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Light and flexible composite nanofibrous membranes for high-efficiency electromagnetic absorption in a broad frequency
摘要： With the fast advancement of up-to-date communication technologies, electromagnetic wave (EMW) absorption materials are widely required for various applications. However, it is still a big challenge to produce lightweight, flexible and high efficiency EMW absorption materials in a broad-ranging frequency. Herein, we designed to fabricate the magnetic and dielectric nanofibrous membranes which can be effectively used as EMW absorption materials by facile electrospinning process. The as-fabricated composite carbon nanofibers (CNFs), which combined the components of nickel, cobalt antioxidant nanoparticles and carbon nanotubes, exhibited outstanding magnetic, dielectric properties and strong absorption ability in a wide frequency range. These nanoparticles encapsulated in CNFs are extremely beneficial to the electrical conductivity of the composites through decreasing the contact loss within the CNFs by formation the metal-metal interfaces. Correspondingly, the RL value of -46.60 dB was reached at 4.88 GHz frequency range with a layer thickness of 5.5 mm for these mechanically light and flexible membranes. The enhanced absorption performance (<?10 dB) in the wide frequency band (4.16-18 GHz) can be achieved by selecting a suitable thickness of the material. Results demonstrate that the permittivity and permeability of developed samples have been largely improved due to the integrated interaction of all introduced components in the structure. The composite membranes are a promising candidate for scalable, lightweight and high performance EMW absorption materials in the frequency range from C band to Ku band (4?18 GHz).
关键词： Magnetic and dielectric properties,permeability,permittivity,carbon nanotubes,electromagnetic wave absorption
更新于2025-09-10 09:29:36
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[IEEE 2018 EMF-Med 1st World Conference on Biomedical Applications of Electromagnetic Fields (EMF-Med) - Split, Croatia (2018.9.10-2018.9.13)] 2018 EMF-Med 1st World Conference on Biomedical Applications of Electromagnetic Fields (EMF-Med) - Modelling of Tissue Dielectric Contribution Within the Sensing Radius of a Coaxial Probe
摘要： The dielectric properties of biological tissues are fundamental for the design of electromagnetic medical devices. Tissue dielectric properties are generally measured using the open-ended coaxial probe technique. While the procedure to dielectrically characterise homogeneous biological tissues is straightforward; of heterogeneous tissues requires conducting a post-measurement histological analysis to accurately associate the measured dielectric properties to the tissue content. To this extent, it is crucial to quantify the sensing volume of the probe, consisting of the sensing radius and sensing depth, and examine how different tissue types contribute to the acquired dielectric signal depending on their distribution within the sensing volume. Since a few studies have modelled the dielectric contribution of tissue samples presenting longitudinal heterogeneities, in this work, the dielectric contribution of tissues within radially heterogeneous samples is modelled for the first time. A nonlinear relationship is found between the contribution of individual tissues to the acquired dielectric data and the volume that each tissue occupies within the radially heterogeneous sample. This work enables prediction of the permittivity of a sample with radial heterogeneities, based on knowledge of the constituent tissues, and provides the basis for accurate dielectric characterisation of heterogeneous samples.
关键词： Biological tissues,sensing radius,dielectric properties,open-ended coaxial probe,numerical simulations
更新于2025-09-10 09:29:36
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Crystallization kinetics and the dielectric properties of SrO-BaO-Nb2O5-B2O3 glass-ceramics
摘要： Glass-ceramics materials of SrO-BaO-Nb2O5-B2O3 system have been prepared by conventional melt-casting followed by controlled crystallization. The crystallization kinetics, phase evolution, microstructure, breakdown strength and dielectric properties have been explored by differential scanning calorimetry (DSC), X-ray diffractometer (XRD), scanning electron microscope (SEM), and multifunction LCR meter. The results reveal that crystallization mechanism of this glass is believed to be three-dimensional interfacial growth. It was observed that predominant crystalline phase is Ba0.39Sr0.61Nb2O6 in these glass-ceramics crystallized at 750 °C, and the grain size increases with increase in crystallization time. The uniform microstructure can be seen clearly in glass-ceramics crystallized at 750 °C for 3 h, and the obtained glass-ceramics was found to possess optimal properties. Moreover, glass-ceramic with a dielectric constant of 58, the dielectric loss of 0.007 and breakdown strength of 1010 kV/cm could be achieved. In addition, energy storage density of glass-ceramics reached a maximal value of 2.62 J/cm3. To our knowledge, studies on SrO-BaO-Nb2O5-B2O3 glass-ceramics without SiO2 as a glass network former are few, and the melting temperature of the B2O3-based glass is lower than that of SiO2-based glass, which is conducive to the purpose of energy saving. These findings indicate that this glass may be a candidate for high energy-storage capacitors.
关键词： Energy storage density,Glass-ceramics,Crystallization,Dielectric properties
更新于2025-09-10 09:29:36
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Temperature-stable dielectric properties from 100 to 375?°C in system (K0.495Na0.495La0.01)(Nb0.997Cu0.0075)O3–Bi(Mg0.5Zr0.5)O3
摘要： (1-x)(K0.495Na0.495La0.01)(Nb0.997Cu0.0075)O3-xBi(Mg0.5Zr0.5)O3 (abbreviated as KNLNC-xBMZ) ceramics were designed and prepared. The phase transition, microstructure and electrical properties of the ceramics were investigated. The phase structures of the ceramics transform from orthorhombic to pseudocubic phases and the grain sizes decrease gradually with BMZ content (x) increasing. Additionally, BMZ additions can significantly enhance the dielectric temperature stability and decrease the dielectric loss of ceramics over a relatively broad temperature range. KNLNC-0.02BMZ ceramics exhibit high dielectric permittivity (er = 1542) and small variation (Der/er150 (cid:2)C B ± 15%) in dielectric permittivity from 100 to 375 (cid:2)C, and low dielectric loss (tand B 2%) in the temperature range of 100–350 (cid:2)C, which suggests that this ceramic is a candidate for high-temperature capacitor application.
关键词： (K0.5Na0.5)NbO3,Lead-free,Dielectric properties,Elevated temperature stability,Microstructure
更新于2025-09-10 09:29:36
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Enhanced energy storage properties of BaTiO3-Bi0.5Na0.5TiO3 lead-free ceramics modified by SrY0.5Nb0.5O3
摘要： In this work, a novel lead-free relaxor-ferroelectric ceramics of (1-x)(0.65BaTiO3-0.35Bi0.5Na0.5TiO3)-xSrY0.5Nb0.5O3 ((1-x)BTBNT-xSYN x ? 0.02e0.12), was designed and prepared by the conventional solid state reaction method. The results show that all of the sintered samples have a perovskite structure. The Curie Temperature (Tc) moves to the low temperature side which causes the high dielectric constant at room temperature, and the ferroelectric hysteresis loop becomes slimmer and slimmer with increasing the content of SYN. Meanwhile, the optimal energy storage properties can be obtained in 0.92BTBNT-0.08SYN ceramic with an impressive discharged energy density (Wrec) of 1.36 J/cm3 under 152 kV/cm, and the charge-discharge ef?ciency reaches 74.3%. Therefore, all these results indicate that (1-x)BTBNT-xSYN lead-free ceramics can be applied for pulsed power capacitors.
关键词： SrY0.5Nb0.5O3,Energy storage,Dielectric properties,Lead-free ceramics
更新于2025-09-10 09:29:36
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Influence of additives on structure and ferroelectric properties of NBT-BT-BMT ceramics
摘要： Influence of various over stoichiometric additives on phase formation, unit cell parameters, microstructure, dielectric and ferroelectric properties of solid solutions 0.8[0.8(Na0.5Bi0.5)TiO3-0.2BaTiO3]-0.2Bi(Mg0.5Ti0.5)O3 system has been studied. The unit cell volume slightly decreased in case of the V2O5 additives but did not change in case of Bi2O3, LiF, and KCl additives. Increase in dielectric parameters ert and tandrt values at the room temperature was revealed for compositions doped by KCl additives, while these parameters decreased in compositions doped by the V2O5 additives. Linear correlation between piezoelectric coefficient d33 measured for separate grains using the Piezoresponse Force Microscopy method and dielectric permittivity ert values at the room temperature was confirmed.
关键词： ferroelectric phase transitions,additives,dielectric properties,perovskite structure,Ceramics (Na0.5Bi0.5)TiO3 - BaTiO3 - Bi(Mg0.5Ti0.5)O3
更新于2025-09-10 09:29:36
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Structural aspects of the high-temperature space charge relaxation in ferroelectric VDF/TFE 94/6 copolymer
摘要： Structural changes in isotropic films of ferroelectric vinylidene fluoride (VDF)/tetrafluoroethylene (TFE) 94/6 copolymers in the metastable state have been studied on heating. The metastable state was ascribed to c-crystals. The dielectric relaxation spectroscopy was employed to study space charge relaxation processes. Two relaxations were observed at high temperatures. One of them was attributed to relaxation of space charge accumulated on the Al electrode which may be partially blocked due to new functional groups formed in the polymer surface. Recrystallization of the film from the melt is accompanied by small a-crystals formation. This results in a decrease in activation energy of the space-charge relaxation process.
关键词： Ferroelectricity,dielectric properties,crystallization,fluoropolymers
更新于2025-09-10 09:29:36
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[IEEE 2018 IEEE 20th International Conference on e-Health Networking, Applications and Services (Healthcom) - Ostrava, Czech Republic (2018.9.17-2018.9.20)] 2018 IEEE 20th International Conference on e-Health Networking, Applications and Services (Healthcom) - Investigation on Dielectric Properties of Glucose Aqueous Solutions at 500 KHz-5MHz for Noninvasive Blood Glucose Monitoring
摘要： Noninvasive blood glucose monitoring (NBGM) provides patient with diabetes a prospective approach with the characteristics of painless and sustainable monitoring. In this study, the dielectric properties of glucose aqueous solutions, namely, deionized water solutions and saline solutions were studied. Specifically, the conductivity and the dielectric constant were measured by using impedance analyzer in the frequencies range of 500 KHz to 5MHz at 25°C. The results showed that both the dielectric constant and the conductivity for the two types of glucose aqueous solutions decreased with the increase of glucose concentration in the above frequency band. By comparing the two solutions with human blood, it was found that the dielectric properties of physiological saline are closer to that of human blood. In the study, saline solution was adopted as research object. In order to formulate the relationship between the dielectric properties of saline solutions and glucose concentration, the third-order Cole-Cole model for each glucose concentration was developed and the coefficient of determination R2 was as higher as 0.99. In addition, a second-order polynomial is used to model the glucose concentration dependence for the Cole–Cole parameters. The result indicates that the NBGM at low frequencies has potentials in practical applications.
关键词： dielectric properties,Cole-Cole parameters,glucose concentration,Noninvasive blood glucose monitoring
更新于2025-09-10 09:29:36
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FeSiAl/ZnO-filled resin composite coatings with enhanced dielectric and microwave absorption properties
摘要： Composite coatings with resin matrix and hybrid fillers of FeSiAl and ZnO powders have been developed for their potential application as microwave absorbing coatings. The effects of FeSiAl and ZnO content on the complex permittivity, complex permeability and reflection loss (RL) of such composite coatings were studied in the frequency range of 8.2–12.4 GHz (X-band). Compared with the complex permeability, the complex permittivity showed more dependence on the absorbent content and the permittivity values increase notably with increasing FeSiAl or ZnO content. Owing to the best impedance matching and appropriate electromagnetic attenuation, the composite coating filled with 35 wt% FeSiAl and 20 wt% ZnO powders exhibits the most desirable microwave absorption properties with the effective absorption bandwidth (< ?10 dB, > 90% absorption) 3.5 GHz in 8.6–12.1 GHz and the strong absorption peak ?40.5 dB at 10.4 GHz, when the thickness is 2.2 mm. The results suggest that FeSiAl/ZnO-filled resin composite coatings could be qualified as good candidates for highly efficient and strong microwave absorbing coatings.
关键词： FeSiAl,dielectric properties,resin composite coatings,microwave absorption,ZnO
更新于2025-09-10 09:29:36
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Crystal structure, microwave dielectric properties and low temperature sintering of (Al0.5Nb0.5)4+ co-substitution for Ti4+ of LiNb0.6Ti0.5O3 ceramics
摘要： The phase composition, microstructure, microwave dielectric properties of (Al0.5Nb0.5)4+ co-substitution for Ti site in LiNb0.6Ti0.5O3 ceramics and the low temperature sintering behaviors of Li2O-B2O3-SiO2 (LBS) glass were systematically discussed. XRD patterns and EDS analysis result confirmed that single phase of Li1.075Nb0.625Ti0.45O3 solid solution was formed in all component. The increase of dielectric constant (εr) is ascribed to the improvement of bulk density. The restricted growth of grain has a negative influence on quality factor (Q×f) value. The τf value could be continuously shifted to near zero as the doping content increases. Great microwave dielectric properties were obtained in LiNb0.6Ti(0.5-x)(Al0.5Nb0.5)xO3 ceramics (x = 0.10) when sintered at 1100℃ for 2 h: εr = 70.34, Q×f = 5144 GHz, τf = 4.8ppm/℃. The sintering aid, LBS glass, can effectively reduce the temperature and remain satisfied microwave performance. Excellent microwave dielectric properties for x = 0.10 were obtained with 1.0 wt. % glass: εr = 70.16, Q×f = 4153 GHz (at 4 GHz), τf = -0.65ppm/℃ when sintered at 925℃ for 2 h.
关键词： LiNb0.6Ti0.5O3 ceramics,low temperature sintering,Li2O-B2O3-SiO2 (LBS) glass,microwave dielectric properties
更新于2025-09-10 09:29:36