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Polarization and acoustic properties of barium-modified lead-free potassium–sodium niobate ceramics
摘要： Results of polarization and polarization switching in samples prepared by solid phase synthesis of the (1-х)(K0.5Na0.5)(Nb0.93Sb0.07)O3–xBaTiO3 + 0.5mol%MnO2 system at x = 0.01, 0.02, and 0.04 (KNNS7–xBT) studied over a wide range of temperatures are reported. The observed features of the dielectric nonlinearity at the ferroelectric and structural phase transitions in the materials are described. The dielectric response data of the samples of different contents of the admixture in the KNNS7–xВT ceramics are compared with the behaviour of their elastic properties.
关键词： dielectric permittivity,polarization,solid solutions,elastic properties,relaxors,ferroelectrics,ceramics
更新于2025-09-23 15:23:52
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Distribution measurement of permittivity by dividing the sample into multisection in the slotted cylindrical cavity
摘要： There are few papers to introduce the distribution measurement of material’s permittivity in the previous work, but the measurement is an important effort to effectively evaluate the inhomogeneity of material’s permittivity. In order to measure the distribution of the relative permittivity with small interval along sample rod, a multisection measurement model has been introduced. The sample is horizontally inserted into the slotted cylindrical cavity with TM0n0 working modes and passes through it to improve the measurement stability. During the measurement, the sample is divided into many sections, and each section is treated as a subsample for the distribution measurement of the permittivity. The traditional perturbation technology is combined with the field analysis of two subsamples in the cavity to calculate the permittivity of all subsamples from the effective permittivity. Based on the theoretical analysis of the simulation results from HFSS, partial error equation is established, and the absolute error of the multisection measurement model is less than 0.1. Besides, the horizontal movement device for the sample movement, support platform with a groove for the sample placement, and vertical cylindrical cavity for the measurement are employed to make up the test setup. Meanwhile, it can provide a stable and rapid measurement. Thus, a fiber reinforced plastic rod has been measured to verify the feasibility of the developed test setup.
关键词： multisection,cylindrical cavity,distribution measurement,relative permittivity
更新于2025-09-23 15:23:52
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Improved reflection technique for the permittivity measurement of ferrites using slotted coaxial samples
摘要： This paper presents the effect of magnetic permeability on the permittivity measurement using coaxial line reflection technique. It discusses in detail about the design aspects, analysis and simulation of the slotted co-axial sample and fixture for dielectric characterization of the ferrites and garnets possessing both dielectric and magnetic properties. This technique makes use of improved coaxial fixture and APC 07 compatible slotted coaxial sample geometry to measure the complex permittivity of the ferrite material. Permittivity is calculated from the impedance of sample loaded fixture, which is independent of magnetic permeability, because of air slot cut in the coaxial hollow cylindrical sample along the length. Characterization data of dielectrics and ferrites is used in design of ferrite circulators, and pulse magnets for particle accelerator applications. This is also used in many other RF applications including design of dielectric resonator for spin wave line width measurement of ferrites. Design work is aimed at accurate measurement of complex permittivity; using reflection measurement in coaxial fixture over a wide frequency range of 20 kHz to 1 GHz. Reflection measurement technique is further explored for accurate measurement of complex permittivity.
关键词： Complex permittivity,Network analyzer,Coaxial open ended fixture,Wide band measurement technique
更新于2025-09-23 15:23:52
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Freeze-drying assisted fabrication of highly homogenized reduced graphene oxide/alumina metacomposites with negative permittivity
摘要： Graphene oxide (GO) was used to fabricated the highly homogenization reduced graphene oxide (RGO)/alumina (Al2O3) metacomposites with low percolation threshold and adjustable negative permittivity by spark plasma sintering method. Compared to the dry grinding method used for the graphene(GR)/Al2O3 and GR/AlN metacomposites reported in our previous work, the highly homogenization RGO/Al2O3 metacomposites were obtained based on freeze-drying. The microstructures and phase composition of the RGO/Al2O3 metacomposites were investigated by ?eld emission scanning electron microscopy, X-ray di?raction and Raman spectroscopy. The dielectric properties including permittivity (ε′ and ε′′), dielectric loss tangent (tan δ), alternating current conductivity (σac) and reactance (Z′′) were discussed in detail. The percolation phenomenon of σac was observed when the content of RGO increased from 13.50 to 15.38 wt%, and the percolation threshold ?tted by the power law was 14.31 wt%, which appeared earlier than the reported GR/Al2O3 and GR/AlN metacomposites. What's more, the negative permittivity behavior was observed when the content of RGO reached 13.50 wt%, which was ascribed to the formation of continuous three-dimensional RGO network among the metacomposites. The RGO13.50/Al2O3 and RGO15.38/Al2O3 metacomposites realized the ε′ transition from negative to positive at 501 and 299 MHz, corresponding to the capacitive-inductive conversion.
关键词： Freeze-drying,Negative permittivity,Highly homogenization,Metacomposites
更新于2025-09-23 15:23:52
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Mitigating the electromagnetic radiation by coupling use of waste cathode-ray tube glass and graphene oxide on cement composites
摘要： With technological development, the rapid growing numbers of electronic devices generate severe electromagnetic interference (EMI) and radiation to human environment. In this study, the coupling effect of graphene oxide (GO) addition (up to 0.10 wt.% of cement) and waste cathode-ray tube (CRT) glass replacement for fine aggregates (30 and 60 wt.%) in cement-based composites on mitigating EMI was studied. The electric permittivity obtained using a decoupling method was applied for evaluating the EMI shielding capacity of cement-based composites, while direct current (DC) electrical resistance measurement is conducted using four-probe method. The DC electrical resistivity of specimens increases insignificantly with increasing in GO content, but remarkably with increasing CRT glass content from 30 to 60 wt.%. The 60 wt.% replacement of waste CRT glass with 0.1 wt.% GO addition increases the relative permittivity by about 50% and 200% when the frequency is in the ranges of 104–5 × 106 Hz and 101–103 Hz, respectively. It is concluded that a significant increase in the permittivity can be obtained owing to the synergetic interaction between waste CRT glass and GO. The improvement in the EMI shielding ability of cement-based composites not only enables the applications of these composites in mitigating electromagnetic pollution, but also promotes large-volume recycling of toxic waste CRT glass.
关键词： Permittivity,Waste CRT glass,Cement composite,Graphene oxide,Electromagnetic interference
更新于2025-09-23 15:23:52
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Low-frequency dielectric spectroscopy and distinct relaxation modes in smectic phases of liquid crystal dimers
摘要： Low-Frequency (LF~20Hz–10MHz) ac field response and relaxation modes are investigated in layered liquid crystalline (LC) smectic phases exhibited by Hydrogen bonded dimers, viz., nOnBA:MA:nOBA’s with sort spacer moiety and long flexible end chains for n=10,11 and 12. Permittivity (ε') and loss (ε'') determined from capacitance and loss factor. Phase transition temperatures (Tc) are determined. Intra-molecular aromatic interaction and storage capacity are evinced by hysteresis behavior. Data of loss ε''(ω) and permittivity ε'r(ω) recorded in smectic phases infers non-Debye type of asymmetric dispersion. Multiple loss peaks in ε''(ω) is argued to involve distinct time scaled relaxations. Relaxation analyzed by Cole-Davidson method. Re-orientation of longitudinal dipole moment μ to the field analyzed. μ is resolved by rigid core, intra-molecular repulsive and flexible end-chain components. Observed distinct time scale response confirms dipolar components. Trends of relaxation frequency, activation energy, loss maxima, dielectric strength and distribution parameter are analyzed in device perspective. Relaxation and order director fluctuations analyzed. ODF suggest the device utility in high temperature smectic phases far away from critical fluctuations.
关键词： Order Director Fluctuations,Relaxation,Permittivity,Resolved dipole moment,Activation energy,Reorientation,Loss
更新于2025-09-23 15:23:52
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A CSRR-Based Sensor for Full Characterization of Magneto-Dielectric Materials
摘要： In this paper, a novel complementary split-ring resonator (CSRR)-based sensor for full characterization of magneto-dielectric materials is proposed. In general, the operation of microwave resonance-based sensor hinges on the shift in the resonance frequency and the change in the quality factor of the loaded structure. However, both the electric permittivity and the magnetic permeability of the material under test (MUT) have similar effect on the response of the sensor that makes the simultaneous determination of the permittivity and permeability challenging. To remove this difficulty, the main idea behind this paper is to localize the highest intensity of the electric and magnetic fields in two separate zones. By the analysis of the measured resonance frequency and quality factor, the real and imaginary parts of the electric permittivity and the magnetic permeability of the MUT can be determined. Although the characterization of the permittivity and permeability of materials using split-ring resonator and CSRR-based sensors has been widely used, to the best of our knowledge, the full characterization of magneto-dielectric materials using a single sensor has not yet been reported in this paper. As a proof of concept, the sensor was fabricated and used to measure the permittivity and permeability of several materials. Strong agreement between the extracted values and the reference data was achieved.
关键词： sensor,Complementary split ring resonator (CSRR),material characterization,split ring resonator (SRR),magneto-dielectric materials,permittivity and permeability
更新于2025-09-23 15:23:52
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Electrical Permittivity and Conductivity of a Graphene Nanoplatelet Contact in the Microwave Range
摘要： This paper investigates the electrical properties in the microwave range of a contact made by graphene nanoplatelets. The final goal is that of estimating the range of values for the equivalent electrical complex permittivity of a contact obtained by integrating low-cost graphene in the form of nanoplatelets (GNPs) into a high-frequency electrical circuit. To this end, a microstrip-like circuit is designed and realized, where the graphene nanoplatelets are self-assembled into a gap between two copper electrodes. An experimental characterization is carried out, both to study the structural properties of the nanomaterials and of the realized devices, and to measure the electromagnetic scattering parameters in the microwave range by means of a microstrip technique. A full-wave electromagnetic model is also derived and used to investigate the relationship between the measured quantities and the physical and geometrical parameters. The combined use of the experimental and simulation results allows for retrieving the values of the equivalent complex permittivity. The equivalent electrical conductivity values are found to be well below the values expected for isolated graphene nanoplatelets. The real part of the electrical relative permittivity attains values comparable to those obtained with GNP nanocomposites.
关键词： nanocomposite,permittivity,scattering parameters,graphene nanoplatelets
更新于2025-09-23 15:23:52
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[IEEE 2018 18th International Symposium on Antenna Technology and Applied Electromagnetics (ANTEM) - Waterloo, ON (2018.8.19-2018.8.22)] 2018 18th International Symposium on Antenna Technology and Applied Electromagnetics (ANTEM) - Cavity Perturbation Technique to Characterize Dielectric Materials at Ka-band
摘要： The characterization of permittivity and dielectric loss of dielectric materials using a perturbation technique is conducted in simulation. The working frequency of this technique has been extended to the Ka-band. Simulation results demonstrate this perturbation technique is suitable for characterization of high permittivity dielectric materials for mm-wave and maintains good accuracy.
关键词： dielectric loss measurement,permittivity measurement,cavity perturbation technique,dielectric materials,Ka-band
更新于2025-09-23 15:23:52
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[IEEE NAECON 2018 - IEEE National Aerospace and Electronics Conference - Dayton, OH, USA (2018.7.23-2018.7.26)] NAECON 2018 - IEEE National Aerospace and Electronics Conference - Impact of dielectric and magnetic losses on the negative index characteristics of a chiral material with first-order sideband dispersion
摘要： Electromagnetic propagation in chiral materials under first-order dispersion is examined for negative indices under non-conductive losses. Three loss scenarios are considered, viz., dielectric (complex permittivity) losses; magnetic (complex permeability) losses; and a combination of both types of losses to investigate the overall impact of the losses on the emergence of negative index bands.
关键词： complex permittivity and permeability,loss compensation,plane wave polarization,material dispersion,negative index bands,Negative refractive index
更新于2025-09-23 15:22:29