The Pennsylvania State University The Graduate School Department of Electrical Engineering ANISOTROPIC METAMATERIALS FOR MICROWAVE ANTENNAS AND INFRARED NANOSTRUCTURED THIN FILMS A Dissertation in Electrical Engineering by Zhihao Jiang 2013 Zhihao Jiang Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2013 The dissertation of Zhihao Jiang was reviewed and approved* by the following: Douglas H. Werner John L. and Genevieve H. McCain Chair Professor of Electrical Engineering Dissertation Advisor Chair of Committee Theresa S. Mayer Distinguished Professor of Electrical Engineering Pingjuan L. Werner Professor of Electrical Engineering Brian Weiner Professor of Physics Kultegin Aydin Professor of Electrical Engineering Head of the Department of Electrical Engineering *Signatures are on file in the Graduate School iii ABSTRACT Wave-matter interactions have long been investigated to discover unknown physical phenomena and exploited to achieve improved device performance throughout the electromagnetic spectrum ranging from quasi-static limit to microwave frequencies, and even at infrared and optical wavelengths. As a nascent but fast growing field, metamaterial technology, which relies on clusters of artificially engineered subwavelength structures, has been demonstrated to provide a wide variety of exotic electromagnetic properties unattainable in natural materials. This dissertation presents the research on novel anisotropic metamaterials for tailoring microwave radiation and infrared scattering of nanostructured thin films. First, a new inversion algorithm is proposed for retrieving the anisotropic effective medium parameters of a slab of metamaterial. Secondly, low-loss anisotropic metamaterial lenses and coatings are introduced for improving the gain and/or bandwidth for a variety of antennas. In particular, a quad-beam high-gain lens for a quarter-wave monopole, a low-profile grounded leaky metamaterial coating for slot antenna, and an ultra-thin anisotropic metamaterial bandwidth- enhancing coating for a quarter-wave monopole are experimentally demonstrated. In the infrared regime, novel nanostructured metamaterial free-standing thin-films, which are inherently anisotropic, are introduced for achieving exotic index properties and further for practical photonic devices. In particular, a low-loss near-infrared fishnet zero-index metamaterial, a dispersion- engineered optically-thin, low-loss broadband metamaterial filter with a suppressed group delay fluctuation in the mid-infrared, and a conformal dual-band near-perfectly absorbing coating in the mid-infrared are experimentally demonstrated. These explorations show the great promise anisotropic metamaterials hold for the flexible manipulation of electromagnetic waves and their broad applicability in a wide spectrum range. iv TABLE OF CONTENTS List of Figures..................................................................................................................... vii Acknowledgements ............................................................................................................. xvi Chapter 1 Introduction ........................................................................................................ 1 1.1 Background ........................................................................................................... 1 1.1.1 Anisotropic Metamaterials ........................................................................... 4 1.1.2 Metamaterial-Enabled High-Gain and Broadband Microwave Antennas ...... 6 1.1.3 Optical Metamaterial Nanostructures ........................................................... 7 1.2 Overview ............................................................................................................... 9 1.3 Original Contributions ........................................................................................... 12 Chapter 2 Effective Medium Parameter Retrieval for Anisotropic Metamaterials ................. 14 2.1 Introduction ........................................................................................................... 14 2.2 Anisotropic Retrieval Method ................................................................................ 16 2.1.1 Scattering from a Homogeneous Anisotropic Slab ....................................... 16 2.1.2 Retrieval Equations ..................................................................................... 18 2.3 Application to A Specific Metamaterial – A SRR-wire Composite Array ............... 22 2.4 Overview ............................................................................................................... 28 Chapter 3 Multi-Beam Transformation Optics Lenses Using Anisotropic Metamaterials ..... 29 3.1 Introduction ........................................................................................................... 29 3.2 Two-/Three-Dimensional Linear Transformation for Highly Directive Emission .... 33 3.2.1 Two/Three Dimensional Linear Coordinate Transformations ....................... 33 3.2.2 Numerical Validations ................................................................................. 37 3.2.3 Wave Propagation in the Transformed Medium ........................................... 40 3.3 Lens Design Using Anisotropic Metamaterial and Associated Simulations ............. 42 3.3.1 Metamaterial Unit Cell Design .................................................................... 43 3.3.2 Integrated Lens Simulation .......................................................................... 44 3.4 Experimental Verification ...................................................................................... 49 3.5 Overview ............................................................................................................... 50 Chapter 4 Low-Profile High-Gain Anisotropic Metamaterial Coating for Slot Antennas ...... 52 4.1 Introduction ........................................................................................................... 52 4.2 Leaky Modes of Grounded Anisotropic Slab .......................................................... 54 4.2.1 Field Equations of a Grounded Anisotropic Slab .......................................... 55 4.2.2 Properties of the Leaky Modes Supported by the Grounded Anisotropic Slab .............................................................................................................. 57 4.2.3 Truncation Effect of the Anisotropic Low Index Slab on the Radiation Pattern .......................................................................................................... 59 4.3 Coating Design Using Anisotropic Metamaterial and Associated Simulations ........ 62 v 4.3.1 Metamaterial Unit Cell Design .................................................................... 63 4.3.2 SIW Fed Slot Antenna Design ..................................................................... 66 4.3.3 Integrated Simulations ................................................................................. 69 4.4 Experimental Verification ...................................................................................... 73 4.5 Overview ............................................................................................................... 74 Chapter 5 Ultra-Wideband Monopole Antenna Using Ultrathin Metamaterial Coating......... 76 5.1 Introduction ........................................................................................................... 76 5.2 Anisotropic Metamaterial Coating Design For S-Band Monopole........................... 77 5.2.1 Unit Cell Design.......................................................................................... 77 5.2.2 Monopole Antenna Coated with Metamaterial ............................................. 79 5.2.3 Principle of Operation ................................................................................. 81 5.2.4 Experimental Verification ........................................................................... 82 5.2.5 Comparison to Sleeve and Dielectric Coated Monopoles ............................. 85 5.3 Anisotropic Metamaterial Coating Design For C-Band Monopole .......................... 86 5.4 Overview ............................................................................................................... 88 Chapter 6 Free-Standing Optical Metamaterials With Near-Zero Phase Delay ..................... 89 6.1 Introduction ........................................................................................................... 89 6.2 Optical ZIM Design and Numerical Results ........................................................... 91 6.2.1 ZIM Design Optimization............................................................................ 91 6.2.2 Numerical Results and Field Properties at ZIM Band ................................... 93 6.3 Fabrication and Characterization of ZIM Sample ................................................... 95 6.3.1 Nanofabrication of the ZIM ......................................................................... 95 6.3.2 Optical Measurement of the Fabricated ZIM Sample ................................... 97 6.4 Comparison to ZIM with Non-Vertical Sidewalls ................................................... 99 6.5 Mid-Infrared ZIM with a Wide Field-Of-View ....................................................... 100 6.6 Overview ..............................................................................................................