Ultrasonic Data Communication Through Petroleum

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ULTRASONIC DATA COMMUNICATION THROUGH PETROLEUM

A Thesis

Presented to

The Graduate Faculty of The University of Akron

In Partial Fulfillment

of the Requirements for the Degree

Master of Science

VRS Raju Rudraraju

May, 2010 ULTRASONIC DATA COMMUNICATION THROUGH PETROLEUM

VRS Raju Rudraraju

Thesis

Approved: Accepted:

Advisor Dean of the College Dr. Nathan Ida Dr. George K. Haritos

Committee Member Dean of the Graduate School Dr. George C. Giakos Dr. George R. Newkome

Committee Member Date Dr. Tom T. Hartley

Department Chair Dr. Alex De Abreu Garcia

ABSTRACT

Non destructive evaluation techniques have many applications such as flaw and leak detection, location determination, estimation of mechanical and physical properties.

One such technique is Ultrasonic testing. The main purpose of this thesis is to transmit data through petroleum using Ultrasonic communication. Although, there are several modulation techniques that can be used to transmit the data, this research work explores one such possible method of communicating through petroleum: Amplitude modulation.

A message signal (square wave) with 1 KHz input frequency and an amplitude of 15 volts peak-to-peak has been transmitted through water after being amplitude modulated with a carrier signal of 2 MHz frequency and an amplitude of 20 volts peak-to-peak. The transmitting transducer is excited with a high voltage signal close to its resonating frequency. The signal at the receiving ultrasonic transducer is demodulated using the peak detection circuit to obtain the original message signal but with attenuation.

Although the transmission medium used for the research is water, it can be performed with petroleum as well since the attenuation properties are quite similar. A considerable portion of the thesis is devoted to the study of properties of ultrasound, oil and petroleum.

iii

DEDICATION

Dedicated to my parents

ACKNOWLEDGEMENTS

I would like to express my appreciation towards my advisory committee: Dr.

Nathan Ida, Dr. George C. Giakos, and Dr. Tom T. Hartley for their time and consideration. I am very grateful for the advice and support of my advisor, Dr. Ida, for his feedback and for keeping me focused in my research. Especially, I liked the fact that I was always given the freedom of thought and expression to carry out my research work.

I would especially like to thank the Electrical and Computer Engineering

Department Chair Dr. Alex De Abreu Garcia for providing financial support throughout my Masters program at The University of Akron. Also, I would like to thank Dr. S I

Hariharan, Dr. John Durkin, Dr. James Grover and Dr. Jay L. Adams for making my teaching experience memorable.

I am grateful to Mrs. Boden for all her efforts from the day I got admitted into the

Masters program, and I extend my sincere thanks to Eric Rinaldo and Greg Lewis for their help.

Most importantly, I would like to thank my lovely parents Mr. Subba Raju and

Mrs. Krishna Veni, and my sweet sister Sridevi for their continuous support and encouragement throughout my life. I would also like to thank my cousins Vani, Rahul,

Sunil, and all my family for their caring nature. I am grateful to Arnaud for all his help when carrying out experiments on water, carbon steel pipes and rods.

TABLE OF CONTENTS

Page LIST OF TABLES ...... ix

LIST OF FIGURES ...... x

CHAPTER

I. INTRODUCTION...... 1

1.1 Non Destructive Testing ...... 1

1.2 Problem Definition ...... 1

1.3 Proposed Communication System...... 3

1.4 Organization of The Study ...... 3

II. BACKGROUND AND RELATED WORK ...... 5

2.1 What is Ultrasonics? ...... 5

2.2 Properties of Ultrasound ...... 6

2.2.1 Amplitude and Intensity ...... 6

2.2.2 Speed of Sound ...... 6

2.2.2.1 Liquids and Gases ...... 7

2.2.2.2 Solids ...... 7

2.2.3 Frequency ...... 9

2.2.4 Acoustic Impedance ...... 10

2.2.5 Reflection and Transmission ...... 11

2.2.6 Attenuation of Ultrasound Beams ...... 12

2.2.6.1 Oil ...... 13

2.2.6.2 Solids ...... 14

2.3 Petroleum ...... 15

2.4 Chemistry of Petroleum ...... 15

2.5 Physical Characteristics of Petroleum ...... 16

2.5.1 Viscosity ...... 16

III. FUNDAMENTAL THEORY ...... 18

3.1 Modulation and Demodulation ...... 18

3.2 Modulation Techniques ...... 18

3.2.1 Amplitude Modulation ...... 19

3.2.1.1 Synchronous Detection ...... 23

3.2.1.2 Modulation Index ...... 24

3.2.2 Frequency Modulation ...... 24

3.2.2.1 Power in an FM Signal and Noise Immunity ...... 26

3.2.2.2 Phase and Frequency Relationship ...... 26

3.2.2.3 Modulation index and Deviation Ratio ...... 28

3.3 Frequency Shift Keying ...... 29

IV. PROPOSED COMMUNICATION SYSTEM ...... 31

4.1 Software Implementation of Amplitude Modulation ...... 31

4.2 Hardware Implementation of the Communication System...... 37

4.2.1 Slew Rate ...... 41

4.3 Equipment Details ...... 46

4.3.1 3311A Function Generator ...... 46

4.3.1.1 Description ...... 46

vii

4.3.1.2 Specifications ...... 46

4.3.1.2.1 Pulse Output ...... 47

4.3.1.2.2 External Frequency Control ...... 47

V. ANALYSIS AND CONCLUSION...... 48

5.1 Analysis of Ultrasonic Wave Propagation Through Water and Steel ...... 48

5.1.1 Ultrasonic Wave Propagation through Water ...... 48

5.1.2 Ultrasonic Wave Propagation through Steel Rod ...... 51

5.1.2.1 Shear Waves ...... 51

5.2 Conclusion ...... 52

REFERENCES ...... 53

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LIST OF TABLES

Table Page

2.1 Ultrasonic frequency ranges and applications ...... 5

2.2 Stiffness of different materials ...... 7

2.3 Velocity and wavelength comparisons of different materials ...... 9

2.4 Density and acoustic impedances of different materials ...... 10

2.5 Reflections between two media ...... 12

2.6 Velocity of sound and absorption coefficient in two oils ...... 14

2.7 Attenuation in different materials ...... 15

5.1 Output voltage at demodulator vs. amplitude of carrier signal ...... 49

5.2 Output voltage at demodulator vs. amplitude of message signal ...... 50

LIST OF FIGURES

Figure Page

1.1 Vessel with series-connected pipes unloading the crude oil ...... 2

1.2 Construction of pipes carrying oil connected end to end ...... 3

2.1 Transverse and longitudinal waves ...... 8

2.2 Reflection and transmission at interfaces ...... 11

2.3 Attenuation of ultrasound ...... 13

2.4 Viscosity of petroleum ...... 17

3.1 Alternating waveform ...... 19

3.2 Amplitude modulated signal ...... 20

3.3 Spectrum of signals ...... 22

3.4 Spectrum of audio signals made up of a range of frequencies ...... 22

3.5 Diode detector circuit ...... 23

3.6 Synchronous AM demodulation ...... 24

3.7 Frequency modulated signal ...... 25

3.8 Frequency shift keying ...... 29

4.1 Amplitude modulation and demodulation setup in simulink ...... 32

4.2 Message signal...... 32

4.3 Carrier signal ...... 33

4.4 Modulated signal for a sinusoidal message input ...... 33

4.5 Modulated signal multiplied by carrier signal ...... 34

4.6 LPF1 signal ...... 34

4.7 LPF2 signal ...... 35

4.8 Demodulated signal for a sinusoidal message input ...... 35

4.9 Modulated signal for a square wave message input ...... 36

4.10 Demodulated signal for a square wave message input ...... 36

4.11 Basic setup for Hardware implementation ...... 37

4.12 Modulation circuit setup for the experiment ...... 37

4.13 Square wave message signal with 1 KHz frequency ...... 39

4.14 Sinusoidal wave carrier signal with 2 MHz frequency ...... 39

4.15 Modulated signal at the end of the amplitude modulation technique ...... 40

4.16 Water as transmission medium and the ultrasonic transducer setup ...... 40

4.17 Pinout diagram of HA-2520/22/25 series ...... 42

4.18 Amplified modulated signal ...... 43

4.19 Output signal at the receiving transducer ...... 44

4.20 Envelope detection circuit ...... 44

4.21 Amplified signal generated at the end of the transducer setup...... 45

4.22 Demodulated signal (Signal at the output of the envelope detection circuit) ...... 45

4.23 3311A function generator...... 46

5.1 Voltage at demodulator vs. Amplitude of carrier signal ...... 49

5.2 Voltage at demodulator vs. Amplitude of message signal ...... 50

5.3 Steel rod with transducer set on two different sides ...... 51

5.4 Steel rod with transducer set on the same side ...... 51

5.5 Voltage variation with distance using the configuration of Figure 5.4 ...... 52

CHAPTER I

INTRODUCTION

1.1 Non Destructive Testing

Non Destructive Testing (NDT) is a very broad, interdisciplinary field that plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion. These tests are performed in a manner that does not affect the future usefulness of the object or material i.e., NDT allows parts and materials to be inspected and measured without damaging them. Because it allows inspection without interfering with a product's final use, NDT provides an excellent balance between quality control and cost-effectiveness. Generally speaking, NDT applies to industrial inspections. While technologies are used in NDT that are similar to those used in the medical industry, typically nonliving objects are the subjects of the inspections.

1.2 Problem Definition

After the extraction of oil from the earth’s core, it is transported either through pipelines or tankers. In the latter case, the vessels (ship) carrying the oil are to be loaded and unloaded as shown in Figure 1.1; during which there is a possibility of leakage in the pipes carrying oil from the vessel to the shore.

Two independent carcasses with an integrated electronic sensor system are designed to contain any leakage from the first carcass while alerting the operator to hose

1 failure. In the event of a leak, light is turned on so that the faulty pipe can be found. The problem is that the sensors which detect leaks are not connected together; so there is no communication. The only way to know if there is a leak is to send a diver to check the status of the sensor.

The goal of this research is to develop a means of communication between all the sensors so that the information could be checked either on the boat or on the shore. The sensors cannot be connected together by wires; so the only way is to use wireless communication. Ultrasound can be used through the oil to transmit data using a transmitter and a receiver.

Figure 1.1: Vessel with series-connected pipes unloading the crude oil.

The setup as shown in Figure 1.2 explains how a leak can be detected. Instead of just using a single pipe to transport the oil, several pipes are connected end-to-end so that even if there is an oil leak or a crack in one of those pipes, it can easily be spotted and the respective pipe could be replaced. The ultrasonic transducers are installed on either side of each of the rubber pipe (pipes are constructed with rubber in order to float on sea water) to detect any oil leakage present in the pipes and send the detected signal back to the control center at the shore or to the ship.

Sensors play an important role in the transmission of data in environments where neither wired nor wireless communication is possible. Specifically, with a transmission

Figure 1.2: Construction of pipes carrying oil connected end to end. medium such as oil, water or gas, the communication becomes even more difficult.

In this thesis, a communication system is developed to transmit data through media like water and crude oil petroleum and a detailed analysis is made on the transmission of ultrasonic waves through these media.

The main purpose of this research study is to transmit data in the form of ultrasonic waves through crude oil petroleum using amplitude modulation and to analyze the propagation of these waves through water, carbon steel pipes, and carbon steel rods.

1.3 Proposed Communication System

The communication system uses ultrasonic transducers, signal generators, voltage amplifiers and modulation and demodulation circuits. Different modulation techniques are discussed in Chapter III for transmitting the ultrasonic waves through petroleum.

Amplitude modulation is employed along with necessary amplifiers to obtain a detectable signal at the receiver because of the simplicity of its design over other modulation techniques.

1.4 Organization of the study

The research study is essentially divided into the following Chapters. This

Chapter gives a brief description of the nondestructive testing, and the problem definition

3 of the thesis. Chapter II provides background on the properties of crude oil petroleum and ultrasound and its properties. Basically, the aim of this Chapter is to get acquainted with the terminology related to ultrasound and the chemistry of petroleum.

The purpose of Chapter III is to get insight into different modulation techniques, like amplitude modulation and frequency modulation, employed to transmit data through crude oil petroleum, water and carbon steel.

The proposed communication system is presented in Chapter IV. This Chapter deals with the software and the hardware implementations of amplitude modulation techniques to transmit the data through water using the ultrasonic transducers and analysis of the transmission of ultrasonic waves through other transmission mediums.

Finally, Chapter V discusses the conclusions drawn and possible recommendations for future work of the research study are discussed.

CHAPTER II

BACKGROUND AND RELATED WORK

2.1 What is Ultrasonics?

Ultrasonics is a term used in acoustics to denote the frequencies which are beyond the limits of hearing of the human ear - that is to say, frequencies of about 20KHz and upwards [1]. The above statement is a very simple and general way of defining ultrasound. This term is by no means limited to sound waves travelling in gases and liquids but includes, in particular, the more complicated elastic waves in solids.

Table 2.1 Ultrasonic frequency ranges and applications.

Application Average Range

Upper limit of human hearing 16 kHz

Defoaming and Degassing 2-30 kHz

Ultrasonic metal working and welding 16-25 kHz

Control applications 16-45 kHz

Ultrasonic cleaning 20-40 kHz

Nondestructive testing (NDT) 1-10 MHz

Ultrasonics is a powerful tool for physics and technology. It allows one to test matter and solid structures not invasively, which is otherwise known as Non-destructive testing.

That is why different fields, as microscopy, medical diagnostics, underground prospecting, transducer technology and material sciences in general, devote so much work to ultrasonic technology [2]. Also, the importance of ultrasound as a valuable tool for the investigation of matter should be pointed out. Unlike electromagnetic waves, any kind of sound can be propagated in a material medium. Sound waves are influenced by a medium, thus the velocities of sound waves, as well as their attenuation, depend in a characteristic way on the nature of the medium.

2.2 Properties of Ultrasound

The properties of ultrasound play an important role in ensuring the transmission of ultrasonic waves through petroleum and other media. The properties are listed below.

2.2.1 Amplitude and Intensity

The variable used to discuss reflection, attenuation and scatter is the pressure amplitude. It is defined as the maximum increase (or decrease) in the pressure relative to ambient conditions in the absence of sound wave. In some applications, it is useful to specify the acoustic intensity. The intensity I, is proportional to the square of the pressure amplitude, P, that is

I = .

2.2.2 Speed of Sound

The speed of sound in any medium is determined primarily by the characteristics of the medium. There is slight dependence on other factors, such as the ultrasonic frequency, but these are so small that they can generally be ignored.

2.2.2.1 Liquids and Gases

Specifically, for longitudinal sound waves in liquids and gases, an expression for the speed of sound, c, is:

ρ c = , where the symbol ρ is the density, and B is a property of the medium, called the bulk modulus. It is a measure of the stiffness of the material, that is, the resistance of the material to being compressed.

Table 2.2: Stiffness of different materials.

Medium Bulk Modulus, B

SI Unit (Pa, N/ m2 ) x 10 9

Air 1.34 X 10 -4

Ethyl Alcohol 1.06

Gasoline 1.3

Glycerin 4.52

Mercury 2.85

SAE 30 Oil 1.5

Seawater 2.34

Water 2.15

2.2.2.2 Solids

In contrast to gases and fluids, solids have the ability to sustain shear stresses. For this reason, in addition to longitudinal waves (oscillation of the particles in the direction of propagation), there also occur transverse waves in which the particles oscillate in a 7 direction normal to the direction of propagation. We consider only isotropic solids in which the elastic properties are independent of the direction.

Figure 2.1: Transverse and longitudinal waves.

Three constants are sufficient to characterize the elastic properties of isotropic solids. In practice, the modulus of elasticity E, the shear modulus G, and Poisson’s ratio

γ, related as:

G = () . The velocity of longitudinal waves in solids is given by the relation:

(1 − ) c = , (1 + ) where c = velocity, d = density.

The velocity of shear/transverse waves is:

G c = . d 2.2.3 Frequency

The usual relation among frequency, velocity, and wavelength holds for ultrasonic waves. They are related as:

c λ = , f where λ = wavelength, c = velocity, f = frequency.

Table 2.3: Velocity and wavelength comparisons of different materials.

Material Velocity Wavelength ( m)

(m/s) 0.5 MHz 1 MHz 2.25 MHz 5 MHz

Air 331 68.8 34.4 15.3 6.88

Aluminum 6220 1244 622 277 124

Glass 5900 1040 520 231 104

Petroleum 1330 - - - -

Silver 3800 - - - -

Steel 5810 162 581 259 116

Transformed oil 1390 278 139 61.8 27.8

Water (fresh) 1430 290 115 64.5 29

Water vapor 401 - - - -

Wood 4170 - - - -

2.2.4 Acoustic Impedance

An important property of media that influences the strength or amplitude of reflected echoes is a quantity called the acoustic impedance. It is defined as the acoustic pressure divided by the resultant particle velocity. For our purposes, the acoustic impedance of a material, z, is equal to the product of the medium density ( ρ) and its speed of sound (c). That is:

z = ρc , Table 2.4: Density and acoustic impedances of different materials.

Material Specific acoustic impedance Density

Pa.s/m gm/cm 3

Air 430 1.205 X 10 -3

Aluminum 17 X 10 6 2.65

Glass 21 X 10 6 5.9

Lubricating oil 1.1 X 10 6 0.8

Petroleum 0.93 X 10 6 0.7

Silver 39 X 10 6 10.5

Steel 47.6 X 10 6 7.85

Transformed oil 0.0128 X 10 6 0.02

Water (fresh) 1.43 X 10 6 1

Water (salt) 1.55 X 10 6 1.025

Wood 1.7 / 3.5 X 10 6 0.5 / 0.8

2.2.5 Reflection and Transmission

Whenever an ultrasound beam is incident on an interface formed by two materials having different acoustic impedances, some of the energy in the beam will be reflected and the remainder transmitted. The amplitude of the reflected wave depends on the difference between the acoustic impedances forming the interface.

Consider the case of normal or perpendicular beam incidence on a large flat interface. A large smooth interface such as depicted in Figure 2.2 is termed a specular reflector. It has dimensions that are much greater than that of the ultrasonic wavelength.

Figure 2.2: Reflection and transmission at interface.

The ratio of the reflected pressure amplitude, Pr, to the incident pressure amplitude, Pi, is called the amplitude reflection coefficient, A.

It is given by:

P Z - Z A = r = 1 2 . Pi Z 1 + Z 2

The energy is proportional to the amplitude squared. Therefore,

  2 Z1 - Z 2 R = R0   ,  Z1 + Z 2 

11 where R = reflected energy and R0 = incident energy.

The ratio of the transmitted pressure amplitude, Pt, to the incident pressure amplitude, Pi, is called the amplitude reflection coefficient, B.

P 2Z B = t = 2 . Pi Z 1 + Z 2

The energy is

  2 2Z 2 T = R0   .  Z1 + Z 2 

A list of values of reflection between two media is shown in the Table 2.5 below.

Strong reflections take place when transmitting from any liquid to any solid.

Table 2.5: Reflection between two media.

Aluminum Steel Glass Water Transformed oil Air

Aluminum 0% 21% 2% 72% 74% 100%

Steel - 0% 31% 88% 89% 100%

Glass - - 0% 65% 67% 100%

Water - - - 0% 0% 100%

Transformed oil - - - - 0% 100%

Air - - - - - 0%

2.2.6 Attenuation of Ultrasound Beams

When sound travels through a medium, its intensity decreases with distance. In idealized materials, sound pressure (signal amplitude) is only reduced by the spreading of

12 the wave. Natural materials, however, all produce an effect which further weakens the sound. This further weakening results from scattering and absorption. Scattering is the reflection of the sound in directions other than its original direction of propagation.

Absorption is the conversion of the sound energy to other forms of energy. The combined effect of scattering and absorption is called attenuation.

Figure 2.3: Attenuation of ultrasound.

Attenuation in liquid is highly dependent on the ultrasonic frequency. In most cases, attenuation is nearly proportional to the distance,

−2α x A = A0 e ,

where A 0 is the amplitude at x=0, and α is defined as the attenuation or absorption coefficient.

2.2.6.1 Oil

The velocity of sound and absorption in castor oil and Dow–Corning 710 phenylated silicone oil (DC-710) are given in the Table 2.6 shown below in the range 0 to

40 °C for a frequency of 1 MHz. 13

Table 2.6: Velocity of sound and absorption coefficient in two oils.

Castor oil DC-710 Silicone oil

Temperature Velocity Absorption Velocity of Absorption

(°C) of sound coefficient sound (ms-1) coefficient

(ms-1) (dBm−1) (dBm−1)

0 1580 225 1446 -

10 1536 138 1409 117

20 1494 83 1378 60

30 1452 50 1349 34

40 1411 32 1321 20

The frequency dependent absorption coefficients (dBm -1) are:

0 1,667 For castor oil (0.4 to 500 MHz): α = α1 MHz (T ) f(MHz) .

0 1.79 For DC-710 silicone oil (2 to 10 MHz): α = α1 MHz (T ) f(MHz) .

2.2.6.2 Solids

Velocities and attenuation constants for various solids in the region of 20 °C are given in Table 2.7. In the case of metals, factors such as texture, cold work, stress, hardening, tempering and aging can cause significant departures from the values given in

Table 2.7. The bracketed Figures following the attenuation are frequencies in MHz.

For many solids, the variation of attenuation with frequency is often approximately linear.

Table 2.7: Attenuation in different materials.

Material Absorption Coefficient (dBm -1)

Aluminum 3 (10 MHz)

Concrete 87 (0.2 MHz)

Glass 17 (10 MHz)

Rubber 130 (0.35 MHz)

Steel 43 (10 MHz)

2.3 Petroleum

Petroleum is a complex mixture of hydrocarbons that occur in the Earth in liquid, gaseous, or solid forms. The term petroleum is often limited to the liquid form, commonly called crude oil, but as a technical term it also includes natural gas and the viscous or solid form known as bitumen. The liquid and gaseous phases of petroleum constitute the most important of the primary fossil fuels.

Liquid and gaseous hydrocarbons are so intimately associated in nature that it has become customary to shorten the expression “petroleum and natural gas” to “petroleum” when referring to both. The word petroleum (literally “rock oil” from the Latin petra,

“rock” or “stone,” and oleum, “oil”) was first used in 1556 in a treatise published by the

German mineralogist Georg Bauer, known as Georgius Agricola.

2.4 Chemistry of Petroleum

Petroleum is a non-uniform material. Its physical and chemical composition can differ not only with the location and the age of the oil field but also with the depth of an individual well. Even two adjacent wells may produce petroleum with distinctly

15 dissimilar characteristics. On a molecular basis, petroleum is a complex mixture of hydrocarbons with small amounts of organic compounds containing sulfur, oxygen and nitrogen as well as compounds containing metallic constituents, particularly vanadium, nickel, iron and copper.

Despite the wide variation in physical properties from the lighter, more mobile crude oils at one extreme, to the heavier asphaltic crude oils at the other extreme, the composition is very similar.

These elements make hydrocarbons which can be divided into three classes:

• Parafins

• Naphthenes

• Aromatics

2.5 Physical Characteristics of Petroleum

The physical characteristics of petroleum like viscosity are discussed in this section. These characteristics play an important role in the transmission of ultrasonic waves through petroleum.

2.5.1. Viscosity

Technically, the viscosity of oil is a measure of the oil’s resistance to shear.

Viscosity is more commonly known as resistance to flow. A high viscosity implies a high resistance to flow while a low viscosity indicates a low resistance to flow. Viscosity varies inversely with temperature. Viscosity is also affected by pressure; higher pressure causes the viscosity to increase.

When viscosity is determined by directly measuring shear stress and shear rate, it is expressed in centipoise (cP) and is referred to as the absolute or dynamic viscosity. In

16 the oil industry, it is more common to use kinematic viscosity, which is the absolute viscosity divided by the density of the oil being tested. Kinematic viscosity is expressed in centistokes (cSt). Viscosity is defined as follows:

ν = . ρ

The units of viscosity are: 1 cP = 0.001 Pa·s = 1 mPa·s

1 cSt= 1 mm 2·s -1 = 10 -6m2·s −1

Figure 2.4: Viscosity of petroleum.

Viscosity data can differentiate petroleum and tar sand bitumen. The viscosity cutoff point is 10,000 centipoises (cP).

Considering this introduction to the properties of ultrasound and of petroleum, the research work is carried out in the following chapters.

CHAPTER III

FUNDAMENTAL THEORY

3.1 Modulation and Demodulation

In general, radio signals can be used to carry information. The information which may be audio, data or other forms, is used to modify i.e., modulate, a single frequency known as the carrier. The information superimposed onto the carrier forms a radio signal which is transmitted to the receiver. After modulation, the information is removed from the radio signal and reconstituted in its original format using the demodulation technique.

All audio signals occupy the same frequency band i.e. between 0 and 20 kHz.

Before being broadcast an audio signal must be moved, or frequency translated to a specific frequency range in order to use the available frequency spectrum. To do this the audio signal (or modulating signal) modulates a much higher radio frequency (the carrier frequency). Each audio signal is assigned a carrier - defining a channel - so that it is possible for the receiver to discriminate between all the streams of signals coming in.

3.2 Modulation Techniques

There are many different types of modulation techniques, but three of them are the most basic. They are:

• Amplitude Modulation

• Frequency Modulation

• Phase Modulation

Each of the above modulation techniques has their own advantages and disadvantages.

The basis of any radio signal or transmission is the carrier. This consists of an alternating waveform like that shown in Figure 3.1. This is generated in the transmitter, and if it is radiated in this form it carries no information – it appears at the receiver as a constant signal.

Figure 3.1: Alternating waveform.

3.2.1 Amplitude Modulation

Possibly the most obvious method of modulating a carrier is to change its amplitude in line with the modulating signal.

The simplest form of amplitude modulation is to employ a system known as 'on– off keying' (OOK), where the carrier is simply turned on and off. This is a very elementary form of digital modulation and was the method used to carry Morse transmissions, which were widely used especially in the early days of 'wireless'. Here, the length of the on and off periods defined the different characters.

More generally, the amplitude of the overall signal is varied in line with the incoming audio or other modulating signal, as shown in Figure 3.2. Here, the envelope of

19 the carrier can be seen to change in line with the modulating signal. This is known as

Amplitude Modulation (AM).

Figure 3.2: Amplitude modulated signal.

A carrier is described by

v = Vc sin( ω c t+ θ).

To modulate the carrier using the amplitude modulation technique, its amplitude is changed in conformity with the level of the audio signal, which is described by

v = Vm sin ω m t.

The amplitude of the carrier varies sinusoidally about a mean of Vc . When the carrier is modulated, its amplitude is varied with the instantaneous value of the modulating signal. 20

The amplitude of the variation of the carrier amplitude is Vm and the angular frequency

of the rate at which the amplitude varies is ωm . The amplitude of the carrier is then:

Carrier amplitude = Vc+ V m sin ω m t and the instantaneous value is

v = {Vcm+ V sin ω mt} * sin ω c t Eqn. 1

= Vccm sin ω t + V sin ( ω mt) sin( ω c t)

Using sin A * sin B = ½ cos (A - B) - ½ sin (A + B) this becomes

v = Vcc sin ω t + ½ V m cos ( ω cm-ω )t + ½ V m cos ( ω cm+ω )t Eqn. 2

This is a signal made up of 3 signal components

• carrier at ωc (rad/s) Frequency is fc = ωc/2 π Hz.

• upper side frequency ωc + ωm (rad/s) Frequency is (ωc + ωm)/2 π = f m + f c Hz.

• lower side frequency ωc - ωm (rad/s) Frequency is (ωc - ωm)/2 π = f m - fc Hz.

The bandwidth (the difference between the highest and the lowest frequency) is

BW = (ωc + ωm) - (ωc - ωc) = 2 * ωm rad/s = ωm/π Hz.

The spectrum of these signals is shown in Fig 3.3. This is described as the signal in the frequency domain, as opposed to the signal in the time domain. In this case the audio signal is made up of a single frequency.

In this example the angular frequencies (expressed in Radians/sec, or kRad/sec, or

Mrad/sec) are shown. In most cases however the frequency is shown (expressed in Hz, or kHz, or MHz).

Lower Carrier Upper Amplitude (V) side side frequency frequency

Angular ω - ω ω ω + ω Frequency c m c c m Bandwidth = 2 * ω m

Figure 3.3: Spectrum of signals.

If the audio signal is made up of a range of frequencies from f1 to f2 (as is normally the case) rather than a single frequency, the output signal will be a band of frequencies, contained in

• the upper side band (USB), inverted and

• the lower side band (LSB), erect.

Carrier Lower Upper Spectrum of Sideband Sideband audio signal Inverted Erect

f1 f - f2 f - f1 f f + f1 f + f2 f2 c c c c c Figure 3.4: Spectrum of audio signal made up of a range of frequencies.

The maximum amplitude in an AM signal is Vc + V m and the minimum amplitude is found to be Vc – Vm.

The demodulation process for AM where the radio frequency signal is converted into an audio frequency signal is very simple. It only requires a simple diode detector circuit like that shown in Figure 3.5. In this circuit the diode rectifies the signal, only 22 allowing the one-half of the alternating radio frequency waveform through. A capacitor is used as a simple low-pass filter to remove the radio-frequency parts of the signal, leaving the audio waveform. This can be fed into an amplifier, after which it can be used to drive a loudspeaker. This form of demodulator is very cheap and easy to implement, and is still widely used in many AM receivers today.

Figure 3.5: Diode detector circuit.

3.2.1.1 Synchronous Detection

The signal may also be demodulated more efficiently using a system known as synchronous detection as shown in Figure 3.6. Here, the signal is mixed with a locally generated signal with the same frequency and phase as the carrier. In this way the signal is converted down to the baseband frequency. This system has the advantage of a more linear demodulation characteristic than the diode detector, and it is more resilient to various forms of distortion. There are various methods of generating the mix signal. One of the easiest is to take a feed from the signal being received and pass it through a very high-gain amplifier. This removes any modulation, leaving just the carrier with exactly the required frequency and phase. This can be mixed with the incoming signal and the result filtered to recover the original audio.

Figure 3.6: Synchronous AM demodulation.

3.2.1.2 Modulation Index

It is often necessary to define the level of modulation that is applied to a signal. A factor or index known as the modulation index is used for this. When expressed as a percentage, it is the same as the depth of modulation. In other words, it can be expressed as:

RMS value of modulating signal M = . RMS value of unmodulated signal

The value of the modulation index must not be allowed to exceed unity, otherwise the envelope becomes distorted and the signal will spread out either side of the wanted channel, causing interference to other users.

3.2.2 Frequency Modulation

While AM is the simplest form of modulation to envisage, it is also possible to vary the frequency of the signal to give frequency modulation (FM). It can be seen from

Figure 3.7 that the frequency of the signal varies as the voltage of the modulating signal changes.

Figure 3.7: Frequency modulated signal.

The amount by which the signal frequency varies is very important. This is known as the deviation, and is normally quoted in kilohertz. As an example, the signal may have a deviation of ±3 kHz. In this case, the carrier is made to move up and down by 3 kHz.

FM is used for a number of reasons. One particular advantage is its resilience to signal-level variations and general interference. The modulation is carried only as variations in frequency, and this means that any signal-level variations will not affect the audio output provided that the signal is of a sufficient level. As a result, this makes FM ideal for mobile or portable applications where signal levels vary considerably. The other advantage of FM is its resilience to noise and interference when deviations much greater than the highest modulating frequency are used. It is for this reason that FM is used for high-quality broadcast transmissions where deviations of ±75 kHz are typically used to

25 provide a high level of interference rejection. In view of these advantages, FM was chosen for use in the first-generation analogue mobile phone systems.

3.2.2.1 Power in an FM Signal and Noise Immunity

The amplitude of an FM signal does not vary. Therefore the power in an FM signal is constant and is always equal to the power of the unmodulated carrier. The power does not depend in any way on the modulation.

Every transmitted signal picks up noise between the transmitter and the receiver.

Usually this noise adds to the amplitude of the signal.

In the case of an AM signal, the function of the radio receiver is to recover the envelope of the signal as this should be an exact copy of the original audio input. If noise changes the amplitude of the signal then the shape of the envelope has changed and the radio receiver will recover the noise - it will reproduce this as part of the audio signal.

The noise will appear in the audio output. AM is susceptible to noise.

In the case of FM the radio receiver does not depend on the amplitude of the envelope to recover the audio signal. If noise has changed the amplitude then the receiver will be able to ignore this. The noise will not be passed on to the audio output. FM is much less susceptible to noise than AM, it permits a much more accurate reproduction of the original audio signal.

3.2.2.2 Phase and Frequency Relationship

Consider any sinusoid signal described by: f(t) = A * cos ωt.

The term ωt is just a number which is increasing all the time. It is the phase of the signal at any time - called the instantaneous phase. If we call the phase ϕ then the sinusoid could also be described by: f(t) = A * cos ϕ ,

26 where ϕ = ω t

dϕ This gives = ω dt

In other words the frequency is just the rate of change of the phase of the signal.

This means that in general:

t ϕ = ∫ ω dt t = 0 or that the phase of the signal is the integral of the frequency.

If the frequency is a constant, as it is most cases you have seen to date, then ϕ = ωt.

But if the frequency is varying all the time, as it does with FM, then we have to use this form for the phase. In general for an FM signal:

t VFM = Vc cos ϕ = Vc cos { ∫ ω dt }. t = 0

Let the carrier have a frequency ωc and let the modulating signal be

f(t) = A * cos ωmt.

The instantaneous frequency deviation is proportional to f(t). If S is the sensitivity of the modulator, then the instantaneous frequency deviation is S * f(t). This gives the instantaneous angular frequency deviation as

∆ω = 2 π S f(t) = 2 π S A * cos ωmt radians.

The maximum frequency deviation occurs when cos ωmt = 1. Therefore the maximum frequency deviation due to a signal of amplitude A is 2 π S A, call this ∆ωmax.

The instantaneous frequency (nominal frequency plus frequency deviation) is therefore

ωi = ωc + 2 π S A cos ωmt = ωc + ∆ωmax cos ωmt.

The instantaneous phase is:

t t t

ϕ = ∫ ωi dt = ∫ ωc dt + ∫ ∆ωmax cos ωmt dt . t = 0 t = 0 t = 0

∆ωmax ϕ = ωc t + sin ωmt. ωm

The equation of the FM wave, i.e. the carrier with frequency deviations, is of the form

(the amplitude of the carrier is V c )

∆ωmax fc (t) = Vc cos ϕ = Vc cos { ωc t + sin ωmt }. ωm

= Vc cos {ωc t + β * sin ωmt }.

For the last step it can be observed that the modulation of an FM signal was defined as: the maximum frequency deviation divided by the frequency of the modulating signal.

From this expression it can be observed that the modulation index also gives the peak phase variation of the carrier in radians.

3.2.2.3 Modulation Index and Deviation Ratio

In many instances a measure known as the modulation index is of value and is used in other calculations. The modulation index is the ratio of the frequency deviation to the modulating frequency, and will therefore vary according to the frequency that is modulating the transmitted carrier and the amount of deviation:

Frequency Deviation M = . Modulation Frequency

However, when designing a system it is important to know the maximum permissible values. This is given by the deviation ratio, and is obtained by inserting the maximum values into the formula for the modulation index:

Maximum Frequency Deviation D = . Maximum Modulation Frequency

3.3 Frequency Shift Keying

Many signals employ a system called frequency shift keying (FSK) to carry digital data as in Figure 3.8. Here, the frequency of the signal is changed from one frequency to another, one frequency counting as the digital 1 (mark) and the other as a digital 0

(space). By changing the frequency of the signal between these two it is possible to send data over the radio.

Figure 3.8: Frequency shift keying.

There are two methods that can be employed to generate the two different frequencies needed for carrying the information. The first and most obvious is to change the frequency of the carrier. Another method is to frequency-modulate the carrier with 29 audio tones that change in frequency, in a scheme known as Audio Frequency Shift

Keying (AFSK). This second method can be of advantage when tuning accuracy is an issue.

CHAPTER IV

PROPOSED COMMUNICATION SYSTEM

This chapter discusses the proposed communication system for the ultrasonic transmission of data through water. The modulation technique used for the transmission is discussed and the analysis of ultrasonic waves through different transmission media such as carbon steel pipes and rods is made.

After careful evaluation of different types of modulation techniques, amplitude modulation was chosen ahead of other modulation techniques because of the simplicity in its design and evaluation.

4.1 Software Implementation of Amplitude Modulation

The amplitude modulation technique was first implemented in Simulink to observe the technique’s results in the ideal case.

The basic setup was implemented in Simulink. In the Simulink model, two signal generators were used to generate the message and the carrier signals. The setup is as shown in Figure 4.1.

The message (with/without a bias/constant) with 1 Hz frequency and the carrier signal with a 20 Hz frequency are fed as inputs to the multiplier block which acts as a modulator to produce the modulated signal. The sample time for the product block is maintained at 0.001s. 31

Figure 4.1: Amplitude modulation and demodulation setup in Simulink.

Scopes are attached to see the output at each of the following: message, carrier and product. The message signal shown below in Figure 4.2 is a sine wave and has a frequency of 1Hz and the carrier signal as shown in the Figure 4.3 has a frequency of 20

Hz.

0.5

0 Message -0.5

-1 0 2 4 6 8 10 Time, s

Figure 4.2: Message Signal.

0.5

0 Carrier

-0.5

-1 0 0.2 0.4 0.6 0.8 1 Time, s

Figure 4.3: Carrier Signal.

The resultant signal after the modulation of the message signal is shown in Figure 4.4.

0.5

Modulated signal Modulated -0.5

-1 0 0.5 1 1.5 2 Time, s Figure 4.4: Modulated Signal for a sinusoidal message input.

Now that the signal is modulated, the demodulation of the signal is carried out using the envelope detection technique. The envelope detection technique is done with the help of a capacitor and resistor, or we can say with the help of a low pass filter (LPF).

In the Simulink model, the carrier signal is multiplied with the modulated signal to obtain a signal shown in Figure 4.5 which is then fed to the first LPF of 5 Hz.

0.5

0 Mod Mod x Carrier -0.5

-1 0 0.5 1 1.5 2 Time, s

Figure 4.5: Modulated signal multiplied by carrier signal.

After the first LPF, the signal looks like Figure 4.6 as shown below.

0.5

0 LPF1

-0.5

-1 0 0.5 1 1.5 2 Time, s Figure 4.6: LPF1 Signal.

From the Figure 4.7 shown above, it still appears to contain a small portion of the high frequency component. This can be removed with the help of another LPF. Now, the demodulated signal is as shown in Figure 4.8.

0.5

0 LPF2

-0.5 0 0.5 1 1.5 2 Time, s Figure 4.7: LPF2 Signal.

0.5

0 Demodulated Signal Demodulated

-0.5 0 2 4 6 8 10 Time, s Figure 4.8: Demodulated Signal for a sinusoidal message input.

From the Figure 4.8, it is observed that the demodulated signal does not contain the high frequency component and the message signal has been regenerated with 1 Hz frequency.

The demodulated signal shown above is for a message signal with sinusoidal input. If a square wave was given as an input at the signal generator in the Simulink, the waveforms for the modulated and the demodulated signals are shown in Figure 4.9 and

Figure 4.10 respectively.

0.5

Modulated signal Modulated -0.5

-1 0 0.5 1 1.5 2 Time, s

Figure 4.9: Modulated signal for a square wave message input.

0.5

-0.5 Demodulated Signal Demodulated

-1 0 1 2 3 4 5 Time, s

Figure 4.10: Demodulated signal for a square wave message input.

From Figure 4.9 it can be observed that when a square wave is given as an input for the message signal along with a sine wave as the carrier signal, the modulated signal has a frequency of the carrier signal. The demodulated signal as shown in Figure 4.10 has the frequency of the message signal and the shape of the signal is similar to a square wave.

4.2 Hardware Implementation of the Communication System

The test apparatus used for the hardware implementation is described in this section. The description of each component in the implementation is discussed in section

4.3 of this chapter. The basic setup is shown in the Figure 4.11.

Figure 4.11: Basic setup for Hardware Implementation.

To generate the message and the carrier signal, two function generators have been used.

Also, two ultrasonic transducers with 0 - 3MHz ultrasonic range have been used to transmit the data.

Figure 4.12: Modulation circuit setup for the experiment.

The square wave message signal of 1 KHz frequency is generated from HP

3311A function generator while the sinusoid wave carrier signal of 2 MHz frequency is generated from Wavetek 182 function generator and fed to the base of the 2N2222A transistor in series with two 1K resistors as shown in Figure 4.12. The emitter of the transistor is grounded while the collector has been given a voltage of 10V. To generate a modulated signal without any noise, the transistor’s collector terminal is coupled to a series and parallel connection of capacitors and resistors.

The values of the capacitors and resistors for the RC circuit are chosen in accordance with the frequency to be permitted.

1 f = . 2πRC

For R=1 KΩ and f = 2 MHz, the value of C is:

1 C = = 80pF. 2π(1K )(2Mhz)

The message and the carrier wave signals generated from the function generators given to the oscilloscope are shown in Figure 4.13 and Figure 4.14 respectively. Note that the amplitude of these signals is a peak-to-peak voltage of 20 volts.

After installation of all the components required i.e., after the construction of the circuit on the breadboard, the output of the modulation circuit (modulated signal) generated is as shown in Figure 4.15.

Figure 4.13: Square wave message signal with 1 KHz frequency.

Figure 4.14: Sinusoidal wave carrier signal with 2 MHz frequency.

The resultant modulated signal is passed through water which acts as a transmission medium in this research. The water is kept in the container and the transducers are installed on either side of the container as shown in the Figure 4.16. 39

Figure 4.15: Modulated signal at the end of the amplitude modulation circuit.

Figure 4.16: Water as transmission medium and the ultrasonic transducer setup.

The modulated signal obtained at the end of modulation circuit has a very low peak-to peak voltage of approximately 0.44 volt. This voltage needed to be increased to a value that could be detectable at the receiving end of the container after the transmission in the medium. In this regard, an operational amplifier is used to amplify the modulated signal. The selection of operational amplifier is made such that it has high slew rate and can be operated for high frequency range. 40

4.2.1 Slew Rate

The slew rate (SR) is defined as the maximum rate of change of the output of an op amp circuit. The SR in general describes the degradation effect on the high frequency response of the active amplifier (one with an op amp) near or at the rated maximum output voltage swing. This effect is generally due to the compensating capacitor and not to the transistor circuits internal to the op amp. In short, the SR effect is due to the maximum supplied current available for charging up the compensating capacitor.

The current required to charge a capacitor is shown in the equation below.

dv i = C . dt

The Slew Rate is found from

dv imax SR = = . dtmax C

The HA-2520/2522/2525 operational amplifier comprises a series of operational amplifiers delivering an unsurpassed combination of specifications for slew rate, bandwidth and settling time. These dielectrically isolated amplifiers are controlled at close loop gains greater than 3 without external compensation. In addition, these high performance components also provide low offset current and high input impedance.

The basic pin diagram of the HA2-2522-2 operational amplifier is as shown in the Figure

4.17.

Having 120V/ s slew rate and 200ns (0.2%) settling time, these amplifiers are them ideal components for pulse amplification and data acquisition designs. These devices are valuable components for RF and video circuitry requiring up to 20MHz gain

Figure 4.17: Pinout diagram of HA-2520/22/25 series. bandwidth and 2MHz power bandwidth. For accurate signal conditioning designs the

HA-2520/2522/2525’s superior dynamic specifications are complemented by 10nA offset current, 100M input impedance and offset trim capability.

The features of theses operational amplifiers are as follows:

• High Slew Rate...... 120V/ s

• Fast Settling ...... 200ns

• Full Power Bandwidth...... 2MHz

• Gain Bandwidth ...... 20MHz

• High Input Impedance ...... 100M

• Low Offset Current ...... 10nA

• Compensation Pin for Unity Gain Capability

The typical applications are:

• Data Acquisition Systems

• RF Amplifiers

• Video Amplifiers

• Signal Generators

Based on the above features, the HA2-2522-2 operational amplifier has been selected to amplify the modulated signal. The amplified signal looks as shown in the

Figure 4.18.

Figure 4.18: Amplified modulated signal.

This signal is given as the input to transmitting transducer of the setup as shown in Figure 4.16. The attenuation of water causes weakening of the signal and hence a signal of lesser peak-to-peak voltage is drawn at the output and is as shown in the Figure

4.19.

It can be observed that, the signal has a very low peak-to-peak voltage of 54.38 milli volts i.e., approximately 0.054 V. Also, the signal’s shape is not just a replica of the amplified modulated signal. The shape of the output signal at the receiving end transducer obtained is due to the reflections in the transmission medium which is water in this case. This amplitude of the signal is not greater than the forward drop voltage (0.3 V) 43

Figure 4.19: Output signal at the receiving transducer. of the germanium diode used in the envelope detection circuit as shown in Figure 4.20.

Thus, before the signal is demodulated using the envelope detection circuit, it is amplified. The amplification is carried out with the same operational amplifier i.e., HA2-

2522-2 and the output signal after the amplification is as shown in the Figure 4.21.

Figure 4.20: Envelope detection circuit.

It can be observed from the Figure 4.21 that the signal has a peak-to-peak voltage of 1.437 volts which is higher than the forward voltage drop (0.3V) of the germanium diode.

Figure 4.21: Amplified signal generated at the end of the transducer setup.

This signal is fed to the envelope detection circuit and the demodulated signal is as shown in the Figure 4.22.

It can be observed that the demodulated signal has a similar frequency (1 KHz) compared to the message signal while the amplitude of the signal is attenuated in the transmission medium.

Figure 4.22: Demodulated signal (Signal at the output of the Envelope detection circuit).

Thus, the proposed communication system essentially transmits a square wave signal with a frequency of 1 KHz through water for a distance of 25 cm.

4.3 Equipment Details

This section gives brief description of the equipment and their specifications used in the research study. The equipment used is as follows.

4.3.1. 3311A Function Generator

4.3.1.1. Description

The 3311A function generator is used to generate a 1 KHz square wave acting as a message signal and is then fed to the modulation circuit. This function generator used for the research study offers a wide functional capability and is as shown in Figure 4.23. This compact unit has seven decades of range from 0.1 Hz to 1 MHz. Pushbutton range and function selection adds convenience to versatility. Added features normally not found on function generators in this price range are 10:1 voltage control and separate pulse output suitable for synchronization or driving TTL logic circuits.

Figure 4.23: 3311A function generator.

4.3.1.2 Specifications

Waveforms: sinusoid, square, triangle, and positive pulse.

Frequency range: 0.1 Hz to 1 MHz in seven decade ranges.

Dial accuracy: ±5% of full scale.

Sine wave total harmonic distortion: < 3% (maximum output amplitude).

Triangle linearity: deviation < 1% from best straight line at 100 Hz (maximum output amplitude).

Square wave transition time: rise time: < 100 ns; fall time: < 100 ns.

4.3.1.2.1 Pulse Output

Output amplitude: > 3 V positive (open circuit) TTL compatible.

Duty Cycle: 13.5 % to 16.5 % of the total period.

Transition times: < 25 ns

4.3.1.2.2 External Frequency Control

VCO range: > 10:1 on any frequency range.

Input requirement: with frequency dial set to 1.0, a linear ramp of 0.0 V to -10 V ± 2V will linearly increase frequency > 10:1.

Input impedance: 10 K Ω ± 10% in parallel with < 60 pFd.

CHAPTER V

ANALYSIS AND CONCLUSION

5.1 Analysis of Ultrasonic Wave Propagation through Water and Steel

The analysis of propagation of ultrasonic waves through water and carbon steel is discussed in this section.

5.1.1 Ultrasonic Wave Propagation through Water

The setup for this experiment is similar to the setup shown in Figure 4.16. The

Wavetek 2 MHz function generator was used to produce a square wave signal with certain amplitude. Two sets of readings were taken. The voltage at the end of the demodulator was noted for Table 5.1 and Table 5.2 when the input message signal’s voltage and the input carrier signal’s voltage were varied. In one set of readings the amplitude of the message signal was kept constant while in the Table 5.2, the amplitude of the carrier signal was kept constant. Table 5.1 shows the readings when the amplitude of the 1 KHz input message signal was kept constant at 15 volts and the output voltage at the end of the demodulator is obtained by varying the amplitude of the 2 MHz carrier signal. The second set of readings are listed in Table 5.2 where the amplitude of the 2

MHz input carrier signal was kept constant at 20 volts and the output voltage values are obtained by varying the amplitude of the 1 KHz input square wave.

The graphs corresponding to Table 5.1 and Table 5.2 are plotted in Figure 5.1 and Figure

5.2 respectively.

Table 5.1: Output voltage at demodulator Vs. amplitude of carrier signal.

2Mhz input sine v oltage in volts Output v oltage at demodulator in mV

19 750

18 556

16 350

14 231

12.8 160

12.2 100

11.2 40

6.8 21

3.6 15

800 700 600 500 400 300 200 100

Voltage at demodulator mV in demodulator at Voltage 0 0 5 10 15 20 Amplitude of 2 MHz carrier signal

Figure 5.1: Voltage at demodulator Vs. Amplitude of carrier signal.

Table 5.2: Output Voltage at demodulator Vs. amplitude of message signal.

1K Hz input Square Voltage(Varied) Output Voltage at demodulator in mV

18 650

15 638

11.2 368

8.8 243

8 162

7.8 112

7.2 45.63

700

600

500

400

300

200

100 Voltage at demodulator mV in demodulator at Voltage 0 0 5 10 15 20 Amplitude of 1 KHz message signal

Figure 5.2: Voltage at demodulator Vs. Amplitude of message signal.

From Figure 5.1 it can be seen that the voltage at the end of the demodulator is almost negligible until an input voltage of approximately 11 volts is applied for the carrier signal.

After 11 volts the output voltage can be seen varying directly proportional to the amplitude of the carrier signal input voltage.

From Figure 5.2, it can be seen that the voltage at the end of the demodulator increases proportionally to the amplitude of the message signal till approximately 10 V and then levels off as the voltage is increased at the input.

5.1.2 Ultrasonic wave propagation through steel rod

Ultrasonic wave propagation through steel rod was considered because the pipes carrying the petroleum were made up of steel. For this experiment, a square rod of section 25mm X 25mm was used. One of the transducers was powered by an alternating signal of 2.1 MHz.

5.1.2.1 Shear waves

For this experiment, one transducer is set at the end of the rod and the other transducer is kept moving on the side.

Figure 5.3: Steel rod with transducers set on two different sides.

The result is a very low signal. When the transducers are side by side (0 cm), the signal is 6 mV. Then it decreases and after few centimeters the output signal is only noise.

If the two transducers are set on the same side the result is different.

Figure 5.4: Steel rod with transducers set on the same side.

The output signal is higher. It might be because there is not only shear waves but also longitudinal waves which reflex on the side.

50 45 40 35 30 25 20

Voltage (mV) Voltage 15 10 5 0 0 5 10 15 20 25 Distance from transducer 1 center to transducer 2 center (cm)

Figure 5.5: Voltage variation with distance using the configuration of Figure 5.4.

From the Figure 5.5 it can be observed that the signal decreases as an exponential.

5.2 Conclusion

The analysis of ultrasonic data communication through different media like water and steel rods is done and it is observed that amplitude modulation efficiently transmits a square wave signal of 1 KHz frequency by using a carrier signal of 2 MHz frequency through water with some attenuation.

The research carried out could well be implemented for petroleum since the attenuation and velocity properties of water and petroleum are quite similar. Also, other modulation techniques like frequency and phase modulation can be implemented to transmit the data through petroleum.

REFERENCES

[1] Dr L. Bergmann, “Ultrasonics and their Scientific and Technical Applications,” London: G. Bell and Sons Ltd., 1938

[2] International School of Physical Acoustics, “Ultrasonic Signal Processing,” World Scientific N.J, 1988

[3] J.G. Speight, “The Chemistry and Technology of Petroleum,” 2007

[4] www.kayelaby.npl.co.uk/general_physics/2_4/2_4_1.html, Dated 10-20-2009

[5] F. Jensen, W. Kuperman, M. Porter, H. Schmidt, “Computational Ocean Acoustics,” (Springer, New York, NY), pp. 11-12 and 52-54, 2000

[6] C.S. Clay, H. Medwin,” Acoustical Oceanography: Principles and Applications,” (John Wiley & Sons, New York, NY), pp. 88 and 98-99, 1977

[7] M. Porter, et al, ”The Kauai Experiment,” in High Frequency Ocean Acoustics, Eds. M. Porter, M. Siderius, and W. Kuperman, American Institute of Physics, pp. 307 – 321, 2004

[8] P.H. Dahl, “Forward scattering from the sea surface and the van Cittert-Zernike theorem,” J. Acoust. Soc. Am., 115(2), pp. 2067-2080, 2004

[9] J. Preisig, G. Deane, “Surface wave focusing and acoustic communications in the surf zone,” J. Acoust. Soc. Am., vol. 116(4), pp. 2067-2080, 2004

[10] S.O. Harrold, D Z Liao and L F Yeung, “Ultrasonic Data Communication Along Large Diameter Water-Filled Pipes,” Proceeding of the IEEE 2 nd Conference on Mechatronics and Machine Vision In Practice, Hong Kong, pp.239-244, Sept. 1995

[11] M. Stojanovic, “Recent Advances in High-Speed Underwater Acoustic communications,” IEEE Journal of Oceanic Engineering, Vol. 21, No. 2, pp.125-136, April 1996

[12] I.F. Akyildiz, D. Pompili, T. Melodia, “Underwater Acoustic Sensor Networks: Research Challenges,” pp.257–281, 2005

[13] J. Zhang, Z.Huang, X. Liu, “Acoustic Communication in Wireless Sensor Networks,” In: CS651, Wireless Sensor Networks, pp. 1–8, December 2005

[14] Long, R., Vine, K., Lowe, M. J. S. & Cawley, The effect of soil properties on acoustic wave propagation in buried iron water pipes. Review of progress in quantitative nondestructive evaluation, vol. 21B, pp. 1310-1317. New York: American Institute of Physics, 2003