percent signal security
hence this system is highly suited to secure communications in defence
communication networks.

6. Economical and low cost per unit length.

MEDICAL ENDOSCOPE

Optical fibers are very much useful in medical field. Using low quality, large
diameter and short length silica fibers we can design a fiber optic endoscope or
fibroscope.
A medical endoscope is a tubular optical instrument, used to inspect or view the
internal parts of human body which are not visible to the naked eye. The
photograph of the internal parts can also be taken using this endoscope.

Construction

Figure shows the structure of endoscope. It has two fibers viz.,

1. Outer fiber (f0)

2. Inner fiber (fi).

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Outer fiber
The outer fiber consists of many fibers bundled together without any particular
order of arrangement and is called incoherent bundle. These fiber bundles as a
whole are enclosed in a thin sleeve for protection. The outer fiber is used to
illuminate or focus the light onto the inner parts of the body.

Inner fiber

The inner fiber also consists of a bundle of fibers, but in perfect order. Therefore
this arrangement is called coherent bundle. This fiber is used to collect the
reflected light from the object. A tiny lens is fixed to one end of the bundle in order
to effectively focus the light, reflected from the object. For a wider field of view
and better image quality, a telescope system is added in the internal part of the
telescope.

Working

Light from the source is passed through the outer fiber (fo). The light is
illuminated on the internal part of the body. The reflected light from the object is
brought to focus using the telescope to the inner fiber (fi).
Here each fiber picks up a part of the picture from the body. Hence the
picture will be collected bit by bit and is transmitted in an order by the array of
fibers.

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 As a result, the whole picture is reproduced at the other end of the receiving
fiber as shown in the figure. The output is properly amplified and can be viewed
through the eye piece at the receiving end.

The cross sectional view is as shown in the figure.

fo fi

C1 C2

In figure, we can see that along with input and output fibers, we have two
more channels namely, (i) Instrumental Channel (C1) and (ii) Irrigation channel
(C2) used for the following purposes.

Instrumental Channel (C1): It is used to insert or take the surgical instruments

needed for operation.

Irrigation Channel (C2): It is used to blow air or this is used to clear the blood in
the operation region, so that the affected parts of the body can be clearly viewed.

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