THIN FILM COATING OF GLASS FABRICS FOR RADAR ABSORBING COMPOSITES A Thesis submitted to the Graduate School of Engineering and Sciences of İzmir Institute of Technology in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE in Physics by Mutlu Devran YAMAN February 2015 İZMİR We approve the thesis of Mutlu Devran YAMAN Examining Committee Members: ______________________________ Prof. Dr. Lütfi ÖZYÜZER Department of Physics, Izmir Institute of Technology ______________________________ Prof. Dr. Metin TANOĞLU Department of Mechanical Engineering, Izmir Institute of Technology ______________________________ Assoc. Prof. Dr. Ekrem ÖZDEMİR Department of Chemical Engineering, Izmir Institute of Technology 05 February 2015 ______________________________ Prof. Dr. Lütfi ÖZYÜZER Supervisor, Department of Physics, Izmir Institute of Technology ______________________________ ______________________________ Prof. Dr. Nejat BULUT Prof. Dr. Bilge KARAÇALI Head of the Department of Physics Dean of the Graduate School of Engineering and Sciences ACKNOWLEDGMENTS First of all, I would like to express my deepest gratitude to my supervisor Prof. Lütfi ÖZYÜZER for valuable discussions, endless support and giving me the possibility of carrying out this studies under his supervision. He always gave me a lot of freedom to perform and design my own experiment. I have really enjoyed working in his laboratory. Also, I am indebted to Prof. Metin TANOĞLU for his valuable comments on my thesis. Moreover, I am grateful to the thesis committee member Assoc. Prof. Ekrem ÖZDEMİR for his valuable comments on my thesis. In addition, I am thankful to Prof. Metin TANOĞLU for his permission to use his laboratories during my experimental studies. Furthermore, I am especially grateful to my laboratory colleagues, Adnan TAŞDEMİR, Metin KURT, Serkan KANGAL, Hasan KÖSEOĞLU and Fatime Gülşah AKÇA for their assistance and supporting in my studies. I would like to thank all OZYUZER Laboratory Members for their kindness and creating a nice and funny atmosphere while studying in laboratory. In addition, special thanks to Göksenin BOZDAĞ. Finally, I would like to express my cordially thanks to my family. Of course I am very grateful to my wife, Zeynep Burçin YAMAN and to my son, Ahmet Deniz YAMAN. They are my biggest supporters in my life. This thesis was partially supported by KOSGEB through facilities of TeknoMa Technological Materials Inc. ABSTRACT THIN FILM COATING OF GLASS FABRICS FOR RADAR ABSORBING COMPOSITES By the invention of radio and micro wave range in electromagnetic spectrum, some radar systems were started to use to predict the range, altitude, direction or speed of objects. During the Second World War, the scenario changed significantly and this led to the development of the radar absorbing materials (RAM’s). Then the stealth technology and Radar Cross Section (RCS) terminologies took place in science research area. To reduce of an objects detectability in the radar detection systems, the reduction of the radar cross section play an important role. For absorbing electromagnetic micro waves, radar absorbing materials have been developed and they consist dielectric and magnetic materials that has capacity for absorbing. In order to increase frequency range (bandwidth) of the absorbance, several materials have been already proposed by several researchers. But nowadays, studies on investigating the radar absorbing structures (RAS) using fiber reinforced polymeric composite materials, are becoming popular research field. The purpose of this study is to design, fabricate and characterize RAS’s based on unidirectional E-glass fiber reinforced epoxy resin composites which can absorb microwave within 2-20 GHz frequency range. Several Jaumann design composite structures were manufactured to achieve radar wave absorbance. In this Jaumann structures, we use different designs in terms of different resistive values of sheets and different thickness of composites. In addition to this, we also focused on the different concentration of additives and distance between resistive sheets. Glass fiber / epoxy system were employed as a base structure. Carbonyl Iron powders were used to change permittivity, permeability and intrinsic impedance values of the structure. To functionalize the glass fibers and to make them conductive, surface of them was metalized by using large area planar magnetron sputtering system. These conducting layers act as a resistive sheet within the composite structure. Surface resistances of resistive sheets used in structures show diversity between ≈ 430 ohms and to 30 ohms. iv ÖZET RADAR SOĞURABİLEN KOMPOZİTLER İÇİN CAM ELYAFLARIN İNCE FİLM KAPLAMALARI Elektromanyetik spektrumdaki radyo ve mikro dalga aralıklarının keşfinden sonra, nesnelerin büyüklüğünü, irtifalarını, yönlerini ya da hızlarını belirlemek için bazı radar sistemleri kullanılmıştır. İkinci dünya savaşı sırasında senaryo önemli ölçüde değişmiş ve bu olay Radar Soğurabilen Malzemelerin (RSM’ler) geliştirilmesine yol açmıştır. Bu sebeple görünmezlik teknolojisi ve radar kesiti terminolojileri bilim araştırma alanında yer almıştır. Radar tespit sistemlerinde, nesnelerin tespit edilebilirliklerini azaltmak istiyorsak, radar kesitinin azaltılası bunda önemli rol oynar. Mikrodalgaların soğurulması için, radar emebilen özelliklere sahip dielektrik ve manyetik malzemeler geliştirilmiştir. Emilimin frekans aralığını (bant genişliğini) arttırmak için, bu güne kadar araştırmacılar tarafından birçok malzeme önerilmiştir. Fakat bu aralar, cam elyaf katkılandırılmış polimerik kompozit malzemeler kullanılarak geliştirilen radar soğurabilen yapılar (RSY), popüler araştırma alanı olmaya başlamıştır. Bu çalışmanın amacı, 2-20 GHz aralığındaki dalgaları emebilen, tekyönlü cam elyaf katkılandırılmış epoksi bağlayıcı kompozitlerin tasarım, üretim ve karakterizasyonlarını yapmaktır. Radar dalgası soğurulması için, birçok Jaumann tipi kompozit yapılar üretilmiştir. Bu Jaumann yapılarda, farklı direnç değerine sahip katmanlar kullanılmış ya da farklı kalınlıklarda değişik tasarımlar yapılmıştır. Buna ek olarak, direnç katmanları arasındaki uzaklıklar değiştirilmiş ve farklı derişimdeki katkı maddelerine sahip yapılar üzerinde de durulmuştur. Cam elyaf / epoksi sistemi temel yapı olarak kullanılmıştır. Kompozit yapının elektrik ve manyetik geçirgenlik katsayıları ile empedansının değiştirilmesi için demir karbonil tozları kullanılmıştır. Cam elyafların fonksiyonelleştirilmesi ve üzerlerinin iletken olması için, geniş alan düzlemsel mıknatıssal saçtırma yöntemi kullanılarak yüzeyleri ince film kaplanarak metalize edilmiştir. Bu iletken yüzeyler kompozit yapı içerisinde direnç katmanı olarak davranırlar. Yüzey dirençleri ≈ 430 ohm’dan başlayarak 30 ohm’a kadar çeşitlilik göstermektedir. v To my Family vi TABLE OF CONTENTS LIST OF FIGURES .......................................................................................................... x LIST OF TABLES ......................................................................................................... xiv CHAPTER 1. INTRODUCTION ..................................................................................... 1 1.1. Radar ....................................................................................................... 1 1.2. History .................................................................................................... 3 1.3. Radar Cross Section (RCS) ..................................................................... 7 1.4. Reflectivity Minimization ....................................................................... 8 1.5. Transmission Line Theory ...................................................................... 9 CHAPTER 2. RADAR ABSORBING ........................................................................... 13 2.1. Classification of Radar Absorbing Materials ........................................ 13 Graded Interfaces-Impedance Matching ........................................ 13 2.1.1.1. Pyramidal Absorbers .......................................................... 14 2.1.1.2. Tapered Loading Absorbers ............................................... 15 2.1.1.3. Matching Layer Absorbers ................................................ 15 Resonant Materials ........................................................................ 16 2.1.2.1. Dallenbach (Tuned) Layer Absorber ................................. 17 2.1.2.2. Salisbury Screen ................................................................. 18 2.1.2.3. Jaumann Type .................................................................... 19 Circuit Analog RAM ..................................................................... 19 Magnetic RAM .............................................................................. 22 Adaptive RAM (Dynamically Adaptive RAM) ............................ 22 2.2. Composite Structures ............................................................................ 22 Polymeric Composites ................................................................... 22 Glass/Epoxy Polymeric Composite Systems ................................. 25 Manufacturing Methods ................................................................. 25 Hand Lay-Up with Compression ................................................... 27 vii 2.3. Absorbing Additives in Composite Structures ..................................... 29 Carbon ............................................................................................ 30 Magnetic Materials ........................................................................ 31 Conducting Polymers ..................................................................... 31 Polypyrrole .................................................................................... 32 Polyaniline ..................................................................................... 32 Tubules and Filaments ................................................................... 32 Chiral Materials ............................................................................. 33 2.4. Optimization of Jaumann Type Radar Absorbing Structures ............... 34 Maximally Flat Design .................................................................. 34 Tschebyscheff (Equal-Ripple) Design ........................................... 34 Gradient Methods .......................................................................... 35 Genetic Algorithm ......................................................................... 35 Other Methods (Finite Element, FDTD and Taguchi Methods) .... 36 CHAPTER 3. EXPERIMENTAL .................................................................................. 37 3.1. Materials ............................................................................................... 37 Thin Film Coating with Magnetron Sputtering ............................. 38 3.2. Mathematical Background for Jaumann Type Structure ...................... 41 Construction of Related Equations for RAS’s ............................... 41 LabVIEW Modelling of Jaumann Type RAS ............................... 46 3.3. Fabrication Process of Polymeric Composite Structures ...................... 47 3.4. Characterization of Radar Absorbing Structures .................................. 49 Microstructural Property Characterization .................................... 50 3.4.1.1. Determination of Fiber Weight and Volume Ratio ............ 50 3.4.1.2. Morphological Analysis by SEM ....................................... 51 3.4.1.3. Optical Microscopy Images and Confirmation .................. 51 Mechanical Property Characterization .......................................... 52 3.4.2.1. Tensile Properties of Structures ......................................... 52 3.4.2.2. Flexural Properties of Structures ....................................... 54 3.4.2.3. Compressive Properties of Structures ................................ 55 3.4.2.4. Charpy Impact Strength Properties of Structures .............. 56 viii Absorption Measurement Properties of Structures ........................ 57 CHAPTER 4. RESULTS AND DISCUSSIONS ........................................................... 59 4.1. What We Manufactured ........................................................................ 59 4.2. Electrical Characterization of Fabrics ................................................... 61 4.3. Microstructural Characterization .......................................................... 63 Fiber Weight and Volume Ratio .................................................... 63 SEM Images and EDX Mapping of the RAS ................................ 67 Optical Microscopy ....................................................................... 88 4.4. Mechanical Characterization ................................................................ 90 Tensile Properties .......................................................................... 91 Flexural Properties ......................................................................... 98 Compressive Properties ............................................................... 105 Impact Behaviour ......................................................................... 112 4.5. Radar Absorbing Properties ................................................................ 115 LabVIEW Confirmation .............................................................. 124 CHAPTER 5. CONCLUSION ..................................................................................... 128 REFERENCES ............................................................................................................. 130 ix LIST OF FIGURES Figure Page Figure 1.1. Illustration of electromagnetic wave spectrum .............................................. 2 Figure 1.2. Spectrum of the using RADAR waves ........................................................... 2 Figure 1.3. Examples of first radar applications system ................................................... 7 Figure 1.4. Multi-section transmission line .................................................................... 10 Figure 1.5. Microwave absorbing layer equivalent electric circuit ................................ 11 Figure 2.1. Pyramidal absorber ....................................................................................... 14 Figure 2.2. Tapered loading absorber a and b) stepped type c) combination of a and b d)smooth type ............................................................................................... 15 Figure 2.3. Matching layer .............................................................................................. 16 Figure 2.4. Dallenbach layer ........................................................................................... 17 Figure 2.5. Salisbury Screen ........................................................................................... 18 Figure 2.6. Jaumann Layers ............................................................................................ 19 Figure 2.7. Circuit analog RAM ..................................................................................... 20 Figure 2.8. Examples of patterns for frequency selective surfaces ................................ 21 Figure 2.9. Step by step schematic illustration of RTM process .................................... 26 Figure 2.10. Schematic illustration of Vacuum Infusion process ................................... 27 Figure 2.11. Illustration of Hand Lay-up with compression process .............................. 28 Figure 3.1. Photo of non-crimp E-Glass fabric, (a) front side, (b) back side, used within the study ....................................................................................................... 37 Figure 3.2. Unmodified (top) vs. Metallized (bottom) E-glass fabric ............................ 39 Figure 3.3. Photo of Magnetron Sputtering unit used for metal coating of fabrics ........ 40 Figure 3.4. ITO coated glass fiber fabric image ............................................................. 41 Figure 3.5. Schematic illustration of (a) Dallenbach layer and (b) circuit equivalent .... 42 Figure 3.6. Schematic illustration of (a) Salisbury screen and (b) circuit equivalent ..... 43 Figure 3.7. Schematic illustration of (a) Jaumann absorber with 2 resistive sheets and (b) circuit equivalent .................................................................................... 45 Figure 3.8. Schematic illustration of (a) Jaumann absorber with 4 resistive sheets and (b) circuit equivalent .................................................................................... 46 Figure 3.9. Step by step manufacturing of composites by hand lay-up technique ......... 48 Figure 3.10. Fabricated one Structure ............................................................................. 48 x