Showing papers by "Xiang Zhang published in 2007"
TL;DR: Experimental demonstration of the optical hyperlens for sub-diffraction-limited imaging in the far field and opens up possibilities in applications such as real-time biomolecular imaging and nanolithography.
Abstract: The diffraction limit of light, which is causd by the loss of evanescent waves in the far field that carry high spatial frequency information, limits the resolution of optical lenses to the order of the wavelength of light. We report experimental demonstration of the optical hyperlens for sub-diffraction-limited imaging in the far field. The device magnifies subwavelength objects by transforming the scattered evanescent waves into propagating waves in an anisotropic medium and projects the high-resolution image at far field. The optical hyperlens opens up possibilities in applications such as real-time biomolecular imaging and nanolithography.
2,047 citations
TL;DR: In this paper, a method to extract effective material properties from reflection and transmission coefficients, which can be measured experimentally, is presented, and the dependency of effective properties on the positions of the boundaries of the acoustic metamaterial is discussed.
Abstract: Acoustic metamaterials can be described by effective material properties such as mass density and modulus. We have developed a method to extract these effective properties from reflection and transmission coefficients, which can be measured experimentally. The dependency of effective properties on the positions of the boundaries of the acoustic metamaterial is discussed, and a proper procedure to determine the boundaries is presented. This retrieval method is used to analyze various acoustic metamaterials, and metamaterials with negative effective properties are reported.
394 citations
TL;DR: It is shown that a FSL can image a subwavelength object consisting of two 50 nm wide lines separated by 70 nm working at 377 nm wavelength and the optical FSL promises new potential for nanoscale imaging and lithography.
Abstract: Far-field optical lens resolution is fundamentally limited by diffraction, which typically is about half of the wavelength. This is due to the evanescent waves carrying small scale information from an object that fades away in the far field. A recently proposed superlens theory offers a new approach by surface excitation at the negative index medium. We introduce a far-field optical superlens (FSL) that is capable of imaging beyond the diffraction limit. The FSL significantly enhances the evanescent waves of an object and converts them into propagating waves that are measured in the far field. We show that a FSL can image a subwavelength object consisting of two 50 nm wide lines separated by 70 nm working at 377 nm wavelength. The optical FSL promises new potential for nanoscale imaging and lithography.
383 citations
TL;DR: In this paper, a linearly polarized electromagnetic wave is shown to change its polarization after passing through an array of magnetic dimers, and the polarization of the transmitted wave rotates counterclockwise at incident light frequencies corresponding to the low energy and clockwise at the high energy magnetic plasmon state.
Abstract: The excitation of optical magnetic plasmons in chiral metallic nanostructures based on a magnetic dimer is studied theoretically. Hybridization of the magnetic plasmon modes and a type of optical activity is demonstrated at near-infrared frequencies. A linearly polarized electromagnetic wave is shown to change its polarization after passing through an array of magnetic dimers. The polarization of the transmitted wave rotates counterclockwise at incident light frequencies corresponding to the low energy and clockwise at the high energy magnetic plasmon state. A metamaterial made of a large number of coupled magnetic dimers could be utilized as a tunable optically active medium with possible applications in optical elements and devices.
228 citations
TL;DR: In this article, negative effective mass density is determined to be the necessary condition for the existence of surface states on acoustic metamaterials, and the microscopic picture of these unique surface states is presented.
Abstract: We report that the negative material responses of acoustic metamaterials can lead to a plethora of surface resonant states. We determine that negative effective-mass density is the necessary condition for the existence of surface states on acoustic metamaterials. We offer the microscopic picture of these unique surface states; in addition, we find that these surface excitations enhance the transmission of evanescent pressure fields across the metamaterial. The evanescent pressure fields scattered from an object can be resonantly coupled and enhanced at the surface of the acoustic metamaterial, resulting in an image with resolution below the diffraction limit. This concept of acoustic superlens opens exciting opportunities to design acoustic metamaterials for ultrasonic imaging.
213 citations
TL;DR: The design, fabrication and characterization of optical hyperlens that can image sub-diffraction-limited objects in the far field are reported, based on an artificial anisotropic metamaterial with carefully designed hyperbolic dispersion composed of curved silver/alumina multilayers.
Abstract: We report here the design, fabrication and characterization of optical hyperlens that can image sub-diffraction-limited objects in the far field. The hyperlens is based on an artificial anisotropic metamaterial with carefully designed hyperbolic dispersion. We successfully designed and fabricated such a metamaterial hyperlens composed of curved silver/alumina multilayers. Experimental results demonstrate far-field imaging with resolution down to 125nm at 365nm working wavelength which is below the diffraction limit.
205 citations
TL;DR: This work presents the first study of subwavelength discrete solitons in nonlinear metamaterials: nanoscaled periodic structures consisting of metal and nonlinear dielectric slabs, and expects these phenomena to inspire fundamental studies as well as potential applications of non linear metammaterials, particularly in subwa wavelength nonlinear optics.
Abstract: We present the first study of subwavelength discrete solitons in nonlinear metamaterials: nanoscaled periodic structures consisting of metal and nonlinear dielectric slabs. The solitons supported by such media result from a balance between tunneling of surface plasmon modes and nonlinear self-trapping. The dynamics in such systems, arising from the threefold interplay between periodicity, nonlinearity, and surface plasmon polaritons, is substantially different from that in conventional nonlinear dielectric waveguide arrays. We expect these phenomena to inspire fundamental studies as well as potential applications of nonlinear metamaterials, particularly in subwavelength nonlinear optics.
203 citations
TL;DR: It is reported that two-dimensional (2D) sub-diffraction-limited images can be theoretically reconstructed by a new metamaterial far-field superlens, composed of a metal-dielectric multilayer and a 1D subwavelength grating.
Abstract: We report that two-dimensional (2D) sub-diffraction-limited images can be theoretically reconstructed by a new metamaterial far-field superlens. The metamaterial far-field superlens, composed of a metal−dielectric multilayer and a one-dimensional (1D) subwavelength grating, can work over a broad range of visible wavelengths intrinsically. The imaging principle and the reconstruction process are described in detail. The 2D sub-diffraction-limited imaging ability enables more applications of the far-field superlens in optical nanoimaging and sensing.
156 citations
TL;DR: It is shown that CRP enhanced myeloma cell proliferation under stressed conditions and protected myelomas cells from chemotherapy drug-induced apoptosis in vitro and in vivo and implicate CRP as a potential target for cancer treatment.
106 citations
TL;DR: In this article, the authors demonstrate that during plasmon nanofocusing in a tapered gap (V groove), local electric field experiences much stronger enhancement than the magnetic field.
Abstract: We demonstrate that during plasmon nanofocusing in a tapered gap (V groove), local electric field experiences much stronger enhancement than the magnetic field. Two distinct asymptotic regimes are found near the tip of the groove: The electric field approaches either zero or infinity when dissipation is above or below a critical level (at a fixed taper angle), or taper angle is smaller or larger than a critical angle (at a fixed level of dissipation). Tapered gaps are shown to be the best option for achieving maximal field enhancement, compared to nanowedges and tapered rods. An optimal taper angle is determined. © 2007 The American Physical Society.
88 citations
TL;DR: In this paper, two types of optical metamaterials operating at near-IR and mid-IR frequencies, respectively, have been designed, fabricated by nanoimprint lithography (NIL), and characterized by laser spectroscopic ellipsometry.
Abstract: Two types of optical metamaterials operating at near-IR and mid-IR frequencies, respectively, have been designed, fabricated by nanoimprint lithography (NIL), and characterized by laser spectroscopic ellipsometry. The structure for the near-IR range was a metal/dielectric/metal stack “fishnet” structure that demonstrated negative permittivity and permeability in the same frequency region and hence exhibited a negative refractive index at a wavelength near 1.7 μm. In the mid-IR range, the metamaterial was an ordered array of fourfold symmetric L-shaped resonators (LSRs) that showed both a dipole plasmon resonance resulting in negative permittivity and a magnetic resonance with negative permeability near wavelengths of 3.7 μm and 5.25 μm, respectively. The optical properties of both metamaterials are in agreement with theoretical predictions. This work demonstrates the feasibility of designing various optical negative-index metamaterials and fabricating them using the nanoimprint lithography as a low-cost, high-throughput fabrication approach.
TL;DR: Experimental results show that feature resolution of better than 50nm is possible using current FSL design and design and fabricate a silver structured one dimensional FSL is designed and fabricated.
Abstract: Contrary to the conventional near-field superlensing, subwavelength superlens imaging is experimentally demonstrated in the far-field. The key element is termed as a Far-field SuperLens (FSL) which consists of a conventional superlens and a nanoscale coupler. The evanescent fields from the object are enhanced and then converted into propagating fields by the FSL. By only measuring the propagating field in the far-field, the object image can be reconstructed with subwavelength resolution. As an example of this concept, we design and fabricate a silver structured one dimensional FSL. Experimental results show that feature resolution of better than 50nm is possible using current FSL design.
TL;DR: A metamaterial comprising an ordered array of four metallic L-shaped components designed to operate in the mid-IR frequency regime has been fabricated and characterized in this article, where the fourfold rotational symmetry of the unit cell should suppress the undesirable bianisotropy observed for split-ring resonators.
Abstract: A metamaterial comprising an ordered array of four metallic L-shaped components designed to operate in the mid-IR frequency regime has been fabricated and characterized. The fourfold rotational symmetry of the unit cell should suppress the undesirable bianisotropy observed for split-ring resonators. Nanoimprint lithography was used to demonstrate scalability for mass production. A dipole plasmon resonance with a negative permittivity and a magnetic resonance with a negative permeability were observed at wavelengths of 3.7 and 5.25μm, respectively, in agreement with theoretical predictions.
TL;DR: In this paper, a rigorous mode matching approach for the exact semi-analytical analysis of surface plasmon propagation across non-uniform semi-infinite dielectric-metal interfaces is presented.
Abstract: We have developed a rigorous mode matching approach for the exact semi-analytical analysis
of surface plasmon propagation across non-uniform semi-infinite dielectric-metal interfaces. We address two key deficiencies of related approaches in the literature: firstly, we resolve issues of accuracy and convergence and secondly, while we focus on the analysis of two-dimensional problems, we present a framework for three-dimensional problems for the first time. Analytical derivations of coupling coefficients between guided and radiation modes allow an efficient scattering matrix formulation to describe general structures with multiple discontinuities. Studies of the reflection, transmission and radiation of surface plasmons incident on both dielectric and metallic surface discontinuities show a correspondence with an effective Fresnel description. We also model a surface plasmon Distributed Bragg Reflector (DBR) capable of reflecting between 80% and 90% of incident surface plasmon power. Radiation mode scattering ultimately limits the DBR’s reflection performance rather than the intrinsic absorption of the metal. Thus alternative plasmonic geometries that suppress radiation modes, such as gap and channel structures, could be superior for the design of strongly reflective DBRs for integration in high Q-factor nano-scale cavities. We anticipate that this method will be an invaluable tool for the efficient and intuitive design of plasmonic devices based on structural non-uniformities.
TL;DR: A one-step electron-beam lithography process for the fabrication of a high-aspect ratio nanopin array is presented, which can lead to ultrasensitive surface-enhanced Raman scattering chemical sensor arrays, etc.
Abstract: A one-step electron-beam lithography process for the fabrication of a high-aspect ratio nanopin array is presented. Each nanopin is a metal-capped dielectric pillar upon a ring-shaped metallic disc. Highly tunable optical properties and the electromagnetic interplay between the metallic components were studied by experiment and simulation. The two metallic pieces play asymmetrical roles in their coupling to each other due to their drastic size difference. The structure can lead to ultrasensitive surface-enhanced Raman scattering chemical sensor arrays, etc.
TL;DR: This all-optical system for achieving parallel and selective control and detection of activity in a large number of neurons is reported and should be adaptable to in vivo applications and could serve as an optical interface for communicating with complex neural circuits.
Abstract: A key technical barrier to furthering our understanding of complex neural networks has been the lack of tools for the simultaneous spatiotemporal control and detection of activity in a large number of neurons. Here, we report an all-optical system for achieving this kind of parallel and selective control and detection. We do this by delivering spatiotemporally complex optical stimuli through a digital micromirror spatiotemporal light modulator to cells expressing the light-activated ionotropic glutamate receptor (LiGluR), which have been labeled with a calcium dye to provide a fluorescent report of activity. Reliable and accurate spatiotemporal stimulation was obtained on HEK293 cells and cultured rat hippocampal neurons. This technique should be adaptable to in vivo applications and could serve as an optical interface for communicating with complex neural circuits.
TL;DR: In this article, an efficient and accurate computational approach using the finite element method in conjunction with a constitutive model of Z-fibre response behavior under mixed mode loading condition is presented.
Abstract: The main objective of this paper is to investigate the benefits of Z-fibre pinning to improve the bonding strength of composite joints. The problem is addressed from a design point of view in order to develop a simulation methodology that can be employed to predict the strength of Z-fibre pinned joints. Firstly, an efficient and accurate computational approach is presented using the finite element method in conjunction with a constitutive model of Z-fibre response behaviour under mixed mode loading condition. The Z-fibre bridging model previously developed by the authors is summarised in the paper. Secondly, the computational approach is demonstrated via the analysis of two structural joints, namely a conventional T-joint and a novel cruciform joint. Comparison with test data confirms the model’s predictive capability.
TL;DR: A novel microfabricated platform that enables a multi-directional stimulation to a cell using topographical cues and demonstrates the importance of actomyosin network in long-range communication and regulation of local actin polymerization activities.
Abstract: Cell migration, which involves complicated coordination of cytoskeleton elements and regulatory molecules, plays a central role in a large variety of biological processes from development, immune response to tissue regeneration. However, conventional methods to study in vitro cell migration are often limited to stimulating a cell along a single direction or at a single location. This restriction prevents a deeper understanding of the fundamental mechanisms that control the spatio-temporal dynamics of cytoskeleton. Here we report a novel microfabricated platform that enables a multi-directional stimulation to a cell using topographical cues. In this device, cells were seeded on a grid-patterned topographically structured surface composed of 2 μm wide and 2 μm high straight ridges. Because the size of a unit grid was smaller than a single cell, each cell was simultaneously experiencing contact guidance leading to different directions. The device showed that healthy cells preferred to align and migrate in the direction of the longer side of the grid. But cells with impaired intracelluar tension force generation exhibited multiple uncoordinated cell protrusions along guiding ridges in all directions. Our results demonstrate the importance of actomyosin network in long-range communication and regulation of local actin polymerization activities. This platform will find wide applications in investigations of signal transduction and regulation process in cell migration.
TL;DR: The tumoricidal mechanism of the anti-beta2M mAbs is further defined and provides strong evidence to support the potential of these mAbs as therapeutic agents for myeloma.
TL;DR: Despite a unique history of antimalarial drugs in Yunnan, its geographical connections with three malarious countries facilitate gene flow among parasite populations and evolution of novel drug‐resistant genotypes, therefore, continuous surveillance of drug resistance in this area is necessary for timely adjustment of local drug policies and more effective malaria control.
Abstract: Resistance of Plasmodium falciparum to chloroquine (CQ) is determined by the mutation at K76T of the P. falciparum chloroquine resistance transporter (pfcrt) gene and modified by other mutations in this gene and in the P. falciparum multidrug resistance 1 (pfmdr1) gene. To determine the extent of polymorphisms in these genes in field P. falciparum isolates from Yunnan province of China, we genotyped the pfcrt codon 76, pfmdr1 codons 86 and 1246. Our results showed that although CQ has been withdrawn from treating falciparum malaria for over two decades, 90.3% of the parasites still carried the pfcrt K76T mutation. In contrast, mutations at pfmdr1 codons 86 and 1246 were rare. Sequencing analysis of the pfcrt gene in 34 parasite field isolates revealed CVIET at positions 72-76 as the major type, consistent with the theory of Southeast Asian origin of CQ resistance in the parasite. In addition, two novel pfcrt haplotypes (75D/144Y/220A and 75E/144Y/220A) were identified. Real-time polymerase chain reaction was used to determine pfmdr1 gene amplification, which is associated with mefloquine resistance. Our result indicated that in agreement with that mefloquine has not been used in this area, most (>90%) of the parasites had one pfmdr1 copy. Genotyping at two hypervariable loci showed relatively low levels of genetic diversity of the parasite population. Meanwhile, 28.4% of cases were found to contain mixed clones, which favour genetic recombination. Furthermore, despite a unique history of antimalarial drugs in Yunnan, its geographical connections with three malarious countries facilitate gene flow among parasite populations and evolution of novel drug-resistant genotypes. Therefore, continuous surveillance of drug resistance in this area is necessary for timely adjustment of local drug policies and more effective malaria control.
TL;DR: In this article, a permittivity renormalization technique is proposed and developed to obtain an explicit analytic expression for the critical gain required to achieve infinite surface plasmon polaritons (SPP) propagation length.
Abstract: The propagation and amplification of surface plasmon polaritons (SPPs) is studied at the interfaces between metals and active media. A permittivity renormalization technique is proposed and developed to obtain an explicit analytic expression for the critical gain required to achieve infinite SPP propagation length. A specific multiple quantum-well (MQW) system is identified as a prospective medium for demonstrating efficient SPP amplification at telecommunication frequencies. The proposed system may have a strong impact on a variety of photonic devices ranging from plasmonic nanocircuits, subwavelength transmission lines and plasmonic cavities to nanosized transducers.
TL;DR: A new kind of metamaterial, an array of periodic gold rod pairs standing on gold substrate, is introduced and an observable negative refraction behavior of EM wave is attained in this structure at wavelength 61.2 microm, providing direct evidence for thenegative refraction property.
Abstract: A new kind of metamaterial, an array of periodic gold rod pairs standing on gold substrate, is introduced in this paper. A commercial electromagnetic mode solver, the High-Frequency Structure Simulator, is employed to explore the propagation property of electromagnetic waves in this system. When an $S$-polarized electromagnetic (EM) wave propagates along the substrate surface, strong magnetic resonance is produced in the far-infrared regime. Based on the simulated $S$ parameters, effective refraction index is retrieved and negative value is obtained over the wavelength range from $49.2\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ to $66.7\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$. A wedge made of this metamaterial with an inclined angle 26.6\ifmmode^\circ\else\textdegree\fi{} is designed. An observable negative refraction behavior of EM wave is attained in this structure at wavelength $61.2\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$. The refractive index is calculated by Snell's law and it is consistent with the retrieved results quite well. This provides direct evidence for the negative refraction property.
TL;DR: It is shown that no long-range eigenmodes exists for these gap plasmon waveguides, and that the reported "modes" are likely to be beams of bulk waves and surface plasmons, rather than guided modes of the considered structures.
Abstract: Satuby and Orenstein [Opt. Express 15, 4247-4252 (2007)] reported the discovery and numerical and experimental investigation of long-range surface plasmon-polariton eigenmodes guided by wide (6 to 12 mum) rectangular gaps in 400 nm thick gold films using excitation of vacuum wavelength lambda(vac) = 1.55 mum. In this paper, we carry out a detailed numerical analysis of the two different types of plasmonic modes in these structures. We show that no long-range eigenmodes exists for these gap plasmon waveguides, and that the reported "modes" are likely to be beams of bulk waves and surface plasmons, rather than guided modes of the considered structures.
TL;DR: Two methods to tune the working wavelength from UV to visible by tuning either the permittivity of the surrounding medium or that of the metal are presented.
Abstract: A far-field optical superlens, which is able to form sub-diffraction- limited images in the far field at UV wavelength, was recently demonstrated. In current work we present two methods to tune the working wavelength from UV to visible by tuning either the permittivity of the surrounding medium or that of the metal. A practical design is provided for each method. The tunable far-field superlens enables possible applications of the far-field superlens in sub-diffraction-limited imaging and sensing over a wide range of wavelength.
01 Jan 2007
TL;DR: This paper presents a model for building cluster distribution analysis based on the Delaunay triangulation skeleton, which obtains a special geometric construction similar to Voronoi diagram that spatially partitions the gap area equally.
Abstract: This paper presents a model for building cluster distribution analysis based on the Delaunay triangulation skeleton. The skeleton connection within the gap area among the building polygons obtains a special geometric construction similar to Voronoi diagram that spatially partitions the gap area equally. Each building polygon is surrounded by a partitioning polygon which can be regarded as the growth region of inner building. Based on this model, several cluster structure variables can be computed, such as the distribution density, the topological neighbour, the adjacent distance and the adjacent direction. Considering the constraints of position accuracy, statistical area balance, orthogonal shape in building generalization, the study presents a progressive algorithm of building cluster aggregation, including the conflict detection (where), the object (who) displacement and the geometric combination (how). The algorithm has been realized in a generalization system and some experiment illustrations are provided in the paper.
TL;DR: Numerical calculations, which agree very well with the experimental observation of evanescent-wave Moiré fringes, elucidate the crucial role of the surface plasmon polaritons.
Abstract: We have demonstrated a surface plasmon polariton mediated optical Moire effect by inserting a silver slab between two subwavelength gratings. Enhancement of the evanescent fields by the surface plasmon excitations on the silver slab leads to a remarkable contrast improvement in the Moire fringes from two subwavelength gratings. Numerical calculations, which agree very well with the experimental observation of evanescent-wave Moire fringes, elucidate the crucial role of the surface plasmon polaritons. The near-field Moire effect has potential applications to extend the existing Moire techniques to subwavelength characterization of nanostructures.
TL;DR: In this article, a one-dimensional magnetic plasmon propagating in a linear chain of single split ring resonators is proposed, where the subwavelength size resonators interact mainly through exchange of conduction current.
Abstract: A one-dimensional magnetic plasmon propagating in a linear chain of single split ring resonators is proposed. The subwavelength size resonators interact mainly through exchange of conduction current, resulting in stronger coupling as compared to the corresponding magneto-inductive interaction. Finite-difference time-domain simulations in conjunction with a developed analytical theory show that efficient energy transfer with signal attenuation of less then 0.57 dB/microm and group velocity higher than 1/4c can be achieved. The proposed novel mechanism of energy transport in the nanoscale has potential applications in subwavelength transmission lines for a wide range of integrated optical devices.
TL;DR: ZrC∕ZrB2 multilayers with nanoscale bilayer periods were synthesized by rf magnetron sputtering, and the analysis of x-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and nanoindentation indicated that multilayer possessed much higher hardness than the rule-of-mixture value of monolithic ZrC and ZrB 2 coatings.
Abstract: ZrC∕ZrB2 multilayers with nanoscale bilayer periods were synthesized by rf magnetron sputtering. The analysis of x-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and nanoindentation indicated that multilayers possessed much higher hardness than the rule-of-mixture value of monolithic ZrC and ZrB2 coatings. A maximum hardness (over 47GPa) was observed in the multilayer with 27.7-nm-thick bilayer period deposited at 400°C. Higher residual stress built in the ZrC layer can be released by periodic insertion of ZrB2 into ZrC layer. The enhanced mechanical properties were related to the multilayered structure with mixed ZrB2(001), ZrB2(002), and ZrC(111) orientations.
TL;DR: Although IgM–/– mice have relatively normal B cell development with IgD BCR replacing IgM BCR, the absence of IgM‐mediated signals has a profound impact on the development of CIA, indicating that IgM plays an important role in the development and pathogenesis of autoimmune arthritis and IgM-mediated signalling is critical in the generation of pathogenic autoreactive antibodies.
Abstract: IgM is one major type of B cell receptor (BCR) expressed on most of the B cells from immature to mature stages. During normal B cell ontogeny, signals transduced through the IgM BCR play an important role in regulating B cell maturation and survival at multiple checkpoints. In addition, IgM BCR is also required for antigen-dependent differentiation and activation of B cells. However, whether IgM BCR-mediated signalling is important for the pathogenesis of autoimmune diseases remains elusive. Using IgM-deficient mice, we examined the effect of absence of IgM on the development of collagen-induced arthritis (CIA), an animal model of rheumatoid arthritis (RA). Compared to their wild-type littermates, IgM-deficient mice were either resistant to arthritis induction or developed significantly less severe arthritis. There was a significant decrease of autoantibody production in IgM-deficient mice, particularly IgG2a antibodies, which is believed to be pathogenic in CIA. Thus, although IgM(-/-) mice have relatively normal B cell development with IgD BCR replacing IgM BCR, the absence of IgM-mediated signals has a profound impact on the development of CIA, indicating that IgM plays an important role in the development and pathogenesis of autoimmune arthritis and IgM-mediated signalling is critical in the generation of pathogenic autoreactive antibodies.
TL;DR: In this article, the authors numerically studied a new type of infrared resonator structure, whose unit cell consists of paired split-ring resonators (SRRs), at different resonant frequencies, the magnetic dipoles induced from the two SRRs within one unit cell can be parallel or antiparallel, respectively.
Abstract: In this paper, we numerically study a new type of infrared resonator structure, whose unit cell consists of paired split-ring resonators (SRRs). At different resonant frequencies, the magnetic dipoles induced from the two SRRs within one unit cell can be parallel or antiparallel, which are defined as symmetric and antisymmetic modes, respectively. Detailed simulation indicates that the symmetric mode is due to magnetic coupling to resonators, in which the effective permeability could be negative. However, the antisymmetric mode originating from strong electric coupling may contribute to negative effective permittivity. Our new electromagnetic resonators with pronounced magnetic as well as electric responses could provide a new pathway to design negative index materials (NIMs) in the optical region.