SYSTEM IDENTIFICATION AND ADAPTIVE SELF-TUNING CONTROL FOR

IMPRESSED CURRENT CATHODIC PROTECTION SYSTEM

EZZ ELDIN BALLA MOHAMED HUSSEIN

A project report submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Electrical - Mechatronics & Automatic Control)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JANUARY 2013

iii

Dedicated to the entire BALLA’s

And to all those that believed in me

iv

ACKNOWLEDGEMENT

First and foremost, my unlimited and sincere appreciation goes to the Lord of

the seven heavens and earth ALLAH (SWT) for His endless mercies, blessings and

guidance through from birth till now and forever. Alhamdullahi Rabi Alalmin.

I shall forever be grateful to my beloved parents, brothers, sisters, their

families and especially my big brother Tayallah Balla and his family for their belief

in me even when I did not and for their unending support, financially; morally,

spiritually and emotionally. To them I am highly indebted and words alone cannot

describe my gratitude. I pray ALLAH (SWT) make you reap the fruit of your labor

with me, Jazakum Allahu Khyran.

My sincere appreciation also goes to my supervisor Prof. Dr. Mohd Fua'ad

Rahmat for his continued guidance, support and encouragement to ensure this work

is a success. And also I would like to thank all my lecturers, friends and classmates in

UTM.

Finally, my earnest appreciation also goes to all my friends, colleagues and

well wishers that contributed to the success of this study. To you all I say thank you

for all support, kindness and your love.

v

ABSTRACT

Pipeline infrastructure has become a very popular tool for transferring and

distributing oil, gas and raw materials. Many of these pipelines extend along

hundreds of miles and pass through remote, harsh and corrosive areas. This raises the

prospect of cracks in their walls and cause leaks. In case of pipelines fail due to

corrosion resulting in leakage, they will often lead to loss of products followed by

environmental and financial damages on a national scale. Therefore, protecting

materials and structures against corrosion is a significant issue especially in tropical

countries such as Malaysia which has high humidity climate (corrosiveness factor).

This latest, promotes the need for specialized research to be done for preventing

corrosion. Consequently, in this study we have focused on the most practical method

of cathodic protection systems which is impressed current cathodic protection

(ICCP) system. This system is widely used to prevent the external corrosion of

carbon steel structures; especially those are used in underground pipelines. Basically,

in this project the theoretical background and the concepts of ICCP systems have

been discussed. An effective laboratory scale for ICCP systems was built according

to specific concepts has been clarified. Then, parametric model of ICCP systems was

obtained using system identification approach. Furthermore, to enhance the

performance of ICCP systems, proportional-integral (PI) and direct self-tuning

generalized minimum variance (ST GMV) controllers have been designed.

Additionally, simulation and experimental works have been carried out to control

ICCP systems at different operating conditions. Finally, the ST GMV controller leads

to improve the system speed response and to decrease the integral of absolute error,

which is lower value compared to close loop using PI controller.

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ABSTRAK

Infrastruktur paip telah menjadi peralatan yang penting untuk memindah dan

mengedarkan minyak, gas dan bahan-bahan mentah. Kebanyakkan paip-paip ini

dipasang diunjurkan jauh sehingga beratus-ratus kilometer. Ada diantara paip-paip

ini melalui kawasan-kawasan pedalaman, termasuk juga kawasan yang berdepan

dengan hakisan. Ini meningkatkan kemungkinan berlaku retakan dan seterusnya

kebocoran. Sekiranya kegagalan sistem perpaipan ini adalah disebabkan oleh hakisan

yang disebabkan oleh kebocoran, ini selanjutnya akan mengakibatkan kerugian

produk, dan kerosakan alam sekitar juga termasuk peningkatan dalam kerugian kos

pada skala peringkat kebangsaan. Oleh yang demikian, bagi negara tropika seperti

Malaysia yang mana iklimnya panas dan lembap, keperluan untuk melindungi

material dan struktur daripada hakisan adalah amat penting. Dalam kajian ini, fokus

kami adalah menggunakan kaedah yang paling praktikal dalam sistem perlindungan

katod, iaitu sistem perlindungan katod arus teruja (ICCP). Sistem ini digunakan

secara meluas untuk mengelakkan hakisan luaran oleh struktur keluli karbon;

terutamanya untuk perpaipan didalam tanah. Pada asasnya, didalam projek ini, latar

belakang teori dan konsep sistem ICCP telah dibincnagkan.satu makmal efektif

untuk sistem ICCP telah dibina berdasarkan konsep tertentu telah dijelaskan.

Kemudian, model parametrik sistem ICCP telah diperolehi dengan menggunakan

sistem pengenalan identiti. Tambahan pula, untuk meningkatkan prestasi sistem

ICCP, pengawal penalaan perkadaran dan penalaan kamiran (PI) juga penalaan diri

langsung dengan varians minimum umu (ST GMV) telah direka. Akhirnya, ST GMV

pengawal mampu memperbaiki kelajuan tindak balas sistem dan mengurangkan

kamiran kesilapan mutlak, yang merupakan nilai yang lebih rendah berbanding

menggunakan pengawal PI gelung tutup.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xiii

1 INTRODUCTION

1.1 Introduction 1

1.2 Background of Study 1

1.3 Significance of Study 3

1.4 Problem Statement 4

1.5 Project Objectives 4

1.6 The Project Scope 4

2 LITERATURE REVIEW

2.1 Introduction 6

2.2 Corrosion Principles and Mechanisms 7

2.2.1 Corrosion Process 7

2.2.2 The Corrosion Cell 8

2.2.2.1 Anode 8

viii

2.2.2.2 Cathode 9

2.2.2.3 Electrolyte 10

2.2.2.4 Metallic Path 10

2.2.3 Corrosion of Underground Pipelines 11

2.2.3.1 Uniform Corrosion 11

2.2.3.2 Pitting Corrosion 12

2.2.3.2 Corrosion Due to Dissimilar Metals 13

2.3 Cathodic Protection Principles and Technique 14

2.3.1 Sacrificial Anodes Cathodic Protection 15

2.3.2 Impressed Current Cathodic Protection 16

2.4 Criteria of Cathodic Protection 18

2.4.1 On-Potential Criteria 19

2.4.2 Off-Potential Criteria 20

2.4.3 Potential Shift Criteria 20

2.5 ICCP Systems Controllers Overview 20

2.5.1 Classical Controllers 21

2.5.2 Fuzzy Logic Controller 21

2.5.2 Neuro-Fuzzy Logic Controller 22

2.6 Adaptive and Self-tuning Control 23

2.6.1 Indirect Self-Tuning Algorithm 24

2.6.2 Direct Self-Tuning Algorithm 25

3 RESEARCH METHODOLOGY

3.1 Introduction 26

3.2 Concepts for Lab-Scale Design to Model ICCP Systems 28

3.3 Experimental Setup 29

3.4 ICCP System Identification Modeling 31

3.5 ST GMV Controller Design 32

3.4.1 Recursive Least Squares Parameters Estimation 32

3.4.2 GMV Control 33

3.4.3 ST GMV Algorithm 35

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4 RESULTS AND DISCUSSION

4.1 Introduction 36

4.2 ICCP Systems Lab-Scale 36

4.3 Modelling of ICCP Systems 39

4.3.1 Preparation to Identification and Data Acquisition 39

4.3.1.1 Finding the Sampling Time 39

4.3.1.2 Input signal for System identification 40

4.3.2 Experimental Setup and Data Acquisition 41

4.3.3 Model Structure Selection 45

4.3.4 Model Estimation and Validation 46

4.3.4.1 Choosing the Best Model 46

4.3.4.2 ICCP Model Residuals 48

4.3.4.3 ICCP Model Properties 48

4.3.4.4 ICCP Model Structure 49

4.4 ICCP System Control Design 51

4.4.1 PI Controller 51

4.4.2 Direct ST GMV Controller 53

4.4.3 ICCP System Controllers Comparison 60

4.4.3.1 Simulation Results 60

4.4.3.1 Experimental Results 61

5 CONCLUSION AND FUTURE WORKS

5.1 Conclusion 63

5.2 Future works 64

REFERENCES 65

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LIST OF TABLES

TABLE NO. TITLE PAGE 4.1 Chemical composition of the carbon steel 38

4.2 Chemical composition of the cast iron 38

4.3 Parameters in Simulink 52

4.4 The comparison of simulation and experimental PI Controller 53

4.5 Parameter values of ICCP model and GMV controller 56

4.6 The comparison of simulation and experimental GMV Controller 59

4.7 The comparison of simulation PI & ST GMV controllers 60

4.8 The comparison of experimental PI & ST GMV controllers 61

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LIST OF FIGURES

FIGURE NO TITLE PAGE

2.1 The corrosion cell 8

2.2 Uniform corrosion 12

2.3 Pitting corrosion 12

2.4 Corrosion due to dissimilar metals 13

2.5 Galvanic energy series 14

2.6 Sacrificial anodes cathodic protection 16

2.7 Sacrificial anodes cathodic protection 17

2.8 Land-based ICCP system with test post 18

2.9 Steel protection criteria 19

2.10 FLC controller for an ICCP system 22

2.11 Neuro-fuzzy controller for an ICCP system 23

2.12 General structure of STC 24

3.1 Flow chart of the project methodology 27

3.2 Schematic diagram of coating defect 28

3.3 ICCP system with coating defects 29

3.4 General block diagram of ICCP systems lab-scale 30

3.5 System identification approach 31

3.6 General structure of ST GMV control 32

4.1 Components of ICCP systems lab-scale 37

4.2 The final setup of the ICCP lab-scale 38

4.3 The step response of the ICCP lab-scale system 39

4.4 MATLAB/ SIMULINK block diagram for 63 bit PRBS 41

4.5 The experimental setup for data acquisition and control design 42

4.6 The block diagrams for ICCP system data acquisition 43

4.7 ICCP system input and output signals for system identification 44

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4.8 The general structure of ARMAX model 45

4.9 The best fit of all estimated ARMAX models 46

4.10 ICCP model residuals 48

4.11 ICCP model overview 49

4.12 ICCP model structure 50

4.13 The block diagram of the PI controller with ICCP model 51

4.14 The block diagram of the PI controller with ICCP lab-scale 52

4.15 The comparison between simulation & experimental PI Controller 53

4.16 The block diagrams of the ST GMV controller 57

4.17 The parameter estimator block diagram 58

4.18 The GMV controller block diagram 58

4.19 The comparison of simulation and experimental GMV controller 59

4.20 The comparison of simulation PI & ST GMV controllers 60

4.21 The comparison of experimental PI & ST GMV controllers 61

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LIST OF ABBREVIATIONS

CP - Cathodic Protection

ICCP - Impressed Current Cathodic Protection

PHMSA - Pipeline and Hazardous Materials Safety Administration

TR - Transformer Rectifier

NACE - National Association of Corrosion Engineers

DC - Direct Current

AC - Alternating Current

PI - Proportional–Integral

PID - Proportional–Integral-Derivative

FLC - Fuzzy Logic Controller

NN - Neural Networks

ST - Self-Tuning

STC - Self-Tuning Control

MV - Minimum Variance

MVC - Minimum Variance Control

GMV - Generalized Minimum Variance

RLS - Recursive Least Square

RE - Reference Electrode

CCSRE - Copper/Copper Sulfate Reference Electrode

DAQ - Data Acquisition Card

PC - Personal Computer

SISO - Single Input Single Output

PVC - Polyvinyl Chloride

PRBS - Pseudo Random Binary Sequence

GUI - Graphical User Interface

ARX - Auto-Regressive with Exogenous Input

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ARMAX - Auto-Regressive Moving Average with Exogenous Input

OE - Output-Error

BJ - Box-Jenkins

RTCS - Real-Time Control System

PEM - Prediction-Error Method

FPE - Final Prediction Error

TF - Transfer Functions

IAE - Integral of Absolute Error

CHAPTER 1

INTRODUCTION

1.1 Introduction

This chapter discusses about the introduction of the study which is consist of;

background of study, significance of study, problem statement, project objectives,

and the project scope.

1.2 Background of Study

The Materials Corrosion phenomenon has become a global significant

problem. Corrosion weakens strength and cause failure on material. The general

definition of corrosion is dissolution or destruction of a material as a result of

electrochemical reactions with its environment. Most of the materials which undergo

corrosion are metals; hence most of the corrosion definitions have been specified to

metals [1, 2]. However, Mars G. Fontana suggested that all materials including

ceramic, polymer and other non-metallic materials which are contributed into the

corrosion should be taken care as well [3].

Protecting materials against corrosion is a significant issue especially in

tropical countries such as Malaysia which has high humidity climate (corrosiveness

2

factor). The annual cost of corrosion in many countries is very high, for example,

“In the United States the annual corrosion cost is USD$ 40 billion or RM 140

billion” [4]. Therefore, preventing corrosion need to be done onto materials in order

to reduce corrosion rate, so that less materials and money being wasted.

However, the previous mentioned definition of corrosion encompasses all

materials, in this project we have concentrated on metal-corrosion which is linked to

the carbon steel that is used in underground pipelines. In the fact that, soil

corrosiveness varies over a wide range as a result of a variety of the compositions

and solutions. Moreover, there are many factors affect the corrosiveness of the soil

such as resistivity, humidity, chlorides, sulfates, temperature and pH [2].

Several approaches have been used to protect materials against corrosion, for

an instant, coating system, cathodic and anodic protection systems. However,

cathodic protection has a great history back to around two centuries. Sir Humphry

Davy reported in 1824 that “copper could be successfully protected against corrosion

by coupling it to iron or zinc. He recommended cathodic protection of copper-

sheathed ships, employing sacrificial blocks of iron attached to the hull in the ratio of

iron to copper surface about 1:100” [5].

In general, cathodic protection (CP) is a technique has been used for a long

time to prevent metal corrosion by making it a cathode of an electrochemical cell.

This technique is universally used in protecting the external surface of pipelines,

underground storage tanks, ship hulls and sub-sea structures, etc. CP was used

mainly to prevent further corrosion after repair of damaged structures. However,

recently cathodic protection has been incorporated in new constructions in an effort

to prevent corrosion from being started by applying one of its two methods; galvanic

anode or impressed current cathodic protection [6, 7].

In this study, we have focused on the most practical method of cathodic

protection which is known by impressed current cathodic protection (ICCP) system.

This system is widely used to prevent the external corrosion of carbon steel

3

structures; especially those are used in underground oil and gas pipelines. The

corrosion protection will be achieved by using ICCP methods, if the impressed

current is adequate to shift the potential of a metal to a level or protection range at

which corrosion is not occurring or negligible.

1.3 Significance of Study

Billions of dollars of crude oil or natural gas are transferred through a

widespread network of pipelines. These merchandises have to be transported

throughout the world via pipeline networks. It is obvious that modern economy relies

on these networks of pipelines that are distributed over hundreds of miles throughout

many areas around the world. Unfortunately these pipelines run through harsh

environments resulting in many problems. Among those are leakage problems.

“According to the US Department of Transportation Pipeline and Hazardous

Materials Safety Administration (PHMSA), 25% of all pipeline failure incidents

reported in the US from 2002 to 2003 were caused by corrosion (leakage main

cause)” [8].

The consequences of leakage can be more than the financial issues. It can

affect people’s lives and the environment. In the oil industry, these consequences are

more noticeable where leaks in pipelines may cause disastrous consequences that can

last for years. For oil and gas companies, pipeline leaks are one of the major causes

of failure because of their significant length in remote and harsh areas. This latest, is

prompting the need of lots research to be done in order to prevent corrosion.

Therefore, in this study we are focusing on enhancing the performance of the ICCP

in order to build strong system against corrosion to save people life as well as the

environment.

4

1.4 Problem Statement

The potential required for impressed current cathodic protection depends

upon the steel being protected from its environment. Output voltage, depending on

desired reference voltage, needs to be controlled and tuned by transformer rectifier

(TR) units of the CP Stations.

Basically, TR unit with high output voltage requires high performance control

to maintain the correct output voltage. Moreover, applying the classical control or

fuzzy logic control based on trail and error and/or training data for the ICCP systems

have shown significant overshoot and oscillation in the output potential. For thes

reasons, more works regarding the tuning of the output of TR units are needed to

achieve better accuracy and performance.

1.5 Project Objectives

1. To build an effective laboratory scale for the Impressed Current Cathodic

Protection (ICCP) system.

2. To obtain a parametric model for the ICCP system.

3. To design, simulate and experiment self-tuning adaptive controller for an

ICCP systems.

1.6 The Project Scope

The scope of this project is to study the impressed current cathodic protection

(ICCP) system and its concepts in preventing the external corrosion of underground

carbon steel pipelines. Then, experimental works will be carried out to build an

effective laboratory scale for ICCP systems. The system would be used for black box

5

identification so that system identification approach will be used to obtain the

mathematical model which represents the ICCP systems. After that, direct self-tuning

generalized minimum variance control would be used to design an adaptive corrosion

controller for this system as well. Finally, experimental work would be carried out to

test the performance of the designed controller.

65

REFERENCES

[1] Roberge PR., “Handbook of Corrosion Engineering”. New York: McGraw-

Hill, 1 P, 1999.

[2] D. A. Jones, Principles and Prevention of Corrosion, 2nd ed. Englewood

Cliffs, NJ: Prentice-Hall, 1996.

[3] Fontana, Mars Guy. Corrosion engineering. Tata McGraw-Hill Education,

2005.

[4] Koh Yee Rui, “Design of lab-scale impressed current cathodic protection

(ICCP) Model for steel plate buried in soil” UTM Bachelor thesis, 2010.

[5] Uhlig.H.H., Winston Revie .R, “Corrosion and Corrosion Control”, John

Wiley and Sons,1985.

[6] Ford, D .J., Tighe, P .K .and Taylor, S .D., “Dynamic characteristic of ship

impressed current protection system”, Journal of Applied Electrochemistry,

Vol.31, No.5, pp.105-113, 2001.

[7] Glass, G .K .and Hassanein, A .M., “Surprisingly effective cathodic

protection”, Journal of Corrosion Science and Engineering, pp.1-8, 2003.

[8] Z. W. Zhang et al., “Leak detection in transport pipelines using enhanced

independent component analysis and support vector machines,” Lecture

Notes in Computer Science, vol. 3611, pp. 95–100, Aug. 2005.

[9] Trethewey K.R., and Chamberlain J., “Corrosion for Science and

Engineering”, 2ed edition, 1996.

[10] AL-Shareefi, Hussein. Neutral network corrosion control by impressed

cathodic protection. Diss. Dalarna University, 2009.

[11] Unified Facilites Criteria UFC “Operation and Maintenance: Cathodic

Protection System”, January 2003, Circular No .579, U.S .Government

Printing Office, Washington, D.C., 1957.

66

[12] Peabody A .W., “Control of Pipeline Corrosion”, NACE,Houston , Texas ,

1974.

[13] Perez, Nestor, “Electrochemistry and Corrosion” .New York :Kluwer

Academic Publishers,32 P, 2003.

[14] A.B.Chance Company, “Helical Screw Foundation System Design Manual

for New Construction,” Copyright Hubbell, Inc. ., 2003.

[15] Romanoff, M., “Underground Corrosion”, National Bureau of Standards,

Circular No. 579, U.S .Government

[16] Pravitasari, A., “Corrosion in Material of Construction”, The Norwegian

University of Science and Technology, Trondheim, Norway :Springer, ISBN

1-85233-758-3, 2003.www.majarimagazine.com.

[17] Ginzel, R.K .& Kanters, W.A., “Pipeline Corrosion and Cracking and the

Associated Calibration Considerations for Same Side Sizing

Applications:”Eclipse Scientific Products Inc., Williamsford, Ontario,

Canada, VOL 7, NO .07, July 2002

[18] AWWA, “Steel Water Pipe :A Guide for Design and Installation, Manual

M11, 4th ed.”,American Water Works Association, Denver, CO ،.2004.

[19] James B. Bushman, P.E. “Corrosion and Cathodic Protection Theory”,

Bushman & Associates,Inc. Medina, Ohio USA

[20] Control of External Corrosion on Underground or Submerged Metallic Piping

System, NACE RP-01-69, National Association of Corrosion Engineers

[21] Nelson E .E., “An Impressed Current Cathodic Protection Systems Applied

to Submarine”, Corrosion, p.121, June 1956 .

[22] http://www.vinapema.com/Default.aspx?opt=menu&idmenu=57&lang=en ,

23.04.2012.

[23] Stephen K .lower, “Electrochemistry”, Simon Fraser University, 1999,

www.chemi.com.

[24] Donald L .Basham, Kathleen I .Ferguson, Dr .jams W .Wright and Dr .Get W

.Moy, “Design :Electrical Engineering Cathodic Protection”, UFC 3-570-

02N, 16 January, 2004, www.ccb.org.

[25] Norsok Standard, “Cathodic Protection”, m-503, September 1997.

67

[26] Electrical Engineering Cathodic Protection, US Army Corps Of Engineering,

Naval Facilities Engineering Command, Air Force civil Engineering Support

Agency, UFC3-570-02N(16 January 2004

[27] D. A. Jones, Principles and Prevention of Corrosion, 2nd ed. Englewood

Cliffs, NJ: Prentice-Hall, 1996

[28] M. A. Akcayol, 2007. Neuro-Fuzzy Controller Implementation for an

Adaptive Cathodic Protection on Iraq-Turkey Crude Oil Pipeline, Taylor &

Francis, Inc. Bristol, PA, USA.

[29] Akcayol, M. A. 2004. Fuzzy logic controlled cathodic protection circuit

design. Gazi University Journal of Science. `

[30] A. Bicer, T. Koc, D. Altiparmak, E. Hasdemir, A. Asan, M.A. Akcayol, H.

Isik, T. Serter, and N. Eyit, “Rehabilitation of cathodic protection systems

project report,” BOTAS, Turkey, 2002.

[31] Åström, Karl Johan, and Björn Wittenmark. "On self-tuning regulators."

Automatica 9.2 (1973): 185-199.

[32] Hou, Guolian, et al. "Application of self-tuning control based on generalized

minimum variance method in evaporator For ORCS." Advanced Mechatronic

Systems (ICAMechS), 2011 International Conference on. IEEE, 2011.

[33] Hoshino, Ryouta, and Yasuchika Mori. "Self-Tuning Control with

Generalized Minimum Variance Control in Continuous Time Domain."

SICE, 2007 Annual Conference. IEEE, 2007.

[34] Astrom, K.J and B. Wittermark. “Self-Tuning Controller Based on Pole-zero

Placement”, Proc. IEE. Vol. 127. Pp. 120-129. (1980).

[35] Clarke, D.W, and P.J. Gawthrop, “Self-Tuning Controller.”, Proc. IEE. Vol.

122, pp. 929 - 934. (1975).

[36] Kamoun, M. and A. Titli, “Implicit Self-Tuning Control for A class of Large-

Scale Systems.”, International Journal of control, Vol. 49, pp. 713-722,

(1989).

[37] NORSWOKTHY, RiCHAKD. "System Used in Conjunction with Cathodic

Protection." Materials performance (2004).

[38] W.K. Lai, M.F. Rahmat,“Modeling And Controller Design Of Pneumatic

Actuator System With Control Valve"international Journal On Smart Sensing

And Intelligent Systems, VOL. 5, NO. 3, September 2012.

68

[39] M. F. Rahmat1, Sy Najib, “Identification and non-linear control strategy for

industrial pneumatic actuator”, International Journal of the Physical Sciences

Vol. 7(17), pp. 2565 - 2579, 23 April, 2012.

[40] Ramos, MA Paz, EQ-M. Marquez, and Ricardo Fernandez del Busto.

"Generalized minimum variance with pole assignment controller modified for

practical applications." Control Applications, 2004. Proceedings of the 2004

IEEE International Conference on. Vol. 2. IEEE, 2004.