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A review of natural materials that exhibit negative permittivity or permeability, including gaseous plasma, metals, superconductors, and ferromagnetic materials, is presented. It is shown that samples made of such materials can store large amount of the electric (magnetic) energy and create plasmonic resonators for certain values of permittivity, permeability, and dimensions. The electric and the magnetic plasmon resonances in spherical samples made of such materials are analyzed using rigorous electrodynamic methods, and the results of the analysis are compared to experimental data and to results obtained with other methods. The results of free oscillation and Mie scattering theories are compared. Similarities and differences between permittivity and permeability tensors for magnetized plasma and magnetized ferromagnetic materials are underlined. Several physical phenomena are explained on the grounds of rigorous electrodynamic analysis and experiments. These phenomena include unequal electric and magnetic energies stored in plasmonic resonators, the small influence of dielectric losses on the Q-factors of magnetic plasmon resonances, the role of radiation and dissipation losses on the properties of plasmonic resonators, and the theoretical possibility of the existence of lightning plasma balls. [ABSTRACT FROM AUTHOR]

Epsilon‐negative materials (ENM) at radio frequency, usually designed based on percolation theory, recently drew much attention because of their potential applications in capacitors, transistors, and antennas. However, randomly distributed conductive functional materials cannot achieve directional long‐range electron transportation within the material, resulting in decreased utilization efficiency. The morphology design of the substrate material can change the distribution state and electron transfer pathway of conductive fillers. By controlling the size of the polystyrene (PS) and the content of multi‐walled carbon nanotubes (MWCNTs), PS/MWCNTs composites with random structures and segregated structures were designed, both of which exhibited negative permittivity with increasing MWCNTs content. Further investigation revealed that negative permittivity behavior is due to the establishment of the conductive network and the plasma oscillation of free electrons. Moreover, components with segregated structures have lower percolation thresholds, as directional electron transport is achieved and conductive fillers are efficiently utilized. This work provides a new method for guiding the electron transport pathway and effectively changing the distribution state of conductive fillers in ENM. Highlights: Negative permittivity is achieved by plasma oscillation at radio frequency.The segregated structure leads to a decrease in the percolation threshold.Epsilon‐negative materials have good prospects in inductive components. [ABSTRACT FROM AUTHOR]

Conductive particle-containing granular composites with tuneable negative permittivity are being studied to improve the performance of electromagnetic devices, such as shielding materials. In this study, we investigated the relative complex permittivity and electrical conductivity of granular composites of polyphenylene sulfide (PPS) resin and Ag-coated Cu flakes in the radio- to microwave-frequency range and compared them with those of PPS/bare Cu flake composites. Electrical conductivity measurements revealed that the PPS/Ag-coated Cu flake composites have a lower percolation threshold (φc) than the PPS/bare Cu flake composites, whereas the electrical conductivity of the PPS/Ag-coated Cu flake composites in the percolated particle state was higher at the same particle volume fraction. At particle contents above φc, a low-frequency plasmonic state of conduction electrons was achieved in the percolated particle chains in both composites, and negative permittivity spectra were obtained. The percolated PPS/Ag-coated Cu flake composites had a negative permittivity up to a higher frequency than the percolated PPS/bare Cu flake composites. Furthermore, the Drude model was used to analyze the negative permittivity spectra of the composites in the percolated particle state. The plasma frequency of the composites with percolated Ag-coated Cu flakes was higher than that of the composites with percolated bare Cu flakes. Thus, coating Ag on Cu particles improved the conductivity of the composite, leading to negative permittivity up to higher frequencies. This study contributes to the enhancement of the negative permittivity achieved by granular composites, which is useful for microwave technology applications. [ABSTRACT FROM AUTHOR]

Highlights Effective and accurate adjustment of negative permittivity behavior is worthy of further investigation. Herein, pyrolytic carbon‐glass fiber felt/epoxy resin (PyC‐GFF/ER) metacomposites with tunable negative permittivity were prepared using an impregnation‐calcination method. The permittivity, electrical conductivity, and electromagnetic shielding performance of the polymer metacomposites were investigated. Due to the inherent three‐dimensional structural network of GFF, the PyC adhering to the surface of glass fiber easily formed a conductive network in the composites. As the PyC content increased in the ER composites, the conductivity mechanism changed from hopping conduction to metal‐like conduction. The ER composites with high PyC contents showed negative permittivity behavior and the epsilon‐near‐zero response owing to the low frequency plasma state of free electrons in the PyC‐conduction network. By controlling the PyC content, the negative permittivity behavior of ER composites could be effectively tuned. With the increase in PyC content, the values of negative permittivity increased, and the epsilon‐near‐zero frequency shifted to a higher frequency. Moreover, the ER composites with high PyC contents showed excellent electromagnetic shielding properties (29.4 dB) at X‐band. This work not only provided a feasible method to realize the tunable negative permittivity of polymer metacomposites, but also promoted its application in the microwave field. The pyrolytic carbon‐glass fiber felt/epoxy resin composites were fabricated. The negative permittivity was first reported in the PyC‐GFF/ER composites. Tunable negative permittivity could be well explained by Drude model. The polymer composites had excellent electromagnetic shielding property. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Percolating composites exhibiting negative permittivity have garnered considerable attention due to their promising applications in the realm of electromagnetic shielding, innovative capacitance devices, coil-less inductors, etc. Nano carbon powder/polyvinylidene fluoride (CP/PVDF) percolating composites were fabricated that exhibit Drude-type negative-permittivity behavior upon reaching the CP percolation threshold. This phenomenon is attributed to the formation of a plasmonic state within the interconnected CP network, enabling the delocalization of electrons under the alternating electric field. Furthermore, a significant (nearly two orders of magnitude) increase in the conductivity of sample is observed at a CP content of 12.5 wt%. This abrupt change coincides with the percolation phenomenon, suggesting a transition in the conduction mechanism. To elucidate this behavior, comprehensive analyses of the phase composition, microstructure, AC conductivity, and relative permittivity were performed. Additionally, the sample containing 5 wt% CP exhibits a remarkably high permittivity of 31.5, accompanied by a relatively low dielectric loss (tanδ < 0.2). The findings expand the potential applications of PVDF, while the fabricated percolating composites hold promise for electromagnetic shielding, antennas, and other electromagnetic devices. [ABSTRACT FROM AUTHOR]

Electromagnetic (EM) metamaterials have garnered considerable attention due to their capacity to achieve negative parameters, significantly influencing the integration of natural materials with artificially structural media. The emergence of carbon aerogels (CAs) offers an opportunity to create lightweight EM metamaterials, notable for their promising EM shielding or absorption effects. This paper introduces an efficient, low‐cost method for fabricating CAs without requiring stringent drying conditions. By finely tuning the ZnCl2/lignin ratio, the porosity is controlled in CAs. This control leads to an epsilon‐negative response in the radio‐frequency region, driven by the intrinsic plasmonic state of the 3D carbon network, as opposed to traditional periodic building blocks. This approach yields a tunable and weakly epsilon‐negative response, reaching an order of magnitude of −103 under MHz frequencies. Equivalent circuit analysis highlights the inductive characteristics of CAs, correlating their significant dielectric loss at low frequencies. Additionally, EM simulations are performed to evaluate the distribution of the electric field vector in epsilon‐negative CAs, showcasing their potential for effective EM shielding. The lignin‐derived, lightweight CAs with their tunable epsilon‐negative response hold promise for pioneering new directions in EM metamaterials and broadening their application in diverse extreme conditions. [ABSTRACT FROM AUTHOR]

Double-negative performance has played a significant role in electronic applications owing to its both permeability and permittivity negative values. Microwave absorption material has a substantial role in electromagnetic shielding, radar absorption, stealth applications, etc. Herein, a novel double-negative metacomposite, SrFe 12 O 19 /rGO, was designed by a simple one-pot hydrothermal method, and the microwave absorption properties of the material were studied in the microwave region from 2 to 18 GHz using VNA analysis. The structural and morphological studies were analysed using XRD, FT-IR, and SEM instrumentation techniques and the magnetic property of the material was studied using VSM analysis. Both studies confirmed the hard magnetic nature of the material. The particle sizes of SrFe 12 O 19 and SrFe 12 O 19 /rGO measured from XRD are 55.60 nm and 41.55 nm, respectively. Hexagonal plate-like morphology were observed from FESEM images. The coercivity of SrFe 12 O 19 /rGO increased, and the magnetocrystalline anisotropy was changed due to the decrease in particle size. The magnetic saturation value decreases due to the presence of non-magnetic rGO. The resultant SrFe 12 O 19 /rGO metacomposite shows negative permittivity and permeability values. The minimum reflection loss values observed for pure and rGO-decorated strontium ferrites are −28.49 dB at 7.76 GHz and −23.78 at 11.04 GHz, respectively. In addition to experimental results, simulation studies were also performed to study the reflection loss with matching thickness using a quarter wavelength mechanism. The results show that this composite can be employed as a left-handed metamaterial that finds applications in absorption, antennas, sensors, wireless power transfer systems, etc. The left-handed metamaterial can shift the frequency region from a lower to a higher frequency region. The rGO decorated metacomposite is a promising material for microwave absorption at higher frequency regions. [ABSTRACT FROM AUTHOR]

Herein, graphene/alumina (GR/Al 2 O 3) 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. [ABSTRACT FROM AUTHOR]

Ceramic-based dielectrics with high permittivity have extensive applications in energy storage, electronic devices, communication, and other fields. However, ceramics with high permittivity based on the classical percolation theory design often have a substantial dielectric loss. To address this contradiction, we designed a sandwich structure with a negative dielectric layer. The sandwich structure comprises BaTiO 3 /Ag ceramics with different silver contents. The intermediate layer of the sandwich structure is composed of materials with negative permittivity, and adding a negative- ε layer enhances the interfacial polarization, increasing permittivity. More importantly, the multi-layer structure hinders the formation of conductive paths along the electric field direction between layers, positively suppressing dielectric loss. When the permittivity reaches 8000, the dielectric loss still does not exceed 0.02. This work provides a new approach to designing dielectric ceramics with high permittivity and low dielectric loss. [ABSTRACT FROM AUTHOR]

Epsilon‐negative materials (ENMs) hold promise for the advancement of the next generation of electronic devices. Most epsilon‐negative materials strongly correlate with metal properties, which limits their applications in electronic packaging. Instead, achieving a negative permittivity in the insulating state is expected to show the decoupling of electrical and thermal conductivities, and experimental demonstration of this behavior is lacking. In this study, multi‐walled carbon nanotubes (MWCNTs)@polydopamine (PDA)‐silver/polyimide (PI) nanocomposites are engineered to achieve weakly negative permittivity, which is attributed to the localized plasma oscillations. The PDA layer and nano‐Ag are exploited to confine electrons with MWCNTs for improving energy transport while perturbing directional current, thereby realizing high thermal conductivity and low electrical conductivity. This work provides insights into the fundamental nature of heat and charge transport in epsilon‐negative systems. [ABSTRACT FROM AUTHOR]

The aircraft collision avoidance system (ACAS) is a surveillance system required in all airplanes to ensure a safe flight. To locate the presence of any surrounding aircraft that may pose a threat, the ACAS sequentially scans the fixed sectors (0° to 90°, 90° to 180°, 180° to 270°, and 270° to 360°) for a specified duration. As a result, ACAS necessitates a highly directional multi-element antenna capable of spanning the whole 360° azimuth plane. Over the past decade, studies on the performance enhancement of ACAS antennas have become increasingly prevalent due to the numerous limitations of the typical ACAS antenna, which include poor gain ( $3.6dB$ ), larger size ( $>\lambda$ ), high side-lobe level ( $-7dB$ ), challenges with beam tuning, etc. The main focus of this study is to improve the gain and bandwidth (BW) of an ACAS antenna using the notion of MTM, hence a novel U and L-shaped compact negative index MTM structure is developed. Because the ACAS antenna broadcasts the signal in the entire azimuth region, the proposed MTM should be competent to endure its double negative behavior for all incident angles; thus, the MTM cell is evaluated for different incident angles ranging from 0° to 360° in the azimuth plane with a 60° offset, and for all incident angles, the proposed design exhibits DNG behavior in the required frequency spectrum. The effective medium ratio (EMR) of 12.86 at 1.06GHz demonstrates the efficacy and compactness of the proposed design. The proposed MTM cell is expanded as a $5\times 4$ array, and placed as a superstrate at a fixed distance from the proposed ACAS antenna, and the MTM-loaded antenna outperforms the conventional antenna in terms of overall gain by 2.09dB and BW by 27.2MHz. Further, for the experimental verification, the MTM cell and its array structures are fabricated, and in both designs, the fabricated results correspond well with the simulated results.

Abstract Epsilon‐negative materials (ENMs) hold promise for the advancement of the next generation of electronic devices. Most epsilon‐negative materials strongly correlate with metal properties, which limits their applications in electronic packaging. Instead, achieving a negative permittivity in the insulating state is expected to show the decoupling of electrical and thermal conductivities, and experimental demonstration of this behavior is lacking. In this study, multi‐walled carbon nanotubes (MWCNTs)@polydopamine (PDA)‐silver/polyimide (PI) nanocomposites are engineered to achieve weakly negative permittivity, which is attributed to the localized plasma oscillations. The PDA layer and nano‐Ag are exploited to confine electrons with MWCNTs for improving energy transport while perturbing directional current, thereby realizing high thermal conductivity and low electrical conductivity. This work provides insights into the fundamental nature of heat and charge transport in epsilon‐negative systems.

This article represents the findings regarding the phase transitions exhibited by a polymeric hydrogel material composed of sodium polyphosphate-polyethylene glycol. These transitions play a crucial role in the generation of ionic plasmons and the manifestation of surface plasmon resonance (SPR) with dielectric permittivity damping within the polymer electrolyte system of the hydrogel. Usually, SPR has been observed in electron-conducting systems within an optical frequency range. However, here SPR is observed in an ionic system within a lower radio frequency range of 104-10 (Parwati et al., 2024) 77 Hz for temperatures exceeding 80 °C. The mechanism responsible for permittivity damping can be elucidated by considering the accumulation of ionic charges at the interface between the electrode and the electrolyte, coupled with a high degree of charge absorption following the Drude model. A power law has been used to describe the resonance that occurs between the applied DC frequency and the motion of charge carrier ions, thus confirming the presence of free ionic motion within the hydrogel matrix. tan δ shows significant energy absorption further substantiating permittivity damping, which transitions from positive to negative values.

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 (SiO 2) 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-SiO 2 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. [ABSTRACT FROM AUTHOR]

A compact new ultra-wideband (UWB) antenna using planar metamaterial (MTM) structures is proposed. The antenna is designed with a double-side planar periodic cell structure. The proposed 3-D unit cell show an artificial negative electric permittivity medium (NEPM), exhibiting a wide electromagnetic bandgap (EBG) created by etching four L-shaped slots on the main square patch and crossed-shaped slots on the ground plane. The proposed antenna fabricated on a 1.52 mm low-cost Rogers RO4003C substrate, is compact, measuring 22.4 × 25.6 mm², with a relative permittivity of 3.38 and a loss tangent of 0.0027. It has a broad bandwidth covering 3.8 GHz to 17.7 GHz, relatively 129%. The average gain over the entire bandwidth is 5.44 dB, with a peak value of 8.55 dB at 15.5 GHz. Design and simulation were carried out using the finite integration technique (FIT)-based CST microwave studio. The measured return loss (S11) of the prototype was in good agreement with the simulated results. The proposed antenna shows satisfactory radiation efficiency, achieving between 80% and 93% over the whole band. The measured gain of the test antenna demonstrates favorable radiation characteristics and shows the stability of radiation patterns at low frequencies. A comparative study with the related literature reviews recently published highlights the compactness of our MTM antenna configuration, presenting a reduction factor between 43.13% and 56.25%. Due to its outstanding performance, the proposed design is positioned as a strong candidate for various UWB applications, and also can be used for satellite communications and radar applications. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

With the development of new metamaterials made of periodic array structures, negative permittivity has recently received more and more attention. However, it is crucial to achieve negative permittivity behavior based on materials' intrinsic properties rather than their synthetically periodic structures, as easy preparation is always a priority. Wearable cloaks, stretchable sensors, thin-film capacitors, and other applications all hold great promise for flexible metacomposites with tunable negative permittivity. Herein, flexible multi-walled carbon nanotube/poly-(vinyl alcohol)/manganese ferrite/active carbon (MWCNT/PVA/Mn ferrite/AC) porous metacomposites with negative dielectric constant were prepared by feasible sol–gel method. The resulting metacomposites with various MWCNT mass values were examined for their ac conductivity behavior, magnetic and dielectric characteristics, impedance, and absorbance performances. The findings indicate that these novel amorphous metacomposites possess exceptional qualities, such as superior impedance matching, magnetic characteristics, exceptional reflectivity, and proficiency as an optical sensor, alongside their negative dielectric constant. [ABSTRACT FROM AUTHOR]

Epsilon‐near‐zero (ENZ) materials, exhibiting unique physical characteristics such as near‐zero refraction, have aroused extensive interest and exhibit great potentials in novel applications of perfect absorbers, high‐harmonic generation, and nonlinear optical response. Here, for the first time, magnetic‐driven broadband ENZ materials are designed by fabricating polyvinyl alcohol (PVA)/Ni@carbon nanotubes (CNTs) films. Dielectric properties including real permittivity (ɛ′), imaginary permittivity (ɛ″), dielectric loss (tanδ), and impedance (Z) are investigated. When Ni@CNTs content reached 30 wt.%, negative permittivity transferred to positive permittivity at ≈11.5 MHz, and epsilon‐near‐zero (|ɛ′| < 1) is realized from ≈9 to 14 MHz, exhibiting broad ENZ bandwidth of ≈5 MHz. Theory calculations confirm that delocalized electrons are introduced from CNTs, which improve the carrier mobility and achieve low frequency dispersion behavior. Longer interfacial polarization electric fields between PVA and CNTs are also demonstrated by theory calculations, enhancing the positive permittivity response to offset negative permittivity response from Ni@CNTs. These two mechanisms result in broadband ENZ at radio frequency. This film also exhibits excellent magnetic actuation ability under magnetic field, broadening applications from ENZ materials to novel fields such as magnetically actuated robots with perfect absorption, magnetic‐driven biomimetic aircrafts with shielding ability, magnetic‐driven photodetectors, etc. [ABSTRACT FROM AUTHOR]

The article investigates a compact low profile guitar shaped antenna loaded with co-directional complementary split ring resonator(CO-CSRR) based on negative permittivity metamaterial for sub-6 GHz 5G applications.The inclusion of metamaterial on the radiator produces two popular frequency bands n78 5G NR (3.13–4.01) GHz and n79 5G NR (4.98–6.19) GHz with gain of 5.75 dBi and 6.3 dBi respectively. The design is able to achieve high impedance bandwidth of 700 MHz and 1040 MHz at 3.6 GHz and 5.2 GHz with low return loss (S11

With the increasing popularity of wearable devices, flexible electronics with a negative permittivity property have been widely applied to wearable devices, sensors, and energy storage. In particular, a low-frequency dispersion negative permittivity in a wide frequency range can effectively contribute to the stable working performance of devices. In this work, polyvinylidene fluoride (PVDF) was selected as the flexible matrix, and copper nanowires (CuNWs) were used as the conductive functional filler to prepare a flexible CuNWs/PVDF composite film with a low-frequency dispersion negative permittivity. As the content of CuNWs increased, the conductivity of the resulting composites increased sharply and presented a metal-like behavior. Moreover, the negative permittivity consistent with the Drude model was observed when CuNWs formed a percolative network. Meanwhile, the negative permittivity exhibited a low-frequency dispersion in the whole test frequency range, and the fluctuation of the permittivity spectra was relatively small (−760 to −584) at 20 kHz–1 MHz. The results revealed that the high electron mobility of CuNWs is reasonable for the low-frequency dispersion of negative permittivity. CuNWs/PVDF composite films with a frequency-independent negative permittivity provide a new idea for the development of flexible wearable electronic devices. [ABSTRACT FROM AUTHOR]

Metacomposites with extraordinary electromagnetic (EM) parameters recently offered a brand-new strategy for EM shielding, but still suffered from the unclear paradigm and regulation mechanism for ε′ -negative and ε′ -near-zero response. Herein, we presented an effective paradigm of binary composites consisting of CaCu 3 Ti 4 O 12 (CCTO) and graphitized-multiwall carbon nanotube (g-MWCNT) which was designed by percolation theory. The ε′ switched from positive to negative with increasing frequency was obtained in g-MWCNT/CCTO composites, which could be explained by electrical dipole resonance of interconnected g-MWCNT clusters. Once the percolated g-MWCNT network is formed, Drude-type ε′ -negative response would be obtained due to the low-frequency plasma oscillation. Epsilon-near-zero effect (at ∼385 MHz and ∼135 MHz) were tuned by adjusting g-MWCNT content, which respectively corresponds to the loss peaks. The EM medium of CCTO/g-MWCNT composites with ε′ -negative or ε′ -near-zero response showed great EM shielding performance at specific frequency region. The g-MWCNT/CCTO metacomposites provide a classical paradigm of ceramic matrix composites for ε′ -negative and ε′ -near-zero response which will guide the practical application of metacomposites in dielectric ceramics and metamaterials, and promote the next steps in EM shielding field. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ruddlesden-Popper oxide Sr2Mn0.7Sn0.3O4 was synthesized by solid state method by calcining at different temperatures between 1200 and 1500°C. The phase evolution during thermal treatments was investigated and it was shown that the powder calcined at 1500°C and ceramics sintered at 1500°C have single phase structure. Rietveld refinement of the XRD data confirmed tetragonal crystal structure having a = b = 3.9425 Å and c = 12.1230Å lattice parameters and I4/mmm space group symmetry. Permittivity (ε), impedance (Z*), dissipation factor (tan δ) and AC conductivity (σAC) of the samples were studied in the frequency range 1 kHz-2MHz and temperature range 60-600°C. An equivalent circuit comprising two parallel R-L elements and one constant phase element (CPE) model fitted the impedance data very well. Components of the equivalent circuit were correlated with compositional micro inhomogeneities in the sintered sample. Resonance-like feature observed in the dissipation factor at a particular temperature is attributed to the cancellation of capacitive and inductive reactants. Negative permittivity and loss of the sintered sample were compared with other ceramic oxides showing negative permittivity.

The article investigates a compact low profile guitar shaped antenna loaded with co-directional complementary split ring resonator(CO-CSRR) based on negative permittivity metamaterial for sub-6 GHz 5G applications.The inclusion of metamaterial on the radiator produces two popular frequency bands n78 5G NR (3.13–4.01) GHz and n79 5G NR (4.98–6.19) GHz with gain of 5.75 dBi and 6.3 dBi respectively. The design is able to achieve high impedance bandwidth of 700 MHz and 1040 MHz at 3.6 GHz and 5.2 GHz with low return loss (S 11 < -15 dB). The antenna offers simulated radiation efficiency of 93.9% at 3.6 GHz and 91.8% at 5.2 GHz making it suitable for 5G communication demands.The equivalent circuit of guitar shaped antenna is presented and the values of lumped elements are calculated. The metamaterial characteristic is verified by Nicholson Ross weir method. A neural network model is developed both in Regression predictive modelling and classification predictive modelling for the proposed guitar shaped antenna using feed forward Levenberg-Marquardt algorithm to predict return lossfor various dimensions of antenna. The model predictsthe data with 90.9% accuracy. The prototype of the antenna is designed with a compact size of 28 × 28 × 1.6 mm3, fabricated on FR4 substrate and experimentally verified. [ABSTRACT FROM AUTHOR]

Ceramic composites with negative permittivity have provoked considerable interests of researchers in electronic and dielectric devices due to the extraordinary electromagnetic performance in radio-frequency (RF) region. Herein, graphene/CaCu 3 Ti 4 O 12 (GR/CCTO) ceramic composites were spark plasma sintered, of which the dielectric and thermal properties were demonstrated at RF region. An electrical percolation was identified with GR content varying from 10 wt% to 14 wt% which presenting as a dramatic increase of ac conductivity. The conduction mechanism changed from hopping conductivity to metal-like conductivity. Meanwhile, the real permittivity (ε′) turned from positive to negative which indicating an intrinsic transition of dielectric response mechanism. Therefore, Drude model was applied to elucidate the RF negative permittivity (ε' < 0) which manifesting the low-frequency plasmonic state of delocalized electrons in composites. The constructed GR networks in composites also leaded to the enhanced thermal conductivity due to the dominating contribution of phonon vibration in GR sheets. Besides, theoretical models of capacitive and inductive equivalent circuits were used on impedance spectra which successfully clarified the inductive character of negative permittivity. This work benefits expounding the generation and regulation mechanism of negative permittivity and will be favorable to exploring brand-new applications of ceramic composites. [ABSTRACT FROM AUTHOR]

The spectral analysis of a dielectric material based on modified Debye model is studied analytically and numerically in this paper. The second-order Debye model is modified to become ten-order Debye model. The ten-order Debye model presents not only an asymmetry of the loss curve but also a double relaxation peak which testifies to the presence of several types of relaxation phenomena in the dielectric materials. The analytical and numerical results obtained confirm that by increasing the resistance and the capacitors the material stabilizes which decreases the area of instability; this highlights clearly the dielectric material response. [ABSTRACT FROM AUTHOR]

Chiral vortices and their phase transition in ferroelectric/dielectric heterostructures have drawn significant attention in the field of condensed matter. However, the dynamical origin of the chiral phase transition from achiral to chiral polar vortices has remained elusive. Here, we develop a phase-field perturbation model and discover the softening of out-of-plane vibration mode of polar vortices in [(PbTiO 3 ) m /(SrTiO 3 ) m ] n superlattices at a critical epitaxial strain or temperature. The softening of the mode leads to the appearance of the axial polarization at vortex cores, resulting in chiral phase transition. It is found that the local negative permittivity plays a crucial role in the enhanced oscillation of axial polarization near the phase transition. Our findings not only reveal the origin of the chiral phase transition of polar vortices but also provide considerable new insight into the dynamics of topological structures and topological phase transitions in ferroelectric systems.