Search

Some of the difficulties in numerical modeling of wireless communication devices for dosimetric evaluations arise from, e.g. incomplete documentation available for the numerical model, such as missing information on dielectric materials or the antenna matching circuitry. This study investigates the impact of these difficulties on the dosimetric results, such as the peak spatial average specific absorption rate at 900 and 1800 MHz and the peak spatial average power density at 28 GHz. The impact of dielectric losses, detuning, and mesh resolution is quantified using different generic and Computer Aided Design (CAD) based models of wireless transmitters. The findings show that the uncertainties of the numerical results due to detuning and mesh resolution can be reduced by normalization to the antenna feedpoint power instead of the feedpoint current. Uncertainties due to variations in dielectric losses can largely be compensated by normalization to the radiated power. [ABSTRACT FROM AUTHOR]

Hexaferrite samples, in which lanthanum (La) and cCobalt (Co) have been substituted (Sr Co 1.5 z La 0.5 z Fe 12 - 2 z O 19 ), were synthesized using the sol–gel combustion method. X-ray diffraction (XRD) measurements revealed that all the samples maintained a magnetoplumbite structure. Fourier-transform infrared (FTIR) spectroscopy showed an absorption peak within the IR range of 1000–380 cm−1, indicating vibrations likely attributed to Fe–O bonds. Substitution caused a non-linear decrement in grain size and the existence of grain clusters in z = 0.1 along with an increment in porosity. The calculated porosity from XRD was consistent with the porosity observed with scanning electron microscopy. Both the dielectric constant and loss tangent parameters were found to be decreased non-linearly with substitution in the low-frequency region. The AC conductivity value decreased from 9.09 × 10−4 to 1.10 × 10−4 Ω−1 m−1 at 2-MHz frequency with Co-La substitution. Non-Debye behavior was noted in all the samples by evaluating the electric moduli and impedance spectra. The conductivity relaxation was dominant over the dielectric relaxation in the samples. [ABSTRACT FROM AUTHOR]

We prepared bulk samples of SrLaLiTe1-xGdxO6; 0 ≤ x ≤ 0.3, using the solid-state method. Measurements carried out on the XRD data recorded at room temperature highlighted changes corresponding to the volume of the unit cell and angle β. Specifically, the undoped composition described a structure of the ordered type containing Li+ and Te6+. Calculations of the octahedral tilt angle indicated a transition from cubic to monoclinic symmetry, accompanied by bending and tilting of the B-O-B'(B = La, B' = Te/Gd) octahedra. FTIR measurements confirmed the existence of molecular bonds in all compositions. UV–visible spectroscopy results indicated a reduced bandgap energy, suggesting enhanced conductivity in the doped samples. SEM and EDX confirmed the elemental composition and revealed particle clustering. Impedance spectroscopy analysis demonstrated increased AC conductivity at higher frequencies. Additionally, a decrease in the grain resistance indicated single dielectric relaxation behavior. A relaxation phenomenon of the non-Debye type was revealed from the Cole–Cole plots attributed to the presence of imperfections within the samples. Dielectric properties showed a reduction in dielectric loss and constant, which was dependent on frequency, attributed to the decrease in overall polarization. [ABSTRACT FROM AUTHOR]

This paper describes a process to obtain magnetite functionalized with carboxymethylcellulose via coprecipitation by means of a preliminary stabilization of magnetite in citric acid. The magnetite assemblies successfully passed in vitro and in vivo tests of bio-compatibility. The measured values for the dielectric loss factor are remarkably high, a prerequisite for the assemblies' potential use as contrast agents. Broadband THz spectroscopy analysis was performed to identify the most relevant frequency bands (here, 3.2–4 THz) where the signal difference between normal cells and cancer cells is relevant for the particles' potential use as contrast agents for THz imaging, with applications in oncology. [ABSTRACT FROM AUTHOR]

Recently, high-performance lead zirconate titanate (Pb( Zr 1 − x Tix)O3, PZT) ferroelectric ceramics have attracted intensive attention due to their wider operating temperature range, better temperature stability, as well as larger piezoelectric properties and higher energy conversion efficiency. In this study, the perovskite-type ferroelectric ceramics with a chemical formula of Pb 0. 9 9 − x Gd 0. 0 1 Srx Zr 0. 5 3 Ti 0. 4 7 O3 (x = 0 and 0.02, abbr. PGZT and PGSZT, respectively) were prepared by the traditional solid-state reaction route. The influences of Sr-doping on the phase structure, dielectric properties, ferroelectric properties and piezoelectric properties of the PGZT ceramics were comprehensively investigated. The field-dependent P–E hysteresis loops of PGSZT were measured in the frequency range of 0.05–10 Hz and temperature range of 20–100∘C. The results show that Sr-doping not only enhances the dielectric permittivity and piezoelectric coefficient of PGZT, but also decreases its dielectric loss tangent, with the d 3 3 value of 473 pC/N, ε r value of 1586 and tan δ value of 0.016 found in PGSZT. Also, PGSZT shows a high Curie temperature ( T C ) of 3 5 0 ∘ C. The underlying mechanisms of the property enhancement were identified as that the introduced Sr 2 + replaces the volatile Pb 2 + located at the A-site of the perovskite structure, thereby reducing the concentration of lead vacancies and promoting the grain growth of the ceramics, consequently enhancing the dielectric and piezoelectric properties of PGZT. On the other hand, the frequency change in the low-frequency range (< 1 Hz) played a significant impact on the remanent polarization ( P r ) and internal biased electric field ( E i ) of PGSZT, but the frequency dependence of coercive field ( E c ) tends to diminish in the high-frequency range (≥ 1 Hz). [ABSTRACT FROM AUTHOR]

In the past, hard electromagnetic wave (EMW) absorbing materials have made breakthroughs in performance improvement, but poor machinability limits their practical applications. Herein, a series of flexible borate ester bonded hydrogels with different water content for EMW absorption were prepared through a simple ultraviolet curing method. By adjusting the water content, the EMW absorption performance of hydrogel can be improved. When the water content reaches 30%, the minimum reflection loss (RLmin) of the hydrogel can be up to -48.70 dB at 1.89 mm and the widest effective absorption bandwidth (EABw, RL ≤ -10 dB) is 5.60 GHz (covering the entire Ku band) when the matching thickness is between 2.09 and 2.17 mm. The efficient absorption performance of the hydrogel benefits from the dipole polarization of water molecules and the interfacial polarization caused by interaction with the polymer network framework under the changing electromagnetic field. In addition, tensile and compressive experiments show that the hydrogel possesses favorable flexibility. This study provides an idea for the preparation of flexible electromagnetic attenuation devices, and the as-synthesized hydrogels have a broad application scenario in the field of wearable EMW-absorbing materials. [ABSTRACT FROM AUTHOR]

The construction of hierarchical structures has been demonstrated to be an effective method for achieving high-performance microwave absorption. In this study, a flower-like MoS2 nanosheet-coated tubular carbon composite with an average diameter of approximately 560 nm was synthesized via a straightforward ion-exchange and pyrolysis strategy. The growth of MoS2 nanosheets, the presence of heterojunction surfaces, and the construction of the hollow structure collectively enhance the dielectric loss of the material, thereby optimizing the microwave absorption properties of the material. The C@MoS2 nanocomposite demonstrates a minimum reflection loss of -66.8 dB and an effective absorption bandwidth of 4.8 GHz when the thickness is only 1.6 mm. This work presents a synergistic strategy for the design of layered hollow structures. [ABSTRACT FROM AUTHOR]

The multi-layer ceramic capacitor (MLCC) is prepared with Bi 1.5 MgNb 1.5 O 7 (BMN) pyrochlores, which has medium dielectric constant, large dielectric tunability, and especially the very small dielectric loss. The multilayer ceramic capacitors with Bi 1.5 MgNb 1.5 O 7 as the dielectric material are prepared by a tape-casting method. The dielectric constant of the BMN thick film was observed to be superior to that of the bulk material, indicating its potential application in electronic devices. The increase in dielectric constant during the preparation of multilayer ceramic capacitors was explained by investigating the interdiffusion between the ceramic thick films and the electrodes. The BMN thick films and Ag 0.7 /Pd 0.3 electrodes showed a dense microstructure and serial interfaces when sintering at 1050 °C for 1.5 h. The capacitor exhibited good temperature stability with a dielectric constant temperature coefficient of −249.94 ppm/°C, a relative dielectric constant of 216, and a dielectric loss of 0.00036. Provides insights for the development and optimization of high-performance dielectric tunable electronic device. [ABSTRACT FROM AUTHOR]

Two ranges of dielectric permittivity (k) increase in polymer composites upon the modification of BaTiO3 filler with multiwalled carbon nanotubes (MWCNTs) are shown for the first time. The first increase in permittivity is observed at low MWCNT content in the composite (approximately 0.07 vol.%) without a considerable increase in dielectric loss tangent and electrical conductivity. This effect is determined by the intensification of filler–polymer interactions caused by the nanotubes, which introduce Brønsted acidic centers on the modified filler surface and thus promote interactions with the cyanoethyl ester of polyvinyl alcohol (CEPVA) polymer binder. Consequently, the structure of the composites becomes more uniform: the permittivity increase is accompanied by a decrease in the lacunarity (nonuniformity) of the structure and an increase in scale invariance, which characterizes the self-similarity of the composite structure. The permittivity of the composites in the first range follows a modified Lichtenecker equation, including the content of Brønsted acidic centers as a parameter. The second permittivity growth range features a drastic increase in the dielectric loss tangent and conductivity corresponding to the percolation effect with the threshold at 0.3 vol.% of MWCNTs. [ABSTRACT FROM AUTHOR]

The rational design of magnetic carbon composites, encompassing both their composition and microstructure, holds significant potential for achieving exceptional electromagnetic wave-absorbing materials (EAMs). In this study, FeCo@CM composites were efficiently fabricated through an advanced microwave plasma-assisted reduction chemical vapor deposition (MPARCVD) technique, offering high efficiency, low cost, and energy-saving benefits. By depositing graphitized carbon microspheres, the dielectric properties were significantly enhanced, resulting in improved electromagnetic wave absorption performances through optimized impedance matching and a synergistic effect with magnetic loss. A systematic investigation revealed that the laminar-stacked structure of FeCo exhibited superior properties compared to its spherical counterpart, supplying a higher number of exposed edges and enhanced catalytic activity, which facilitated the deposition of uniform and low-defect graphitized carbon microspheres. Consequently, the dielectric loss performance of the FeCo@CM composites was dramatically improved due to increased electrical conductivity and the formation of abundant heterogeneous interfaces. At a 40 wt% filling amount and a frequency of 7.84 GHz, the FeCo@CM composites achieved a minimum reflection loss value of −58.2 dB with an effective absorption bandwidth (fE) of 5.13 GHz. This study presents an effective strategy for developing high-performance EAMs. [ABSTRACT FROM AUTHOR]

The sintering shrinkage behavior, viscosity, microstructures, phase composition, dielectric properties and chemical compatibility with Ag of a novel low-temperature co-fired ceramic (LTCC) material, (1- x) CaO-B 2 O 3 -SiO 2 -ZrO 2 (CBSZ) + x Ca 0.99 Cu 0.01 SiO 3 (x = 0, 5, 10, 15 and 20 wt%) glass/ceramics were discussed. The partial dissolution of the Ca 0.99 Cu 0.01 SiO 3 ceramic powder in CBSZ glass will form additional liquid phase and make viscosity decrease, which could promote the densification of CBSZ/Ca 0.99 Cu 0.01 SiO 3 composite. The introduction of Ca 0.99 Cu 0.01 SiO 3 will form heterogeneous nucleus and promote the crystallization of samples. The CBSZ/Ca 0.99 Cu 0.01 SiO 3 composite with 10 wt% Ca 0.99 Cu 0.01 SiO 3 content sintered at 875 ºC for 30 min has a dielectric constant ε r = 6.05, a dielectric loss tan δ = 1.18 × 10−3 @ 13.76 GHz, flexural strength = 176 MPa, CTE = 7.7258 × 10−6/ºC, and shows good chemical compatibility when co-fired with Ag electrode. These results indicate that CBSZ glass/Ca 0.99 Cu 0.01 SiO 3 ceramic composites have a potential to meet the demand of LTCC applications. [ABSTRACT FROM AUTHOR]

This paper presents a complete analysis of the electrical and dielectric characteristics of N i C o 2 O 4 (NCO) bulk ceramic synthesized by the co-precipitation process as a future electronic device material. The structural analysis following the synthesis process revealed the formation of cubic-phase spinel NCO in the shape of nanospheres, with an approximate diameter of 25 nm. The present study aimed to examine the relationship between capacitance and conductance for the NCO under investigation, focusing on their frequency and temperature dependencies. The frequency range of interest ranged from 100 Hz to 1.5 MHz, while the temperature range considered was from 300 K to 450 K. The C/f plot has exhibited the phenomenon of negative capacitance, which may be attributed to the augmentation of polarization and the incorporation of additional minority carriers inside the structure. The dielectric parameters, such as permittivity, dielectric loss, alternating current conductance, and electrical modulus, were determined by capacitance and conductance measurements, taking into account their frequency and temperature reliance. All dielectric calculations were influenced by negative capacitance measurements. The negative capacitance feature of N i C o 2 O 4 is attributed to the ferroelectric properties of the Ni and Co elements in its composition. In conclusion, this paper has made a valuable contribution to the existing body of literature by enhancing our comprehension of the negative capacitance behavior and dielectric characteristics of the NCO. [Display omitted] [ABSTRACT FROM AUTHOR]

Graphene nanoplatelets (GNPs) and spinel ferrites (SFs) composites enhance their properties and enable multifunctional applications, ranging from electronics to environmental and biomedical fields. This study investigates the Ni 0.4 Cd 0.6 Fe 2 O 4 /x-GNPs (x = 0 %, 2.5 %, and 5 %) [ NCF/0%GNPs, NCF/2.5%GNPs, and NCF/5%GNPs ] composites prepared via sol-gel auto combustion (SGAC) synthesis and their enhanced magneto-dielectric characteristics. XRD analysis confirmed the formation of a single-phase spinel matrix of NCF/GNPs composites and observed that the crystallite size (D) was enhanced from 22.8 nm to 33.6 nm with the increasing concentration of GNPs. Moreover, the bandgap energy (E g) was reduced with the incorporation of GNPs in the NCF sample. The dielectric constant and tangent loss were enhanced with the addition of GNPs in the NCF spinel lattice. The saturation magnetization and microwave operating frequency were reduced from 97.42 emu/g to 55.13 emu/g and 21.49 GHz–11.97 GHz, respectively, while the coercivity was observed to increase from 92.66 Oe to 263 Oe with the incorporation of GNPs in the NCF lattice. The study highlights the potential of NCF/GNPs composites for applications in electronics, energy storage, sensors, and biomedical devices. [Display omitted] • Sol-gel auto-combustion synthesis of NCF/GNPs composites. • Single-phase spinel matrix NCF/GNPs composites were observed via XRD. • The bandgap energy was reduced with the incorporation of GNPs. • The magnetic and dielectric properties were enhanced with the addition of GNPs. • The potential of NCF/GNPs composites for applications in electronics, energy storage, sensors, and biomedical devices. [ABSTRACT FROM AUTHOR]

A series of Zn 1- x Cu x ZrNb 2 O 8 (x = 0.000, 0.003, 0.010, and 0.050) ceramics with low dielectric loss and intermediate dielectric constants were synthesized by a conventional solid-phase reaction method. The terahertz dielectric performances of Zn 1- x Cu x ZrNb 2 O 8 (x = 0.000, 0.003, 0.010, and 0.050) ceramics have been investigated by using the Rietveld refinement method, scanning electron microscopy, Raman spectroscopy, and terahertz time-domain spectroscopy. The microscopic morphology analysis shows that the appropriate amount of Cu2+ content can make the specimen have the most uniform and medium-sized grains, which can minimize the dielectric loss in the terahertz range. Raman mapping reveals that the stress distribution is not uniform in different grains or in different regions of the same grain. The internal stresses affect the interatomic distances and influence the electronic properties, thus increasing the lattice anharmonicity and dielectric losses. In addition, the dielectric constant of the specimen in the terahertz range is mainly determined by the ionic polarization. For Zn 0.997 Cu 0.003 ZrNb 2 O 8 sintered at 1240 °C, low dielectric losses (< 4 × 10−3 @ 0.40 THz) and intermediate dielectric constant (∼22.95 @ 0.40 THz) were obtained, which make it promising for applications in terahertz dielectric filters. [ABSTRACT FROM AUTHOR]

In this work, a technique for constructing a three‐dimensional (3D) skeleton of hexagonal boron nitride (h‐BN) using sugar as the fulcrum and preparing composites by embedding in the epoxy (EP) in a vacuum environment is proposed. The study of thermal conductivity (TC) in polymer composites is conducted through a blend of techniques: laser flashing, theoretical modeling, and finite element simulation. The h‐BN skeleton exhibits a honeycomb structure through the scanning electron microscopy findings. Further investigation using finite element simulation demonstrates that conductive networks are formed by the h‐BN skeleton within the composites, leading to a notable enhancement in TC. Specifically, the composite for h‐BN/EP reaches a TC of 2.25 W/m K when composed of 52 vol% h‐BN. A dielectric loss of 0.008 for the composite with the same h‐BN loading shows a considerable improvement. The compressive yield strength of the 3D h‐BN/EP composites reached 312 MPa at 5 vol% h‐BN loading. [ABSTRACT FROM AUTHOR]

High efficiency thermal insulation materials are highly desirable in aerospace industry, whereas combining low density and low thermal conductivity of thermal insulation materials still remains a challenge. In this work, a series of fluorinated polyimide foams (PIFs) based on 4,4‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) were successfully prepared by microwave‐assisted powder foaming. The modification of fluorination decreased the melt strength while simultaneously enhanced the thermal properties of fluorinated PIFs through the high bonding energy of CF bond. Thus, fluorinated PIFs exhibited one of the lowest densities of reported PIFs, among them, the density of PIF6FDA‐DMBZ was as low as 9.34 kg m−3. The glass transition temperature of all fluorinated PIFs was greater than 295°C. Microwave‐assisted foaming optimized the cell structure effectively, resulting in the thermal conductivity of PIF6FDA‐ODA as low as 0.029 W m−1 K−1. The incorporation of hexafluoroisopropylidene groups reduced the polarization and enhanced the free volume of fluorinated PIFs, leading to hydrophobic characteristics (CA >105°) and ultra‐low dielectric loss properties (tan δ <0.001 at 20 GHz). PIF6FDA‐ODA demonstrated the most excellent comprehensive performance. The excellent comprehensive performance of fluorinated PIFs indicated their potential application as thermal insulation and wave‐transparent materials in aerospace, railway, and shipbuilding industries. [ABSTRACT FROM AUTHOR]

This study utilizes the strong complexation effect of polydopamine on metal ions and constructs multilayer carbon magnetic heterostructures on the surface of carbon fibers through the in situ reduction method, thereby obtaining a new type of multilayer carbon‐based composite absorbing material. The absorption properties at different layers were analyzed and compared through various characterization methods. Finally, the double‐layer structure demonstrated outstanding electromagnetic wave absorption characteristics, exhibiting a wide effective absorption bandwidth of 7.24 GHz and robust absorption of −44.48 dB, all within a mere thickness of 3.5 mm. Therefore, excellent market prospects for this material are anticipated. Highlights: A multilayer carbon magnetic heterostructure absorbing material was constructed on micrometer‐scale carbon fibers. The test results show that a wide effective absorbing bandwidth of 7.24 GHz and a minimum reflection loss of −44.48 dB are obtained when the composite thickness is 3.5 mm.The prepared multilayer absorbing composites can adapt to a variety of application scenarios and have excellent application prospects in the industry.The self‐polymerization of dopamine and complexation of metal ions were used to construct multilayer absorbing materials, and the dielectric loss and magnetic loss capacity of the carbon fibers improved. [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]

Highlights: Asymmetrically coordinated Co–N4–O sites on N-doped carbon nanofiber were prepared. Co–O coordination along the axial direction led to enhanced dielectric polarization loss. Multifunctional films were developed for practical application in harsh environments. Single-atom materials have demonstrated attractive physicochemical characteristics. However, understanding the relationships between the coordination environment of single atoms and their properties at the atomic level remains a considerable challenge. Herein, a facile water-assisted carbonization approach is developed to fabricate well-defined asymmetrically coordinated Co–N4–O sites on biomass-derived carbon nanofiber (Co–N4–O/NCF) for electromagnetic wave (EMW) absorption. In such nanofiber, one atomically dispersed Co site is coordinated with four N atoms in the graphene basal plane and one oxygen atom in the axial direction. In-depth experimental and theoretical studies reveal that the axial Co–O coordination breaks the charge distribution symmetry in the planar porphyrin-like Co–N4 structure, leading to significantly enhanced dielectric polarization loss relevant to the planar Co–N4 sites. Importantly, the film based on Co–N4–O/NCF exhibits light weight, flexibility, excellent mechanical properties, great thermal insulating feature, and excellent EMW absorption with a reflection loss of − 45.82 dB along with an effective absorption bandwidth of 4.8 GHz. The findings of this work offer insight into the relationships between the single-atom coordination environment and the dielectric performance, and the proposed strategy can be extended toward the engineering of asymmetrically coordinated single atoms for various applications. [ABSTRACT FROM AUTHOR]

This study explored the synthesis and sintering of potassium sodium niobate (KNN) nanoparticles, emphasizing morphology, crystal structure, and sintering methods. The as-synthesized KNN nanoparticles exhibited a spherical morphology below 200 nm. Solid state sintering (SSS) and laser-induced shockwave sintering (LISWS) were compared, with LISWS producing denser microstructures and improved grain growth. Raman spectroscopy and x-ray diffraction confirmed KNN perovskite structure, with LISWS demonstrating higher purity. High-resolution x-ray photoelectron spectroscopy spectra indicated increased binding energies in LISWS, reflecting enhanced density and crystallinity. Dielectric and loss tangent analyses showed temperature-dependent behavior, with LISWS-3 exhibiting superior properties. Antenna performance assessments revealed LISWS-3's improved directivity and reduced sidelobe radiation compared to SSS, attributed to its denser microstructure. Overall, LISWS proved advantageous for enhancing KNN ceramics, particularly in antenna applications. [ABSTRACT FROM AUTHOR]

This paper presents accurate, prompt, and cost‐effective relative permittivity and loss tangent measurements of low‐loss dielectrics such as DuPontTM VESPEL® SP‐1 and VictrexTM polyetherketone (PEEK) 450G, which are commonly used materials in space communication antennas. It is essential for an antenna engineer to have the information regarding the electrical properties, that is, dielectric permittivity, dielectric loss tangent, magnetic permeability, and magnetic loss tangent at the frequency of interest. The test method relies on the accurate measurements of the S‐parameters of the sample under test by means of Through‐Reflect‐Line (TRL) calibration using a Vector Network Analyzer (VNA). Nicholson‐Ross‐Weir (NRW) method is employed to get the conversion from S‐parameters to both complex permittivity and permeability values of the samples. The experimental results are verified with the literature data of Teflon and relative permittivity and loss tangent measurements of VESPEL® SP‐1 (εr=3.119±0.043 ${\varepsilon }_{r}=3.119\pm 0.043$, tanδ=(20.893±4.042)*10−3 $\tan \delta =(20.893\pm 4.042)* {10}^{-3}$) and PEEK 450G (εr=3.119±0.015 ${\varepsilon }_{r}=3.119\pm 0.015$, tanδ=(5.654±1.877)*10−3 $\tan \delta =(5.654\pm 1.877)* {10}^{-3}$) are presented for X‐band (8‐10 GHz) frequencies. [ABSTRACT FROM AUTHOR]

Lead‐free potassium sodium niobate (KNN) ferroelectrics have emerged as promising alternatives to lead‐based materials due to their reduced toxicity and sometimes enhanced properties. The opportunity to modify the ferroelectric properties by doping, nevertheless, differs from lead‐based ceramics. A much lower impact with increasing dopant concentration was observed. This study systematically investigates the differences in defect chemistry of Na0.475K0.475Li0.065Nb0.92Ta0.08O3 ceramics through iron (Fe) acceptor doping and calcium (Ca) donor doping at varying concentrations. From the defect chemical point of view, it becomes evident that the impact of intrinsic defects on the electrical properties exceeds the effect of extrinsic defects induced by doping. The performance of the donor‐doped (Ca2+) ceramics closely resembles that of undoped KNN. Thus, hardly any change in ferroelectric properties and conductivity is observed. For the Fe‐doped samples, the conductivity and its contribution to the dielectric loss increased, which is not to the benefit of an application as a ferroelectric. Therefore, the concepts of "softening" and "hardening" of ferroelectric properties by doping are incompatible with regularly sintered KNN ceramics. [ABSTRACT FROM AUTHOR]

Dense (Pb0.92Ba0.08)Nb2O6‐xmol% MnO2 with 0.25 wt% TiO2 ceramics with a single orthorhombic phase were synthesized through a conventional solid‐state reaction method. Excellent piezoelectric performance (d33 = 90 pC/N) and low dielectric loss (tan δ = 0.5%) are achieved in Mn‐doped samples. Interestingly, the dielectric anomalies are observed in the temperature range of 300–400°C, which could be completely suppressed through Mn doping. The dielectric anomalies are associated with thermally activated domain wall motion, which could be constrained by the defect dipoles produced by Mn doping. More importantly, all samples experience about 12% performance degradation below 300°C, attributed to an accelerated aging process at elevated temperatures. After thermal aging, the samples exhibit excellent performance stability within the temperature range of 25–450°C, showing no further degradation. The results indicate that the PbNb2O6‐based ceramics are promising high‐temperature piezoelectric materials for piezoelectric devices operating at temperatures up to 450°C. [ABSTRACT FROM AUTHOR]

Low insulation resistivity is a key factor limiting the practical application of colossal permittivity (CP) ceramics in electronic components. In this study, BaTiO3–0.01Ta2O5–xAl2O3 (BTAx, x = 0.005, 0.01, 0.015, 0.02) CP ceramics with high insulation resistance were successfully prepared by sintering in N2. In particular, BTA0.015 ceramic exhibits CP (εr = 2.01 × 105, 1 kHz), low dielectric loss (tanδ = 0.044, 1 kHz), high insulation resistivity (ρv = 1.4 × 109 Ω cm, DC voltage (DC) 100 V), and superior frequency and thermal stability (20 Hz–1 MHz, room temperature–350°C). The polarization mechanism, dielectric and insulating properties were investigated by different atmosphere processing, scanning electron microscopy (SEM) X‐ray photoelectron spectroscopy (XPS), and impedance analysis. Moderate doping of Al2O3 facilitates the construction of electron‐pinned defect dipoles, which improves the dielectric properties. In addition, the ceramics feature an extremely fine grain size, which is conducive to suppressing the long‐range migration of delocalized electrons. The combination of electron pinning defect dipole effects and internal barrier layer capacitance effects are the responsible for the giant dielectric constant. This research shows that the defect dipole‐dependent polarization can be employed to design highly insulating BaTiO3‐based CP ceramics. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the impact of the Kovar glass content on the mechanical and electrical properties of Si3N4–Kovar composites sintering at air atmosphere. To achieve this, Si3N4–Kovar composites were prepared using molding technology with the Kovar glass powder ranging from 20 to 70 wt%. The phase composition, morphology, bulk density, apparent porosity, flexural strength at room temperature, dielectric constant, and dielectric loss of the composites were all examined in relation to changing the Kovar glass content. During the sintering process, the α‐quartz on the surface of Si3N4 particles acted as the crystal nucleus, inducing the crystallization of the glass at the wetting position that the Kovar glass and the surface of the Si3N4 particles. A small amount of the β‐quartz phase was crystallized at 750–850°C, followed by a large amount of the β‐quartz phase crystallizing above 900°C. Additionally, some β‐quartz phase transformed into the metastable β‐cristobalite phase that could exist below 1470°C. During the cooling process, the β‐cristobalite phase transformed into a low‐temperature α‐cristobalite phase, while the β‐quartz phase transformed into a low‐temperature α‐quartz phase. The results indicate that the Si3N4–Kovar glass composite with 60 wt% the Kovar glass content sintered at 900°C exhibits higher density (1.88 g/cm3), lower porosity (25.4%), higher flexural strength (55.34 MPa), lower dielectric constant (3.46), and lower dielectric loss (4.26 × 10−3). [ABSTRACT FROM AUTHOR]

High thermal conductivity (k) epoxy resin (EP) composites are widely used in electronic devices and power equipment where timely heat dissipation is urgently desirable. However, achieving a balance between high-k values and excellent dielectric properties such as breakdown strength (Eb) is challenging, which subsequently affects their applications in high-voltage fields. Enhancing the intrinsic k of cured EP is the key to addressing this dilemma. Along this line, in this work, a liquid crystal (LC) epoxy (LCE, BE) with biphenyl mesogenic unit was synthesized and introduced into commonly used EP E-51 to currently promote the k and Eb of the blends. The findings demonstrate that the EP blends' k increases with the BE loading due to the formation of multi-scale ordered domains resulting from the self-assembly of biphenyl mesogenic units, which establish the heat-conductive channels for phonon transport. These ordered domains further induce charge traps and efficiently impede the migration of charge carriers. So, the simultaneous enhancement of k and Eb along with low dielectric permittivity and loss are achieved in the E-51/BE blends. Moreover, two curing agents also affect the structure, thermal and dielectric performances of the blends. The prepared BE/E-51 blends with enhanced k and Eb showcase potential applications as thermal management materials in microelectronic devices and electrical power systems. [ABSTRACT FROM AUTHOR]

Nanoparticles (NPs), especially inorganic NPs, have been used as fillers to improve the insulation properties of polymers. However, inorganic NPs is difficult to disperse well in polymer matrix, which inhibit the development of insulating nanocomposites for high-voltage direct current power cable. Therefore, it is necessary to improve the dispersion of NPs in the polymer matrix in order to make NPs play a greater role. In this work, polystyrene NPs (PS-NPs) were synthesized and used as fillers to improve the insulation properties of LLDPE. SEM images show that PS-NPs are monodispersed in LLDPE matrix without thermal fusion when the content of PS-NPs is less than 1 wt%. The results of DSC illustrate that the addition of PS-NPs had no effected on thermal behavior of LLDPE. With the introduction of PS-NPs, the DC breakdown strength of LLDPE/PS-NPs is first increased and then decreased. The highest value of 346.5 kV/mm is obtained by PS-0.1 with 0.1 wt% of PS-NPs. The electric conductivity of all LLDPE/PS-NPs composites are decreased comparing with neat LLDPE. Meanwhile, PS-NPs had no significant influence on the dielectric permittivity and dielectric loss of the complex. Therefore, PS-NPs is an alternative option to improve the insulating performance, and our results provide a way for the development of nanocomposites insulating material. [ABSTRACT FROM AUTHOR]

In this study, starch-graft-poly (methyl methacrylate) (starch-g-PMMA) composites doped with different amounts (5, 10, and 15 wt%) of cadmium sulfide (CdS) particles were fabricated for electrical measurements using in-situ polymerization technique. The structural characterization of the samples was studied. The dielectric and conductivity properties of the composites were investigated using impedance analyzer depending on the frequency (100 Hz–20 kHz) at room temperature. Spectroscopy revealed that the dielectric constant (ε′), dielectric loss (ε′′), and real (Z) components of impedance are found to decrease with increasing frequency for both starch-g-PMMA and starch-g-PMMA (5, 10, and 15 wt%) composites. On the contrary, the AC conductivity (σac) of samples increased with increasing frequency. In addition, ε′ and ε′′ values of starch-g-PMMA were lower than composites that added CdS. When the CdS content increased from 0 to 15%, ε′ increased from 5.62 to 15.10 at 100 Hz. AC conductivity was improved after adding the CdS particles. The maximum conductivity value for starch-g-PMMA15%CdS is found to be 3.07 × 10–7 at 100 Hz. When the dielectric properties of composites are evaluated, it is concluded that it is an exciting material for electronic applications in technology. [ABSTRACT FROM AUTHOR]

Solar irradiance received at the lunar surface is crucial for interpreting brightness temperatures detected by orbiters and for understanding the thermal, physical, and dielectric properties of the lunar regolith. We developed a real‐time effect solar irradiance (ESI) model that accounts for the influence of surface relief and terrain shading. This model was integrated with a standard thermal model to examine ESI fluctuations and their impacts on the diurnal physical temperature variations. To assess the effects of spatial resolution, we selected four locations with significant ESI disparities for simulation, then compared lunar surface temperatures at various spatial scales, ranging from 20 m to 25 km. Utilizing brightness temperature data obtained from the Chang'E‐2 (CE‐2) microwave radiometer (MRM), we integrated the shallow physical temperature profiles with the radiative transfer equation to simulate brightness temperatures and determine dielectric loss at different frequencies. In the Von Kármán crater, the received ESI exhibits a cyclical pattern of approximately 18 years and areas with rugged topography may exhibit larger ESI variations (∼7%). We found that the spatial resolution of ESI has a minimal effect on the physical and brightness temperatures at resolutions of 10 km or coarser. At the shallow layer, the average dielectric loss values are 0.0128–0.0170, 0.0083–0.0110, 0.0055–0.0073, and 0.0061–0.0081 for the CE‐2 frequencies of 3, 7.8, 19.35, and 37 GHz, respectively. The integration of real‐time ESI modeling, thermal dynamics, radiative transfer equations, and observational data enhances our comprehension of the physical temperature profile and thermal characteristics of shallow regolith. Plain Language Summary: The combination of solar irradiance and temperature data sets detected by orbiters can help to explain the temperature variation and thermophysical properties of shallow lunar surface. This study develops a real‐time effect solar irradiance (ESI) model that takes into account the influence of lunar topography and integrates it with a thermal model to simulate physical temperature variations within the Von Kármán crater. We compared lunar surface physical temperature profiles at spatial resolutions of 20, 240, 500 m, 1, 5, 10, 15, and 25 km, each exhibiting distinct ESI characteristics, to assess the impact of spatial resolution. We then simulated the temperature data in the four frequencies consistent with Chang'E‐2 (CE‐2) microwave radiometer and obtained the average ranges of dielectric loss. At 3, 7.8, 19.35, and 37 GHz, the average dielectric loss ranges were determined to be 0.0128–0.0170, 0.0083–0.0110, 0.0055–0.0073, and 0.0061–0.0081, respectively. These findings provide valuable insights for analyzing lunar surface temperature and observed brightness temperature, as well as for inverting physical and dielectric properties of the shallow regolith (e.g., dielectric loss). Key Points: Analyzing lunar shallow temperature variation with real‐time effect solar irradiance (ESI) model considering terrain influenceAssessing the real‐time ESI impact on physical and brightness temperature curves at diverse spatial resolutionsEstimating the dielectric loss of shallow regolith by coupling simulated brightness temperature data with observations [ABSTRACT FROM AUTHOR]

In this work, the calcium-lead arseborate glass's basic components were doped with an equal amounts of NiCl2 and CoCl2, separately, to obtain two different glass samples that were dubbed the Ni-doped sample and the Co-doped sample. The fast quenching method was used to prepare that samples, while UV-vis and X-ray diffraction (XRD) patterns were used to characterize them. The XRD patterns of Ni-doped and Co-doped glass samples reveal amorphous structures with short-range order. While both contain similar components, nickel and cobalt additions result in distinct diffraction humps. The Ni-doped sample exhibits wider transmission windows and sharper band edges compared to the Co-doped sample. Additionally, Ni-doped glass shows higher maximum absorbance, suggesting suitability for energy storage, while Co-doped glass is better for UV-blocking applications. The absorption index, crucial for light-matter interaction, reflects optical relaxation processes and is influenced by material composition and structure. Dielectric loss factors were determined using the Drude-Lorentz model, highlighting the importance of understanding absorption index and optical relaxation in materials science. The resonance frequency of Co-doped glass is lower than that of Ni-doped glass, resulting in the absorption index and dielectric loss reaching their maxima at lower energy values for Co-doped glass. Furthermore, the Plasmon frequency in Co-doped glass is higher than in Ni-doped glass, indicating its superior ability to screen incident photons. Additionally, the scattering time for Co-doped glass is lower than for Ni-doped glass, suggesting that the Ni-doped sample has larger interatomic distances. [ABSTRACT FROM AUTHOR]

A series of CaMgGe2O6 ceramics doped with Zn2+ ions were designed and fabricated using the solid-state reaction method. The impact of cation doping on sintering behavior, crystal structure, microstructure, and dielectric properties was systematically investigated. Incorporating Zn2+ ions into the crystal structure optimized the sintering process to enhance densification. Analysis of the crystal structure revealed slight changes in lattice parameters and unit cell volume upon introduction of Zn2+ dopants, indicating successful incorporation without significant alteration to the overall structure. Microstructural characterization revealed that increasing Zn2+ content resulted in a finer microstructure with a more uniform grain size distribution. Furthermore, substitution of Zn2+ effectively reduced dielectric loss in CaMgGe2O6 ceramics while maintaining a stable dielectric constant, making them suitable for high-frequency applications. Among all compositions tested, CaMg0.8Zn0.2Ge2O6 exhibited exceptional performance with a Q×f value reaching 64,980 GHz along with an εr of 7.88 and τf of -36.9 ppm/°C. [ABSTRACT FROM AUTHOR]

Many superconducting on-chip filter-banks suffer from poor coupling to the detectors behind each filter. This is a problem intrinsic to the commonly used half-wavelength filter, which has a maximum theoretical coupling of 50 %. In this paper, we introduce a phase-coherent filter, called a directional filter, which has a theoretical coupling of 100 %. In order to study and compare different types of filter-banks, we first analyze the measured filter frequency scatter, losses, and spectral resolution of a DESHIMA 2.0 filter-bank chip. Based on measured fabrication tolerances and losses, we adapt the input parameters for our circuit simulations, quantitatively reproducing the measurements. We find that the frequency scatter is caused by nanometer-scale line width variations and that variances in the spectral resolution is caused by losses in the dielectric only. Finally, we include these realistic parameters in a full filter-bank model and simulate a wide range of spectral resolutions and oversampling values. For all cases, the directional filter-bank has significantly higher coupling to the detectors than the half-wave resonator filter-bank. The directional filter eliminates the need to use oversampling as a method to improve the total efficiency, instead capturing nearly all the power remaining after dielectric losses. [ABSTRACT FROM AUTHOR]

The opposing effects of interface effect on phonon heat conduction and microwave absorption hinder the integration of thermal conduction with microwave absorption. Reconciling this contradiction by rationally optimizing the material structure remains a challenge. Herein, Fe2N@CNTs with heterogeneous interfaces and multi‐dimensional encapsulated structures are fabricated through in situ chemical vapor deposition (CVD) to realize excellent thermal conductivity and microwave absorption. When the mass fraction of active material is 40 wt.%, the thermal conductivity (λ//) of Fe2N@CNTs composite films is 6.69 W m−1 K−1. The minimum reflection loss (RLmin) is up to −54.55 dB at a thickness of 3.43 mm, and the effective absorption bandwidth (EAB) is 5.52 GHz at 1.82 mm. The well‐designed Fe2N@CNTs is an ideal model for gaining insight into electron transportation and phonon multi‐dimensional heat transport. Heterogeneous interface improves the dielectric loss and facilitates microwave and phonon absorption and conversion. The multi‐dimensional encapsulation structure increases the electron transport path and phonon heat transport paths making axial and radial co‐transfer possible. The multi‐dimensional encapsulation structure demonstrates extremely high microwave absorption and thermal management capabilities, which open up new possibilities for multifunctional applications in host materials with internal hollows. [ABSTRACT FROM AUTHOR]

Y-type hexaferrite ceramic materials of nominal composition Ba 2 Co 2 Cr x Y x Fe 12-2x O 22 (x = 0.00, 0.03, 0.06, 0.09, and 0.12) were synthesized by sol-gel auto combustion route. Y-type hexaferrites are technologically important ceramic materials for fabricating modern electronic devices and microwave absorbers due to their unique electrical and dielectric properties and reflection loss behavior. XRD classifies the single-phase formations with space group R 3 ‾ m. The crystallite size of the synthesized samples was calculated in (34–41) nm range. The specific absorption band in FTIR spectra approves the (Fe–O) stretching vibrations at wavenumbers 446 and 478 cm−1. The substitution of iron by Cr3+ and Y3+ increases DC resistivity from 1.03 × 1011 to 1.17 × 1012 Ω cm by limiting the electrons jumping between ferrous and ferric ions. The activation energy and drift mobility were also calculated among the substituting content of Cr3+-Y3+. The dielectric response in 1 MHz–6 GHz frequency was determined and the effect of substitution has been observed. The Maxwell-Wagner (MW) bilayer model is used to study dispersion in dielectric parameters with reference to applied frequency. The maximum values of dielectric losses were obtained at 6 GHz in the range of 0.37–0.60. The coercivity values confirms the soft magnetic nature of synthesized samples. The microwave absorption (MW) properties of synthesized materials were improved upon Cr3+-Y3+ substitution. Minimum reflection loss R Lmin = −66 dB (99.99% absorption of MW) at 1.46 GHz frequency and 1.96 mm thickness was obtained for x = 0.09 composition. All investigated samples are efficient materials for stealth technology, radar cross-reduction, EM interference shielding, and high-frequency applications. [ABSTRACT FROM AUTHOR]

Amorphous Li 3 PS 4 , Li 2.94 Mn 0.06/n PS 4 (M = Mg, Ca, Al) and Li 2.94 Ca 0.03 PS 3.94 Xy 0.06/y (X = N, I) solid electrolytes were successfully prepared by planetary ball-milling method. Their structure was investigated using XRD and Raman spectroscopy. The data obtained from complex impedance spectroscopy was analyzed to study the ionic conductivity and relaxation dynamics in the prepared samples. The data was interpreted using conductivity isotherms, electrical modulus and dielectric loss tangent. Among the samples, Li 2.94 Al 0.02 PS 4 exhibited highest ionic conductivity at 25 °C, which was about 6.6 x 10−4 Scm−1. Electrical modulus and dielectric loss tangent analysis suggested that grain boundary polarization and ionic conductivity increased with multivalence cation doping. [ABSTRACT FROM AUTHOR]

In this paper, layered porous SiC scaffolds were prepared by freeze casting and sintering, and then followed by loading polypyrrole (PPy) on its surface by in-situ polymerization to obtain porous SiC/PPy composites with different PPy content. The loaded PPy forms a good three-dimensional (3D) conductive network, thus the electrical conductivity and the dielectric loss capability of the sample is improved. Moreover, the porous structure provides more SiC-PPy heterogeneous interfaces for charge accumulation, leading to interfacial polarization and relaxation, further enhancing the microwave absorption performance. Compared with pure SiC particles, SiC/PPy-25 shows an increase in the minimum reflection loss (RL) from −8.64 to −39.1 dB, effective absorption bandwidth (RL < −10 dB) of 4.72 GHz, and comparatively thinner matched thickness of 1.7 mm. We provide a microwave absorption material with simple synthesis, high efficiency and wide application prospect. [ABSTRACT FROM AUTHOR]

Boron nitride (BN) has excellent high temperature resistance, thermal conductivity, strong insulation, and wave-transparent properties. Spherical BN is an essential filler in polymer matrix composites due to good particle mobility and high filler content. In this paper, we present a large-scale preparation for BN microspheres with uniform particle size distribution in the range of 1.0–2.8 μm via solvothermal method at low cost and high yield (∼90%), which is two orders of magnitude lower than the diameter of the spherical BN prepared by other methods. BN microspheres can achieve good crystallinity (>70%) and high purity (>99.9%) at 800 °C. The temperature resistance study showed that the BN microspheres could maintain the dense particle morphology at 1200 °C. In addition, the prepared BN microspheres have good dielectric and thermal conductivity properties (dielectric constant ∼3.4, dielectric loss ∼2.0 × 10−3, and thermal conductivity of 9.8 W m−1 K−1), which show great potential in the field of wave-transparent and thermal conductive composites. The synthesis process of BN microspheres proposed in this study provides a new idea for the preparation of ceramic micro or nano materials by polymer-derived ceramics. [ABSTRACT FROM AUTHOR]

Copper calcium titanate (CaCu 3 Ti 4 O 12 , CCTO) ceramics are receiving a great deal of attention for advanced electronic and energy storage device applications owing to their giant permittivity response and good temperature stability. However, the development and real applications of CCTO ceramics are generally restricted by their large dielectric loss and low breakdown electric field strength. In the present study, a novel type of perovskite-like Na 1/3 (Ca 1/2 Sr 1/2) 1/3 (Bi 1/2 Y 1/2) 1/3 Cu 3 Ti 4 O 12 (NCSBYCTO) ceramics were designed via multiple elements strategy based on the high-entropy concept. Consequently, all the NCSBYCTO ceramics present a giant permittivity response (103∼104), good stability of temperature and frequency, and remarkable relaxation characteristics, especially the NCSBYCTO ceramic sintered at 1050 °C exhibits a relative balance between the giant permittivity of about 7.0 × 103–9.5 × 103 and the lower dielectric loss of approximately 0.043–0.294 at a frequency range of 104–106 Hz under room temperature. Furthermore, all the NCSBYCTO ceramics present an obvious nonlinear characteristic. More encouragingly, a higher breakdown field strength of around 2552.56 V/cm accompanied by a larger nonlinear coefficient of about 6.48 is achieved in the NCSBYCTO ceramic sintered at 1070 °C. A significant electrical heterogeneity structure and electron defect structure induced by the existence of mixed-valence Cu+/Cu2+ and Ti3+/Ti4+ are also found in the NCSBYCTO ceramics. The giant permittivity response, low dielectric loss and improved nonlinear properties can be considered the synergistic effect of the defect mechanism and the internal barrier layer capacitor model. This finding offers a route for designing giant permittivity ceramics with brilliant dielectric properties and nonlinear behaviors, which is expected to benefit dual-functional device applications of capacitors and varistors. [Display omitted] • A novel type of Na 1/3 (Ca 1/2 Sr 1/2) 1/3 (Bi 1/2 Y 1/2) 1/3 Cu 3 Ti 4 O 12 perovskite-like ceramics were developed via multiple elements strategy. • All the NCSBYCTO ceramics exhibit a giant permittivity response (103∼104) and good stability of temperature and frequency. • A relative balance between the giant permittivity and a lower dielectric loss is achieved in the NCSBYCTO ceramic sintered at 1050 °C. • The NCSBYCTO ceramic sintered at 1070 °C shows a higher E b of 2552.56 V/cm and a larger α of 6.48. • The electron defect mechanism and IBLC model can synergistically explain the enhanced electrical properties. [ABSTRACT FROM AUTHOR]

Bioderived carbon materials have garnered considerable interest in the fields of microwave absorption and shielding due to their reproducibility and environmental friendliness. In this study, KOH was evenly distributed on biomass Tremella using the swelling induction method, leading to the preparation of a three-dimensional network-structured hierarchical porous carbon (HPC) through carbonization. The achieved microwave absorption intensity is robust at −47.34 dB with a thin thickness of 2.1 mm. Notably, the widest effective absorption bandwidth, reaching 7.0 GHz (11–18 GHz), is attained at a matching thickness of 2.2 mm. The exceptional broadband and reflection loss performance are attributed to the 3D porous networks, interface effects, carbon network defects, and dipole relaxation. HPC has outstanding absorption characteristics due to its excellent impedance matching and high attenuation constant. The uniform pore structures considerably optimize the impedance-matching performance of the material, while the abundance of interfaces and defects enhances the dielectric loss, thereby improving the attenuation constant. Furthermore, the impact of carbonization temperature and swelling rate on microwave absorption performance was systematically investigated. This research presents a strategy for preparing absorbing materials using biomass-derived HPC, showcasing considerable potential in the field of electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

This study presents the characterization and optimization of BaTiO3-doped ZnO-based varistors for electrical and electronic applications. The varistors were prepared using a conventional ceramic procedure and were sintered at a temperature of 1,000 °C with different concentrations of BaTiO3 (0 and 3 mol%) added to the Bi2O3/ZnO-based varistor composition (99.5 mol% ZnO and 0.5 mol% Bi2O3). The results showed that the addition of BaTiO3 led to the formation of various oxides and solid solutions, such as Bi12TiO20, BaTiO3, and (Bi2O3)0.80 (BaO)0.20. The dielectric constant and grain size decreased with increasing BaTiO3 content, while the non-linearity coefficient, electric fields (Eb) increased, and dielectric loss (Tand) decreased. The optimized varistor contains 2 mol% BaTiO3 and an electric field of 148.08 V/mm, which are superior to those of the BaTiO3/Bi2O3/ZnO-based varistor. During this study, we were able to observe that a slight addition of BaTiO3 will increase the breakdown voltage and the coefficient of nonlinearity and this will allow us to develop lowdimensional varistors and install them in the high-voltage domain. [ABSTRACT FROM AUTHOR]

(1-x) BaTiO3-x ZnO ceramics with x values of 0, 0.5, 1, and 2 wt. % were prepared using the solid-state method. The effect of adding zinc oxide nanoparticles on the densification, microstructure, and dielectric properties of barium titanate ceramics was investigated. Barium titanate powder was synthesized at a temperature of 1200 °C using the solidstate method. The samples were then prepared by pressing and sintered at 1280 °C. The addition of 2 wt. % zinc oxide nanoparticles increased the density of the barium titanate ceramics from 93.5 % to 98.2 % and reduced the porosity from 6.5 % to 1.8 %. The samples containing zinc oxide nanoparticles exhibited a dense microstructure with grain growth. An increase in the content of zinc oxide nanoparticles led to a decrease in the dielectric constant and dielectric loss (tangent delta) of the barium titanate ceramics. The sample containing 2 wt. % zinc oxide nanoparticles revealed the lowest dielectric constant value. At a frequency of 1 kHz, the dielectric constant of barium titanate decreased from 1745 to 895 for the sample containing 2 wt. % zinc oxide nanoparticles. The dielectric loss of the samples containing zinc oxide nanoparticles at high frequencies (above 1 kHz) were all around 0.025, which showed a significant reduction compared to the dielectric loss of barium titanate ceramics (around 0.065). The addition of 1 wt. % zinc oxide nanoparticles caused a decrease in the remnant polarization of barium titanate from 3.7 μC/cm² to 1.2 μC/cm². The coercive field for these samples was measured to be around 3.3 kV/cm. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ceramics / Taoci Xuebao is the property of Journal of Ceramics Editorial Office 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.)

Copyright of Journal of Henan University of Technology Natural Science Edition is the property of Henan University of Technology Journal Editorial Department 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.)

The effect of sintering temperature on the microstructure and electrical properties of ZnO–Bi2O3 varistor ceramics was studied in the present work. Results demonstrate that the Bi-rich phase ZnBi38O60 is generated at the ZnO grain boundaries in the prepared varistor ceramics over a range of 850–1000°C. As the sintering temperature increases, the Bi-rich insulator layer tends to widen, and the average grain size increases to 13.22 μm. The switching field, breakdown strength ( E 1 mA ), and nonlinear coefficient (α) increase, while the leakage current density ( J L ) decreases, because of an increase in barrier height ( φ B ). In addition, the sintering temperature promotes a decrease in the dielectric constant ( ε a ) and an increase in dielectric loss. The ZnO–Bi2O3 varistor ceramic sintered at 1000°C exhibits excellent overall electrical properties, with a switching field of 228.04 V/mm, E 1 mA of 379.76 V/mm, α of 6.02, J L of 140 μA/cm2, φ B of 0.39 eV, and ε a of 172.87 at 1 kHz. [ABSTRACT FROM AUTHOR]

Fe3O4-CuO-MgNb2O6 ternary ceramics were synthesized using solid reaction sintering and the microwave absorption performance was investigated. Remarkable absorption characteristics were observed in the composite material, with optimal reflection loss of −53.3 dB at 8.6 GHz and effective bandwidth of 3.8 GHz (6.9–10.7 GHz) at a thickness of 2.8 mm. The decrease in porosity and simultaneous increase in grain size impact the motion of domain walls, leading to magnetic loss. Furthermore, reduction in porosity facilitates closer proximity of grains, thereby reducing high-resistivity borders and improving the mobility of carriers. Consequently, this leads to an increase in the imaginary part of the complex permittivity. The introduction of three phases and grain growth synergistically contribute to interface and dipolar polarization, further enhancing the dielectric loss and properties related to microwave absorption. The Ansys HFSS (high-frequency structure simulator) results also prove that larger grain size positively affects impedance matching and microwave absorption performance in ceramics. By controlling the grain size of Fe3O4-CuO-MgNb2O6 ternary ceramics, it becomes possible to tailor the microwave absorption properties. [ABSTRACT FROM AUTHOR]

High-performance microwave-absorbing composites have attracted considerable attention in the field of electronic technology and telecommunications. These materials utilize stoichiometric combinations of components to enhance the magnetic parameters and reduce dielectric losses. In this work, microwave emulsion was used to synthesize magnetic nanocomposites with different concentrations of MgFe2O4 nanoparticles in polystyrene (PST). Samples of pure ferrite and PST were mixed in various amounts to form a ferrite polymer (FP-1, FP-2, FP-3, and FP-4, with 25%, 50%, 75%, and 100% ferrite, respectively). These composites were characterized using x-ray diffraction (XRD), dielectric characteristics, and vibrating-sample magnetometry (VSM). The XRD results showed that MgFe2O4 particles were evenly dispersed throughout single-phase PST. The crystallite size increased from 2 nm to 44 nm by mixing ferrites in PST. The dielectric properties were reduced as the percentage was decreased. The VSM tests indicated that all nanocomposites showed narrow loops and ferromagnetic behavior. The magnetic parameters decreased by adding the PST in magnesium ferrite components. The saturation magnetization decreased from 70 emu/g to 18 emu/g, remanence magnetization decreased from 21 emu/g to 5 emu/g, and coercivity decreased from 38 Oe to 8 Oe. All the above parameter results suggest that due to the high dielectric loss at high frequencies, magnesium spinel ferrites may be suitable for microwave absorption applications. [ABSTRACT FROM AUTHOR]

The study of marine lubricants using modern methods for quality control and diagnostics of engine conditions is an important task. The solution to this task determines the technical condition of ships, their performance, and accident-free operation in maritime transport. In this study, the properties of several marine motor oils were studied using broadband dielectric spectroscopy. The complex dielectric constant, conductivity, and loss tangent of base oil, Shell Rimula 15W40 oil fresh and used for 250 and 500 h were studied. The influence of the test voltage frequency and temperature on the selected electrical parameters was determined. In used oils, the DC conductivity decreases slightly, which is apparently due to the depletion of additives. The increase in the conductivity of all studied oils with increasing current frequency is caused by the displacement current. It is shown that dielectric losses increase with frequency as long as the polarization has time to follow the change in the field. A shift in the frequency at which the maximum loss occurs with a change in temperature was discovered. The activation energies of polarization and conductivity were determined. The thermal activation energies obtained from the conductivity and dielectric constant are not significantly different. For the first time, the distributions of the dielectric constant relaxation times for the studied lubricating oils have been obtained. The dielectric relaxation time distribution function depends on the composition of additives in the oil, wear particles, contaminants, and the chemical degradation of the oil during operation. For the first time, correlations have been established between conductivity and dielectric constant at different temperatures and frequencies. These correlations can be used to select frequency ranges that provide stable parameter values and maximum diagnostic ability. [ABSTRACT FROM AUTHOR]

This paper describes the technological process used to manufacture composite paints with a high content of metallic microparticles (Al and Fe) for automotive electromagnetic compatibility applications. The thickness of the deposited paint layer was larger for paints with a greater metal content, regardless of the plastic support used for paint deposition. The roughness of paint layers with a greater content of metal particles was about 30%–35% higher than that of layers with a lower metal particle content, regardless of the metal type. The surface roughness of paint layers containing Al was at least 2.5-times higher than that of paint layers containing Fe, an aspect that could be explained by the better formulation of the paint containing Fe. The dielectric loss and conductivity values crucially depend on the plastic substrate used, meaning that the dipolar polarization of the substrate enhances the effect of conductive paints. Based on the dielectric properties measured at 10 kHz, the optimal recipe for efficient electromagnetic compatibility was found to be 20 wt.% Fe powder, deposited on a sandblasted polycarbonate (PC) substrate. It is expected that formulations of paints with a high percentage of metallic particles will effectively compete with traditional plastic metallization technologies. [ABSTRACT FROM AUTHOR]

Thermoplastic polyimides (TPIs) can meet the requirements of advanced electronic packaging such as flexible copper clad laminate (FCCL) applied under extreme conditions, attributed to their excellent thermal stability, mechanical properties, electrical insulation and chemical resistance. With the increasing demands for electronic devices, such as applications in high‐frequency communication, it is highly desirable to develop high‐performance TPI with good thermoplasticity, thermal stability, mechanical properties and dielectric properties. However, there is a trade‐off between thermoplasticity and other properties. Herein, we introduce an effective strategy to afford TPIs with good performance by copolymerization of a diamine monomer consisted of a coplanar aromatic carbazole group and a short flexible linkage methylene group. On the one hand, short flexible linkages help improve the flexibility of polymer chains and are not too much to enable small‐scale molecular motions below Tg. On the other hand, coplanar aromatic donor groups benefit to strong charge transfer complex (CTC) interaction and π‐π stacking interaction. Based on this strategy, the resultant TPI possesses good thermoplasticity with a proper Tg of 348 °C. Meanwhile, it preserves a low coefficient thermal expansion of 48 ppm K−1, low dielectric constant/dielectric loss factor of 3.27/0.0073 at 10 GHz, and tensile strength of ca. 78 MPa. [ABSTRACT FROM AUTHOR]

Electromagnetic Ion Cyclotron (EMIC) wave scattering has been proved to be responsible for the fast loss of both radiation belt (RB) electrons and ring current (RC) protons. However, its role in the concurrent dropout of these two co‐located populations remains to be quantified. In this work, we study the effect of EMIC wave scattering on both populations during the 27 February 2014 storm by employing the global physics‐based RAM‐SCB model. Throughout this storm event, MeV RB electrons and 100s keV RC protons experienced simultaneous dropout following the occurrence of intense EMIC waves. By implementing data‐driven initial and boundary conditions, we perform simulations for both populations through the interplay with EMIC waves and compare them against Van Allen Probes observations. The results indicate that by including EMIC wave scattering loss, especially by the He‐band EMIC waves, the model aligns closely with data for both populations. Additionally, we investigate the simulated pitch angle distributions (PADs) for both populations. Including EMIC wave scattering in our model predicts a 90° peaked PAD for electrons with stronger losses at lower pitch angles, while protons exhibit an isotropic PAD with enhanced losses at pitch angles above 40°. Furthermore, our model predicts considerable precipitation of both particle populations, predominantly confined to the afternoon to midnight sector (12 hr < MLT < 24 hr) during the storm's main phase, corresponding closely with the presence of EMIC waves. Key Points: An updated RAM‐SCB model is used to study the concurrent dropout of radiation belt (RB) electrons and ring current (RC) protons driven by EMIC wave scatteringRAM‐SCB simulations including Electromagnetic Ion Cyclotron wave scattering better capture the observed losses of both RB electrons and RC protonsSimulated pitch angle distributions (PADs) of electrons peak at 90° with more losses at lower angles; protons show isotropic PADs with enhanced losses above 40° [ABSTRACT FROM AUTHOR]