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- 2018
- arbitrary coupling coefficients
- Dielectric resonator
- filtering
- coupler
- filtering balun
- dual-band
- dual-mode dielectric resonator (DR)
- Electronic Science and Technology
- Nantong University
- Sun Yat-Sen University
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Three-Dimensional Holographic Electromagnetic Imaging for Accessing Brain Stroke
摘要： The authors recently developed a two-dimensional (2D) holographic electromagnetic induction imaging (HEI) for biomedical imaging applications. However, this method was unable to detect small inclusions accurately. For example, only one of two inclusions can be detected in the reconstructed image if the two inclusions were located at the same XY plane but in different Z-directions. This paper provides a theoretical framework of three-dimensional (3D) HEI to accurately and effectively detect inclusions embedded in a biological object. A numerical system, including a realistic head phantom, a 16-element excitation sensor array, a 16-element receiving sensor array, and image processing model has been developed to evaluate the effectiveness of the proposed method for detecting small stroke. The achieved 3D HEI images have been compared with 2D HEI images. Simulation results show that the 3D HEI method can accurately and effectively identify small inclusions even when two inclusions are located at the same XY plane but in different Z-directions. This preliminary study shows that the proposed method has the potential to develop a useful imaging tool for the diagnosis of neurological diseases and injuries in the future.
关键词： brain stroke,sensor array,dielectric properties,electromagnetic induction imaging,magnetic induction tomography
更新于2025-09-09 09:28:46
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Characterization of additively manufactured cellular alumina dielectric structures
摘要： Additive manufacturing (AM, also known as 3D printing) can produce novel three-dimensional structures using low-loss dielectric materials. This enables the construction of dielectrics with complex shapes that enable innovative microwave applications such as resonators, filters, and metamaterial lenses. This paper addresses the production and characterization of cellular structures of various designed densities created with a low loss ceramic material, alumina (aluminum oxide), via vat photopolymerization. The permittivity of these printed structures is variable over roughly an octave, with a range of relative permittivites from 1.78 to 3.60, controlled via part geometry.
关键词： electromagnetic metamaterials,dielectric materials,ceramics,printing,design for manufacture
更新于2025-09-09 09:28:46
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First-principles investigation of the electronic band structures and optical properties of quaternary <i>A</i> Ba <i>MQ</i> <sub/>4</sub> ( <i>A</i> = Rb, Cs; <i>M</i> = P, V; and <i>Q</i> = S) metal chalcogenides
摘要： In this paper, we study the optoelectronic properties of quaternary metal chalcogenide semiconductor ABaM Q4 (A = Rb, Cs; M = P, V; and Q = S) compounds using state-of-the-art density functional theory (DFT) with TB-mBJ approximation for the treatment of exchange-correlation energy. In particular, the electronic and optical properties of the relaxed geometries of these compounds are investigated. Our first-principles ab-initio calculations show that the CsBaPS4 and RbBaPS4 compounds have direct bandgaps whereas the CsBaVS4 compound exhibits indirect bandgap nature. Importantly, the theoretically calculated values of the bandgaps of the compounds are consistent with experiment. Furthermore, our analysis of the electronic charge densities of these compounds indicates that the above quaternary chalcogenides have mixed covalent and ionic bonding characters. The effective masses of these compounds are also calculated which provide very useful information about the band structure and transport characteristics of the investigated compounds. Similarly, high absorptivity in the visible and ultraviolet regions of the electromagnetic spectrum possibly predicts and indicates the importance of these materials for potential optoelectronic applications in this range.
关键词： energy band structure,electronic charge densities,optical conductivity,Chalcogenides,refractive index,dielectric constants,optical reflectivity
更新于2025-09-09 09:28:46
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Metal-Organic Framework Derived Hierarchical Co/C@V2O3 Hollow Spheres as a Thin, Lightweight and High-Efficiency Electromagnetic Wave Absorber
摘要： Developing high-efficiency electromagnetic (EM) wave absorbing materials with light weight, thin thickness and wide absorption bandwidth is highly desirable for ever-developing electronic and telecommunication devices. Herein, hierarchical metal-organic framework (MOF)-derived Co/C@V2O3 hollow spheres were designed and synthesized through a facile hydrothermal, precipitation and pyrolysis method. The composite exhibits both excellent impedance matching and light weight due to the rational combination of hollow V2O3 spheres and porous Co/C. Additionally, multiple components enable a large dielectric and magnetic loss of the composite, giving rise to enhanced EM wave absorption performance with a maximum reflection loss (RL) of -40.1 dB and a broad effective absorption bandwidth (RL < -10 dB) of 4.64 GHz at a small thickness of 1.5 mm. This work provides insights into the design of hierarchical hollow and porous composites as a thin and lightweight EM wave absorbers with efficient absorption, which can also be extended to energy storage, catalysis and sensing.
关键词： Co/C@V2O3 composites,metal-organic framework,hierarchical hollow spheres,dielectric/magnetic composites,electromagnetic wave absorption
更新于2025-09-09 09:28:46
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Temperature and frequency effect on the electrical properties of bulk nickel phthalocyanine octacarboxylic acid (Ni-Pc(COOH)8)
摘要： The AC conductivity of nickel phthalocyanine octacarboxylic acid was investigated from 100 Hz to 1 MHz and temperature from 290 to 423 K. The AC conductivity was found to vary with frequency (σ(f)) and form two dispersion regions; the associated exponent factor “s” values were found to vary from 1.17 to 1.34 and from 0.42 to 0.67 (< 1). The value and temperature dependent of s are found in agreement with conduction mechanism models of large-polaron tunneling and the correlated barrier hopping, at the first and the second regions, respectively. The real and the imaginary parts of the dielectric constant were observed to decrease as the frequency increases indicating the pronounce contribution of low-frequency polarization mechanisms. Furthermore, the activation free energy ?F, enthalpy ?H, and entropy ?S of the sample were calculated as well.
关键词： enthalpy,polarization mechanisms,AC conductivity,activation free energy,dielectric constant,nickel phthalocyanine octacarboxylic acid,entropy
更新于2025-09-09 09:28:46
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Investigation on Structural and Dielectric Properties of Silica Nanoparticles Incorporated Poly(Ethylene Oxide)/Poly(Vinyl Pyrrolidone) Blend Matrix Based Nanocomposites
摘要： Inorganic and organic materials based polymer nanocomposite (PNC) films, comprising silica (SiO2) nanoparticles as inorganic filler and the polymer blend of poly(ethylene oxide) (PEO) and poly(vinyl pyrrolidone) (PVP) as organic matrix (i.e., (PEO–PVP)-x wt% SiO2; x = 0, 1, 3 and 5) have been prepared by the solution-casting method. These PNC films are characterized by employing the scanning electron microscopy (SEM), X-ray diffractometer (XRD), Fourier transform infrared (FTIR) spectroscopy, and the dielectric relaxation spectroscopy (DRS). The effect of SiO2 nanofiller on the spherulite and porous morphology, miscibility of the polymers, PEO crystallite size, the degree of crystallinity, polymer–polymer and polymer-nanoparticle interactions, and from 20 Hz to 1 MHz range dielectric and electrical dispersion behaviour and also the structural dynamics of these PNC materials have been investigated. The porous morphology, structures of miscible phases, and the PEO crystallite length greatly alter with the incorporation of merely 1 wt% SiO2 in the polymer blend matrix which further changes with the increase of nanofiller concentration up to 5 wt%. The real part of complex permittivity over the radio frequency range (20 kHz–1 MHz) for these PNC films is found about 2 and their dielectric loss tangent values below 0.03, at the room temperature, which are significantly low. The contribution of interfacial polarization effect at lower audio frequencies enhances the complex permittivity of these materials linearly in the range 2 to 4 with the decrease of frequency from 1 kHz to 20 Hz confirming their frequency tunable dielectric behaviour. The dielectric study of 3 wt% SiO2 containing PNC film in the temperature range 30–60 °C reveals its thermally activated dielectric characteristics, and the temperature dependent values of dielectric relaxation time and dc electrical conductivity obey the Arrhenius behaviour with activation energies in the range 0.2–0.3 eV. The dielectric and electrical parameters ascertain the promising applications of these PNC films in the development of novel electroactive functional materials, and also their use as the dielectric substrate and electrical insulating polymeric nanodielectrics for the fabrication of flexible-type naturally degradable organoelectronic devices.
关键词： Electrical conductivity,FTIR,XRD,Dielectric properties,Polymer nanocomposite
更新于2025-09-09 09:28:46
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Electromechanical properties of ternary BiFeO3?0.35BaTiO3–BiGaO3 piezoelectric ceramics
摘要： In the present work, composition dependent crystal structure, ferroelectric, piezoelectric, and temperature dependent dielectric properties of the BiGaO3-modified (1–x)(0.65Bi1.05FeO3–0.35BaTiO3) (BFBT35–xBG, where x = 0.00–0.03) lead-free ceramics were systematically investigated by solid-state reaction method, followed by water quenching process. The substitution of BG successfully diffuses into the lattice of the BFBT ceramics, without changing the pseudo-cubic structure of the samples. The scanning electron microscopy (SEM) results revealed that the average grain size was increased with BG-content in BFBT system. The BFBT–xBG ceramics showed a maximum in permittivity (?max) at temperatures (Tmax) above 500 °C in the compositional range of 0.00 ≤ x ≤ 0.03. The electro-strain is measured to be 0.125% (d*33 ~ 250 pm/V) under unipolar fields (5 kV/mm) for BFBT–0.01BG ceramics. The same composition (x = 0.01), large static piezoelectric constant (d33 ~ 165 pC/N) and electromechanical coupling factor (kp ~ 25%) were obtained. The above investigated characterizations suggests that BFBT–BG material is favorable for piezoelectric and high temperature applications.
关键词： Lead-free,Dielectric,Piezoelectric,Ferroelectric,BiFeO3–BaTiO3
更新于2025-09-09 09:28:46
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Evolution of ferroelectric and piezoelectric response by heat treatment in pseudocubic BiFeO3–BaTiO3 ceramics
摘要： Heat treatment of ceramics is an important process to tailor the fine electromechanical properties. To explore the criteria for optimized heat treatment in a perovskite structure of (1–x)Bi1.05FeO3–xBaTiO3 (BF–BT100x) system, the structural phase relation, ferroelectric and piezoelectric response of BF–BT36 and BF–BT40 ceramics prepared by furnace cooling (FC) and quenching process were investigated. The X-ray diffraction examination showed single pseudocubic perovskite structure for all the ceramics. The homogenous microstructure was obtained for all ceramics with relatively large grain size in the furnace cooled samples. Well saturated ferroelectric hysteresis loops and enhanced piezoelectric constant (d33 = 97 pC/N) were achieved by quenching process. Dielectric curve of BF–BT36 showed large dielectric constant at its Curie temperature, however, BF–BT40 showed diffused relaxor-like dielectric anomalies. Quenched BF–BT36 samples showed typical butterfly like field induced strain curves, however negative strain decreased in BF–BT40 ceramics. From these investigated study, it is observed that BF–BT ceramics are very sensitive to the heat treatment process (furnace cooling and quenching) on the dielectric, electromechanical properties.
关键词： Quenching process,Electric field induced strain,Dielectric relaxation,BF–BT
更新于2025-09-09 09:28:46
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Structural and electrical properties of Gd-doped BiFeO3:BaTiO3 (3:2) multiferroic ceramic materials
摘要： Gadolinium doped BiFeO3:BaTiO3 (3:2) polycrystalline multiferroic ceramics have been prepared by high-temperature solid state reaction technique. X-ray diffraction (XRD) analysis at room temperature of the prepared materials confirmed the formation of the compounds with rhombohedral crystal structure. The average particle size of as prepared samples have been found in the range of 35 nm to 55 nm for different doping concentrations. The average grain size of as prepared samples are less than 100 nm which is confirmed from SEM study. The SEM of annealed compounds showed the uniform distribution of grains and the formation of dense ceramic with average grain size in the order of 4 μm. Dielectric studies of the materials reveals that the dielectric constant ( εr ) and tangent loss (tan δ) decreases with doping concentrations at room temperature. The variation of εr and tan δ with temperature was explained on the basis of Maxwell–Wagner mechanism. The values of grain resistance ( Rb ) and grain capacitance (Cb) were obtained from Nyquist plots for the different doping concentrations at 300 °C. The activation energy ( Ea ) was calculated from the curve of frequency dependent ac conductivity ( σac ) within the range 0.19 eV to 0.45 eV. The remnant polarization of the samples (0.53 μC/cm2) was measured from polarization versus electric field (P–E) hysteresis curves. The ferromagnetic behaviour of the Gd-doped BiFeO3:BaTiO3 (3:2) sample has been studied by SQUID for the lowest doping concentration. The value of remnant magnetization was found 0.0235 emu/g at room temperature.
关键词： multiferroic ceramics,dielectric properties,ferroelectric properties,Gd-doped BiFeO3:BaTiO3,ferromagnetic properties
更新于2025-09-09 09:28:46
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Influence of Bi Substitution on the Microstructure and Dielectric Properties of Gd3Fe5O12 Ceramics
摘要： The exponential growth in microwave communications in recent years demands innovations and high yield microwave materials. Rare earth iron garnets are well known for their remarkable performance in microwave devices owing to their superior features. In this work we investigate the microstructure and dielectric properties of Bismuth substituted Gd3Fe5O12 ceramics prepared by the conventional solid state reaction route. The variation of lattice parameter, microstructure, permittivity, quality factor and temperature coef?cient of resonant frequency (sf) of Gadolinium Iron Garnet (GIG) with several concentrations of bismuth was investigated. The Bi3+ ion is effectively incorporated into Gadolinium Iron Garnet, due to which the sintering temperature is considerably reduced, and the densi?cation is improved signi?cantly. Moreover, with increase in Bi concentration, the dielectric constant of GIG also increases, while the quality factor is slightly reduced, which is correlated with the higher ionic polarizability of bismuth. At an appreciably low sintering temperature of 1050(cid:2)C, Gd2BiFe5O12 possess a porosity corrected relative permittivity value of 27.3 ± 0.2, unloaded quality factor (Qu 9 f) of 2990 ± 60 GHz (f = 7.3 GHz) and temperature coef?cient of resonant frequency + 60 ± 1 ppm/(cid:2)C.
关键词： microstructure,Low-temperature sintering,microwave dielectric properties,garnet structure
更新于2025-09-09 09:28:46