Negative Permittivity Research Articles

Exploring localized ENZ resonances and their role in superscattering, wideband invisibility, and tunable scattering

While the role and manifestations of the localized surface plasmon resonances (LSPRs) in anomalous scattering, like superscattering and invisibility, are quite well explored, the existence, appearance, and possible contribution of localized epsilon-near-zero (ENZ) resonances still invoke careful exploration. In this paper, that is done along with a comparison of the resonances of two types in the case of thin-wall cylinders made of lossy and loss-compensated dispersive materials. It is shown that the localized ENZ resonances exist and appear very close to the zero-permittivity regime, i.e., at near-zero but yet negative permittivity that is similar to the ENZ modes in thin planar films. Near- and far-field characteristics of the superscattering modes are investigated. The results indicate that the scattering regimes arising due to LSPRs and localized ENZ resonances are distinguishable in terms of the basic field features inside and around the scatterer and differ in their contribution to the resulting scattering mechanism, e.g., in terms of the occupied frequency and permittivity ranges as well as the sensitivity to the wall thickness variations. When the losses are either weak or tend to zero due to the doping with gain enabling impurities, the sharp peaks of the scattering cross-section that are yielded by the resonances can be said to be embedded into the otherwise wide invisibility range. In the case of lossy material, a wide and continuous invisibility range is shown to appear not only due to a small total volume of the scatterer in the nonresonant regime, but also because high-Q superscattering modes are suppressed by the losses. For numerical demonstration, indium antimonide, a natural lossy material, and a hypothetical, properly doped material with the same real part of the permittivity but lower or zero losses are considered. In the latter case, variations of permittivity with a control parameter can be adjusted in such a way that transitions from one superscattering mode to another can be achieved. In turn, transition from the strong-scattering to the invisibility regime is possible even for the original lossy material. The basic properties of the studied superscattering modes may be replicable in artificial structures comprising natural low-loss materials.

Morphology dependent negative dielectric permittivity in spinel ferrite nanostructures

Metamaterials with negative dielectric permittivity has become a research hotspot due to their potential efficacy in various electromagnetic utilizations, such as, filter and antenna design, novel capacitance and inductor design, electromagnetic absorber etc. This study unfurls immense possibilities of inducing metamaterial properties such as negative dielectric permittivity in Magnesium Ferrite, a naturally occurring compound, just by restructuring the morphology. Herein, we report the correlation between structural, dielectric, and magnetic properties of the system in the same chemical composition but different morphologies, namely, nano solid spheres (NSSs) and nano hollow spheres (NHSs). Strikingly, only NHSs show negative dielectric permittivity owing to the Lorentz dielectric resonance in the vicinity of a metamagnetic transition. Further investigations show that the hollow cores and greater number of interfaces in NHSs, in comparison to NSSs, cause the uncompensated charges to accumulate within them and release at some frequencies and temperatures, leading to the backscattering of dipoles, which in turn induces the resonance. NSSs with stronger anti-ferromagnetic interaction and impermeable morphology do not show any sign of negative dielectric permittivity.

Symmetrically structured epsilon negative metamaterial for antenna gain enhancement

An epsilon negative metamaterial (MTM) is presented in this article that bears a symmetrical structure and shows a transmission coefficient (S21) resonance at 2.78 GHz. The proposed MTM unit cell comprises an outer square ring with horizontally oriented splits, connected along the vertical axis to a circular inner ring featuring vertically oriented splits, forming an interconnected structure. The electrical dimension of the MTM cell is 0.08λ × 0.084λ, and here wavelength, λ is determined at 2.4 GHz. The MTM shows negative permittivity, near zero permeability as well as refractive index. The electric field, Magnetic field, and current distribution have been analyzed to realize resonance behavior. The compactness of the MTM is identified through an effective medium ratio (EMR) of 12.2. Moreover, an equivalent circuit is modeled and Advanced Design Systems (ADS) is utilized to confirm its performance. The prototype of the metamaterial is developed and a measured result is taken that exhibits a well-matching with the simulation result. Application of this metamaterial is checked through designing and developing an antenna and MTM is used as a superstrate over the antenna. Both the simulation and measured results reveal that as a superstrate, MTM helps to increase the antenna gain by more than 100% with less effect on the bandwidth. Thus, this new metamaterial can be a good candidate as an antenna element for increasing performance. Moreover, the proposed antenna-MTM system can be utilized for wireless power transmission as it provides an adequate gain in a compact 3D structure.

Electrodynamic Formulas for Media with Negative Permittivity

Electrodynamic formulas widely used in the description of objects containing dielectric media give results contrary to physics in the case when the permittivity of the medium takes a negative value. The problem is solved by refined formulas that allow calculating the electric potentials of the point charge and the point dipole moment, the capacitance of the capacitor, as well as the energy density of the electromagnetic field and the quality factor of the material. The formulas are valid for any media, both with positive and negative real part of the complex permittivity.

Negative permittivity enhanced reflection and adsorption of electromagnetic waves from carbon fiber felt/carbon nanotubes

Negative permittivity generated by plasma oscillations enhances the electromagnetic interference reflection and absorption performance of CFF/CNTs through strong impedance mismatch and multiple loss mechanisms.

Design and Analysis of Multi-Analyte Detection Based Biosensor in the Visible to Near-Infrared (VNIR) Region.

This manuscript introduces a highly sensitive dual-core photonic crystal fiber (PCF) based multi-analyte surface plasmon resonance (SPR) sensor, possessing the ability to detect multiple analytes at once. A chemically stable thin plasmonic substance of gold (Au) layer, holding a thickness of 30 nm, is employed to the outer portion of the stated design that manifests a negative real permittivity. Moreover, an ultra-thin film of aluminum oxide (Al2O3) , having a thickness of 10 nm, is inserted into the exterior of the gold film to calibrate the resonance wavelength as well as magnify the coupling strength. The performance of the sensor is rigorously explored employing the finite element method (FEM), where numerical investigation confirms that the intended sensor model exhibits a peak amplitude sensitivity (AS) of 2606 RIU-1 , as well as a highest wavelength sensitivity (WS) of 20,000 nm/RIU. The achieved outcomes affirm that the sensor design can be conceivably applied in numerous biological; as well as biochemical analyte refractive index (RI) detection to realize the relevant significant applications in the visible to near-infrared (VNIR) region of 0.5 to [Formula: see text].

N-Type redox-tuneable conducting polymer optical nanoantennas.

Conducting polymers can be dynamically switched between being optically metallic (negative real permittivity) and dielectric (positive real permittivity) by varying their redox state. This has enabled nanoantennas with plasmonic resonances that can be reversibly turned on/off, opening for applications in dynamic metaoptics, reflective displays, and smart windows. However, previous reports on conducting polymer plasmonics were limited to p-type polymers. Here, we show that a highly conducting n-type polymer, called poly(benzodifurandione) (PBFDO), can also provide optically metallic properties and be used to make dynamic optical nanoantennas. The doped version of the polymer becomes metallic at wavelengths above around 700 nm, leading to plasmonic extinction peaks for nanodisks made from the material. These peaks can be reversibly switched off and on electrically or chemically by varying the doping level of the polymer. The study extends the field of dynamic polymer plasmonics to n-type materials and broadens the application areas of PBFDO.

A Reduction Method of Phantom Shell Effects for APD Extraction Using Negative Permittivity Material

A Reduction Method of Phantom Shell Effects for APD Extraction Using Negative Permittivity Material

Active tuning of anisotropic phonon polaritons in natural van der Waals crystals with negative permittivity substrates and its application in energy transport

Active tuning of anisotropic phonon polaritons in natural van der Waals crystals with negative permittivity substrates and its application in energy transport

Establishing the correlation of negative permittivity and AC conductivity of La2−xSrxNiO4 (x = 0, 0.1, 0.3, 1.0) for microwave shielding applications

In Sr-doped La2NiO4, we observed plasma-like negative permittivity behavior along with enhanced shielding effectiveness. The primary shielding mechanism was reflection, attributed to intense impedance mismatching.

Weakly negative permittivity: metal–organic frameworks derived cobalt nanoparticles encapsulated by positive-hexagon-shaped carbon nanosheets

Weakly negative permittivity: metal–organic frameworks derived cobalt nanoparticles encapsulated by positive-hexagon-shaped carbon nanosheets

A nested square combination of ε-negative high EMR symmetric metamaterial structure for triple band wireless applications

In this article, a novel metamaterial is presented that is constructed with split ring resonators (SRR) arranged in a nested square configuration. The proposed metamaterial unit cell is constructed over a 1.5 mm thick FR-4 substrate with electrical dimensions of 0.11 λ × 0.11 λ, where λ is the wavelength calculated at 2.8 GHz. The resonating patch contains five interconnected nested squares, including two square split ring resonators (SSRRs). The unit cell exhibits three distinct frequencies at 2.8 GHz, 5.8 GHz, and 11.2 GHz, with corresponding magnitudes of −45 dB, −50 dB, and −30 dB, respectively. Negative permittivity (ε-Negative) is observed in frequency ranges of 2.3–3.20 GHz, 4.4–6.9 GHz, and 10.8–11.30 GHz, with near-zero refractive index. The simulated outcome acquired in CST microwave studio is subsequently confirmed using analogous circuit modeling in Advanced System software (ADS). Moreover, the prototype of the proposed metamaterial is developed that shows similar resonances obtained in the simulation. The effective medium ratio (EMR) of the unit cell is calculated and a high EMR of 8.3 expresses the compactness of the metamaterial. Due to its structural compactness, this new metamaterial with ε-negative, near zero refractive index, and triple band resonance properties holds significant potential for wireless applications such as radar systems, satellite communications, and wireless sensor networks.

Flexible MWCNT/PVA/Mn Ferrite/AC Metacomposites with Tunable Negative Permittivity for Low-Frequency Reflectors and Optical Sensors

Flexible MWCNT/PVA/Mn Ferrite/AC Metacomposites with Tunable Negative Permittivity for Low-Frequency Reflectors and Optical Sensors

Extremely low-frequency plasmonic state achieved in AC-ZnO polymer composite for tuned negative permittivity applications

Flexible composites with negative permittivity behaviour have generated a lot of attention due to their potential applications in the electromagnetic field and novel capacitance. This work aimed to design and explore surface microstructure-induced negative permittivity flexible composites for their metamaterial properties. The composites were synthesized using poly (methyl methacrylate) or PMMA, activated carbon (AC), and zinc oxide (ZnO) through an in-situ polymerization process. The composite was designed to acquire negative permittivity in the extremely low-frequency regime by increasing the AC and ZnO filling content. The microstructure formation, real permittivity, and ac conductivity of the composites were investigated, and it was observed that the negative permittivity and its magnitude could be controlled by changing the amount of the filler, AC_ ZnO. Flexible composites with suitable permittivity values for ELF applications can create heavy industrial demand.

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.

Orthogonal centre ring field optimization triple-band metamaterial absorber with sensing application

This paper provides a metamaterial for microwave absorbers relying on asymmetric square split rings with a partial E shape in the centre-based resonator. The wideband frequency range shows its sensing capabilities in identifying various oil samples. The optimized MTM unit cell has electrical dimensions of 0.122λο × 0.122λο, where is λο the predicted wavelength at 3.64 GHz resonance frequency, for a total size of 10 × 10 mm2. The FR-4 dielectric substrate, 1.6 mm in thickness, produces the unit cell. The MTM has a maximum absorption peak of 91.46 % at 3.64 GHz, 99.72 % at 5.99 GHz, 96.89 % at 7.47 GHz, and 98.45 % at 10.01 GHz. This MMA has four absorption peaks, making it suitable for use in the triple band (S, C, and X). The centre split gaps and partial E shapes increase unit cell absorption, and the defective CSRR back layer structure improves the transmission coefficient. High absorption is influenced by the central split gaps and an appropriate electric field and magnetic field optimized in the centre ring when the structure is in an Orthogonal orientation. The research used a frequency domain solver operating between 2 and 12 GHz. The scattering characteristics (coefficient of transmission) of the relevant unit cell's equivalent circuit were confirmed using ADS software and the CST result. At frequencies between 3 and 5 GHz, the proposed asymmetric unit cell functions as a double negative (DNG) metamaterial absorber due to its negative permeability and permittivity. Since oil samples have different dielectric constants, the resonance frequency and Q factor are likewise different. Here, we receive a spectrum of frequencies that can be adjusted for use in sensing. The data showed that the suggested sensor is sensitive enough to pick up a variety of oils. The proposed sensor is useful for various applications, from liquid detection to microfluidic sensing and beyond, due to its cheap cost, high sensitivity, high-quality factor, and high electromagnetic radiation (EMR).

Temperature dependence of negative permittivity behavior in graphene/alumina ceramic metacomposites

Herein, graphene/alumina (GR/Al2O3) ceramic metacomposites with negative permittivity were prepared by hot press sintering to investigate the inherent connection between negative permittivity and external temperature. An electrical percolation phenomenon was observed in the composites with the increasing GR content. The permittivity changed from positive to negative, which was motivated from the formation of continuous three-dimensional GR networks in the composites. The negative permittivity was attributable to low-frequency plasma state of the freed electrons in the GR networks. In addition, the negative permittivity behavior was temperature-dependent in the composites with high GR contents. The higher external temperatures led to the larger absolute values of negative permittivity, and yet the negative permittivity varied very little by applying various temperature, compared to changing the additive amount of GR. As the external temperature elevated, the variation amplitude of negative permittivity enlarged in the composites with higher GR contents.

Tunable Negative Permittivity in Graphene/Poly(Vinylidene Fluoride) Composites with Low Percolation Threshold

Recently, metamaterials with fascinating dielectric behavior have drawn much attention for their potential applications. Herein, percolating graphene/poly(vinylidene fluoride) (GR/PVDF) composites consisting of GR sheets homogeneously dispersed in PVDF matrix are fabricated via hot‐pressing method in 20 Hz–1 MHz frequency regions, of which simultaneously realizing negative permittivity with low percolation threshold. It is demonstrated that the negative permittivity of GR/PVDF composites is resulted from the low‐frequency plasma oscillation of free electrons, and a universal regulatory mechanism of the Drude model is analyzed. At the same time, rapid formative 3D GR conductive networks contributed to the low percolation threshold (7.78 wt%) of composites. Moreover, it is shown that electrical percolation occurs in samples as GR content exceeds percolation threshold, indicating a typical metal‐like behavior. In addition, the reactance is discussed according to the equivalent circuit analysis. This work constructed the metacomposites with low filler content, which is a benefit for practical applications in electromagnetic devices.

Understanding the negative permittivity behavior of polyvinyl alcohol based metamaterials under radio frequency

Functional metamaterials that exhibit negative dielectric permittivity through percolative network formation have attracted immense attention due to their significant potential for a wide range of applications in electronic devices. Negative permittivity has taken off as a research topic recent years in percolative composites. The polymer nanocomposites (PVA/H-Pa-G) were prepared using the α-Fe2O3 modified GNP and HCl doped polyaniline (Pani) based nanofillers (H-Pa-G). The as prepared samples were characterized in order to analyze their dielectric response for understanding the negative permittivity behavior. Below the percolation threshold for the polymer nanocomposite with 0.10%, 0.25% H-Pa-G nanofiller weight fraction, an increase in σac conductivity is observed with increase in frequency. The dielectric study confirmed the negative permittivity behavior for the polymer nanocomposite (0.50%, 1.00% and 2.00%) above the percolation threshold. This can be mainly attributed to the presence of the conductive network of H-Pa-G nanofiller in the PVA matrix. On the contrary, the positive permittivity is due to the insulative nature of PVA matrix. The empirical data of real permittivity was fitted using the Drude model that corresponded well with the experimental data with the fp = 1.31 GHz which is further certified by the equivalent circuit model fitting. This proposed work strongly suggest the implication of the as prepared polymer nanocomposite for the negative permittivity materials based applications.

Controlling Thermal Radiation in Photonic Quasicrystals Containing Epsilon-Negative Metamaterials

The transfer matrix approach is used to study the optical characteristics of thermal radiation in a one-dimensional photonic crystal (1DPC) with metamaterial. In this method, every layer within the multilayer structure is associated with its specific transfer matrix. Subsequently, it links the incident beam to the next layer from the previous layer. The proposed structure is composed of three types of materials, namely InSb, ZrO2, and Teflon, and one type of epsilon-negative (ENG) metamaterial and is organized in accordance with the laws of sequencing. The semiconductor InSb has the capability to adjust bandgaps by utilizing its thermally responsive permittivity, allowing for tunability with temperature changes, while the metamaterial modifies the bandgaps according to its negative permittivity. Using quasi-periodic shows that, in contrast to employing absolute periodic arrangements, it produces more diverse results in modifying the structure’s band-gaps. Using a new sequence arrangement mixed-quasi-periodic (MQP) structure, which is a combination of two quasi periodic structures, provides more freedom of action for modifying the properties of the medium than periodic arrangements do. The ability to control thermal radiation is crucial in a range of optical applications since it is frequently unpolarized and incoherent in both space and time. These configurations allow for the suppression and emission of thermal radiation in a certain frequency range due to their fundamental nature as photonic band-gaps (PBGs). So, we are able to control the thermal radiation by changing the structure arrangement. Here, the We use an indirect method based on the second Kirchoff law for thermal radiation to investigate the emittance of black bodies based on a well-known transfer matrix technique. We can measure the transmission and reflection coefficients with associated transmittance and reflectance, T and R, respectively. Here, the effects of several parameters, including the input beam’s angle, polarization, and period on tailoring the thermal radiation spectrum of the proposed structure, are studied. The results show that in some frequency bands, thermal radiation exceeded the black body limit. There were also good results in terms of complete stop bands for both TE and TM polarization at different incident angles and frequencies. This study produces encouraging results for the creation of Terahertz (THz) filters and selective thermal emitters. The tunability of our media is a crucial factor that influences the efficiency and function of our desired photonic outcome. Therefore, exploiting MQP sequences or arrangements is a promising strategy, as it allows us to rearrange our media more flexibly than quasi-periodic sequences and thus achieve our optimal result.