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Dual-Band Binary Metamaterial Absorber Based on Low-Permittivity All-Dielectric Resonance Surface
摘要： A binary-structured metamaterial absorber (BMA) consisting of a low-permittivity dual-layer all-dielectric resonance surface (ADRS) and re?ector was simulated and experimentally validated. Analyses of relative impedance, electric/magnetic ?eld and power loss density indicated that the proposed BMA exhibits two absorption peaks at 14.65 GHz and 16.61 GHz, resulting from the magnetic and electrical responses of ADRS, respectively. The dependences of absorption properties on the dimensions of the ADRS and material parameters of the ADRS are discussed. It is concluded that the upper layer of the ADRS acts as an impedance-matching layer directly in?uencing the absorption intensity, while the bottom layer offers frequency selectivity in the 13–15 GHz range. The current design uses a low-permittivity ADRS, with simpli?ed design and easy preparation and is notably different from conventional ternary-structured metamaterial absorbers based on a metallic resonance surface. The simplicity of the proposed BMA makes it a promising low-cost ambient temperature alternative to conventional metamaterial absorbers and could open up practical applications.
关键词： Binary-structured metamaterial absorber,simpli?ed design and easy preparation,frequency selectivity,low-permittivity all-dielectric resonance surface
更新于2025-09-10 09:29:36
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Hydrogen-bonded and supramolecular ferroelectricity in a new hybrid (C<sub>12</sub>H<sub>25</sub>NH<sub>3</sub>)<sub>2</sub>CoCl<sub>4</sub>
摘要： A new organic-inorganic layered halide perovskite ((C12H25NH3)2CoCl4) has been synthesized and characterized by: chemical analysis, X-ray powder diffraction, differential scanning calorimetry, and differential thermal analysis thermographs. The dielectric and ferroelectric properties have been investigated. Analysis of the ac conductivity σac (ω, T) measured in the temperature interval from 110K to 370K and at selected frequencies in the range 1 kHz< f<100 kHz and the results show that the Jonscher universal power law is accurately obeyed. The existence of ferroelectricity has been demonstrated by the hysteresis P-E loop. The collective data evidenced that the hybrid behaves as a proper ferroelectric rather than a relaxor one and undergoes an order-disorder ferroelectric phase transition at the Curie temperature Tc (Tc?360K) accompanied with a structural distortion from an intercalated to non- intercalated state as the other Co and/or Zn hybrids. Since the room temperature space group of the hybrid is centrosymmetric (P21/c), the ferroelectricity should be due to the supramolecular interaction which results from the induced dipoles. The hydrogen bonding system of the type N-H....Cl plays the key role in the mechanism of supramolecular ferroelectricity.
关键词： ac induced conductivity and complex dielectric permittivity,phase transition,Supramolecular ferroelectricity,polarization
更新于2025-09-10 09:29:36
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Optical and Magneto-Optical Properties of Multilayer Nanosized [Co/TiO2]n Films
摘要： The optical and magneto-optical properties of the metal–dielectric multilayer [Co/TiO2]n structures with 2–4-nm-thick layers prepared on a silicon substrate Si(001) by ion-beam deposition have been studied. The complex permittivity of multilayer [Co/TiO2]n structures has been measured by the optical ellipsometry technique in the spectral range of 0.6–5.6 eV and analyzed using the optical reflection matrices for isotropic multilayer dielectric structures taking into account the optical losses and also using the method of anisotropic effective medium. The magneto-optical Kerr effect has been measured by the polarimetric technique in the spectral range of 1.2–4.5 eV in the polar and longitudinal geometries. The magnetic anisotropy type is determined on the base of the field dependences of the magneto-optical Kerr effect. It is found that the nanosized [Co/TiO2]n structures can be considered as artificial optically uniaxial media with a strong magnetic and optical anisotropy at room temperature.
关键词： silicon substrate,Co/TiO2,magneto-optical properties,multilayer nanosized films,optical properties,complex permittivity,magneto-optical Kerr effect,magnetic anisotropy,optical ellipsometry,ion-beam deposition
更新于2025-09-10 09:29:36
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Structural and dielectric properties of BaTi0.5 (Co0.33 Mo0.17) O3 perovskite ceramic
摘要： The polycrystalline sample BaTi0.5 (Co0.33 Mo0.17) O3 was synthesized by the sol-gel method. The effect of replacing titanium by cobalt and molybdenum on the structural and electrical properties of our compound was investigated. The results of X-ray diffraction (XRD) at room temperature showed a pure tetragonal perovskite. The electrical response was studied by complex impedance spectroscopy over a broad frequency range (30 - 106 Hz) at different temperatures. The values of ac conductivity were fitted by Jonscher’s law σ(ω) = σDC + Aωn and supported by the correlated barrier hopping (CBH) mechanism. Complex impedance analysis confirmed the existence of an electrical relaxation in the compound. The dielectric constant and the dielectric loss decreased with the increase in frequency. This behavior can be explained by the presence of the Maxwell–Wagner type of polarization responsible for the electric conduction. The modulus plots were characterized by the Havriliak–Negami (H-N) and the empirical Kohlrausch–Williams–Watts (K.W.W.) functions. The Normalized plot of the imaginary part of modulus indicates that the dynamical processes are temperature independent.
关键词： Impedance spectroscopy,Sol-gel processes,Permittivity,X-ray diffraction,Conductivity
更新于2025-09-10 09:29:36
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Polydimethylsiloxane-PbZr <sub/>0.52</sub> Ti <sub/>0.48</sub> O <sub/>3</sub> nanocomposites with high permittivity: Effect of poling and temperature on dielectric properties
摘要： Polydimethylsiloxane (PDMS)/lead zirconate titanate (PbZr0.52Ti0.48O3, PZT)-based nanocomposites with high dielectric constant (permittivity, k) are prepared through room temperature mixing. The effect of PZT loading on electrical and mechanical properties of the PDMS–PZT composites is extensively studied. It is found that there is signi?cant increase in permittivity with PZT loading and decrease in volume resistivity. All the composites have low dielectric loss compared to permittivity value. It is observed that there is increase in permittivity and decrease in volume resistivity of composites after poling, which is due to the dipolar polarization. It is found that both permittivity (ε0) and alternating current conductivity (σ ac) are increased with temperature at low frequency (1 Hz) and decreased with temperature at high frequency (1 MHz). The above composites are sensitive to external pressure and can be used as pressure/force sensor. The tensile strength and % elongation at break decreases with PZT loading, which is due to the nonreinforcing behavior of PZT ceramic. PZT particles distribution and dispersion in PDMS matrix are observed through ?eld emission scanning electron microscopy, high resolution transmission electron microscopy, and atomic force microscopy/scanning probe microscopy. Thermal stability of composites increased with the PZT loading which is due to higher thermal stability of PZT particles compared to PDMS matrix.
关键词： PZT,temperature,permittivity,polydimethylsiloxane,nanocomposite
更新于2025-09-10 09:29:36
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Optical and Electrical Characterization of Pure PMMA for Terahertz Wide-band Metamaterial Absorbers
摘要： The characteristics of relative permittivity and reflectance for poly (methyl methacrylate) (PMMA) films prepared by spin-coating were investigated and an excellent wideband terahertz (THz) metamaterial absorber (MA) had been fabricated by employing PMMA film as the dielectric layer. XRD and AFM indicated that all the PMMA films with thicknesses from 11 to 17 μm were amorphous and extremely smooth with roughness about 0.203 nm. Raman results demonstrated that vibration strength of the same covalent bonds tends to be consistent with an increase in film thickness. The dual beam laser interferometer (DBLI) was employed to study the influence of applied frequency and thickness on the relative permittivity, and the results exhibited dielectric constants increased from 2.88 to 4.04 with the thickness increasing from 9 to 14 μm. And the dielectric constants for PMMA films with a certain thickness (8 μm) gradually declined when the applied frequency increased from 100 to 105 Hz; besides, the dielectric constant in THz band was forecasted approximately 2.5. The terahertz time domain spectrometer (THz-TDS) results revealed that the THz reflectance was of gradual degradation from 80 to 58% at 3.2 THz, as the thickness increased from 11 to 17 μm. In addition, the UV-VIS spectrum showed that thickness had little effect on reflectance and transmittance in visible region, leading to the almost same Eg (energy gap) about 3.7 eV. At last, by employing PMMA film as the dielectric layer, a highly wideband metamaterial absorber with absorption > 80% from 4.1 to 7.4 THz was fabricated.
关键词： Terahertz,Metamaterial absorber,PMMA,Reflectance,Permittivity
更新于2025-09-10 09:29:36
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Systematic tuning of the photo-dielectric effect in Ba(Al <sub/>1–</sub><sub/><i>x</i> </sub> Zn <sub/><i>x</i> </sub> ) <sub/>2</sub> O <sub/>4–δ</sub>
摘要： Systematic tuning of photo-induced enhancement of the dielectric permittivity (i.e., the photo-dielectric effect) in Ba(Al1–xZnx)2O4–d (BAZ-x) has been demonstrated by changing Zn concentration x and intensity of the incident light. The relative change of the dielectric permittivity (e0), defined as De0/dark, increases linearly with an increase in the Zn concentration (x), finally reaching approximately 30% at 1 MHz. The dependence of De0/dark on the intensity of the incident light shows a two-step growth as the irradiation light intensity increases, suggesting the existence of multiple photo-induced processes influencing the photo-dielectric effect of BAZ-x. The results of the present study not only give a clue to the mechanism of the photo-dielectric effect but also aid in the development of innovative photo-tunable functional devices.
关键词： light intensity,dielectric permittivity,Zn concentration,photo-dielectric effect,Ba(Al1–xZnx)2O4–d
更新于2025-09-10 09:29:36
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Characterization of core–shell nanostructure consisting Si–Au–SiO2 based on manipulation of optical properties
摘要： In this article, we investigated some physical characteristics of core–shell nanostructure in optical regime and perturbation has been also introduced as an effective method in shaping of optical properties. The proposed nanostructures are composed of the selected materials as: Silicon, Silicon Dioxide and Gold. At first, the extinction cross section spectra are calculated for multilayer core–shell nanostructures in optical range and the configuration effect of the constructed materials in a multilayer nanostructure are investigated for determination of Plasmon range. Then, the new structures of core–shell nanoparticles (gold–silicon) are presented, which have an amount of impurity particle in their shells as perturbation and also their extinction cross section spectra are calculated. The obtained results in this article give a proper approach about perturbation effect in broadening, sharpening and shifting of optical response which are decisive factors especially nano-network systems. Indeed, it has been proposed that the impurity particles in the shells can be a mechanism for tuning of optical characteristics of the presented nanoparticles in practical fields and also creation of local oscillations as plasmonic resonances in a considered optical range. Besides, redshift in extinction cross section can be also created by particle perturbation. At the end, the effective permittivity of the perturbed core-shells are extracted. The optional frequency range is selected between 300 and 900 (THz).
关键词： Effective permittivity,Perturbation,Nanoparticle impurity,Extinction cross section,Core–shell nanostructure,Plasmonic resonance frequency
更新于2025-09-09 09:28:46
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A Review of Manufacturing Materials and Production Methods for Frequency-Selective Structures [Wireless Corner]
摘要： This article presents a review of frequency-selective structure (FSS) manufacturing materials and production methods ranging from the common printed circuit board (PCB)-based designs to textile, ink, metal, or fluid prototypes. Our work gathers some of the most relevant solutions published by the scientific community and considers several examples depicted for each case. Additionally, the main physical parameters that may have a significant impact on FSS performance have been identified, e.g., electrical conductivity of the FSS conductive element and the relative permittivity and thickness of the FSS dielectric material. Finally, a comparative analysis of the materials and techniques is presented, which highlights the benefits and limitations of each solution.
关键词： printed circuit board,relative permittivity,metal,Frequency-selective structures,fluid prototypes,textile,ink,electrical conductivity,production methods,manufacturing materials
更新于2025-09-09 09:28:46
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Free-Space Materials Characterization by Reflection and Transmission Measurements using Frequency-by-Frequency and Multi-Frequency Algorithms
摘要： The knowledge of the electromagnetic constitutive properties of materials is crucial in many applications. Free-space methods are widely used for this purpose, despite their inherent practical difficulties. This paper describes an affordable free-space experimental setup for the characterization of flat samples in 1–6 GHz in a non-anechoic environment. The extracted properties are obtained from the calibrated Scattering Parameters, using a frequency-by-frequency solution or a multi-frequency reconstruction. For the first, we describe how the Time-Domain Gating can be implemented and used for filtering the signals. For the latter, a weighting factor is introduced to balance the reflection and transmission data, allowing one to have a more favorable configuration. The different role of transmission and reflection measurements on the achievable results is analyzed with regard to experimental uncertainties and different noise scenarios. Results from the two strategies are analyzed and compared. Good agreement between simulation, measurement and literature is obtained. According to the reported results for dielectric materials, there is no need of filtering the data by a Time-Domain Gating in case of the multi-frequency approach. Experimental results for Polymethylmethacrylate (PMMA) and Polytetrafluorethylene (PTFE) samples validate both the setup and the processing.
关键词： free-space method,permeability,conductivity,non-destructive testing,extraction algorithms,permittivity,time-domain gating,free-space calibration,scattering parameters,material characterization
更新于2025-09-09 09:28:46