Negative Values Of Permittivity Research Articles

Equivalent circuit technique for designing split ring resonator based metasurfaces

Metasurfaces are two-dimensional artificially engineered structures capable of manipulating the phase, direction and orientation of electromagnetic waves by exhibiting simultaneously negative values of permittivity and permeability. These unconventional properties have been tailored and explored in many applications such as in bio-sensors, waveguides and antennas. The split ring resonators are the commonly used constituent meta-atoms of metasurfaces whose design and analysis rely on commercially available numerical electromagnetic fields (EM) solvers and experimental analysis. These numerical EM solvers are based on meshing and partitioning of graphical structures into the desire grids or patches to solve Maxwell equations in discrete form. However, graphical rendering and meshing of 3D objects requires significant space-time computational resources to analyze the structure. With the cost of licenses of EM solvers being very expensive, analytical solution were explored. The use of LC resonant frequency analytical formula provides an approximate value of resonant frequency which is less accurate and does not gives information about the current characteristics induced on the constinuent meta-atom of a metasurface. This paper presents an analytical approach to the design and analysis of a doubly split double rings (DSRR) using lumped element equivalent circuit that can be solved by mesh network analysis. The resonant frequency is extracted from the induced current characteristics which agrees with simulations and experimental results. The resonant frequency errors for a single DSRR unit cell ranged from1.05% to 7%, and for two coupled DSRR unit cells, they ranged from 1.4% to 11%.

Tunable negative permittivity performance of carbon/silicon dioxide ceramic metacomposites under external DC bias voltage

Metacomposites with negative permittivity have gained increasing momentum in recent years due to their unique electromagnetic characteristics and considerable potential application. However, how to adjust negative permittivity is still a big technical challenge to overcome. In this paper, silicon dioxide (SiO2) ceramic metacomposites consisting of carbon fibers (CFs) were fabricated by vacuum hot press sintering, and their negative permittivity might be modified by adjusting the filler content and applying external direct current (DC) bias voltages. As the CF content increased, the electrical conductivity of composites increased markedly, and the conduction mechanism transformed to a metal-like conductivity from hopping conductivity. The permittivity values of composites with high CF contents were negative at the test frequency range owing to the appearance of a low plasmonic state of unbound electrons in the percolating carbon networks. The conductivity of the composites increased when DC bias voltage was applied, because some of the accumulated local electrons at the CF-SiO2 interface could absorb energy and become free electrons. Larger bias voltages led to increased concentration of free electrons, so the absolute values of the negative permittivity raised according to the Drude model and the frequency band of negative permittivity became wider. This work presents an effective approach for adjusting the negative permittivity value and frequency band, which is advantageous in clarifying the realization and regulation mechanisms of negative permittivity.

Rotational symmetry engineered, polarization and incident angle-insensitive, perfect metamaterial absorber for X and Ku band wireless applications

In this paper, a square enclosed split-maze shaped metamaterial absorber is proposed for X and Ku band wireless applications. Two square metal enclosures were introduced around the split-maze structure to make it rotational symmetric and thus insensitive to cross-polarization. The proposed absorber has shown maximum absorptions at 9.33 GHz, 12.83 GHz, 13.86 GHz, and 15.61 GHz with single negative value of permittivity. The absorber is insensitive to the incident angle of applied EM waves for normal and oblique incidence up to 180 degrees. In addition, it was proved co- & cross-polarization insensitive due to the symmetric structure of the patch. A comprehensive equivalent circuit analysis was done to explain the fundamental EM behaviour of the metamaterial structure, and the circuit outputs coincided with the simulation results. Finally, the metamaterial was measured for both unit cell, and the array after fabrication and simulation results were validated. The proposed MMA is suitable for wireless applications in devices, especially for sensing, EM energy harvesting, EM coupling reduction, and antenna gain enhancement purposes.

Characteristics of Left Handed Materials

Researchers have been interested in studying so-called Left-Handed Metamaterials LHM, which are artificial materials. These materials have unusual characteristics, like negative permittivity and permeability, and therefore negative index. This paper has been discussed some characteristics of LHM by designing a square split ring resonator SRR and simulating with CST microwave studio (Computer Simulation Technology) to get S-parameters. The broadband frequencies (0-30) GHz were taking to specify the effective range of frequencies to work with, which was found to be between (8- 14) GHz. Then, the parameters of SRR have been varied such as split width on, gap width, metal width, rod width and metal material. The measurements show some of parameters have been affected the values of resonance frequency and the others are not. Also, the negative values of permittivity, permeability, and refractive index have been approved.

Overview on metamaterial: History, types and applications

Metamaterial has received great interest during the last ten years in distinct field, owing of its key characteristics such as enhancement in bandwidth, radiated power, directivity and controls the direction of electromagnetic radiation. It is a smart or a new class of manmade invented materials that can achieve electromagnetic properties that do not occur naturally, such as electromagnetic cloaking or negative index of refraction. These materials exhibit negative value of permittivity, permeability and refractive index. In addition, metamaterial extract their properties from their structure rather than the material of which they are composed of. Further, these materials exhibit excellent design flexibility with their customized properties and their tunability under external stimuli. Due to these attractive properties, metamaterials have enabled the development of new devices and concepts and possible utilization in diverse novel applications. Thus, metamaterials find wide application in medical sector, automotive, aerospace, and many other devices (biosensor, crowd control, absorbers, antennas, optical filters, infrastructure monitoring, smart solar power management, energy harvesters and even shielding structure from earthquakes etc). Hence the aim of this paper is to provide a comprehensive overview of different metamaterial, historical development and their applications in different sectors. In addition, perspective about the challenges and future scope for development of metamaterial is also presented, so that this article could become the torch bearer for the new researchers working in the area of advanced materials.

Complex-scaling method for the complex plasmonic resonances of planar subwavelength particles with corners

A subwavelength metallic particle supports localized surface plasmons for some negative permittivity values, which are eigenvalues of the self-adjoint quasi-static plasmonic eigenvalue problem (PEP). This work investigates the existence of complex plasmonic resonances for a 2D particle whose boundary is smooth except for one straight corner. These resonances are defined using the multivalued nature of some solutions of the corner dispersion relations and they are shown to be eigenvalues of a PEP that is complex-scaled at the corner, the finite element discretization of which yields a linear generalized eigenvalue problem. Numerical results show that the complex scaling deforms the essential spectrum (associated with the corner) so as to unveil both embedded plasmonic eigenvalues and complex plasmonic resonances. The later are analogous to complex scattering resonances with the local behavior at the corner playing the role of the behavior at infinity. These results corroborate the study of Li and Shipman (2019) [35], which proved the existence of embedded plasmonic eigenvalues and discussed the construction of particles that exhibit complex plasmonic resonances.

Effect of direct–current biasing on the adjustable radio-frequency negative permittivity characteristics of Bi2SiO5/multiwall carbon nanotube metacomposites

Multiwall carbon nanotube (MWCNT) based metacomposites with negative permittivity have received significant interest over the past decade due to their unique electromagnetic properties. Here, markedly percolating Bi2SiO5 (BSO)/MWCNT metacomposites with adjustable negative permittivity were prepared by the facile hydrothermal method. Three-dimensional conductive networks formed by interconnected MWCNT are present in BSO/MWCNT metacomposites with 10 and 20 wt% of MWCNT. The detailed microstructure and resistivity studies of the metacomposites led to realize that the adjustable negative permittivity of the BSO/MWCNT metacomposites attributes to the low-frequency plasmon resonance of free Drude carriers. In this work, the effect of the direct-current biasing voltage in the radio frequency region is investigated on the negative permittivity characteristics. For below percolation threshold (fc) metacomposites, the Maxwell-Wagner polarization effects increase in low-frequency region immediately after dc bias is applied. In case of above percolation threshold (fc) metacomposites, the Drude free carrier concentration increases due to the formation of conductive network among MWCNT led to the rise of negative permittivity values in the low frequency region. This work provides a novel strategy for the adjustment of the negative permittivity value, which can expand the potential application in the field of sensors based on the changes in permittivity properties.

Negative dielectric permittivity of PVDF nanocomposites induced by carbon nanofibers and polymer crystallization

AbstractNegative permittivity is a key characteristic of the distinctive metamaterials, a novel class of artificial materials with particular electromagnetic properties. Negative permittivity has been realized in metallic structures with special designs, but rarely achieved in polymer nanocomposites. Our recent studies discover that negative permittivity can be attained from randomly distributed carbon nanofiber (CNF) filled poly(vinylidene fluoride) (PVDF) composites over a wide frequency range, and the negative permittivity values are strongly influenced by CNF and PVDF crystalline structures. The effects of CNF on the crystallization of PVDF, and the resultant negative dielectric permittivity of CNF/PVDF composites influenced by crystallization of PVDF and CNF, are investigated. It is revealed that the introduction of CNF not only affects the dielectric permittivity directly, but also causes indirect effects to the dielectric permittivity through influencing the crystallization of PVDF. In particular, due to addition of more CNF, a α‐ to β‐phase transformation in PVDF is found to affect permittivity of the nanocomposites. Furthermore, the permittivity of CNF/PVDF composites are increased considerably (“more negative”) with more CNF, and is affected noticeably by crystalline structures of PVDF. The lowest negative permittivity achieved is −2,500 for the nanocomposite with 5 wt% CNF at 5 kHz.

Tunable left-hand characteristics in multi-nested square-split-ring enabled metamaterials

Left-hand materials have drawn increasing attention from many disciplines and found widespread application, especially in microwave engineering. A sandwiched metamaterial consisting of multi-nested square-split-ring resonators on the top side and a set of wires on the back side is proposed. Scattering parameters are retrieved by high-frequency structure simulator (HFSS) software based on the finite element method. Effects of square-split-ring number on the left-hand characteristics containing negative values of permittivity, permeability, and refractive index have been intensively investigated. Simulated results show that obvious resonant left-hand characteristics could be observed within 8–18 GHz, and the resonant frequency counts are inclined to be in direct proportion to the square-split-ring number over 8–18 GHz. Besides, the proposed sandwiched metamaterial with three square-split-ring resonators and three wires presents the widest frequency band of left-hand characteristics in a range of 8–18 GHz. Further, electromagnetic field distributions demonstrated that the induced magnetic dipole dominates the resonant absorption. The multi-peak resonance characteristics of square-split-ring resonant structure are considered to be a promising candidate for selective-frequency absorption or modulation toward microwave frequency band.

Two‐dimensional Ti3C2Tx/poly(vinylidene fluoride) metacomposites with weakly negative permittivity

AbstractIn recent years, random metacomposites with tunable negative permittivity have aroused widespread attention because of their distinctive properties and broad potential prospects. It is indicated that an enormously negative permittivity with a large value is not conducive to performance optimizing and impedance matching. In this article, the 2D Mxene Ti3C2Tx was selected as the conductive phase instead of metal and carbon materials to fabricate Ti3C2Tx/poly(vinylidene fluoride) metacomposites. The results of dielectric properties indicated that the conductive Ti3C2Tx networks were formed by Ti3C2Tx contacting with each other near the percolation threshold (ƒc). The as‐obtained metacomposites containing 75 wt% Ti3C2Tx generated percolating phenomenon. Additionally, when the fraction of Ti3C2Tx was below ƒc, the frequency dispersion behaviors of conductivity were in accordance with the Jonscher's power law, which proved that conducting mechanism was dependent on hopping conduction. While above ƒc, the conductivity conformed to the Drude model and Lorentz model, which demonstrated a conductive behavior. Furthermore, the real part of permittivity transformed to negative value at 75 wt%, which can be explained as the existence of the low‐frequency plasma oscillation and electric‐dipole‐induced resonance. The dielectric loss of the metacomposite was also analyzed by the imaginary permittivity spectra. Small negative permittivity values in the range of −550 to −400 were observed, owing to the low free carrier concentration in composites. The appearance of weakly negative permittivity opened up a new direction in negative dielectric materials by 2D layered Ti3C2Tx nanomaterials.

Застосування провідникових метаструктур у радіотехнічних засобах для передавання та випромінювання ЕМ хвиль (огляд)

In the presented paper the review of the major possible applications of a wire medium in different radio engineering field is performed. The structures possess the unique properties such as a negative value of permittivity. Three types of wire media shapes are considered which include structures with parallel (superlens), tapered (hyperlens) and irregular (brush) metallic wires allocations. Modern progress allows a number of approaches (from usual mechanic arrangement to chemical synthesis) to realize wire media of different shape for their utilizing in frequency range from microwave to optics and higher. Superlens can be applied to narrow and broadband energy transfer of electromagnetic waves including photovoltaic devices, imaging, endoscopy, spectroscopy and many others. The broadband effect was shown recently in [9] by the investigation of EM power transfer between two waveguides through a wire media slab that became the first experimental evidence of analytical hypothesis of [12]. It was a beginning point to develop of wire media endoscopes in [15] which shown the nature of non-Fabri-Perot minima and maxima of dispersion function as the vortex modes as well as reliability of endoscope operation under the huge bend. The wire media such as hyperlens and irregular one can find applications in antennas development that operate in the wide frequency range. Comparison of Parcell factor dispersions of these two kinds of metamaterials shows different results due to hyperlens, despite the possibility to radiate at interresonant frequencies, stays resonant structure in general. Instead, a wire medium brush is characterized by the continuing Parcell factor spectrum. It is possible in consequence of the structure shape that can be considered as a set of a huge number of local hyperlenses with different parameters that reradiate and amplify EM field of another local hyperlenses and so on. As the result a wide frequency range can be covered (from 1 up to 5 GHz in [18]).

Modified-Segmented Split-Ring Based Polarization and Angle-Insensitive Multi-Band Metamaterial Absorber for X, Ku and K Band Applications

A novel modified-segmented split-ring based symmetric metamaterial absorber is introduced in this paper for X, Ku, and K band applications. The perfect absorption was achieved with a total of 1.91 GHz absorption bandwidth using the conventional FR4 substrate without resistive lumped elements. EM waves were applied in TEM mode at both normal and oblique incidence up to 90° and the same absorptance was found at 11.23 GHz, 14.18 GHz, 17.37 GHz, and 19.18 GHz with the maximum of 85.51%, 99.13%, 98.19%, and 90.8% absorptance respectively. This absorption performance was proved for both co- and cross-polarization analysis. Double negative values of permittivity and permeability up to 17.37 GHz and single negative values of either permittivity or permeability at 19.18 GHz were achieved. An equivalent circuit analysis also proved its performance capability, which makes it a perfect metamaterial absorber. Finally, the comparison of the design with recently published works in terms of unit cell size, absorption band, maximum polarization angles, and cross-polarized absorptivity proved it as a better candidate for the potential use as a perfect absorber.

AlN-SWCNT Metacomposites Having Tunable Negative Permittivity in Radio and Microwave Frequencies.

Discovery of plasmon resonance and negative permittivity in carbon allotropes at much lower frequencies than those of metals has evoked interest to develop random metacomposites by suitable means of addition of these dispersoids in an overall dielectric matrix. Random metacomposites have always the advantage for their easy preparation techniques over those of their regular arrayed artificial counterpart. However, thermal management during the heat generation by electromagnetic attenuation in metamaterials is not yet studied well. The present communication discusses the dielectric permittivities and loss parameters of aluminum nitride-single-wall carbon nanotube (AlN-SWCNT) composites considering high thermal conductivities of both materials. The composites are dense and have been prepared by a standard powder technological method using hot pressing at 1850 °C under a nitrogen atmosphere. Increase in the negative permittivity value with SWCNT concentration (1, 3, and 6 vol %) in the composites had been observed at low frequencies. Characterization of the materials with Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and microstructure analysis by scanning and transmission electron microscopy (TEM) revealed the survivability of the SWCNTs and the nature of the matrix-filler interface. Plasmonic resonance following Drude's law could be observed at much lower plasma frequencies than that of pure SWCNT and for very little SWCNT addition. Exhibition of the negative permittivity has been explained with relation to the microstructure of the composites observed from field emission scanning electron micrographs (FESEM), TEM images, and the equivalent circuit model. High energy conversion efficiency is expected in these composites due to the possession of dual functionalities like high thermal conductivity as well as high negative permittivity, which should ensure the application of these materials in wave filter, cloaking device, supercapacitors, and wireless communication.

Reverse design of negative permittivity property in Nickel-Network/Epoxy composites

Epsilon-negative materials are usually prepared by additive manufacturing, while a reverse design method needs to be developed to construct the epsilon-negative materials by subtractive manufacturing. Here the Nickel-Network/Epoxy composites were prepared via a chemical corrosion and curing process. The connectivity of nickel network was weakened by chemical corrosion, which was companied with a change of conductivity mechanism from metal-type conductivity to the hopping conductivity. The negative permittivity value could be effectively adjusted by corroding the nickel network, which was attributed to low-frequency plasmonic state of nickel network. The reverse design method provided a novel and more flexible method to construct the desired the epsilon-negative materials.

Tunable negative permittivity in Ti3SiC2 MAX phase/Polymethyl methacrylate metacomposites at radio-frequency region

Metacomposites with negative permittivity have triggered tremendous fundamental and practical attention in recent years. In this paper, Ti3SiC2 MAX phase/Polymethyl methacrylate (PMMA) metacomposites with different Ti3SiC2 content were prepared. Weakly negative permittivity value (between [Formula: see text] and 0) was observed near percolation (Ti3SiC2 content of 60[Formula: see text]wt.%), attributing to moderate carrier concentration in Ti3SiC2 networks, and negative permittivity was tuned by tailoring conductive Ti3SiC2 networks. AC conductivity spectra and negative permittivity spectra of composites over percolation were explained by Drude model, indicating metal-like conduction behavior and low-frequency plasmonic oscillation in composites. The impedance response of composites was analyzed by equivalent circuit models, manifesting correspondence between inductor and negative permittivity. This work presented a new type of metacomposite constructed by Ti3SiC2 MAX phase and further revealed the generation mechanism of negative permittivity, which will greatly facilitate the practical applications of MAX phase in metacomposites.

Bandwidth enhancing method using tri‐ring resonator metamaterial for small devices

AbstractMetamaterials are composite structures of the specific behavior for electromagnetic properties of permittivity, permeability, and refraction, which are not commonly found in regular materials. Metamaterial structure, which has negative value of permittivity and permeability that shows passband response in transmission line, where as if any of these two properties has opposite polarity then it shows stopband response. These behaviors of metamaterial are frequency dependent and have resonance for particular frequencies. At frequency resonance, the traditional metamaterials have narrow band response and to improve its frequency bandwidth, a method using tri‐ring resonator is proposed with increasing number of order of resonator. The proposed metamaterial structure is simulated in fullwave simulator and MATLAB tool is used to analyze the properties of metamaterial structure from simulated S‐parameter. Proposed technique gives flexibility to use the design for multiple application like, rejection filter for Bluetooth 2.4 GHz, Wi‐Fi (2.4 and 5 GHz), WiMAX (2.5 and 3.4 GHz), and 5G (3.4‐3.8 GHz).

Three-dimensional graphene network supported by poly phenylene sulfide with negative permittivity at radio-frequency

Percolative composites with negative permittivity can be promising candidates for metamaterials, but there is still a need about efficient method to adjust the permittivity value. Here graphene/poly phenylene sulfide composites were prepared and the dielectric property was studied. By gradually increasing the graphene content, three-dimensional conductive network could be constructed, accompanied by a change in the conductive mechanism from hopping conduction to metal-like conduction. Negative permittivity was achieved, and the Drude model indicated that negative permittivity came from the plasma oscillation in graphene network. The equivalent circuit analysis demonstrated that interconnection of graphene was the most crucial factor to adjust the negative permittivity value. That is, negative permittivity value can be effectively adjusted by graphene content. These findings may pave a way to simply and efficiently control negative permittivity and imply promising applications in modern electrical and electronic industries.

Regulation mechanism of negative permittivity in poly (p-phenylene sulfide)/multiwall carbon nanotubes composites

Negative permittivity behavior has attracted extensive attention recently owing to its remarkable properties and potential for developing metamaterials. In this paper, the relative complex permittivity and ac conductivity of poly (p-phenylene sulfide)/multiwall carbon nanotube composites were investigated. Both the negative permittivity and ac conductivity behaviors could be explained by Drude model which was attributed to the low frequency plasmons. Small negative values of permittivity have been observed by controlling the multiwall carbon nanotubes contents, meanwhile the weakly negative permittivity possessing good frequency stability. This work provides an alternative to achieve tunable and weakly negative permittivity for the polymer based composites.

Metamaterial inspire multiband monopole antenna with defected ground structure

This article represents the design and analysis of a compact antenna of size 34mmX18mmX1.6mm on FR-4 substrate material. The designed antenna is having a slot at the partial ground for all iterations are observed and it is analysed with the help of ANSYS 17 Electronics Desktop. A new unit cell design which exhibits the metamaterial property is also analyzed with the help of unit cell analysis. The negative permittivity value is extracted, and that unit cell is implemented in the proposed antenna. The enhanced results have been carried out with comparing iteration wise. The proposed antenna has radiation efficiency of 94%, it works in the range of for LTE (33-37) band at 1.95-2.04 GHz, WiMAX band 2.87-3.76 GHz and LTE (43-44) bands 5.92-7.2 GHz.

Tunable and weakly negative permittivity in carbon/silicon nitride composites with different carbonizing temperatures

Despite the exotic electromagnetic properties have been demonstrated in metamaterials to date, how to effectively adjust negative electromagnetic parameters remains a challenge. Tunable negative permittivity is essential for the metamaterials to satisfy a variety of practical applications, such as capacitor, microwave absorbing and shielding. Here, we fabricated a random metamaterial, carbon/silicon nitride (C/Si3N4) composite, using a feasible impregnation-pyrolysis method. The microstructure and dielectric property of the composites with different heat treatment temperatures (HTTs) and carbon contents were investigated. The amorphous carbon membrane adhered on the rod-like Si3N4 grains. The negative permittivity behavior combined with inductive character was obtained in the composites, which was attributed to the low frequency plasmonic state generated from the formative conducting carbon networks. The magnitude of negative permittivity is demonstrated to be successfully adjusted by controlling the HTT and carbon content. The result is in good agreement with the analysis of Drude model. Interestingly, a weakly negative permittivity behavior was observed in the measured frequency, showing small negative values of permittivity between −50 and −10, which was ascribed to a moderate carrier concentration provided by the carbon networks. This work provides an effective way to achieve the tunable and weakly negative permittivity in random metamaterials.