Metamaterials: Fundamentals and Applications in the Microwaveandopticalregimes by GEORGE V
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SCANNING THE ISSUE Metamaterials: Fundamentals and Applications in the MicrowaveandOpticalRegimes By GEORGE V. ELEFTHERIADES, Fellow IEEE Guest Editor NADER ENGHETA, Fellow IEEE Guest Editor etamaterials are artificially structured media with unusual Typically, metamaterials are peri- electromagnetic properties ranging from radio frequency odic structures consisting of subwave- and microwaves all the way up to optical frequencies. In its length metalo-dielectric scatterers modern form, the field of Bmetamaterials,[ which has its having a periodicity that is much Mroots in the history of artificial dielectrics, is just over ten years old but has already smaller than the impinging and guided attracted strong interest from many researchers around the globe. Suddenly, wavelengths (although nonperiodic classical electromagnetism took on a metamaterials are also entirely possi- fresh and exciting perspective reveal- ble). These constituent scatterers or ing that there are fascinating phenom- Binclusions[ behave like Bartificial ena still awaiting to be discovered and This Special Issue on molecules[ that scatter an incident corresponding applications to be in- Metamaterials: Artificially electromagnetic wave giving rise to vented. In particular, all this richness is macroscopic effective material param- associated with the notion of the Engineered Materials with eters such as a permittivity, a perme- macroscopic constitutive parameters Electromagnetic ability, and a refractive index. Although such as the permittivity and perme- Properties covers topics the term Bmetamaterial[ is relatively ability. What would be possible if we on prescribing material new, a precursor concept dates back to were able to synthesize materials with parameters to obtain the late part of the nineteenth century user-defined constitutive parameters? exotic new functions, in the work of Jadagis Chunder Bose on The richness of these possibilities the rotation of the plane of polarization becomes more evident when we recall physically implementing by his man-made twisted structures, the fact that material parameters can in metamaterials, and resembling chiral structures [1]. In general be anisotropic tensors which applying them in the 1914, Karl Ferdinand Lindman investi- can also be spatially inhomogeneous microwave and optical gated artificially engineered chiral (varying from point to point). More- domains. media, which he constructed by a over, they can attain values previously collection of wire helices [2]. This not considered, and they can even mix was followed by a few other researchers together the electric and magnetic response of a material. This Special Issue in the first half of the twentieth century contains 16 papers written by some of the internationally renowned leaders in the studying some other man-made mate- field who discuss how to prescribe material parameters to obtain exotic new rials. In the late 1940s, 1950s, and functions, how to physically implement such metamaterials, and how to apply 1960s, Bartificial dielectrics[ became a them in the microwaves and optical domains. subject of interest, when Winston E. Kock of the Bell telephone laboratories Digital Object Identifier: 10.1109/JPROC.2011.2161808 developed this concept in order to 1618 Proceedings of the IEEE | Vol. 99, No. 10, October 2011 0018-9219/$26.00 Ó2011 IEEE Scanning the Issue realize lightweight lenses at microwave Veselago in 1967 [6], the intriguing split-ring resonators. The paper makes frequencies (in the 3Y5-GHz range), and groundbreaking notion of the use of a rigorous homogenization where the wavelength is long (several Bperfect lens[ proposed by Pendry in treatment of these metamaterials. centimeters) and thus the correspond- 2000 [14], and the experimental ver- Moreover, an exciting application of ing natural dielectric lenses are bulky ification of the negative-index meta- such magnetic metamaterials is de- and heavy [3]. The corresponding materials in the microwave regime by scribed for enhancing the resolution Bartificial molecules[ were electrically Shelby, Smith, and Schultz in 2001 [9] of surface coils in magnetic resonance small metallic disks periodically ar- stimulated interest in these materials imaging (MRI). The paper by Alu` and ranged in a lens shape. The interest in and led to the expansion and growth in Engheta describes the possible idea for artificial complex materials, particular- this field in the 2000s. The field of realization of metamaterials in the ly chiral materials, was resurrected in metamaterials has now reached a optical regime based on lumped optical the 1980s and 1990s, mostly with the variety of disciplines such as physics, nanocircuit element concepts. The view towards applications in micro- electrical engineering, material science, paper establishes a way to realize wave radar absorbing materials and mathematics, mechanics, acoustics, nanocapacitors and nanoinductors us- other microwave devices and compo- fluidics, and chemistry just to name ing dielectric and plasmonic nanopar- nents [4]. A comprehensive review of a few. ticles. It also presents a method of artificial dielectrics, including a rigor- The first paper in this Special combining these elements to synthe- ous mathematical treatment, from that Issue is by Kundtz, Smith, and Pendry size complex optical nanocircuits by era can be found in [5]. who introduce and review the notion treating the displacement current using In the present context, metama- of Btransformation optics[ (TO) as a well-known low-frequency circuit terials can be defined as artificially powerful technique for designing theory techniques. Finally, the paper engineered materials with electro- electromagnetic metamaterials based establishes a method for designing 0-D, magnetic properties that are inacces- on the invariance of Maxwell’s equa- 1-D, 2-D, and 3-D optical metamaterial sibleinnatureoraredifficultto tions. Specifically, at the heart of TO structures based on transmission-line obtain in natural materials, but are lies the use of coordinate transforma- concepts thus helping to decrease physically realizable. One of the early tions which can be translated to losses and improve bandwidth. The examples of metamaterials is the material parameters. In this way, following paper by Valentine, Zhang, so-called Bnegative-index,[Bleft- several novel electromagnetic device Zentgraf, and Zhang presents the so- handed[ or Bdouble negative[ meta- examples are introduced and dis- called cascaded Bfishnet[ structures for material which is characterized by cussed including cloaks, beam shif- building broadband low-loss negative- simultaneously negative permittivity ters, and beam splitters. refraction metamaterials. It deals with and permeability, thus implying a The following paper by Zedler and design, fabrication, and characteriza- negative index of refraction. These Eleftheriades introduces a method for tion of such materials. The paper shows media were theoretically suggested synthesizing TO metamaterials at how coupling of unit cells leads to and studied by Victor Veselago in the microwaves (hence more appropriate- lower loss and a high figure of merit. 1960s [6]. Inspired by the work of ly Btransformation electromagnetics[) Kildishev, Borneman, Shalaev, and Pendry [7], [8], Shelby, Smith, and using loaded transmission lines. These Drachev in their paper give an overview Schultz experimentally demonstrated metamaterials are in general inhomo- of some principles in the development the first left-handed metamaterial in geneous and anisotropic with nonzero of bianisotropic homogenization tech- 2001 using arrays of wires (giving rise off-diagonal material parameters. A niques for metamaterials, and provide to negative permittivity) and split-ring few examples of microwave devices examples in passive and active optical resonators (giving rise to negative per- are described including broadband metamaterials. meability) at microwave frequencies cloaks and flattened retroreflectors. The next group of six papers [9]. In the electrical engineering com- The next paper by Alitalo and describes specific applications of munity, a different realization ap- Tretyakov describes an alternative metamaterials at microwave and opti- proach has also been considered at approach for cloaking based on trans- cal frequencies. The paper by Dura´n- microwaves using 2-D loaded networks mission-line metamaterials, and also Sindreu, Ve´lez, Siso´,Ve´lez, Selga, of transmission lines [10], [11], which gives a brief overview of some other Bonache, and Martin reviews recent were subsequently extended to the cloaking techniques. advances in metamaterial transmission optical regime [12]. Typically this The next four papers deal with lines based on loading with split-ring transmission-line approach leads to specific ideas for realizations of meta- resonators. The paper highlights the reduced transmission losses and wide materials with user-defined param- advantages of transmission-line meta- bandwidths due to the tight coupling eters. The paper by Marque´s, Jelinek, materials and describes a number of of the constituent unit cells [13]. The Freire, Baena, and Lapine discusses the enabled microwave applications. Such pioneering work on the concept of realization of 3-D magnetic metamater- applications include compact wideband negative-index metamaterials by ials at microwave frequencies using filters and power splitters. Caloz in his Vol. 99, No. 10, October 2011 | Proceedings of the IEEE 1619 Scanning the Issue paper reviews the theory