Department of Radio Science and Engineering Aalto- The thesis is devoted to metasurfaces, which Ra'di Younes are composite layers designed to manipulate DD Functional Metasurfaces electromagnetic waves. The appeal of these 211 / functional metasurfaces lies in their ability 2015 to control the flow of electromagnetic waves in electrically thin planar structures. This Functional Metasurfaces thesis studies different functional Younes Ra'di metasurfaces such as off-band-transparent absorbing metasurfaces, off-band- transparent reflecting metasurfaces, Huygens' metasurfaces, and parity-time- symmetric teleportation devices. It also indicates likely research avenues for the future. Inductive layer (jX) Loss (Rl) dl da Gain (Ra) 4 1 0.5 2 Standing-wave 0 l region 0 0 (V/m) x/ total total E -2 -0.5 -4 -1 -4 -2 0 2 4 z/l0 l0/4 3l0 l0/4 h jX jX -h h 0 0 0 9HSTFMG*agfggd+ ISBN 978-952-60-6566-3 (printed) BUSINESS + ISBN 978-952-60-6567-0 (pdf) ECONOMY 0 0 0 ISSN-L 1799-4934 0 in in in in ISSN 1799-4934 (printed) ART + in Z Z Z Z ISSN 1799-4942 (pdf) DESIGN + Z ARCHITECTURE UniversityAalto Aalto University School of Electrical Engineering SCIENCE + Department of Radio Science and Engineering TECHNOLOGY www.aalto.fi CROSSOVER DOCTORAL DOCTORAL DISSERTATIONS DISSERTATIONS 2015 Aalto University publication series DOCTORAL DISSERTATIONS 211/2015 Functional Metasurfaces Younes Ra'di A doctoral dissertation completed for the degree of Doctor of Science (Technology) to be defended, with the permission of the Aalto University School of Electrical Engineering, at a public examination held at the lecture hall S1 of the school on 18 December 2015 at 14:00. Aalto University School of Electrical Engineering Department of Radio Science and Engineering Supervising professor Professor Sergei Tretyakov, Aalto University, Finland Preliminary examiners Professor Maria Kafesaki, University of Crete, Greece Professor Anthony Grbic, University of Michigan, USA Opponent Professor Stefano Maci, University of Siena, Italy Aalto University publication series DOCTORAL DISSERTATIONS 211/2015 © Younes Ra'di ISBN 978-952-60-6566-3 (printed) ISBN 978-952-60-6567-0 (pdf) ISSN-L 1799-4934 ISSN 1799-4934 (printed) ISSN 1799-4942 (pdf) http://urn.fi/URN:ISBN:978-952-60-6567-0 Unigrafia Oy Helsinki 2015 Finland Abstract Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Younes Ra'di Name of the doctoral dissertation Functional Metasurfaces Publisher School of Electrical Engineering Unit Department of Radio Science and Engineering Series Aalto University publication series DOCTORAL DISSERTATIONS 211/2015 Field of research Radio Engineering Manuscript submitted 1 September 2015 Date of the defence 18 December 2015 Permission to publish granted (date) 9 November 2015 Language English Monograph Article dissertation (summary + original articles) Abstract This thesis studies the use of functional metasurfaces composed of single arrays of polarizable unit cells in order to manipulate electromagnetic waves. The main topics that are studied are absorbing metasurfaces, metamirrors, Huygens' metasurfaces, and parity-time-symmetric metasurfaces. In the first part of the thesis, we introduce the general theory of off-band-transparent absorbing metasurfaces. First, we consider metasurfaces which symmetrically absorb electromagnetic waves hitting any of their sides. As an example for symmetric absorbing metasurfaces, we introduce a novel off-band-transparent light absorber composed of a single array of core-shell particles. We continue this study by introducing the concept of asymmetric absorbing metasurfaces. We study single-layer sheets which work as total absorbers only from one side and investigate what functionalities can be engineered for illumination from the opposite side. The second part of the thesis is devoted to the concept of off-band-transparent reflecting metasurfaces. We consider both symmetric and asymmetric metamirrors. We show how arrays of electrically small resonant bianisotropic particles can be employed to fully reflect electromagnetic plane waves hitting any of their sides while enabling independent and full control over the phase of waves reflected from their different sides. The third part of the thesis focuses on the concept of Huygens' metasurfaces. We first present the concept of symmetric and asymmetric transparent metasurfaces. We introduce one-way transparent metasurfaces which offer controllable functionalities for waves hitting their non- transparent sides. We furthermore introduce the concept of all-angle Huygens' metasurfaces. These metasurfaces are reflectionless for any arbitrary input wavefront while enabling manipulation of transmitted waves in unprecedented ways. In the last part of the thesis, we study the concept of parity-time-symmetric metasurfaces. Utilizing these metasurfaces, it is shown how electromagnetic plane waves can be fully recreated behind a highly reflecting metallic screen. The proposed structure works as a new form of one-dimensional cloak which is capable of cloaking an almost fully reflective metallic screen in both spectrally and angularly selective manner. Keywords Metasurfaces, Absorbers, Reflectors, Transparency, Bianisotropy, Parity-time symmetry ISBN (printed) 978-952-60-6566-3 ISBN (pdf) 978-952-60-6567-0 ISSN-L 1799-4934 ISSN (printed) 1799-4934 ISSN (pdf) 1799-4942 Location of publisher Helsinki Location of printing Helsinki Year 2015 Pages 119 urn http://urn.fi/URN:ISBN:978-952-60-6567-0 Preface This thesis summarizes selected results obtained at the Department of Radio Science and Engineering of Aalto University under the supervision of Prof. Sergei Tretyakov. My warmest thanks and gratitude go to my supervisor, Prof. Sergei Tretyakov, for accepting me as a doctoral student and for his trust, en- couragement, and guidance during these years. You have been a tremen- dous mentor for me. I would like to thank you for allowing me to grow as a research scientist. Your advice on both research as well as on my career have been priceless. I would also like to thank Prof. Constantin Simovski. I very much appre- ciate many discussions I had with you on some of research works included in this thesis. In full gratitude I would like to acknowledge all my co-authors, col- leagues, and all staff members in the Department of Radio Science and Engineering, especially the present and former members of our scientific group: Dr. Igor Nefedov, Dr. Pekka Alitalo, Dr. Antti Karilainen, Dr. Constantinos Valagiannopoulos, Dr. Dmitry Morits, Dr. Mohammad Al- booyeh, Mr. Teemu Niemi, Mr. Joni Vehmas, Mr. Viktar Asadchy, Mr. Mohammad Sajjad Mirmoosa, Mr. Mikhail Omelyanovich, Mr. Sergei Ko- sulnikov, Mr. Pavel Voroshilov, Ms. Svetlana Tcvetkova, and Mr. Amr Elsakka. I wish to thank Prof. Maria Kafesaki and Prof. Anthony Grbic for ac- cepting to review this thesis. My sincere gratitude and special thanks for all the joint work, discus- sions, and guidance go to Prof. Constantin Simovski, Prof. Andrea Alù, Prof. Richard Ziolkowski, Prof. Ari Sihvola, Dr. Andrey Osipov, Dr. Iñigo Liberal, Dr. Dimitrios Sounas, Mr. Viktar Asadchy, and Mr. Dimitris Tzarouchis. 5 Preface During this thesis work I have received financial support from the Aalto ELEC Doctoral School, the Nokia Foundation, and the HPY Research Foundation. All this support is most gratefully acknowledged. Words cannot express how grateful I am to my mother, brother, mother- in-law, and father-in-law for all of the sacrifices that they have made on my behalf. Thank you for your support and encouragement during the whole course of my studies. Finally, but most importantly, I wish to thank my beloved wife Hoda, for all her love, constant support, and bringing so much happiness into my life. Your encouragement, patience, and unwavering love were undeniably the bedrock upon which the past five years of my life have been built. Espoo, November 16, 2015, Younes Ra’di 6 Contents Preface 5 Contents 7 List of Publications 9 Author’s Contribution 11 List of Abbreviations 13 List of Symbols 14 1. Introduction 18 1.1 From metamaterials to metasurfaces .............. 19 1.2 Homogenization of metasurfaces . ............... 23 2. Absorbing metasurfaces 28 2.1 Symmetric absorbing metasurfaces ............... 28 2.1.1 Contributions of this thesis (summary of related pub- lications) .......................... 31 2.2 Asymmetric absorbing metasurfaces .............. 32 2.2.1 Contributions of this thesis (summary of related pub- lications) .......................... 35 3. Reflecting metasurfaces (Metamirrors) 36 3.1 Symmetric metamirrors ..................... 37 3.2 Asymmetric metamirrors ..................... 37 3.2.1 Contributions of this thesis (summary of related pub- lications) .......................... 39 4. Huygens’ metasurfaces 40 4.1 Transparent metasurfaces .................... 41 7 Contents 4.1.1 Symmetric transparent metasurfaces ......... 41 4.1.2 Asymmetric transparent metasurfaces ......... 42 4.1.3 Contributions of this thesis (summary of related pub- lications) .......................... 44 4.2 All-angle Huygens’ metasurfaces ................ 44 4.2.1 Theory ........................... 44 4.2.2 Contributions of this thesis (summary of related pub- lications) .......................... 46 5. PT -symmetric metasurfaces 47 5.1 Design principles ......................... 48 5.2 Contributions of this thesis (summary of related publications) 53 6. Conclusions 54 References 56 Errata 66 Publications 67 8 List of Publications This thesis consists of an overview and of the following publications