Showing papers on "Metamaterial absorber published in 2007"

Negative refraction in semiconductor metamaterials.

Abstract: An optical metamaterial is a composite in which subwavelength features, rather than the constituent materials, control the macroscopic electromagnetic properties of the material. Recently, properly designed metamaterials have garnered much interest because of their unusual interaction with electromagnetic waves. Whereas nature seems to have limits on the type of materials that exist, newly invented metamaterials are not bound by such constraints. These newly accessible electromagnetic properties make these materials an excellent platform for demonstrating unusual optical phenomena and unique applications such as subwavelength imaging and planar lens design. 'Negative-index materials', as first proposed, required the permittivity, epsilon, and permeability, mu, to be simultaneously less than zero, but such materials face limitations. Here, we demonstrate a comparatively low-loss, three-dimensional, all-semiconductor metamaterial that exhibits negative refraction for all incidence angles in the long-wave infrared region and requires only an anisotropic dielectric function with a single resonance. Using reflection and transmission measurements and a comprehensive model of the material, we demonstrate that our material exhibits negative refraction. This is furthermore confirmed through a straightforward beam optics experiment. This work will influence future metamaterial designs and their incorporation into optical semiconductor devices.

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.

Properties of planar electric metamaterials for novel terahertz applications

Abstract: Planar electric metamaterials are experimentally studied in transmission and reflection utilizing terahertz time-domain spectroscopy. Electrically resonant behavior is observed and provides an estimate of the frequency-dependent transmissivity, reflectivity, and absorptivity of metamaterial composites. Numerical simulations are in good agreement with the measured results and provide additional information helpful in understanding their electromagnetic response. Our results and approach help define the boundaries of a metamaterials-based design paradigm and should prove beneficial in future terahertz applications, particularly with respect to novel filtering, modulation, and switching devices. In addition, this work clarifies some of the mechanisms that limit efficient metamaterials operation at higher-frequencies.

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.

Near-perfect absorption by a flat metamaterial plate

Abstract: The paper shows that under certain circumstances a monochromatic filament source located above a plane surface coated with a metamaterial does not illuminate the upper half space. New designs of electromagnetic field absorbers and resonators are suggested. They can be constructed with the help of metamaterials.

Artificial phonon-plasmon polariton at the interface of piezoelectric metamaterials and semiconductors

Abstract: We studied a polariton formed at the interface between a piezoelectric metamaterial and a semiconductor or metallic metamaterial. The piezoelectric metamaterial consists of periodically poled domains that has an optical phonon frequency in the terahertz ranges. When the piezoelectric metamaterial is in contact with a semiconductor or metallic metamaterial substrate, the coupling between the metamaterial’s optical phonons and the substrate’s plasmons results in the formation of a type of artificial surface polariton: phonon-plasmon polariton. The effective dielectric constant of the piezoelectric metamaterial is theoretically derived and the strong dispersion and band gap phenomena of the phonon-plasmon polariton are investigated. The artificial surface phonon-plasmon polariton may offer opportunities in optical science such as acoustic excitation of surface plasmons and vice versa.

Beyond 3G: Metamaterials application to the air interface

Abstract: We have presented the first metamaterial MIMO antenna array implemented in a commercially available 802.1 In wireless LAN access point. Despite the extremely small size of the metamaterial array, its performance equals that of the much larger conventional antenna solution. The metamaterial antenna array utilized existing PCB fabrication technology and was readily integrated into the access point.

Performance enhancement of small antennas using metamaterials —challenges and future directions

Abstract: In this review paper we take a critical look at the problem of performance enhancement of small antennas using metamaterials We first review the definitions of metamaterials that have been used in the literature, and then introduce our own classification of metamaterials in the microwave regime - that are artificial dielectrics - by dividing them into two broad sub-categories Representative examples of antenna / metamaterial composites are presented and the paper concludes some thoughts on future directions of Metamaterial Research, focusing on the aspect of performance enhancement of small antennas

Semiconductors: a new class of metamaterials.

Abstract: Conventional metamaterials that show negative refraction suffer from high intrinsic losses and are difficult to fabricate. A novel anisotropic semiconducting metamaterial offers a solution.

From photonic crystals to metamaterials: physical insights and engineering aspects

Abstract: This paper presents conceptual studies of photonic band-gap (PBG) crystals and metamaterials. It is highlighted that the band-gap phenomenon of PBG structures is coming from the periodicity of structure, while a metamaterial can be effectively accomplished using the electric and magnetic dipole moments, where the periodicity may not be a big factor. An advanced FDTD analysis is applied to comprehensively obtain a physical insight of metamaterials. The results are integrated into the design of a novel high-performance all-dielectric metamaterial. An all-dielectric metamaterial is free of conduction loss and can provide a relatively wideband material performance by increasing the couplings between the inclusions. Engineering challenges and practical issues are addressed.

Miniaturization of waveguide antennas using electromagnetic metamaterials

Abstract: In the era of miniaturized hand - held devices rectangular waveguides have been replaced by planar guiding structures in many of the applications for miniaturizations. Use of waveguides is inevitable in many applications. Waveguides offer a number of advantages over planar guiding structures, viz., lower loss and high power handling capability, absence of substrate mode losses etc. Waveguide manufacturing cost and their size at microwave frequencies are the biggest disadvantages. Over the years a number of researchers have tried to miniaturize waveguides. Classical waveguide miniaturization is by filling the waveguides with a dielectric yielding to size reduction of 1/ relative to an empty waveguide. The disadvantages of such dielectric filled waveguides are, high cost and such waveguides cannot be used as an antenna. In this thesis we propose an open - ended rectangular waveguide antenna loaded with broadside coupled split - ring resonators (BC-SRR) radiating below the cutoff frequency of the waveguide. An X-Band, open - ended waveguide antenna loaded with BC-SRR operating in a 5.5-6.7 GHz frequency band was designed, fabricated and tested.

Metamaterials for transparency and total scattering reduction

Abstract: In this paper, the authors theoretically discuss the underlying mechanisms and physical insights on the role of plasmonic metamaterial covers in reducing scattered fields from single and collections of objects.

Some Considerations on Radiation Properties of Antennas Embedded into Low-permittivity Metamaterial

Abstract: Gain increase and radiation properties of a quarter wavelength monopole, an open rectangular waveguide and a rectangular horn antenna embedded into a low-permittivity wire-based metamaterial are studied. Measurement results confirm that metamaterial used for embedding of the antennas contributes to the increase of the antenna gain. Lower the antenna gain, the gain improvement achieved by the metamaterial slab is larger. The influence of dimensions and thickness of the metamaterial slab on the gain improvement and radiation patterns is investigated. The results show that for thin slabs the gain improvement weakly depends on the slab cross section area, while for thick slabs larger cross section allows significantly better focusing of the radiated waves.

Metamaterials for Novel Terahertz and Millimeter Wave Devices

Abstract: We present experimental results of metamaterials operating at terahertz and mm-wave frequencies. Metamaterials consist of a single layer of 200 nm thick gold on a doped or undoped semiconducting substrate. By optical and electronic doping of supporting semiconducting substrates we show external control of planar arrays of metamaterials, characterized with terahertz time domain spectroscopy. Both methods yield meta-material / semiconductor devices which can be utilized as switches or modulators, enabling modulation of THz transmission by 50 percent. Experiments are supported by simulations and results agree well. Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum and will undoubtedly play a key role in future demonstrations of novel high-performance devices.

Metamaterials and their THz applications

Abstract: We present experimental results of metamaterials operating at terahertz and mm-wave frequencies Metamaterials consist of a single layer of 200 nm thick gold on a doped or undoped semiconducting substrate By optical and electronic doping of supporting semiconducting substrates we show external control of planar arrays of metamaterials, characterized with terahertz time domain spectroscopy Both methods yield meta-material / semiconductor devices which can be utilized as switches or modulators, enabling modulation of THz transmission by 50 percent Experiments are supported by simulations and results agree well Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum and will undoubtedly play a key role in future demonstrations of novel high-performance devices

Practical applications of metamaterial-based structures in microwave systems

Abstract: In this paper, metamaterial-based transmission lines will be discussed, with a focus placed on how these structures can be utilized in microwave systems. The different devices necessary for a basic dual-band receiver will be discussed and it will be shown how these dual-band components can be realized using metamaterial-based structure. Also, two different types of two-dimensional beam scanning systems will be introduced that utilize both one and two dimensional metamaterial-based structures.

Electrical Control of Terahertz Metamaterials

Abstract: The metamaterials resonant response significantly enhances THz-wave/material interaction. We demonstrated real-time switchable THz metamaterial via external voltage bias to modify the metamaterial capacitive elements, thereby achieved effective control and manipulation of freely propagating terahertz waves.

Opto-electronic control of terahertz metamaterials

Abstract: We demonstrate external control of metamaterials operating at terahertz frequencies. Through photodoping of semiconducting substrates, used to support metamaterial arrays, we show ultrafast switching times. New metamaterial "grids" are presented, which may be formed by the union of electric metamaterials arrays. Metamaterial grids are then utilized to form a Schottky contact are used to demonstrate voltage switching of the metamaterials resonance. Both devices presented may be utilized to form novel devices at terahertz frequencies and also scaled to other energy regimes of interest.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The role of ideal and inclusion-made Single NeGative Metamaterials to achieve the extraordinary transmission through a sub-wavelength hole

Abstract: In this contribution, we propose a new metamaterial-based setup to increase the transmission through a sub- wavelength hole. Conventional setups are based on the excitation of suitable leaky modes supported by the metallic screen hosting the hole. Periodic corrugations placed on the screen allow to excite such modes. On the other hand, the employment of dedicated covers made by metamaterials with constitutive parameter values close to zero has been also shown to be effective to enhance the transmission through the hole. In order to squeeze the dimensions of the covers, a suitable pairing of Single NeGative metamaterials has been recently proposed. However, all these techniques based on the excitation of leaky modes either propagating on the screen or along the metamaterial slab(s) require a quite large area around the sub-wavelength hole where to host the corrugations or place the covers. The setups we propose in this contribution, instead, are again based on the employment of Single NeGative metamaterials, but they do not require the excitation of the leaky modes. For this reason, the area occupied by the cover is of the same order of magnitude of the hole. The role of the Single NeGative metamaterial cover is presented in the paper, along with the analytical formulation and some numerical results showing the effectiveness of the proposed setups.