Showing papers on "Metamaterial antenna published in 2007"

Method for retrieving effective properties of locally resonant acoustic metamaterials

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.

Antennas based on metamaterial structures

Abstract: Techniques, apparatus and systems that use one or more composite left and right handed (CRLH) metamaterial structures in processing and handling electromagnetic wave signals. Antennas and antenna arrays based on enhanced CRLH metamaterial structures are configured to provide broadband resonances for various multi-band wireless communications.

Antennas, Devices and Systems Based on Metamaterial Structures

Abstract: Techniques, apparatus and systems that use one or more composite left and right handed (CRLH) metamaterial structures in processing and handling electromagnetic wave signals. Antenna, antenna arrays and other RF devices can be formed based on CRLH metamaterial structures. The described CRLH metamaterial structures can be used in wireless communication RF front-end and antenna sub-systems.

Subwavelength resolution with a negative-index metamaterial superlens

Abstract: Negative-index metamaterials are candidates for imaging objects with sizes smaller than a half-wavelength. The authors report an impedance-matched, low loss negative-index metamaterial superlens that is capable of resolving subwavelength features of a point source with a 0.13λ resolution, which is the highest resolution achieved by a negative-index metamaterial. By separating two point sources with a distance of λ∕8, they were able to detect two distinct peaks on the image plane. They also showed that the metamaterial based structure has a flat lens behavior.

Phase-varying metamaterial for compact steerable directive antenna

Abstract: The design of a locally phase-varying one-dimensional metamaterial working near 10 GHz is reported. It is made from a capacitive and an inductive grid. The phase-varying behaviour is obtained with a regular incrementation of the spacing between each unit cell of the capacitive grid in one direction. This composite metamaterial is then used as a partially reflecting surface in a resonant Fabry-Peacuterot type cavity together with a patch antenna to constitute a compact steerable directive printed antenna. A plusmn20deg deflection of the antenna beam is obtained

A novel flat lens horn antenna designed based on zero refraction principle of metamaterials

Abstract: In this paper, a horn antenna filled with a metamaterial structure as lens inner the aperture is presented. Unlike conventional curve lenses, the lens is designed in the present work using a fully flat structure, which results in a great improvement for the directivity of the horn antenna based on the zero refraction characteristics of the metamaterial. In this structure, a periodic-structure metamaterial with three-layer metal grids is designed using the CST Microwave Studio for optimization and its zero refraction property is validated. For the characterization of the antenna, the electric-field distribution in radiation area, reflection parameter (S11), gain and radiation pattern are calculated. The results show that the gain of a wide flare angle horn antenna is enhanced with over 2 dB between 16.10–17.30 GHz after the metamaterial is utilized. Therefore, the metamaterial lens horn structure results in a miniaturized antenna design approach compared to the optimum conventional horn of the same aperture size and gain in the interested frequency band.

Combinations of low/high permittivity and/or permeability substrates for highly directive planar metamaterial antennas

Abstract: An investigation of planar metamaterial antennas consisting of grounded metamaterial substrates with low and/or high values of the electric permittivity and/or the magnetic permeability excited by dipole sources is presented. Their performances are characterised in terms of their capability to radiate high levels of power density in the broadside direction and to produce narrow pencil beams pointing at broadside with high directivity. To achieve a high directivity, a pair of weakly attenuated cylindrical leaky waves is excited along the metamaterial substrate; sufficient conditions are established for the existence of such leaky waves in terms of the values of the substrate permittivity and permeability. Approximate closed-form expressions are derived for the phase and attenuation constants of the leaky waves. Numerical results are given in order to illustrate the radiative features of this class of antennas and to validate the theoretical analysis.

Special Issue on Metamaterials EBG Combinations of low/high permittivity and/or permeability substrates for highly directive planar metamaterial antennas

Abstract: G. Lovat, P. Burghignoli, F. Capolino and D.R. JacksonAbstract: An investigation of planar metamaterial antennas consisting of grounded metamaterialsubstrateswithlowand/or highvaluesoftheelectric permittivity and/orthemagneticpermeabilityexcited by dipole sources is presented. Their performances are characterised in terms of their capa-bilitytoradiatehighlevelsof powerdensityinthebroadside direction andtoproducenarrow pencilbeams pointing at broadside with high directivity. To achieve a high directivity, a pair of weaklyattenuated cylindrical leaky waves is excited along the metamaterial substrate; sufficient conditionsare established for the existence of such leaky waves in terms of the values of the substrate permit-tivity and permeability. Approximate closed-form expressions are derived for the phase and attenu-ation constants of the leaky waves. Numerical results are given in order to illustrate the radiativefeatures of this class of antennas and to validate the theoretical analysis.1 IntroductionPeriodic structures made of metallic and/or dielectricinclusions in a uniform host medium may be represented,in suitable frequency ranges, as homogeneous artificialmaterials (metamaterials) that show novel and interestingelectromagnetic features. One of these features is thecreation of highly directive radiation beams from simplesourcessuchasdipolesorslotsplacedinside suchmaterials,as was obtained in the pioneering work of Gupta [1],Poilasne et al. [2] and Enoch et al. [3] For a detailedhistorical overview of such enhanced-directivity antennas,we address the reader to the Introduction of Lovat et al.[4]. The structures considered here consist of a groundedmetamaterial layer that may have either high or lowvalues of permittivity and/or permeability, excited byeither an electric or a magnetic dipole source. Such struc-tures are different from those where a cavity is createdunder a partially reflective surface that is formed by high-permittivity dielectrics [5–7], metallic FSS layers [8, 9]or other periodic dielectric structures [10, 11]. Althoughdifferent in structure, the metamaterial antennas consideredin this work are similar in terms of the mechanism ofradiation: in fact, all the antennas in [1–11] radiate anarrow beam because the feed excites slowly attenuatingleaky waves, as demonstrated in the work of Lovat et al.[4] and Jackson and Oliner [6].Thetheorybehindagroundedslabmadeofsuchmetama-terials is revisited here, assuming a homogeneous isotropicmedium with parameters m

Electronically reconfigurable metamaterial for compact directive cavity antennas

Abstract: The modelling and characterisation of an electronically controllable metamaterial partially reflecting surface to a resonant cavity antenna near 8 GHz is considered. The metamaterial considered is composed of a composite phase varying metamaterial, by the insertion of active electronic components, and is proposed for the design of the reconfigurable Fabry-Perot cavity antenna. An adjustable resonance frequency between 7.9 and 8.2 GHz is obtained and a drastic enhancement in the directivity of the antenna is also observed for a cavity thickness as small as lambda/75.

Enabling RF/microwave devices using negative-refractive-index transmission-line (NRI-TL) metamaterials

Abstract: Metamaterials are artificially engineered structures with unusual electromagnetic properties. In this article, we review the implementation of isotropic metamaterials that exhibit a negative permittivity and a negative permeability, thus leading to a negative index of refraction. Specifically, the article focuses on transmission-line metamaterials, which are planar structures comprising a network of distributed transmission lines loaded periodically with inductors, L, and capacitors, C, in a "high-pass" configuration. The periodic unit cell is much smaller than the wavelength, thus leading to an effective medium in which the lumped loading elements can be either discrete (chip) or printed. Based on such negative-refractive-index transmission-line (NRI-TL) metamaterials, several RF/microwave devices are presented, including microwave lenses that can overcome the diffraction limit, compact phase-shifting lines and associated broadband series-fed power dividers, electrically small antennas, antenna feed networks and baluns, backward leaky-wave antennas, and high-directivity coupled-line couplers and reflectometers.

Simulation of a metamaterial containing cubic high dielectric resonators

Abstract: Simulation results of a metamaterial structure which uses cubic high dielectric resonators, periodically embedded in a low dielectric background in a cubic lattice, are presented. Cubic dielectric resonators have degenerate modes, which imply that the TE and TM modes have the same resonant frequency. The proposed metamaterial shows the negative refractive index characteristics around the resonance frequency of the cubic resonators, and since no plasmonic components are involved, the losses are expected to be low.

Metamaterials with negative permeability and negative refractive index: experiments and simulations

Abstract: We report the transmission characteristics of split-ring resonator and left-handed metamaterials (LHM) in the microwave frequency regime. A left-handed transmission band is observed at the frequencies where both dielectric permittivity and magnetic permeability are negative. The reflection characteristics of ordered and disordered LHMs are studied. The two-dimensional LHM structure is verified to have a negative refractive index. We employed three different methods to observe negative refraction: the beam shift method, refraction through wedge-shaped negative-index metamaterial, and phase-shift experiments.

Compact dual-band resonator using anisotropic metamaterial

Abstract: A dual-band resonator with compact size, such as a resonant type dual-band antenna, which uses an anisotropic metamaterial is described. The artificial anisotropic medium is implemented by employing a composite right/left-handed transmission line. The dispersion relation and the antenna physical size only depend on the composition of the unit cell and the number of cells used. By engineering the characteristics of the unit cells to be different in two orthogonal directions, the corresponding propagation constants can be controlled, thus enabling dual-band antenna resonances. In addition, the antenna dimensions can be markedly minimized by maximally reducing the unit cell size. A dual-band antenna is also described which is designed for operation at frequencies for PCS/Bluetooth applications, and which has a physical size of 1/18λ0 x 1/18λ0 x 1/19λ0, where λ0 is the free space wavelength at 2.37 GHz.

Experimental validation of negative refraction of metamaterial composed of single side paired S-ring resonators

Abstract: A one-dimensional metamaterial structure is realized by printing subwavelength paired S-shaped metallic strips only on one side of a dielectric substrate. The simultaneously negative effective permittivity and permeability of such metamaterial are retrieved from the scattering parameters yielded in the numerical simulation. Experiments aimed to verify the transmission and refraction properties of the metamaterial are conducted, and the results show the existence of the negative refraction within the same frequency band, as indicated in the simulation. The proposed structure design makes it easy to fabricate and provides feasibilities for making controllable metamaterial by incorporating itself with lumped active elements.

Low frequency lumped element-based negative index metamaterial

Abstract: A lumped element-based negative index metamaterial (NIM) was designed, fabricated, and tested for operation at 400MHz in the ultrahigh frequency (UHF) band. At 400MHz the measured real part of the index of refraction of this NIM was nreal=−3.11 with a loss that was less than 1dB∕cm using unit cells whose overall size d was λ∕d∼75. The NIM bandwidth was >10% in the neighborhood of 400MHz.

A directive patch antenna with metamaterial structure

Abstract: A new method to improve the gain of patch antenna with metamaterial composed of ring aperture lattice is presented. The influences of the number of metamaterial layers and a comparison of electromagnetic characteristics between the conventional patch antenna and the new metamaterial patch antenna are studied by using numerical simulation method. Then, a patch antenna with the metamaterial is fabricated and measured. The simulation and experimental results show that this method is effective and this structure can realize congregating the radiation energy, thus the gain of the antenna with metamaterial can greatly increase when compared with the conventional one. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 456–459, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22146

Analytical and numerical investigation of the radiation and scattering from concentric metamaterial cylinders excited by an electric line source

Abstract: [1] An antenna configuration consisting of an arbitrarily located electric line source radiating in the presence of a pair of concentric metamaterial cylinders is investigated analytically and numerically. The near- and far-field properties of these structures are analyzed through an investigation of such parameters as the total radiated power, directivity, and total as well as differential scattering cross sections. The results obtained for these metamaterial structures are compared to those for the corresponding structures made of conventional materials. It is shown that electrically small concentric metamaterial structures can be designed to be resonant and to possess advantageous radiation and scattering characteristics in contrast to the corresponding structures made of conventional materials. More specifically, it is shown that metamaterial structures lead to significant enhancements of the total radiated power as well as the total and differential scattering cross sections. Moreover, the feasibility of controlling the directivity pattern of the electrically small metamaterial structures through appropriate locations of the electric line source is demonstrated. The effects of the dispersion and loss present in the metamaterials are taken into account to study the bandwidth properties of these resonant configurations.

Low-index metamaterial designs in the visible spectrum.

Abstract: Low-index metamaterial designs in the visible spectrum that are impedance matched to free space are presented. The unit cell of the periodic metamaterial design incorporates a magnetic resonator and silver meshes for respective control of the effective permeability and permittivity. A genetic algorithm is employed to optimize the metamaterial design to achieve a desired set of values for the index of refraction and the intrinsic impedance. Two example GA optimized designs are provided which target the important special cases of a zero and unity index of refraction.

A Metamaterial T-Junction Power Divider

Abstract: A metamaterial based compact microstrip T-junction power divider working at 10GHz is proposed. The metamaterial unit cell consists of microstrip gaps and via holes whose behavior is equivalent to the combination of series capacitors and shunt inductors respectively, that is, a dual transmission line (high-pass) configuration. By adjusting the parameters of these structures, the characteristics of the Metamaterial-medium can be set to achieve a desired phase shift. To validate the design, a T-junction power divider is fabricated and measured. A 70% reduction of the length of the impedance transformer, without significant performance degradation, has been achieved

Double-Lorentz Transmission Line Metamaterial and its Application to Tri-Band Devices

Abstract: A double-Lorentz (DL) transmission line (TL) metamaterial is proposed for the first time. Both effective material parameters mueff and epsiveff of the corresponding line exhibit a Lorentz-type dispersion, hence the proposed terminology double-Lorentz. This type of TL presents the interest of being intrinsically tri-band, while the previously reported composite right/left-handed TL metamaterial is only dual-band. The DL TL theory is fully derived and demonstrated experimentally by a microstrip implementation. The tri-band property of the DL TL is illustrated by the design of a tri-band lambda/4 impedance transformer and a systematic design procedure is described.

Volumetric negative-refractive-index medium exhibiting broadband negative permeability

Abstract: In this article, a broadband, volumetric, negative-refractive-index metamaterial is presented and its operation is explained. The structure achieves a negative permeability bandwidth of 60% using a periodic cage of backward-wave transmission lines. The permeability is negative over a broad bandwidth due to contradirectional coupling between a backward wave guided by a transmission line and a forward, free-space wave. Negative permittivity is realized using an array of inductively loaded wires. Propagation within the infinite negative-refractive-index (NRI) medium as well as transmission through finite slabs of the NRI medium is presented. The results demonstrate that the proposed NRI medium exhibits a refractive index equal to −1 at 2.45 GHz and is well matched to free space throughout the NRI bandwidth.

Wakefield generation in metamaterial-loaded waveguides

Abstract: Metamaterials (MTMs) are artificial structures made of periodic elements and are designed to obtain specific electromagnetic properties. As long as the periodicity and the size of the elements are much smaller than the wavelength of interest, an artificial structure can be assigned a permittivity and permeability, just like natural materials. Metamaterials can be customized to have the permittivity and permeability desired for a particular application. When the permittivity and permeability are made simultaneously negative in some frequency range, the metamaterial is called double-negative or left-handed and has some unusual properties. For example, Cherenkov radiation (CR) in a left-handed metamaterial is backward; radiated energy propagates in the opposite direction to particle velocity. This property can be used to improve the design of particle detectors. Waveguides loaded with metamaterials are of interest because the metamaterials can change the dispersion relation of the waveguide significantly. Slow backward waves, for example, can be produced in a MTM-loaded waveguide without corrugations. In this paper we present theoretical studies of waveguides loaded with an anisotropic and dispersive medium (metamaterial). The dispersion relation of a MTM-loaded waveguide has several interesting frequency bands which are described. We present a universal method to simulate wakefield (CR) generation in a waveguide loaded with a dispersive and anisotropic medium. This method allows simulation of different waveguide cross sections, any transverse beam distribution, and any physical dispersion, of the medium. The method is benchmarked against simple cases, which can be theoretically calculated. Results show excellent agreement.

Improved patch antenna performance by using a metamaterial cover

Abstract: A new patch antenna system with a metamaterial cover is presented in this paper. The impedance, radiation pattern, and directivity of such an antenna are studied. A performance comparison between the conventional patch antenna and the new metamaterial patch antenna is given. The results show that the directivity of the metamaterial patch antenna is significantly improved. The effect of the metamaterial cover’s layer numbers on the radiation pattern of the patch antenna is also studied.

Resolution antenna array using metamaterials

Abstract: An antenna array includes at least one transmit array comprising a plurality of metamaterial elements. The antenna array further includes at least one near-field stimulator for inputting electromagnetic signal to the transmit array so that a sub-wavelength target is illuminated with an electromagnetic wave.

Bandwidth Enhancement of Microstrip Antennas with Metamaterial Bilayered Substrates

Abstract: Cavity resonator is introduced into microstrip structure. By eliminating the frequency parameter of cavity modes, microstrip antennas with metamaterial bilayered substrates are demonstrated the bandwidth enhancement. Lossy effects on the performance of the antennas are also considered. Finally, for less intricate antenna realization, single negative metamaterial-based microstrip antennas are designed with the same scheme and also achieve greatly enhanced bandwidth.

Superlens from complementary anisotropic metamaterials

Abstract: Metamaterials with isotropic property have been shown to possess novel optical properties such as a negative refractive index that can be used to design a superlens. Recently, it was shown that metamaterials with anisotropic property can translate the high-frequency wave vector k values from evanescence to propagating. However, electromagnetic waves traveling in single-layer anisotropic metamaterial produce diverging waves of different spatial frequency. In this work, it is shown that, using bilayer metamaterials that have complementary anisotropic property, the diverging waves are recombined to produce a subwavelength image, i.e., a superlens device can be designed. The simulation further shows that the design can be achieved using a metal/oxide multilayer, and a resolution of 30 nm can be easily obtained in the optical frequency range.

Photonic Metamaterials

Abstract: We review some of our recent results on photonic metamaterials operating at optical frequencies. In a series of interferometric pulse propagation experiments on negative index metamaterials, we have demonstrated simultaneous negative phase and group velocity of light at 1.5 mum wavelength. By optimizing the structure parameters and utilizing silver instead of gold, the losses of the negative index metamaterial have been reduced significantly. Further downscaling of the lattice constant has brought the negative refractive index to the red end of the visible spectrum. We have also fabricated negative index metamaterials with up to three functional layers. Besides of unusual dispersion properties, metamaterials can also exhibit very interesting polarization effects. We have performed experiments and numerical calculations for a chiral planar metamaterial design. This design comprises dense arrays of double-layer gammadions. The excitation of anti-symmetric current oscillations in the two layers leads to pronounced circular dichroism.

Design and Experiment of One Dimension and Two Dimension Metamaterial Structures for Directive Emission

Abstract: A new method to improve the gain of monopole and patch antenna with one dimension and two dimension metamaterial structures is presented. The analytical permittivity models of metamaterial are derived using the transmission line method. Then the monopole and patch antenna with the metamaterial are fabricated and measured. The experimental results show that this method is effective and these structures can realize congregating the radiation energy, thus the gain of these antennas with metamaterial increase greatly compared with the conventional ones.

Electromagnetic composite metamaterial

Abstract: An electromagnetic composite metamaterial including an electromagnetic medium and a plurality of spaced electromechanical resonators disposed in or on the electromagnetic medium configured to control electromagnetic wave propagation properties in the electromagnetic composite metamaterial

Applications of MM Wave Microstrip Antenna Arrays

Abstract: Microstrip antennas posses attractive features such as low profile, light weight, small volume and low production cost. In addition, integrating the microstrip feed structure with the radiating elements on the same substrate attains the benefit of a compact low cost feed network. However, losses in the microstrip feed network form a significant limit on the possible applications of microstrip antenna arrays in mm wave frequency range. However, in some applications the radiators in the array are not connected by an array feed network. In these applications we may benefit from the advantages of microstrip antennas. In this paper we describe the development and applications of mm wave microstrip arrays. MM wave microstrip antenna arrays may be employed in communication links, seekers and detection arrays. The arrays consists around 256 elements to 1024 elements. Design considerations of the antenna and the feed network are given in this paper. Optimization of the antenna and feed network allows us to design microstrip antenna arrays with high efficiency.