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Design, Fabrication and Testing of Tunable RF Meta-Atoms Derrick Langley

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Design, Fabrication and Testing of Tunable RF Meta-Atoms Derrick Langley Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 6-14-2012 Design, Fabrication and Testing of Tunable RF Meta-atoms Derrick Langley Follow this and additional works at: https://scholar.afit.edu/etd Part of the Engineering Science and Materials Commons Recommended Citation Langley, Derrick, "Design, Fabrication and Testing of Tunable RF Meta-atoms" (2012). Theses and Dissertations. 1128. https://scholar.afit.edu/etd/1128 This Dissertation is brought to you for free and open access by the Student Graduate Works at AFIT Scholar. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of AFIT Scholar. For more information, please contact [email protected]. k DESIGN, FABRICATION AND TESTING OF TUNABLE RF META-ATOMS DISSERTATION Derrick Langley, Captain, USAF AFIT/DEE/ENG/12-04 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. The views expressed in this dissertation are those of the author and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the U.S. Government. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. AFIT/DEE/ENG/12-04 DESIGN, FABRICATION AND TESTING OF TUNABLE RF META-ATOMS DISSERTATION Presented to the Faculty Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Derrick Langley, B.S.E.E., M.S.E.E. Captain, USAF June 2012 APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. AFIT/DEE/ENG/12-04 DESIGN, FABRICATION AND TESTING OF TUNABLE RF META-ATOMS Derrick Langley, B.S.E.E, M.S.E.E. Captain, USAF Approved: Ronald A. Coutu, Jr., Ph.B., P .E. (Chairman) l ~ ..L-(kL{ 2-D Uv ins, Ph.D. (Member) Date chael A. Marcm1ak, Ph.D. (Member) Accepted: I J"" ~ z.o I 2. M. U. Thomas, Ph.D. Date Dean, Graduate School of Engineering and Management AFIT/GDE/ENG/12-04 Abstract Metamaterials are engineered structures designed to alter the propagation of electromagnetic waves incident upon the structure. The focus of this research was the effect of metamaterials on electromagnetic signals at radio frequencies. RF meta-atoms were investigated to further develop the theory, modeling, design and fabrication of metamaterials. Comparing the analytic modeling and experimental testing, the results provide a deeper understanding into metamaterials which could lead to applications for beam steering, invisibility cloaking, negative refraction, super lenses, and hyper lenses. RF meta-atoms integrated with microelectromechanical systems produce tunable meta- atoms in the 10 – 15 GHz and 1 – 4 GHz frequency ranges. RF meta-atoms with structural design changes are developed to show how inductance changes based on structural modifications. RF meta-atoms integrated with gain medium are investigated showing that loss due to material characteristics can be compensated using active elements such as a Low Noise Amplifier. Integrating the amplifier into the split ring resonator causes a deeper null at the resonant frequency. The research results show that the resonant frequency can be tuned using microelectromechanical systems, or by induction with structural designs and reduce loss associated with the material conductivity by compensating with an active gain medium. Proposals that offer future research activities are discussed for inductance and active element meta-atoms. In addition, terahertz (THz), infrared (IR), and optical structures are briefly investigated. iv Acknowledgements First, I must thank my wife and kids for their prayers and support during this endeavor. They were like a lighthouse beacon’s light in the dark showing and providing me support during these three years. Dr. Ronald A. Coutu Jr., you have been a wonderful advisor who helped me stay focused while on the long path to completion. I must also extend a debt of gratitude to my committee members, Dr. Peter J. Collins and Dr. Michael A. Marciniak, whose mentoring advice, and keen insights were integral to the success of this research. Special thanks to the Air Force Research Laboratory (AFRL), Materials and Manufacturing Directorate, Wright-Patterson AFB, Ohio for the financial support provided for this research. An additional thank you goes to the AFRL Sensors Directorate, Components Division, Devices for Sensing Branch who allowed me to spend lots of time utilizing their clean room facility to construct my research components. It was great to use the facility for building components and asking questions on problem areas. And Drs. Elizabeth A. Moore and Versalle “Verb” F. Washington, thanks for the editorial comments on my dissertation. To my friends in the PhD-11 class, I could not have asked for any better classmates. You all made the stress level so low with our various family outings, soccer games, and overall wonderful camaraderie. Derrick Langley v Table of Contents Page Abstract .......................................................................................................................................... iv Acknowledgements ......................................................................................................................... v Table of Contents ........................................................................................................................... vi List of Figures ................................................................................................................................. x List of Tables ............................................................................................................................... xvi List of Symbols ........................................................................................................................... xvii List of Abbreviations .................................................................................................................. xxii I. Introduction ................................................................................................................................. 1 1.1. Long Term Problem ............................................................................................................. 4 1.2. Contributions........................................................................................................................ 5 1.3. Publications .......................................................................................................................... 6 1.4. Dissertation Organization .................................................................................................... 8 II. Background .............................................................................................................................. 10 2.1. Metamaterials ..................................................................................................................... 10 2.1.1. Metamaterials Effective Parameters ........................................................................... 10 2.1.2. Meta-atom Equivalent Circuit Modeling .................................................................... 17 2.1.2.1. Lumped Elements ................................................................................................ 18 2.1.2.2. Equivalent Circuit Modeling ................................................................................ 25 2.1.3. Retrieval Process for Effective Parameters ................................................................. 28 2.1.4. Compensating for loss at resonant frequency ............................................................. 30 2.2. Microelectromechanical Systems ...................................................................................... 30 2.2.1 MEMS Fabrication....................................................................................................... 31 vi Page 2.2.1.1. Bulk Micromachining .......................................................................................... 32 2.2.1.2. Micromolding ...................................................................................................... 33 2.2.1.3. Surface Micromachining (polyMUMPS ®, SUMMIT V ™) .............................. 34 2.2.1.4. MEMS Fabrication Method for Meta-atoms ....................................................... 37 2.2.2. Actuation Methods ...................................................................................................... 37 2.2.3. Electrostatic Actuation ................................................................................................ 39 2.2.3.1. Fringe effect on cantilevers .................................................................................. 44 2.2.3.2. Dielectric effect on cantilevers ............................................................................ 44 2.2.3.3. Cantilever thickness variation .............................................................................. 45 2.2.3.4. Anchor Moment ................................................................................................... 45 2.3. Summary ............................................................................................................................ 46 III. RF Metamaterial Structures ...................................................................................................
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