UNIVERSITI PUTRA MALAYSIA

FABRICATION AND CHARACTERIZATION OF SOME NiZn-BASED

FERRITE MULTILAYER INDUCTORS (MLIS)

LUCIA LIEW WOAN SHYAN

FSAS 2000 45

FABRICATION AND CHARACTERIZATION OF SOME NiZn-BASED

FERRITE MULTILAYER INDUCTORS (MLIS)

LUCIA LIEW WOAN SHYAN

MASTER OF SCIENCE UNIVERSITI PUTRA MALAYSIA

2000

FABRICATION AND CHARACTERIZATION OF SOME NiZn-BASED FERRITE MULTILAYER INDUCTORS (MLIS)

By

LUCIA LIEW WOAN SHYAN

Thesis Submitted in Fulfilment of the Requirements for the Degree of Master of Science in the Faculty of Science

U niversiti Putra malaysia

September 2000

DEDICATIONS

To

Dear Mom and Dad, brothers and sisters

11

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirement for the degree of Master of Science

FABRICATION AND CHARACTERIZATION OF SOME NiZn-BASED FERRITE MUL Tll,A YER INDUCTORS (MLIS)

By

LUCIA LIEW WOAN SHY AN

September 2000

Chairman: Associate Professor Mansor Hashim, Ph.D.

Faculty: Institute of Advanced Technology

The multilayer inductor is particularly important as a highly stable, easy to use

and miniaturised component in electronic systems, such as radios, VCRs and

computers. There were two main tasks in this research project, one was to

make a proper preparation set-up, and the other was to measure the inductance

and the reciprocal of the Q factor of the multilayer inductors produced. Layers

of ferrite sheets were stacked together with silver layers in between by means

of tape casting method. End metallization was applied to make contact with

the inner conductors. Bulk and multilayered components of the same

dimension were made to undergo parallel conventional sintering. The

experimental work resulted in the complete construction of a tape-casting set­

up. The measured L values were in the range of 10-1 to lOS Henries and L fell

rapidly with frequency from 1kHz to 30MHz. The energy was represented by

111

lIQ ranged from 10-3 to 10 and also fell rapidly within the same frequel\cy

range.

IV

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains.

PEMBENTUKAN DAN PENCIRIAN INDUKTOR PELBAGAI

LAPISAN (MLIS) }'ERIT NiZn

Oleh

LUCIA LIE\V \VOAN SHYAN

September 2000

Pengerusi: Profesor Madya Mansor Hashim, Ph.D.

Fakulti: lnstitut Teknologi Maju

lnduktor multi lapisan adalah penting terutamanya sebagai komponen

berkestabilan tinggi, mudah digunakan dan bersaiz amat kecil dalam sistem

elektronik seperti radio, VCR dan komputer. Ada dua objektif utama dalam

kerja peyelidikan ini. Salah satu daripadanya ialah penyediaan satu set alat

yang sesuai untuk pengeluaran komponen pelbagai Iapisan, manakala yang satu

lagi ialah mengukur induktans dan salingan faktor Q induktor pelbagai lapisan

yang dihasilkan. Lapisan ferit diletakkan berselang-seli dengan lapisan perak

Hujung susunan ini dikemaskan dengan meletakkan lapisan perak untuk

dijadikan konduktor. Toroid dan komponen pelbagai lapisan disinter bawah

keadaan pembakaran selari. Kerja ujikaji ini menghasilkan suatu binaan

lengkap peralatan tuangan-pita. Nilai L yang diukur berada dalam julat 10-1 ke

1 0) henry dan L menyusut cepat dengan frckucnsi daripada 1 kHz to 30MHz.

v

Kehilangan tenaga yang diwakili oleh l/Q berada dalam julat 10-3 ke 10; ia

juga menyusut cepat dengan frekuensi dalam julat yang sarna.

VI

ACKNO\VLEDGEMENTS

First of all, I would like to extend my deepest gratitude to God the Almighty,

for giving me the strength, the faith, the wisdom, the confidence, the courage,

and the helps needed to complete my thesis.

Secondly, I would like to give my greatest appreciation to my dear supportive

supervisor, PM Dr. Mansor Hashim, for his superb supervision, generosity,

patience, endurance, and dedication throughout the whole of this project. Also

not forgetting my supervisory committee members: Dr. Jumiah Bt Hassan and

PM Dr. Salleh Bin Hj. Hamn, and Prof. Dr. Abdul Halim Shaari, the

chairperson of the Examination Committee.

I would also like to thank Dr. M. K Vidyadaran, Mr. Ho Oi Kuan, Miss Azilah

Bt. Abdul Jalil, and all the staff of Dept. of Vet. Sci., UPM, for their help

during my SEM session.

Many thanks also for Khoon, San, Kak Ana, lab mates, and friends, especially

Fanny, for their generous assistance and encouragement, and also the

technicians, Mr. Nordin and Mr. Roslim, and the lab assistants Pak Mat Rasa.

Finally, special thanks to my parents, brothers and sisters, especially Nancy

who has helped a lot, and brothers and sisters in Christ, for praying earnestly

forme.

VII

I certify that an Examination Committee met on 28 September 2000 to conduct the final examination of Lucia Liew Woan Shyan on her Master of Science thesis entitled "Fabrication And Characterization Of Some NiZn-based Ferrite Multilayer Inductors (MLIs)" in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 1981 . The Committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follows:

Abdul Halim Shaari, Ph. D Professor Faculty of Science and Environmental Studies Universiti Putra Malaysia (Chairman)

Mansor Bin Hashim, Ph.D Associate Professor Institute of Advanced Technology Universiti Putra Malaysia (Member)

Jumiah Bt Hassan, Ph. D Lecturer Faculty of Science and Environmental Studies Universiti Putra Malaysia (Member)

Salleh Bin Hj. Harun, Ph. D Associate Professor Faculty of Science and Environmental Studies Universiti Putra Malaysia (Member)

HAZALI-MOHA YIDIN, Ph. D Professor/Deputy Dean of Graduate School, Universiti Putra Malaysia

Date: 2 8 NOV 2000

viii

This thesis submitted to the Senate of Universiti Putra Malaysia has been accepted as fulfilment of the requirement for the degree of Master of Science.

Date: 1 1 JAN 2001

ix

1 hereby declare that the thesis is based on my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UPM or other institutions.

x

LUCT

Date: :2.3 - J' - ;WOO

TABLE OF CONTENTS

Page

DEDICATIONS ... ... ... ... .. , ... ...... '" ., . ... .......... '" ... ... ... .... 11 ABSTRACT ..... , ... ... ... ... . , . ..... , ...... ... ....... '" ., . ..... , '" ... .... 111 ABSTRAK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v ACKNOWLEDGEMENTS ... . . . .. . ... ... ... ............ . . .. . . . ... . . . ... VB APPROVAL SHEETS ... ... .... . . ... ... ... . .. ... ... ... .. . ...... ...... . .... V1l1 DECLARATION FORM ... ... ...... ... ... ... .. . .... ... ... .. . . ..... .. , ... x LIST OF TABLES ... ....... ... ... ... ... ... ....... ... ... ... ... ... ... ... .... XIV LIST OF FIGURES .... ... ........ ... ............ ...... ......... ... ...... ... x"V LIST OF PLATES ..... ... . . . ...... ... ... . .. ... ... ... . . . ... ... ... ... .. , .. XVll LIST OF SYMBOLS & ABBREVIATIONS .... ... ... ...... .......... XVlll

CHAPTER

I INTRODUCTION

Ferrites ., . ...... ... ... ...... ... ... ...... ........... ... ... . ,. 1 Nickel Zinc Ferrite . . . . . . . . , . . ... . . . . . . . . , . . . . . . , . . . . . . . . 2 Some Magnetic Parameters ... ... ...... ... ... ... ........ 2 Mutilayer Inductor ............ ... ... ...... ... ... ... ....... 4 Objectives .. . .. . ... ... . , . ..... , '" ...... ... ........ , ... ... ... 5

n LITERATURE REVIEW

Intr� ... ........ ... ... . .. ... . . . ...... ... ... . .. ... .... 7 "Some Aspects on Ni-Zn Ferrites ..... ... ... ...... ........ 7 Trend in Modem Technology .... , ... ... ... ... ... ... ... ... 9 Multilayer Components ........ ...... ... ... ... ... ... ... ... 10 Configurations and Parameters ... ... ... . ,. ... ... ... ... .... 12

ill SOME BASIC THEORY

Electromagnetic ..... ...... . ..... .. , ...... ... ... . , . ... .. , 15 Definition for B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Magnetic Field Due to Current .. . . .. ... . ... . . .. , . . . . . . . . . 1 6 Current-flow Direction of the Magnetic Field... ... ... .... 17 Inductance ... ... . .. ...... . .. ... ... .... ,. ... ... ... ... ... ..... 19 Power/Energy Relationships for Inductors... . . . . .. . . . 23 Magnetic Flux Density Tn A Multilayer Inductor .... 24 Crystal Structure ofNi-Zn Ferrites ... ... ... ... ...... ..... 26 Ionic Charge Balance and Crystal Structure ...... '" .... 27 Site Preferences of the Ions ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Xl

xii

Interactions Between Magnetic Moments On the Site I..attice ......... ... ... ... ...... ... ... ... ............ ... ... 29

The Magnetic Properties ofFerrites . . . . . . . . . . . . . .. . . . . .. . 31 Intrinsic Properties . . . . . . . . . .. . . . . '" . . . . . . '" . . . . . 31 Extrinsic Properties ... .... .. ... ... . .. ... ... ... . . . . 34

Effect of Grain Size and Porosity on Permeabil ity . . . . . 39

Tape Casting . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . ... . . . . . . . . . 41 Tape Casting Process ... ...... ...... ...... ... ...... ... ..... 42 Skin Depth ... . .... . . ..... . .... . . .. ... .. . .... .... . .. . . .... . .. . , 45

IV SOME BASIC CONSIDERATION ON MULTILAYER

Int rod uction .. . . . . . .. ... .. . ... . . . ... . .. ... .. . .. . .. . ... ... . .. 46 Deflocculant . . . . . . . . , . . . . . . . . . ... . .. .. . ... .. . . . . . . . . .. .. . . . , 47 Sur factant . . . .. , ... . . . . . . . . . .. . .. . ... ... . . . . .. .. . .. . ... . . . . . . 4 7 Binder ..... . . . . . .. . .. ... .. . . . . . . . ... ... ... ... ... . . .. ..... . .... 49 Pla sticize r... .. . . . . .. . . . . . .. .. . ... .. . ... ... . . . . . . .. . . . . ... . . . .. 50 Lubricant . . . . . . . . . . . , .. . . . . . . . .. . . . . . . . . .. . . . . .. . . . . . . . .. . . . . 51 VISCOSIty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Num be r o f Layer s ... . . , . . . . . , '" .. . . . . . , . . . . . , . . .. '" . .. . 53 Wet Laye r Thickne ss . .. ... ... . . , ... ...... . . . ... . " ... . . . .. 54 Control of Cast Defects . . . . . . . . . . . .. . . . . . . . . . . .. . . . .. .. , ... 54

V METHODOLOGY

Introduction .. . ... . .. ... .. . . . . . . , . . . . , . ... '" ... . . . ... ... .. 56 Experiments . .. ... ... ........... . .. . ......... ... . . . .. . . . . .. 59

Two Stage-milling .... .. ...... ...... .. , . .... , ... 60 Weighing . . . . . . . .. . . . . . ,. . .. . . . . . . ... .. . ... .... . . . 60 Mixing . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . , . ... 61 . Pre-smtenng . .... . ... .. . '" . .. . . . ... . . . . . . . .. . .. .. . 62 Add ition of ZnO , Bi nde r and Lu bricant ... . .. . 62 Crushing and Sieving . . . . . . . . . . . . . . . . . . . . . ... . . . . 63 Forming . . . . . . . .. . . . ... . . . . . . . . . .. . .. . . . . . . . . . . . . . . 64 Sinte ring . ... . ... . . .. .. . . .. . . . . . . . . . . . . . . , .. . .. . . . . 66

VI RESULTS AND DISCUSSION

Introduction ' " .. . . . . . . . . . . . . ... ... .. . ... . .. ... ... . .. . . . .. . . 68 Experimental Set-up .. . . .. . . . . . . .. . . . . . . . . ,. ... ... . .. .. . . 68 Rheology of Slurry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , '" .. . .. . 69 Electrical Analysis of Inductance and Loss Factor

l/Q . . . . . , '" .. , ... ... ... . ,. '" .,. ... ... ... ... ... .... ..... 70 Microstructure Analysis . .. . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . 80

Xli

VII CONCLlJSION AND SUGGESTIONS

Conclusions Suggestions

87 88

BffiLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . 90 APPENDIX A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 APPENDIX B . . . . . . . . . . . . . . . . .. . . . . .. . . . ... . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . 97 APPENDIX C '" .. , ... ... ... ... ...... ...... ... '" ... ... ... ...... '" ... ... ... . 98 VITA '" ... '" ........ , ... '" ...... ..... . ......... ... ...... ... ... ...... '" '" .... 99

xiii

LIST OF TABLES

Table

2. 1 Some diment ions of multilay er induct ors manufact ured

Page

by AEM ,Tn c. . . . . . . ... ... ... ... ... ... ... ... ... ...... ...... ... ... ...... 12

2.2 S ome Feat ures of Mult ilay er In duct ors Man ufact ured by AEM,ln c. ... .. . . . . . .. . . . ... .... . .... ..... . .. . ... ......... ... ...... 13

2.3 S ome Diment ions of Mult ilay er Ind uct ors Man ufact ured by TO KO . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . ......... ... ...... ... 13

2.4 S om e Featu res of M utt itay er In duct ors Manufact ured by TO KO .. . . .. . . . . . . .. . .. . . . . .. . . ... . . . . . ... . . . . . . . . .. . .. . .... ... . . . . 13

2.5 Som e Dim en tions of Multilay er Inducto rs Manu factu red by TRIGON CO M PO NEN TS. .. . . . ... .. . . . . .. . .. . .. . . . .... .. . .. . 14

2.6 S om e Feat ures of Multilay er In ducto rs Ma nu factu red by TRIGON CO MPON ENTS. .. ... .. . . . . . . . . . .. . . .. . . . .. . . . . . .. . 14

3 .1 Si te Pr eferenc e and Ma gnetic Mom ent for Som e Metal Ion s.. . 29

4.1 S om e Comm on Plas ticiz er .... . . . .. .. . ... . . . '" . . , . .. . ..... ........ , 5 1

4.2 Comm on Lu bricants . . . . . , ... ... .. . . . .. . . . . .. . . ... . . . .. ... . .. . .. .. . .. 53

S. l Stag e I o f the Two Stag e-m illing . . . . . . .... . _ _ . . .. . _ _ . . . . . . _ _ . .. . .. 60

5.2 Sta ge IT o f the Two Sta ge-millin g .. . ....... . , .... . .. . . . .. . .. ... . ,. 60

XlV

LIST OF FIGlJRES

Figure Page

3.1 Magnetic Field Pattern of a Single and Long-straight Wire... . .. . 16

3.2 Magnetic Field Pattern of a Current Flowing Through a Planal Round-turn . . . . . , '" ... '" ... ... ... .. , '" .. , ... ......... .. , ... ... . 17

3.3 Magnetic Field Pattern of a Long-solenoidal Wire... ... ... ... ... .. 18

3.4 The Magnetic Field, B, set up by a Current i in a solenoid ... '" .... 20

3.5 Circuit Symbol For An Inductor, Along With Associated Reference Direction For Current and Voltage .... , . ........... , ... ... 22

3.6 Construction of A Multilayer Inductor... ... ... ... ...... ... ... ...... 25

3.7 Current Flow Along AB Direction in Fig 3.6... ... ... ... ... ... ..... 25

3.8 Magnetic-flux Density Configuration of A Multilayer Inductor Cross-sectional Area ...... .. . . , .......... ......... ... .. , ... " . . .. ... ... 26

3.9 Crystal Lattice of Spinel Structure ..... , ... ........... , ... ... ... ... ... 28

3.10 Ferrimagnetism; (a) antiparallel alignment of moments of two sublattices, (b) the net magnetic moment of the lattice. .. . . . . . . ... . . . 30

3.11 Magnetization Curve of a Material with Magnetic Anisotropy.... 32

3.12 . Schematic of Continuous Tape Casting Apparatus ... ......... '" '" 44

4.1 Structure of a surfactant molecule and its oriented adsorption at water-oil and water-air interface ... . .. ......... ... '" .. , 49

4.2 Molecular Structures of Hydrocarbon Chain and Fully Hydrolyzed Polyvinyl Alcohol ... ... ..... , '" ... ... ... ... ... ... 50

5.1 HP16334A test Fixture ... ... ...... ... ... ... '" ... ... ... ... ... ... ... .... 58

5.2 Experimental Flow Chart......... ... ............ ... ... ...... ... ........ 59

6.1 Schematic of Tape Casting Apparatus... . .. ... ... ... ... ... ... ... ... ... 69

6.2 Graph Inductance, Lp, Versus Frequency of Sample 102,202,302 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . '" '" ... ... 71

xv

6.3 Graph Lp Versus Co-firing Temperatures of Sample 102,202, and 302 at Frequencies 10kHz, 50kHz, and 100kHz ........... , '" 71

6.4 Graph Lp Versus Particle Size of Sample 102,202, and 302 at Frequencies 10kHz, 50kHz, and 100kHz ... ...... . .. ... . ' . .. 72

6.5 Graph lIQ Versus Frequency of Sample 102 ... . ,. '" .. , '" ......... 73

6.6 Graph 1/Q Versus Frequency of Sample 202 ... ...... .. , . , . ' " .. , ... 74

6.7 Graph lIQ Versus Frequency of Sample 302... ... ... ... ... ... ...... 74

6.8 Graph lIQ Versus Frequency of Sample 102,202, and 302... ... . 75

6.9 Graph lIQ Versus Co-firing Temperatures of Sample 102,202, and 302 at Frequencies 10kHz, 50kHz, and 100kHz ........ , .,. .... 76

6.10 Graph l/Q Ve rsus Particle Size of Sample 102, 202, and 302 at Frequencies 10kHz, 50kHz, and 100kHz ... ...... ... '" ... . 76

6.11 Graph Inductance, Lp Versus Frequency of Sample T002... ... . 78

6.12 Graph l/Q Versus Frequency of Sample T002... ... ......... ... .... 78

6.13 SEM Photo Shows the Microstructure of Top Ferrite Layer Before Final Co-firing ... . ..... ... .. . ... ... '" ...... '" ... ... ... ... ... ... ... ... ... . 80

6.14 (a), ( b) and (c) Shows the SEM Microstructure of Ferrite Layer Co-fired at 620°C/8h . . . . . . . . . . . . ... . . . . . . . . . ... ... . . . ... ... . . . ... ... ... ... 80

6.15 SEM Photo Shows the Microstructure of Ferrite Layer Co-fired at 600°C/8h ... '" ............ ... '" ......... ...... ... ... '" ...... '" ... ..... 83

6.16 (a), (b) SEM Photo Shows the Microstructure of Ferrite Layer Co-fired at 55 0°C/8h ... ... ... ... ... ... '" ... ... ... ... ... ... ... ..... 83

6.17 SEM Photo Shows the Imperfections Between Silver and Ferrite Layer. ................. ......... ..... , ... ... ... ............... ... '" 85

6.18 SEM Photo Shows the Silver End-termination of the Multilayer Inductor. .. ... . . . ... ... ... ... .. . ... ... ... ... ... .. . ... ... .. . ... ... ... ... ... . 85

XVI

LIST OF PLATES

�� h�

5. 1 Electronic Analytical Balance . .. .. . .. .. .. .. .. , ....... ...... '" ... ... .... 61

5.2 Siever and Crusher. . . . . . . . . '" '" ..... , ... '" .. , ... '" '" ... .. , ... '" ... .. 64

5.3 Mould . . . . . . . . , . . . . . . . . . . . . ' " ' " . . . . . , . . , . . . . . . . . . . . . . . . . . . . . . . . . . . , .. , ..... 65

5.4 Pressing Machine ... '" ... .. , .. , .. , ., . ......... ... ... '" '" ... . ,. '" ... ... 65

5.5 Electric Furnace .. . . . , .. , '" .. , ... '" '" ... . .. ...... '" ... ... ... ... ... ... ... 67

xvii

LIST OF SYMBOLS AND ABBREVIATIONS

A cross sectional area

B induction

Bs saturated induction

Di inner diameter

Do outer diameter

f frequency

h hour

H applied field

He coercive force

HK saturated anisotropy field

K anisotropy energy

L inductance

L/J length

Ms saturation magnetisation

N number of wire turns

PYA polyvinyl alcohol

Q quality factor

RLF relative loss factort

tan B loss tangent

T thickness

XVIII

W width

XRD X-Ray Diffraction

� magnetic moment

�B Bohr magneton

J..1,) permeabil ity of free space

J..l permeability

J..li initial permeability

�' real part of permeability

J..l" imaginary part of permeability or magnetic loss

p resistivity

y Gyromagnetic ratio

ill angular velocity

a internal stress

A magnetostriction

XIX

CHAPTER I

INTRODUCTION

Ferrites

Ferrites are magnetic ceramic materials, containing mostly iron which is derived

from Fe2+O.Fe;+. 03 , and mix with other oxides and carbonates in powdered

form, arranged in such a manner to produce spontaneous magnetisation (Gerald,

1975� Standley, 1972� Crangle, 199 1). There are soft ferrites as wen as hard

ferrites. Soft ferrites become magnetised by relatively low-strength magnetic

field When the applied field is removed, they returned to a state of relatively low

residual magnetism, whereas hard ferrites need high magnetising field and high

remnant magnetism to become magnetised. Since the pioneering works of Snoek

(1936) and Takei (1939), a very large number of studies have been published by

other ferrite scientists, and have generated a wide range of technological

applications (Snelling). In recent years, the rapid developements in the electronic

and electric industries, have created even larger and dynamic changes on the

demands for the uses of ferrites.

Ferrites are ferrimagnetic materials which have domain structures and hysteresis

loops, similar to those of ferromagnetic materials. They have three distinct

crystal structures: the hexagonal magnetoplumbite, dodecahedral garnet and the

spinel structure (Crangle, 1991� Standley, 1972). Hexagonal magnetoplumbite is

a hard ferrite structure, dodecahedral garnet and the spinel are soft ferrite

2

structures. Soft ferrites are used for applications in which the material must be

easily magnetised and demagnetised such as cores for power transformers, small

electronic transfonners etc. On the other hand, hard magnetic materials are used

for applications requiring pennanent magnets which do not demagnetise easily

such as the pennanent magnets in loudspeakers, telephone receivers, and

automotive starting motors. Anyway, it is the soft ferrites that are of concern in

this research project.

Nickel Zinc Ferrite

The type of ferrite which is used in this research work is Nickel Zinc (NiZn)

ferrite. It was developed for a wide range of applications where high

penneability and low loss were the main requirements. NiZn ferrite is still one of

the most important ferrites for such applications and constitutes a substantial

portion of present day soft ferrite production. NiZn ferrites have been extensively

used as core materials for large number of devices and electrical components such

as inductors, transfonners, antenna rods etc.

Some Magnetic Parameters

One of the most important pammeters in magnetic materials evaluation is the

permeability. Permeability is an extrinsic property and can be defines as ratio of

induction, B to the magnetizing field H.

3

B 1-1=-H

Permeability can also be written in complex form, where the real part f.l' showed

the energy stored, expressing the component of B in phase with H and the

imaginary part ll" indicating the energy dissipated, expressing the component of

B out of phase with H.

The permeability concept can be extended to include the losses. For time

hannonic fields,

H = Hoexp(joot)

where 00 is the angular frequency and t is the time. The dissipation can be

described as the phase difference between H and B, o. In the complex notation,

the frequency dependency of permeability becomes

ll(W) = B exp j(id +0) H exp(ja>t)

which would give us, again,

4

where J.1" can actually be obtained from the relation

ll" = �l' tan 0

Permeability can not only be influenced by the chemical composition and

crystal structure, but is also strongly dependent on microstructure, temperature,

stress and time after demagnetization.

Multilayer Inductors

"Multi _" comes from the word "multiple" which means having many parts or

elements, or a quantity which contains another quantity an exact number of times

as we use in mathematics.

Multilayer chip inductors were introduced in 1987 and soon became the inductive

components of choice for many design engineers. For example, Toko, a Japanese

company, introduced the first microminiature multilayer chip inductor LL2012 in

the year 1992. And soon it became the inductive components of choice for many

design engineers.

Multilayer technology offers three advantages:

I. Monolithic structure which is good for high reliability

2. Magnetic shielding which is excellent for very high density applications

3. Low mounting cost as multilayer (chip) inductors do not require winding