There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

A recently published theory has suggested that a cloak of invisibility is in principle possible, at least over a narrow frequency band. We describe here the first practical realization of such a cloak; in our demonstration, a copper cylinder was "hidden" inside a cloak constructed according to the previous theoretical prescription. The cloak was constructed with the use of artificially structured metamaterials, designed for operation over a band of microwave frequencies. The cloak decreased scattering from the hidden object while at the same time reducing its shadow, so that the cloak and object combined began to resemble empty space.

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Metamaterial Electromagnetic Cloak at Microwave Frequencies

Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat’s principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces.

http://www.zenogaburro.it/papers/LightPropagation.pdf

Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction

Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

Metamaterials and transformation optics play substantial roles in various branches of optical science and engineering by providing schemes to tailor electromagnetic fields into desired spatial patterns. We report a theoretical study showing that by designing and manipulating spatially inhomogeneous, nonuniform conductivity patterns across a flake of graphene, one can have this material as a one-atom-thick platform for infrared metamaterials and transformation optical devices. Varying the graphene chemical potential by using static electric field yields a way to tune the graphene conductivity in the terahertz and infrared frequencies. Such degree of freedom provides the prospect of having different "patches" with different conductivities on a single flake of graphene. Numerous photonic functions and metamaterial concepts can be expected to follow from such a platform.

http://science.sciencemag.org/content/suppl/2011/06/08/332.6035.1291.DC1/Vakil-SOM.pdf

Transformation Optics Using Graphene

The possibility of using plasmonic and metamaterial covers to drastically reduce the total scattering cross section of spherical and cylindrical objects is discussed. While it is intuitively expected that increasing the physical size of an object may lead to an increase in its overall scattering cross section, here we see how a proper design of these lossless metamaterial covers near their plasma resonance may induce a dramatic drop in the scattering cross section, making these objects nearly "invisible" or "transparent" to an outside observer--a phenomenon with obvious applications for low-observability and noninvasive probe design. Physical insights into this phenomenon and some numerical results are provided.

/pdf/achieving-transparency-with-plasmonic-and-metamaterial-c3bwqtt3iw.pdf

Achieving transparency with plasmonic and metamaterial coatings

Preface. Contributors. PART I: DOUBLE-NEGATIVE (DNG) METAMATERIALS. SECTION I: THREE-DIMENSIONAL VOLUMETRIC DNG METAMATERIALS. CHAPTER 1: INTRODUCTION, HISTORY, AND SELECTED TOPICS IN FUNDAMENTAL THEORIES OF METAMATERIALS (Richard W. Ziolkowski and Nader Engheta). 1.1 Introduction. 1.2 Wave Parameters in DNG Media. 1.3 FDTD Simulations of DNG Media. 1.4 Causality in DNG Media. 1.5 Scattering from a DNG Slab. 1.6 Backward Waves. 1.7 Negative Refraction. 1.8 Phase Compensation with a DNG Medium. 1.9 Dispersion Compensation in a Transmission Line Using a DNG Medium. 1.10 Subwavelength Focusing with a DNG Medium. 1.11 Metamaterials with a Zero Index of Refraction. 1.12 Summary. References. CHAPTER 2: FUNDAMENTALS OF WAVEGUIDE AND ANTENNA APPLICATIONS INVOLVING DNG AND SNG METAMATERIALS (Nader Engheta, Andrea Alu, Richard W. Ziolkowski, and Aycan Erentok). 2.1 Introduction. 2.2 Subwavelength Cavities and Waveguides. 2.3 Subwavelength Cylindrical and Spherical Core-Shell Systems. 2.4 ENG-MNG and DPS-DNG Matched Metamaterial Pairs for Resonant Enhancements of Source-Generated Fields. 2.5 Efficient, Electrically Small Dipole Antennas: DNG Nested Shells. 2.6 Efficient, Electrically Small Dipole Antennas: ENG Nested Shells-Analysis. 2.7 Efficient, Electrically Small Dipole Antennas: HFSS Simulations of Dipole-ENG Shell Systems. 2.8 Metamaterial Realization of an Artificial Magnetic Conductor for Antenna Applications. 2.9 Zero-Index Metamaterials for Antenna Applications. 2.10 Summary. References. CHAPTER 3: WAVEGUIDE EXPERIMENTS TO CHARACTERIZE PROPERTIES OF SNG AND DNG METAMATERIALS (Silvio Hrabar). 3.1 Introduction. 3.2 Basic Types of Bulk Metamaterials with Inclusions. 3.3 Theoretical Analysis of Rectangular Waveguide Filled with General Metamaterial. 3.4 Investigation of Rectangular Waveguide Filled with 2D Isotropic ENG Metamaterial. 3.5 Investigation of Rectangular Waveguide Filled with 2D Isotropic MNG Metamaterial. 3.6 Investigation of Rectangular Waveguide Filled with 2D Uniaxial MNG Metamaterial. 3.7 Investigation of Rectangular Waveguide Filled with 2D Isotropic DNG Metamaterial. 3.8 Investigation of Subwavelength Resonator. 3.9 Conclusions. References. CHAPTER 4: REFRACTION EXPERIMENTS IN WAVEGUIDE ENVIRONMENTS (Tomasz M. Grzegorczyk, Jin Au Kong, and Ran Lixin). 4.1 Introduction. 4.2 Microscopic and Macroscopic Views of Metamaterials. 4.3 Measurement Techniques. 4.4 Conclusion. Acknowledgments. References. SECTION II: TWO-DIMENSIONAL PLANAR NEGATIVE-INDEX STRUCTURES. CHAPTER 5: ANTENNA APPLICATIONS AND SUBWAVELENGTH FOCUSING USING NEGATIVE-REFRACTIVE-INDEX TRANSMISSION LINE STRUCTURES (George V. Eleftheriades). 5.1 Introduction. 5.2 Planar Transmission Line Media with Negative Refractive Index. 5.3 Zero-Degree Phase-Shifting Lines and Applications. 5.4 Backward Leaky-Wave Antenna Radiating in Its Fundamental Spatial Harmonic. 5.5 Superresolving NRI Transmission Line Lens. 5.6 Detailed Dispersion of Planar NRI-TL Media. Acknowledgments. References. CHAPTER 6: RESONANCE CONE ANTENNAS (Keith G. Balmain and Andrea A. E. Luttgen). 6.1 Introduction. 6.2 Planar Metamaterial, Corner-Fed, Anisotropic Grid Antenna. 6.3 Resonance Cone Refraction Effects in a Low-Profile Antenna. 6.4 Conclusions. Acknowledgments. References. CHAPTER 7: MICROWAVE COUPLER AND RESONATOR APPLICATIONS OF NRI PLANAR STRUCTURES (Christophe Caloz and Tatsuo Itoh). 7.1 Introduction. 7.2 Composite Right/Left-Handed Transmission Line Metamaterials. 7.3 Metamaterial Couplers. 7.4 Metamaterial Resonators. 7.5 Conclusions. References. PART II: ELECTROMAGNETIC BANDGAP (EBG) METAMATERIALS. SECTION I: THREE-DIMENSIONAL VOLUMETRIC EBG MEDIA. CHAPTER 8: HISTORICAL PERSPECTIVE AND REVIEW OF FUNDAMENTAL PRINCIPLES IN MODELING THREE-DIMENSIONAL PERIODIC STRUCTURES WITH EMPHASIS ON VOLUMETRIC EBGs (Maria Kafesaki and Costas M. Soukoulis). 8.1 Introduction. 8.2 Theoretical and Numerical Methods. 8.3 Comparison of Different Numerical Techniques. 8.4 Conclusions. Acknowledgments. References. CHAPTER 9: FABRICATION, EXPERIMENTATION, AND APPLICATIONS OF EBG STRUCTURES (Peter de Maagt and Peter Huggard). 9.1 Introduction. 9.2 Manufacturing. 9.3 Experimental Characterization of EBG Crystals. 9.4 Current and Future Applications of EBG Systems. 9.5 Conclusions. References. CHAPTER 10: SUPERPRISM EFFECTS AND EBG ANTENNA APPLICATIONS (Boris Gralak, Stefan Enoch, and G-erard Tayeb). 10.1 Introduction. 10.2 Refractive Properties of a Piece of Photonic Crystal. 10.3 Superprism Effect. 10.4 Antenna Applications. 10.5 Conclusion. References. SECTION II: TWO-DIMENSIONAL PLANAR EBG STRUCTURES. CHAPTER 11: REVIEW OF THEORY, FABRICATION, AND APPLICATIONS OF HIGH-IMPEDANCE GROUND PLANES (Dan Sievenpiper). 11.1 Introduction. 11.2 Surface Waves. 11.3 High-Impedance Surfaces. 11.4 Surface Wave Bands. 11.5 Reflection Phase. 11.6 Bandwidth. 11.7 Design Procedure. 11.8 Antenna Applications. 11.9 Tunable Impedance Surfaces. 11.10 Reflective-Beam Steering. 11.11 Leaky-Wave Beam Steering. 11.12 Backward Bands. 11.13 Summary. References. CHAPTER 12: DEVELOPMENT OF COMPLEX ARTIFICIAL GROUND PLANES IN ANTENNA ENGINEERING (Yahya Rahmat-Samii and Fan Yang). 12.1 Introduction. 12.2 FDTD Analysis of Complex Artificial Ground Planes. 12.3 Various Complex Artificial Ground-Plane Designs. 12.4 Applications of Artificial Ground Planes in Antenna Engineering. 12.5 Summary. References. CHAPTER 13: FSS-BASED EBG SURFACES (Stefano Maci and Alessio Cucini). 13.1 Introduction. 13.2 MoM Solution. 13.3 Accessible Mode Admittance Network. 13.4 Pole-Zero Matching Method for Dispersion Analysis. 13.5 Conclusions. Acknowledgments. References. CHAPTER 14: SPACE-FILLING CURVE HIGH-IMPEDANCE GROUND PLANES (John McVay, Nader Engheta, and Ahmad Hoorfar). 14.1 Resonances of Space-Filling Curve Elements. 14.2 High-Impedance Surfaces Made of Space-Filling Curve Inclusions. 14.3 Use of Space-Filling Curve High-Impedance Surfaces in Antenna Applications. 14.4 Space-Filling Curve Elements as Inclusions in DNG Bulk Media. 14.5 Conclusions. References. Index.

Metamaterials: Physics and Engineering Explorations

In this Letter, we demonstrate theoretically that electromagnetic waves can be ``squeezed'' and tunneled through very narrow channels filled with $\ensuremath{\epsilon}$-near-zero (ENZ) materials. We show that the incoming planar wave front is replicated at the output interface, independently of the specific geometry of the channel. A closed analytical formula is derived for the scattering parameters of a particular class of geometries. It is discussed that in some cases the isotropy of the ENZ material may not be an issue. A metamaterial realization of an anisotropic ENZ material is suggested and numerically studied.

/pdf/tunneling-of-electromagnetic-energy-through-subwavelength-sg0f1z8rq6.pdf

Tunneling of electromagnetic energy through subwavelength channels and bends using ε-near-zero materials

A form of optical circuitry is overviewed in which a tapestry of subwavelength nanometer-scale metamaterial structures and nanoparticles may provide a mechanism for tailoring, patterning, and manipulating local optical electric fields and electric displacement vectors in a subwavelength domain, leading to the possibility of optical information processing at the nanometer scale. By exploiting the optical properties of metamaterials, these nanoparticles may play the role of "lumped" nanocircuit elements such as nanoinductors, nanocapacitors, and nanoresistors, analogous to microelectronics. I show that this concept of metamaterial-inspired nanoelectronics ("metactronics") can bring the tools and mathematical machinery of the circuit theory into optics, may link the fields of optics, electronics, plasmonics, and metamaterials, and may provide road maps to future innovations in nanoscale optical devices, components, and more intricate nanoscale metamaterials.

/pdf/circuits-with-light-at-nanoscales-optical-nanocircuits-2on39xsgmd.pdf

Nader Engheta

Papers

Transformation Optics Using Graphene

Achieving transparency with plasmonic and metamaterial coatings

Metamaterials: Physics and Engineering Explorations

Tunneling of electromagnetic energy through subwavelength channels and bends using ε-near-zero materials

Circuits with Light at Nanoscales: Optical Nanocircuits Inspired by Metamaterials