Добірка наукової літератури з теми "EPSILON NEGATIVE MEDIA (ENG)"

We propose a design of narrow-band multi-channel optical filter using multiple stacks of unit cell consisting of trilayer of Doubly positive medium (DPS)–Doubly negative medium (DNG)–Epsilon negative medium (ENG). Finite Difference Time Domain (FDTD) technique is used to numerically simulate the effect of optical thickness of DPS, DNG and ENG media on tunability of the transmission spectrum of such a medium. We also demonstrate the control on the number of channels at different frequencies that can be transmitted through such medium.

This article discusses the physical theory and mathematical modeling of epsilon-negative (ENG) material. Numerical simulation results are also given in later part of this article, and they prove that this kind of material has a great shielding effect. We mainly focus on the modeling and simulation of one dimensional epsilon-negative (ENG) material. First we set up a Drude model to theoretically simulate ENG material, and then use the finite difference time-domain methods to analyze the electromagnetic wave propagation in our shielding material.

A comprehensive review of the fundamentals and applications of epsilon-negative materials is presented in this paper. Percolative composites, as well as homogeneous ceramics or polymers, have been investigated to obtain the tailorable epsilon-negative properties. It's confirmed the anomalous epsilon-negative property can be realized in conventional materials. Meanwhile, from the perspective of materials science, the relationship between the negative permittivity and the composition and microstructure of materials has been clarified. It's demonstrated that the epsilon-negative performance is attributed to the plasmonic response of delocalized electrons within the materials and can be modulated by it. Moreover, the potential applications of epsilon-negative materials in electromagnetic interference shielding, laminated composites for multilayered capacitance, coil-less electric inductors, and epsilon-near-zero metamaterials are reviewed. The development of epsilon-negative materials has enriched the connotation of metamaterials and advanced functional materials, and has accelerated the integration of metamaterials and natural materials.

This paper presents a new planar particle that shows negative effective permittivity under irradiation by an electromagnetic wave. The mutual coupling between the couples of these particles is studied in particular. The response of this particle sensitive to an electric field is strongly anisotropic. The particle is aimed to be used to compose an isotropic epsilon-negative metamaterial in two forms. First, a unit cell of the metamaterial consists of a cube bearing six particles on its faces, located with specific orientations. The experiments showed that this unit cell is suitable for manufacturing an isotropic epsilon-negative metamaterial obtained by arranging these cells in a 3D cubic periodic system. The second form of an epsilon-negative metamaterial with an isotropic response consists of the planar particles themselves, distributed quasi-randomly, composing a 2D system and/or of particles placed in spherical shells and distributed fully randomly in a hosting material forming a 3D system. The isotropy of these systems was verified by measurements in a rectangular waveguide.

A high gain omnidirectional antenna with low profile is proposed and is investigated numerically and experimentally. Based on the conventional center-fed circular epsilon-negative (ENG) zeroth-order resonator (ZOR) antenna, dendritic structure negative permeability metamaterial (NPM) is used as the substrate to enhance the gain of the omnidirectional antenna. The experimental results show that the gain of a center-fed circular ENG ZOR antenna with NPM substrate is enhanced about 2.2 dB, and the efficiency is enhanced about 38%, in the whole broad operating bandwidth as compared to that of the antenna without NPM substrate, which can be used to improve the reliability of wireless communications.

In this work, we developed a unique mathematical model to solve dispersion relation for surface polaritons (SPs) in artificial composite materials grating. Here, we have taken two types of materials for analysis. In the first case, the grating composed of epsilon-negative (ENG) material and air interface. In second case, grating composed of left-handed materials (LHMs) and ENG medium interface is considered. The dispersion curves of both p and s polarized SPs modes are obtained analytically. In the case of ENG grating and air interface, polaritons dispersion curves exist for p-polarization only, whereas for LHM grating and ENG medium interface, the polaritons dispersion curves for both p and s polarization are observed.

Radio frequency (RF) blackout and attenuation have been observed during atmospheric reentry since the advent of space exploration. The effects range from severe attenuation to complete loss of communications and can last from 90 s to 10 min depending on the vehicle’s trajectory. This paper examines a way of using a metasurface to improve the performance of communications during reentry. The technique is viable at low plasma densities and matches a split-ring resonator (SRR)-based mu-negative (MNG) sheet to the epsilon-negative (ENG) plasma region. Considering the MNG metasurface as a window to the exterior of a reentry vehicle, its matched design yields high transmission of an electromagnetic plane wave through the resulting MNG-ENG metastructure into the region beyond it. A varactor-based SRR design facilitates tuning the MNG layer to ENG layers with different plasma densities. Both simple and Huygens dipole antennas beneath a matched metastructure are then employed to demonstrate the consequent realization of significant signal transmission through it into free space beyond the exterior ENG plasma layer.

Decreasing the Radar Cross Section (RCS) is investigated in electromagnetic materials, i.e. double-positive (DPS) , double-negative (DNG) , epsilon-negative (ENG) and mu-negative (MNG) materials. The interesting properties of these materials lead to a great flexibility in manufacturing structures with unusual electromagnetic characteristics. The valid conditions for achieving the transparency and gaining resonance for an electrically small cylinder are established, in this corresponding The effect of incidence direction on RCS inclusive of transparency and resonance conditions is also explored ,through computer simulations for an electrically small cylinder.

This study presents a double-inverse-epsilon-shaped, triple-band epsilon-negative (ENG) metamaterial with two split ring resonators (SRRs). The proposed unit cell comprises a single slit two SRRs with two inverse-epsilon-shaped metal bits. Rogers RT6002, of dimension 10 × 10 × 1.524 mm3, is used as a substrate. An electromagnetic simulator CST microwave studio is used to investigate the effective medium parameters of the material. The proposed metamaterial shows three resonance peaks that are demarcated at the frequencies 2.38 GHz, 4.55 GHz and 9.42 GHz consecutively. The negative permittivity of the metamaterial is observed at the frequency ranges of 2.39–2.62 GHz, 4.55–4.80 GHz and 9.42–10.25 GHz. The goodness of the material was presented by the effective medium ratio (EMR) of the unit cell at 12.61. In addition, the simulated results are authenticated by using different electromagnetic simulators such as HFSS and ADS for the equivalent circuit model, which exhibits insignificant disparity. The anticipated scheme was finalised through some parametric analyses, together with configuration optimisation, different unit cell dimensions, several substrate materials, and altered electromagnetic (EM) field transmissions. The proposed triple band (S-, C- and X-bands) with negative permittivity (ε) metamaterial is practically used for numerous wireless uses, for instance, far distance radar communication, satellite communication bands and microwave communication.

The transmission properties of a periodic structure consisting of alternating metal layers and air layers are studied by numeric methods. The metal layers are the epsilon-negative (ENG) materials. The interaction of the evanescent waves in metal layers and propagation waves in air layers forms some special transmission bands. Given proper structure parameters, one transmission frequency only allows one incident direction in the low frequency range. This structure can simultaneously achieve frequency filtering and direction filtering.

Planar technology has gained a lot of popularity since its inception due to various advantages it offered to the scientific world such as, light weight, compact size, ease of fabrication and integration, suitability of mass production and compatibility with planar solid state devices. However they also have certain drawbacks in terms of bandwidth, further miniaturization, gain, efficiency, etc. Metamataterials are introduced in the late 60s by a Russian physicist Victor Veselago [1], which were further investigated by Pendry et. al. [2] and are an active area of research these days. Metamaterials are the artificially engineered structures that offer extraordinary electromagnetic properties not found in nature such as epsilon negative media (ENG), mu negative media (MNG), double negative media (DNG), photonic band gap structures etc. They consist of multiple unit cells whose dimensions are much smaller than l0/4, where l0 is the wavelength corresponding to the highest frequency of operation, to achieve homogenization. It was discovered that these materials alter the behaviour of electromagnetic waves in an unconventional way leading to important phenomenon such as, reversal of Snells Law, Doppler effect and Vavilov-Cerenkov radiation. Due to the extraordinary behaviour of metamaterials they are used to improve the properties of various planar devices and components which are discussed earlier. They can be used to improve antenna’s gain, directivity, bandwidth and size, filter’s size, roll off, out of band rejection levels and bandwidth. They are used for multiple frequency operation. They are also being used for the development of super lenses, ultrathin perfect absorbers, cloaks, high sensitivity and high resolution sensors, phase compensator etc. The main focus of this thesis is on metamaterial based antennas, filters and absorbers. Chapter 3 presents the design of a compact, low-profile, coplanar waveguide (CPW)-fed metamaterial inspired dual band microstrip antenna for WLAN application. To achieve the goal a triangular split ring resonator (TSRR) is used along with an open ended stub. The proposed antenna has a compact size of 20×24 mm2 fabricated on an FR-4 epoxy substrate with dielectric constant (er=4.4). The antenna provides two distinct bands I from 2.40-2.48 GHz and II from 4.7-6.04 GHz with reflection coefficient better than -10 dB, covering the entire WLAN (2.4/5.2/5.8 GHz) band spectrum. The performance of this metamaterial inspired antenna is also studied in terms of the radiation pattern, efficiency, and realized gain. The antenna is practically fabricated and tested to show good agreement with the simulated results. Chapter 4 is divided into four sections. The first section presents a compact, low-profile Band Stop Filter (BSF) designed using Complimentary Split Ring Resonator (CSRR). An equivalent circuit model is also presented along with the simplified mathematical approach to extract the parameters of the circuit model. This paper also presents the effect of variation in the dimensions of split rings on characteristics of BSF. The proposed BSF has a compact size of 27×20 mm2 designed on FR-4 substrate with dielectric constant (er)=4.3. The filter provides complete suppression of the band at 2.4 GHz. The design and circuit analysis of this metamaterial based filter is presented in terms of reflection coefficient, transmission coefficient and impedance curve. The second section presents the design and analysis of a metamaterial inspired Bandstop Filter (BSF) providing suppression of frequency at 3 GHz. The overall size of proposed BSF is 20mm×20mm×1.6mm. Further,the extraction of lumped parameters of the designed BSF using simulated results is presented and validation of the results using equivalent circuit simulation is also presented. The third section presents a comparison based study of microstrip transmission line based bandstop filters taking different complementary resonators on the ground plane. Six metamaterial resonators unit cells have been investigated from the literature. The dimensions are optimized to operate at 3 GHz and then their comparative analysis is performed based on various properties of filters such as insertion loss, 3 dB v bandwidth, quality factor (Q), shape factor, overall size, unit cell size and group delay. There are a number of metamaterial based resonators available in literature, so the objective of this section of the chapter is to provide a comparative analysis so that the user can point out the best configuration required while designing the bandstop filter that suits the desired specification and also helps in developing the future ideas by taking into account the advantages of the available structures. The forth section presents a compact, low-profile, Band Pass Filter (BPF) based on balanced Dual Composite Right/Left Handed (D-CRLH) Transmission Line (TL) is presented in this chapter. A balanced D-CRLH TL can be used to provide wideband filter characteristics due to no frequency separation between the RH and LH frequency bands. The proposed D-CRLH TL is designed using U-shaped complementary split ring resonator (UCSRR). The extraction of equivalent circuit model of proposed UCSRR unit cell is also performed. Further, the bandwidth of the proposed filter is enhanced by using the concept of electric and magnetic coupling between the slot lines. The proposed via less BPF has a compact size of 15×15 mm2 designed on an FR-4 substrate with dielectric constant(er)=4.3. The design analysis of proposed bandpass filter is presented in terms of reflection coefficient, transmission coefficient, impedance curve, propagation constant and group delay. Chapter 5 presents a novel resonant metamaterial absorber exhibiting five resonant peaks with absorptivity more than 90% in the range from S band to Ku band for radar cross-section reduction and other FCC-airborne applications. The structure is designed on a low cost FR-4 substrate with 1 mm thickness which is equivalent to l /17.75 where l is the wavelength corresponding to maximum resonant frequency of absorption, showing its ultrathin nature. The fourfold symmetry of the design results in polarization insensitivity and provides an angular stability up to 60◦ of incident angle. The multiband characteristics are obtained by combining three different geometries in a single structure. Performance of the absorber is studied in terms of absorptivity, material parameters, normalized impedance, polarization insensitivity and oblique incidence. Finally, the design is fabricated on a 200×200mm2 FR-4 substrate and measurements are performed. Further, the chapter also presents a closed meander line shaped vi metamaterial absorber operating at 3.5 GHz WiMAX band. The proposed metamaterial absorber unit cell has a compact size of 0.11l0×0.11l0 design on an ultrathin FR-4 substrate with thickness 0.018l0, where l0 is the wavelength corresponding to operating frequency. The proposed absorber shows an absorptivity of 98.5 % at the intended frequency. The design is evolved from a simple square loop to a symmetrical meander line structure whose dimensions are optimized to operate at 3.5 GHz WiMAX band. An equivalent circuit model is also defined to depict the electrical properties of the structure. The proposed design also shows insensitivity to polarization as well as change in incident angle of the wave over a wide-angle (upto 60◦) for both TE and TM polarization. The proposed structure is a good candidate for radar cross section reduction of an antenna. Chapter 6 demonstrates the use of metamaterial absorber (MA) to achieve high isolation between two patch antennas in a 2-element MIMO system operating at 5.5 GHz resonant frequency useful for WiMAX application. The proposed flower shaped MA, designed on a 9×9mm2 FR-4 substrate with 1 mm thickness, exhibits near unity normalized impedance at 5.5 GHz with an absorptivity of 98.7 %. A 4 element array of the MA is arranged in the form of a line in the middle of the two radiating patches in order to suppress the propagation of surface current between them at the operating frequency. Using the proposed flower shaped MA, an isolation of nearly 35 dB is achieved. The MIMO structure is studied in terms of return loss, isolation, overall gain, radiation pattern, Envelope Correlation Coefficient (ECC), Diversity Gain (DG), and Total Active Reflection Co-efficient (TARC) etc. The structure is finally fabricated and measured to show good agreement with the simulated results.