Showing papers on "Metamaterial antenna published in 2008"

Three-dimensional optical metamaterial with a negative refractive index

Abstract: Metamaterials are artificially engineered structures that have properties, such as a negative refractive index, not attainable with naturally occurring materials. Negative-index metamaterials (NIMs) were first demonstrated for microwave frequencies, but it has been challenging to design NIMs for optical frequencies and they have so far been limited to optically thin samples because of significant fabrication challenges and strong energy dissipation in metals. Such thin structures are analogous to a monolayer of atoms, making it difficult to assign bulk properties such as the index of refraction. Negative refraction of surface plasmons was recently demonstrated but was confined to a two-dimensional waveguide. Three-dimensional (3D) optical metamaterials have come into focus recently, including the realization of negative refraction by using layered semiconductor metamaterials and a 3D magnetic metamaterial in the infrared frequencies; however, neither of these had a negative index of refraction. Here we report a 3D optical metamaterial having negative refractive index with a very high figure of merit of 3.5 (that is, low loss). This metamaterial is made of cascaded 'fishnet' structures, with a negative index existing over a broad spectral range. Moreover, it can readily be probed from free space, making it functional for optical devices. We construct a prism made of this optical NIM to demonstrate negative refractive index at optical frequencies, resulting unambiguously from the negative phase evolution of the wave propagating inside the metamaterial. Bulk optical metamaterials open up prospects for studies of 3D optical effects and applications associated with NIMs and zero-index materials such as reversed Doppler effect, superlenses, optical tunnelling devices, compact resonators and highly directional sources.

Experimental demonstration of frequency-agile terahertz metamaterials

Abstract: Metamaterials exhibit numerous novel effects1,2,3,4,5 and operate over a large portion of the electromagnetic spectrum6,7,8,9,10. Metamaterial devices based on these effects include gradient-index lenses11,12, modulators for terahertz radiation13,14,15 and compact waveguides16. The resonant nature of metamaterials results in frequency dispersion and narrow bandwidth operation where the centre frequency is fixed by the geometry and dimensions of the elements comprising the metamaterial composite. The creation of frequency-agile metamaterials would extend the spectral range over which devices function and, further, enable the manufacture of new devices such as dynamically tunable notch filters. Here, we demonstrate such frequency-agile metamaterials operating in the far-infrared by incorporating semiconductors in critical regions of metallic split-ring resonators. For this first-generation device, external optical control results in tuning of the metamaterial resonance frequency by ∼20%. Our approach is integrable with current semiconductor technologies and can be implemented in other regions of the electromagnetic spectrum. Metamaterials that possess frequency tunability enable new device functions. By external optical control through the incorporation of semiconductors in metallic split-ring resonators, the researchers provide an elegant solution to frequency-agile terahertz metamaterials.

Metamaterial antenna arrays with radiation pattern shaping and beam switching

Abstract: Apparatus, systems and techniques for using composite left and right handed (CRLH) metamaterial (MTM) structure antenna elements and arrays to provide radiation pattern shaping and beam switching.

Tunable transmission and harmonic generation in nonlinear metamaterials

Abstract: We study the properties of a tunable nonlinear metamaterial operating at microwave frequencies We fabricate the nonlinear metamaterial composed of double split-ring resonators and wires where a varactor diode is introduced into each resonator so that the magnetic resonance can be tuned dynamically by varying the input power We show that at higher powers the transmission of the metamaterial becomes power dependent, and we demonstrate experimentally power-dependent transmission properties and selective generation of higher harmonics

CPW-Fed Multi-Band Omni-Directional Planar Microstrip Antenna Using Composite Metamaterial Resonators for Wireless Communications

Abstract: A novel approach for the design of a compact multiband planar microstrip antenna is presented. This type of antenna is composed of composite metamaterial resonators (including conditional microstrip resonators and metamaterial resonators), and fed by signal feed. A sample antenna with composite closed-ring resonator and split-ring resonator (SRR) fed by 50 Ω coplanar waveguide (CPW) developed on FR4 epoxy substrate for multi-band wireless communication applications is presented. Appropriate design of the composite structure resulted in three discontinuous resonant bands. The fundamental magnetic resonant and electric resonant frequency of SRR and the first electric resonant frequency of the closed-ring resonator were combined to form low, middle, and high resonant band. The properties of this antenna are investigated by theoretical analysis and finite element method (FEM) simulations. The numerical results show that the proposed antenna has good impedance bandwidth and radiation characteristics in the three operating bands which cover the required band widths of the 2.4/5.2/5.8GHz wireless local-area networks (WLAN) and 3.5/5.5 GHz worldwide interoperability for microwave access (WiMax) with return loss of better than 10 dB. The antenna also has stably omni-directional H-plane radiation patterns within the three operating bands.

A d.c. magnetic metamaterial

Abstract: Electromagnetic metamaterials are a class of materials that have been artificially structured on a subwavelength scale. They are currently the focus of a great deal of interest because they allow access to previously unrealizable properties such as a negative refractive index. Most metamaterial designs have so far been based on resonant elements, such as split rings, and research has concentrated on microwave frequencies and above. Here, we present the first experimental realization of a non-resonant metamaterial designed to operate at zero frequency. Our samples are based on a recently proposed template for an anisotropic magnetic metamaterial consisting of an array of superconducting plates. Magnetometry experiments show a strong, adjustable diamagnetic response when a field is applied perpendicular to the plates. We have calculated the corresponding effective permeability, which agrees well with theoretical predictions. Applications for this metamaterial may include non-intrusive screening of weak d.c. magnetic fields.

Dual-band planar electric metamaterial in the terahertz regime

Abstract: We present the design, fabrication, and measurement of a dual-band planar metamaterial with two distinct electric resonances at 1.0 and 1.2 THz, as a step towards the development of frequency agile or broadband THz materials and devices. A method of defining the effective thickness of the metamaterial layer is introduced to simplify the material design and characterization. Good agreement between the simulated and measured transmission is obtained for the fabricated sample by treating the sample as multi-layer system, i. e. the effective metamaterial layer plus the rest of the substrate, as well as properly modeling the loss of the substrate. The methods introduced in this paper can be extended to planar metamaterial structures operating in infrared and optical frequency ranges.

Nonlinear magnetic metamaterials

Abstract: We study experimentally nonlinear tunable magnetic metamaterials operating at microwave frequencies. We fabricate the nonlinear metamaterial composed of double split-ring resonators where a varactor diode is introduced into each resonator so that the magnetic resonance can be tuned dynamically by varying the input power. We demonstrate that at higher powers the transmission of the metamaterial becomes power-dependent and, as a result, such metamaterial can demonstrate various nonlinear properties. In particular, we study experimentally the power-dependent shift of the transmission band and demonstrate nonlinearity-induced enhancement (or suppression) of wave transmission.

The microstrip antenna

Abstract: The microstrip antenna with circular polarization characteristics have been presented. The antenna includes rectangular circular with auxiliary microstrip resonators with relative length.

Efficient metamaterial-inspired electrically-small antenna

Abstract: Planar (two-dimensional) and volumetric (three-dimensional), metamaterial-inspired, efficient electrically-small antennas. The electric-based and magnetic-based antenna systems are shown to be naturally matched to a source and are linearly scalable to a wide range of frequencies. The systems include a radiating element that is fed by the source through a finite ground plane via a feedline and an electrically-small, one-unit cell made of a metamaterial that is adapted to match the input impedance of the antenna.

Material parameter retrieval procedure for general bi-isotropic metamaterials and its application to optical chiral negative-index metamaterial design.

Abstract: A chiral optical negative-index metamaterial design of doubly periodic construction for the near-infrared spectrum is presented. The chirality is realized by incorporating sub-wavelength planar silver-alumina-silver resonators and arranging them in a left-handed helical (i.e., stair-step) configuration as a wave propagates through the metamaterial. An effective material parameter retrieval procedure is developed for general bi-isotropic metamaterials. A numerical design example is presented and the retrieved effective material parameters exhibiting a negative index of refraction are provided.

Characterization of microstrip patch antennas on metamaterial substrates loaded with complementary split‐ring resonators

Abstract: We present characteristics of microstrip patch antennas on metamaterial substrates loaded with complementary split-ring resonators (CSRRs). The proposed antenna utilizes CSRRs in the ground plane altering the effective medium parameters of the substrate. To characterize the performance of the CSRR loaded microstrip antenna, the metamaterial substrate has been modeled as an effective medium with extracted constitutive parameters. Simulation results were verified by experimental results. The experimental results confirm that the CSRR loaded patch antenna achieves size reduction as well as bandwidth improvement. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2131–2135, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23596

Unified Homogenization Theory for Magnetoinductive and Electromagnetic Waves in Split Ring Metamaterials

Abstract: A unified homogenization procedure for split-ring metamaterials taking into account time and spatial dispersion is introduced. It is shown that electromagnetic and magnetoinductive waves propagating in the metamaterial are obtained from this analysis. Therefore, the proposed time and spatially dispersive permeability accounts for the characterization of the complete spectrum of waves of the metamaterial. Finally, it is shown that the proposed theory is in good quantitative and qualitative agreement with full wave simulations.

Characterization of miniaturized metamaterial resonators coupled to planar transmission lines through parameter extraction

Abstract: In this paper, a method for obtaining the electrical characteristics of metamaterial resonators coupled to planar transmission lines is proposed This parameter extraction technique is based on the comparison between the measured (or full wave electromagnetic simulated) transmission and reflection characteristics of a host line loaded with such resonators and those obtained from its lumped element equivalent circuit model (previously reported by some of the authors) The resonant particles considered in this study are split ring resonators, spiral resonators, and other electrically small resonant particles based on two metal levels The interest in this technique lies in the lack of analytical models providing the electrical parameters of several of the considered ultrasmall resonator topologies (due to their complexity) From the extracted parameters, it is concluded that the circuit models predict very accurately the frequency responses of the considered structures for the different resonators under stu

Design of Single PIN Shorted Three-Dielectric-Layered Substrates Rectangular Patch Microstrip Antenna for Communication Systems

Abstract: In this paper, we have simulated a single-pin-shorted microstrip line fed three-dielectric-layer (with different permittivity and thickness) rectangular patch microstrip antenna for all those communication systems whose limited antenna size is premium. Low permittivity hard foam has been used as one substrate to achieve wide bandwidth. The simulation of this proposed antenna has been performed by using CST Microwave Studio, which is a commercially available electromagnetic simulator based on the finite difference time domain technique.

Single-layer metallization and via-less metamaterial structures

Abstract: Techniques and apparatus based on metamaterial structures provided for antenna and transmission line devices, including single-layer metallization and via-less metamaterial structures.

Retrieving effective parameters for quasiplanar chiral metamaterials

Abstract: We introduce and compare two approaches for retrieving quantitatively the effective chirality of metamaterials at normal incidence. The retrieval employs either the reflected and transmitted amplitude of a plane wave illuminating a finite three-dimensional (3D) metamaterial or the dispersion relation of the pertinent Bloch modes in an infinite metamaterial. Both approaches are applied to characterize a 3D metamaterial consisting of a stack of metallic gammadions separated by dielectric films. It will be shown that the results coincide if transitional effects between the metamaterial and the environment can be neglected.

New Concept Conformal Antennas Utilizing Metamaterial and Transformation Optics

Abstract: In this letter, we show by theoretical analysis and computer simulation that conformal antennas can be designed using metamaterial with inhomogeneous constitutive parameters by applying the electromagnetic coordinate transformation approach, which is the technique used to realize electromagnetic invisibility. We demonstrate that, a source of arbitrary shape and position in the free space can be replaced by an properly designed metamaterial coating with current distributed on the inner surface and would not be detected by outer observers, because the emission of the source can be controlled at will in this way. As examples, we design two conformal antennas by transforming a simple dipole antenna and a standard array antenna separately to illustrate the possible applications of this kind of transformation.

Beam-Scanning Performance of Leaky-Wave Slot-Array Antenna on Variable Stub-Loaded Left-Handed Waveguide

Abstract: Metamaterial is an artificial material in which the effective phase constant can be controlled by the internal physical periodic structure of the transmission line. Effective phase constant is designed to be of any value, which may be small, large, approximately zero, or negative, attained by changing the dimensions of the periodic structure. Miniaturization of the antenna and wide design flexibility of radiation patterns can be expected from the use of metamaterials. In this work, we developed a leaky-wave slot-array antenna on a variable stub-loaded left-handed waveguide. The radiation pattern of the fabricated antenna was measured and the characteristics of the left-handed transmission line were observed. Moreover, performance of beam-scanning by changing the length of the stubs on the waveguide was confirmed experimentally.

Automotive radar using a metamaterial lens

Abstract: An example apparatus comprises an electromagnetic source, such as an antenna, a metamaterial lens, and a reflector The antenna is located proximate the metamaterial lens, for example supported by the metamaterial lens, and the antenna is operable to generate radiation when the antenna is energized The reflector is positioned so as to reflect the radiation through the metamaterial lens The reflector may have a generally concave reflective surface, for example having a parabolic or spherical cross-section The metamaterial lens may have an area similar to that of the aperture of the reflector In some examples, the antenna is located proximate a focal point of the reflector, so that a generally parallel beam is obtained after reflection from the reflector

Metamaterial Superstrate and Electromagnetic Band-Gap Substrate for High Directive Antenna

Abstract: A high directive planar antenna made from a metamaterial superstrate and an electromagnetic band-gap (EBG) substrate has been investigated. A patch antenna surrounded with EBG structures is used as the radiation source. The CST Microwave Studio is used for the simulation. The results show that the gain of the antenna with metamaterial is 21.6 dB at the operating frequency of 14.6 GHz. Compared with the patch feed with the same aperture size but without the metamaterial superstrate, the performance of the antenna is improved obviously and the gain increases about 12.4 dB.

Negative-zero-positive metamaterial with omega-type metal inclusions

Abstract: We report on a negative-zero-positive metamaterial based on an omega-type microstructure with special attention on the nonvanishing group velocity for a zero refractive index. We first investigate the dispersion characteristics by full wave analysis, by stressing the necessary conditions of equality between the electric and magnetic plasma frequencies which are characteristic of the dispersion of the effective permittivity and permeability. Also, tuning of the gapless transition frequency between the left and right-handed dispersion branches was analyzed when the permittivity of the host substrate is changed. Last, we demonstrate experimentally the balanced composite character of the dispersion by frequency and angle-resolved transmission measurements, carried out at centimeter wavelengths on slabs and wedge-type prototypes, respectively.

A three-dimensional isotropic transmission-line metamaterial topology for free-space excitation

Abstract: This work proposes a three-dimensional isotropic transmission-line metamaterial topology for free-space excitation whose negative-refractive-index properties are validated by full-wave simulation. The topology is based on a physical realization of the symmetrical condensed node of transmission-line matrix modeling, but reverses the positions of the inductive and capacitive lumped elements in order to yield an isotropic negative refractive index and good matching to free space.

An approach to equivalent circuit modeling of rectangular microstrip antennas

Abstract: Computation of the broadband matching potential of a microstrip antenna requires the wideband lumped equivalent circuit of the antenna. The general topology of the equivalent circuit of rectangular microstrip patch antennas has been used to model the feed- point impedance of microstrip antennas over a wide frequency band and equivalent circuit parameters are determined using optimization techniques. The proposed procedure overcomes the problems of physical realizability of the equivalent circuit and estimation of the starting values of the optimization. Applying this technique, wideband lumped equivalent circuits of a rectangular and E-shaped microstrip antenna have been computed which are in good agreement with measurement data from 0.1 to 6 GHz.

Synthesis of transmission line models for metamaterial slabs at optical frequencies

Abstract: We study the scattering parameters of typical transmission line resonant circuits and their corresponding nonlocal effective material parameters at optical frequencies using transmission line theory. We find that each circuit has specific features in terms of nonlocal permittivity and permeability and can be utilized to quantitatively synthesize transmission line circuit models for metamaterial slabs. As application examples, we construct circuit models for cut wires, cut-wire pairs, metallic meshes, and mesh pairs. Moreover, we calculate local material parameters in a simple way using fitted impedance parameters together with a transmission line homogenization procedure. Using transmission line (TL) models, we show how the material parameters can be optimized in actual metamaterials. The physical dependence of circuit parameters on structure geometries validates our TL model further.

Transmission properties of composite metamaterials in free space

Abstract: We present free-space microwave measurements on composite metamaterials (CMMs) consisting of split ring resonators (SRRs) and wires on alternating boards, also known as left-handed material (LHM). Our experiments are based on a type of CMMs with unique configurations and the transmission measurements performed in free space exhibit a pass band extending from 10.5 to 13.5 GH. The widely belief of the pass band is that the stop bands of the SRRs alone and the wires alone constitute a clear demonstration of left-handed (LH) behaviour. The LH behaviour only take place in the medium with simultaneously negative permittivity epsiv, and permeability mu, also called double negative materials.

Left handed metamaterial design for microstrip antenna application

Abstract: This paper describes the design and simulation of the left-handed metamaterial structure incorporated with a single microstrip patch antenna The combination of the modified square rectangular split ring (SRR) and the capacitance loaded strip (CLS) was used to obtain the negative value of permeability, mur and the negative permittivity, epsivr From the simulation done, the gain of the antenna has been increased up to 4 dB This had proven that the LH MTM can enhance the gain of the antenna

Multi-Metamaterial-Antenna Systems with Directional Couplers

Abstract: Examples of apparatus and techniques for providing metamaterial (MTM) multi-antenna array systems with directional couplers for various applications.

Metamaterial structure having negative permittivity, negative permeability, and negative refractivity

Abstract: Provided is an unlimited single-layer metamaterial structure having negative permittivity and negative permeability in a frequency bandwidth desired by a user. The metamaterial structure includes: a dielectric having a single layer structure having a permittivity or a multi-layer structure in which at least one layer has a different permittivity; and a single conductor disposed in the dielectric, wherein the metamaterial structure has a permittivity, a permeability, and a refractivity that have 0 or a negative value in a predetermined frequency band.

Experimental Confirmation of Guidance Properties Using Planar Anisotropic Left-Handed Metamaterial Slabs Based on S-Ring Resonators

Abstract: We experimentally studied the guidance properties of the S-shaped metamaterial slabs. A peek of transmitted power due to the bulk guidance modes is observed in the negative band of the metamaterial,which is larger than a conventional dielectric waveguide made of FR4. The peek transmission frequency is shown related with the change of the negative band of the S-shaped metamaterial slab. Our results show good agreement with the theoretical predictions.