Showing papers on "Dielectric loss published in 2019"

Pea-like Fe/Fe3C Nanoparticles Embedded in Nitrogen-Doped Carbon Nanotubes with Tunable Dielectric/Magnetic Loss and Efficient Electromagnetic Absorption

Abstract: One-dimensional microstructure has been regarded as one of the most desirable configurations for magnetic carbon-based microwave absorbing materials (MAMs). Herein, pea-like Fe/Fe3C nanoparticles embedded in nitrogen-doped carbon nanotubes (Fe/Fe3C@NCNTs) are successfully prepared through a direct pyrolysis of the mixture of FeCl3·6H2O and melamine under inert atmosphere. The chemical composition and microstructural feature of these Fe/Fe3C@NCNTs composites are highly dependent on the pyrolysis temperature. As a result, their electromagnetic properties can be also manipulated, where dielectric loss gradually decreases with the increasing pyrolysis temperature and magnetic loss presents a reverse variation trend. When the pyrolysis temperature reaches 600 °C, the as-obtained composite, Fe/Fe3C@NCNTs-600 can perform a maximum reflection loss of −46.0 dB at 3.6 GHz with a thickness of 4.97 mm and a qualified bandwidth of 14.8 GHz with the integrated thickness from 1.00 to 5.00 mm. It is very interesting that...

Oriented Polarization Tuning Broadband Absorption from Flexible Hierarchical ZnO Arrays Vertically Supported on Carbon Cloth

Abstract: A novel strategy is used to design large-scale polarized carbon-based dielectric composites with sufficient interaction to electromagnetic waves. Highly uniform polar zinc oxide arrays are vertically grown on a flexible conductive carbon cloth substrate (CC@ZnO) via an in situ orientation growth process. Anion regulation is found to be a key factor to the morphology of hierarchical ZnO arrays including single-rod, cluster and tetrapod-shaped. As a typical dielectric loss hybrid composite, the electromagnetic parameters of the CC@ZnO system and charge density distribution in polarized ZnO rods confirm that the 3D intertwined carbon cloth is used as a conductive network to provide ballistic electron transportation. Moreover, the defect-rich ZnO arrays are well in contact with the CC substrate, favoring interface polarization, multiscattering, as well as impedance matching. Surprisingly, the efficient absorption bandwidth of the CC@ZnO-1 composite can reach 10.6 GHz, covering all X and Ku bands. The oriented ZnO possesses oxygen vacancies and exposure to a large amount of intrinsic polar surfaces, encouraging the polarization behavior under microwave frequency. Optimized CC@ZnO materials exhibit fast electron transportation, strong microwave energy dissipation, and superior wide absorption. The results suggest that the CC@ZnO composites have promising potential as flexible, tuning, and broadband microwave absorbers.

Microwave dielectric properties of low firing temperature stable scheelite structured (Ca,Bi)(Mo,V)O4 solid solution ceramics for LTCC applications

Abstract: In the present work, a systematic study on microwave properties of Ca1-xBixMo1-xVxO4 (0.2 ≤ x ≤ 0.5) solid solution ceramics synthesized by using the traditional solid-state reaction method was conducted. A scheelite structured solid solution was formed in the composition range 0.2 ≤ x ≤ 0.5. We successfully prepared a microwave dielectric ceramic Ca0.66Bi0.34Mo0.66V0.34O4 with a temperature coefficient of resonant frequency (TCF) near to zero and a low sintering temperature by using (Bi, V) substituted (Ca, Mo) in CaMoO4 to form a solid solution. The Ca0.66Bi0.34Mo0.66V0.34O4 ceramic can be well sintered at only 870 °C and exhibits good microwave dielectric properties with a permittivity (er) ˜21.9, a Qf ˜18,150 GHz (at 7.2 GHz) (Q = quality factor = 1/dielectric loss; f = resonant frequency), a TCF ˜ + 0.1 ppm/°C. The chemical compatibility with silver indicated that the Ca0.66Bi0.34Mo0.66V0.34O4 ceramic might be a good candidate for the LTCC applications.

Fabrication of core-shell structured Ni@BaTiO3 scaffolds for polymer composites with ultrahigh dielectric constant and low loss

Abstract: Dielectric composites have drawn increasing attention owing to their wide applications in electrical systems. Herein, a novel design of dielectric composites consisting of core-shell structured porous Ni@BaTiO3 scaffolds infiltrated with epoxy was developed. It is demonstrated that the dielectric constants of the composites could be as high as 6397@10 kHz, which is approximately 1777 times higher than pure epoxy matrix (er ≈ 3.6@10 kHz). Meanwhile, the dielectric loss (tanδ ≈ 0.04@10 kHz) remains comparable to that of pure epoxy (tanδ ≈ 0.01@10 kHz). It is believed that the strong charge accumulation and interfacial polarizations on the huge interfaces, especially the Ni/BaTiO3 and Ni/epoxy interfaces, give arise to the substantially enhanced er. Besides, the sintered insulating BaTiO3 coating can block the transportation of charge carriers, resulting in the low loss. The ultrahigh dielectric constants and low loss make these composites promising candidates for microstrip antennas, field-effect transistors and dielectric capacitors.

Synthesis of Fe3O4/carbon foams composites with broadened bandwidth and excellent electromagnetic wave absorption performance

Abstract: Fabricating of bio-derived electromagnetic wave absorbing materials has become hotspot. However, many bio-derived absorbers still suffer from thicker matching thickness limiting their application. Herein, porous carbon foams derived from fish skin have been synthesized through a simple hydrothermal method for the first time. Then Fe3O4 nanospheres with diameter of 30 nm were uniformly imbedded into the carbon matrix via refluxing and annealing treatment. By controlling the precursor ratio of Fe(NO3)3·9H2O and carbon, optimized microstructure and component can be easily realized. As expected, the novel Fe3O4/C foams show outstanding electromagnetic wave absorption performance compared with single carbon foams. When the loading filler ratio was 25 wt%, the minimum RL value of FC-3 can reach −47.3 dB with a small matching thickness of 1.9 mm. Moreover, the effective absorption bandwidth was 5.68 GHz (12.16–17.84 GHz) with the thickness of 2.2 mm. The thin matching thickness could ascribe to the addition of Fe3O4 nanospheres which could introduce more dielectric loss and magnetic loss. Moreover, the matching thickness of FC-3 is much thinner than other reported bio-derived materials. This investigation could be a perspective paving for the fabrication and mechanism research of electromagnetic wave absorber derived from animal organs.

High Dielectric Constant and Low Dielectric Loss via Poly(vinyl alcohol)/Ti 3 C 2 T x MXene Nanocomposites.

Abstract: As a new class of two-dimensional materials, the MXene family has triggered attention because of its unique electrical and mechanical properties. MXene's excellent electrical conductivity and hydrophilicity make it an ideal option for polymer nanocomposite fabrication. For the first time, polymer nanocomposites of polyvinyl alcohol (PVA)/Ti3C2T x (MXene) were used for charge storage applications in the X-band frequency range (8.2-12.4 GHz). By implementing solution casting and vacuum-assisted filtration (VAF), flexible thin films with exceptional dielectric properties (solution casting @ 10.0 wt % MXene: e' = 370.5 and tan δ = 0.11 and VAF @ 10.0 wt % MXene: e' = 3166 and tan δ = 0.09) were fabricated. The reported dielectric constants in this study are among the highest values obtained in X-band frequency with low dielectric losses. This outstanding performance originates from the high electrical conductivity of synthesized Ti3C2T x MXene (σ ≈ 1.4 ± 0.077 × 106 S/m; the highest reported value for Ti3C2T x MXene to date in the literature), great dispersion state, and the nacre-like structure of the polymer nanocomposites. Combining the exceptional properties of MXene with the effective nacre-like structure, PVA/MXene nanocomposites can be used as a novel charge storage material, fulfilling the requirements of flexible electronics and energy storage devices.

Fabrication of Three-Dimensional Flower-like Heterogeneous Fe3O4/Fe Particles with Tunable Chemical Composition and Microwave Absorption Performance

Abstract: Heterogeneous Fe3O4 and Fe composites are highly desirable for microwave absorption application because of their complementary electromagnetic (EM) properties. With three-dimensional (3D) Fe2O3 as a sacrificing template, we realize the construction of Fe3O4/Fe composites with tunable chemical composition, and more importantly, these composites inherit the unique 3D microstructure from their precursor. The change in chemical composition produces significant impacts on the EM functions of these composites. On the one hand, dielectric loss can be improved greatly through positive interfacial polarization and reach the peak when the mass contents of Fe3O4 and Fe are 72.1 and 27.9 wt %, respectively. On the other hand, high Fe content slightly pulls down magnetic loss in the low-frequency range but favors strong magnetic loss in the high-frequency range because of the breakthrough of Snoek's limitation. The attenuation constant reveals that dielectric loss dominates overall consumption of incident EM waves. As a result, the optimized composite, F-350 (the reduction of Fe2O3 is conducted at 350 °C), shows the best microwave absorption performance, whose strongest reflection loss is -56.0 dB at 17.5 GHz and the effective bandwidth can cover the frequency range of 12.0-15.5 GHz with the thickness of 1.5 mm. Furthermore, an ultrawide effective bandwidth of 15.3 GHz can be achieved with the integrated thickness of 1.0-5.0 mm. Such a performance is superior to those of many reported Fe3O4/Fe composites, and a comparative analysis manifests that good microwave absorption of F-350 is also benefited from its unique 3D architecture.

A versatile foaming platform to fabricate polymer/carbon composites with high dielectric permittivity and ultra-low dielectric loss

Abstract: There is an urgent need for dielectric-based capacitors to manage the increase in storage systems related to renewable energy production. Such capacitors must have superior qualities that include light weight, a high dielectric constant, and ultra-low dielectric loss. Poly(vinylidene fluoride) (PVDF)/carbon (carbon nanotube (CNT) or graphene nanoplatelet (GnP)) nanocomposite foams are considered promising alternatives to solid PVDF/carbon nanocomposites. This is because they have excellent dielectric properties, which are due to the preferred orientation of their carbon materials occurring in the foaming process. In the PVDF/carbon foams, their microcellular structure significantly influenced their electrical conductivity and dielectric properties. In the PVDF/CNT composite foams, the electrical conductivity was increased by an increased degree of foaming that was below a critical foaming degree. The CNTs even formed conductive networks and this caused current leakage. Thus, in the PVDF/CNT foam sample with an expansion ratio of 4.0 where a high dielectric constant of 80.6 was obtained, a relatively high dielectric loss of 3.51 was observed at the same time. In the PVDF/GnP composite foams, the presence of a microcellular structure forcefully increased the distance between GnPs. This induced and produced the insulating quality of the PVDF/GnP foams. In addition, the parallel graphene nanoplatelets that accompanied this process were close together, and they isolated the polymer layer, or air, as a medium between themselves. An unprecedentedly high dielectric constant of 112.1 and an ultra-low dielectric loss of 0.032 at 100 Hz were obtained from the PVDF/GnP composite foam with a high expansion ratio of 4.4 due to charge accumulation at the aligned conductive filler/insulating polymer (or air bubble) interface.

Multilayer-structured transparent MXene/PVDF film with excellent dielectric and energy storage performance

Abstract: Exploring polymer-based composites with a high dielectric constant and energy density simultaneously, as well as low dielectric loss, is of crucial importance because of their potential applications in modern electronics and electric power systems. Here, a multilayer-structured Ti3C2Tx MXene/poly(vinylidene fluoride) (PVDF) film with a high dielectric constant and ultralow dielectric loss is fabricated via spin coating, spray coating and hot-press methods. 4MXene/5PVDF (namely four layers of MXene and five layers of PVDF) exhibits a high dielectric constant (41) and an ultralow dielectric loss (0.028, smaller than that of pure PVDF) at 1 kHz. Surprisingly, the MXene/PVDF films show good broadband dielectric behaviors and the dielectric constant of 4MXene/5PVDF can reach up to 32.2 at 1 MHz, which can remain as high as 78.4% of that at 1 kHz. Based on the crystalline phase transformation and temperature dependence of electrical modulus results, the excellent dielectric properties are attributed to the enhanced interfacial polarization. The multilayered structure can efficiently prevent the formation of a conductive network across the entire film, leading to suppressed dielectric loss, a comparative breakdown strength with pure PVDF and a maximum discharge energy density of 7.4 J cm−3. This work provides a promising design paradigm to construct polymer films with a high dielectric constant and low dielectric loss.

Effect of SiC nanowires on the high-temperature microwave absorption properties of SiCf/SiC composites

Abstract: SiC-nanowire-reinforced SiCf/SiC composites were successfully fabricated through an in situ growth of SiC nanowires on SiC fibres via chemical vapour infiltration. The dielectric and microwave absorption properties of the composites were investigated within the frequency range of 8.2–12.4 GHz at 25–600 °C. The electric conductivity and complex permittivity of the composites displayed evident temperature-dependent behaviour and were enhanced with increasing temperature. The composites exhibited superior microwave absorption abilities with a minimum reflection loss value of −47.5 dB at 11.4 GHz and an effective bandwidth of 2.8 GHz at 600 °C. Apart from the contribution of the interconnected SiC nanowire network and multiple reflections, the excellent microwave absorption performance was attributed to dielectric loss that originated from SiC nanowires with abundant stacking faults and heterostructure interfaces. Results suggested that the composites are promising candidates for high-temperature microwave absorbing materials.

High Kinetic Inductance Nb N Nanowire Superinductors

Abstract: We demonstrate that a high kinetic inductance disordered-superconductor nanowire can realize a circuit element - known as a superinductor - with a characteristic impedance greater than the quantum resistance (RQ=h/4e2≃6.5kΩ) and a quality factor of 25 000 at single-photon excitation. By examining loss rates, we demonstrate that the microwave dissipation can be fully understood in the framework of two-level-system dielectric loss. Superinductors can suppress the quantum fluctuations of charge in a circuit, which has applications, for example, in devices for quantum computing, photon detection, and other sensors based on mesoscopic circuits.

Determining Interface Dielectric Losses in Superconducting Coplanar-Waveguide Resonators

Abstract: Superconducting quantum circuits are a leading candidate technology for large-scale quantum computing and simulation. Future scaling and improvements in device performance hinge upon a more detailed understanding of the sources of dielectric loss in these systems, yet standard techniques cannot separate the contributions from distinct dielectric regions to the aggregate device performance. This study presents a method for assessing the separate loss contributions from each material interface and bulk dielectric within such a circuit, enabling targeted improvements in performance by both informing device design and providing feedback to assess microfabrication techniques.

BST-P(VDF-CTFE) nanocomposite films with high dielectric constant, low dielectric loss, and high energy-storage density

Abstract: Free-standing, flexible, and transparent ceramic-polymer nanocomposite films with a uniform thickness of about 5 μm were fabricated using a simple spin-coating process, in which the polymer solution with a high concentration was used. Ba0.5Sr0.5TiO3 (BST) nanoparticles and P(VDF-CTFE) 91/9 mol.% (VC91) copolymer were used as ceramic filler and polymer matrix, respectively. Microstructures, dielectric properties, and energy-storage performances of the BST-VC91 nanocomposite films have been investigated. With increasing volume fraction of BST, the dielectric constant increases, while the dielectric loss decreases. A dielectric constant of about 38.4 at 100 Hz associated with a dielectric loss of only about 0.02 was obtained in the nanocomposite film with 40 vol% of BST. It is experimentally found that the temperature dependences and the frequency dispersions of dielectric properties were strongly influenced by the volume fraction of BST, especially at high temperatures. Good temperature stability and small frequency dispersion of dielectric constant can be obtained in the BST-VC91 nanocomposite films with 40 vol% and 50 vol% of BST, which are also associated with a low dielectric loss. It is concluded that the motion of the polymer chains is the micro-origin of the relaxation process observed at high temperatures. With increasing volume fraction of BST, the dielectric breakdown strength decreases, while the maximal polarization and remnant polarization increase. The maximal charge-energy density and discharge-energy density of about 21.7 J/cm3 and 7.5 J/cm3 are obtained in the BST-VC91 nanocomposite film with 30 vol% BST under 2500 kV/cm, which are more than 2 times larger than those observed in pure VC91 film under the same electric field.

Wheat straw-derived magnetic carbon foams: In-situ preparation and tunable high-performance microwave absorption

Abstract: Recently, biomass-derived three-dimensional (3D) porous carbon materials have been gaining more interest as promising microwave absorbers due to their low cost, vast availability, and sustainability. Here, a novel 3D interconnected porous magnetic carbon foams are in-situ synthesized via a combination of sol-gel and carbonization process with wheat straw as the carbon source and FeCl3·6H2O as the magnetic regulating agent. During the process of foams formation, the lignocelluloses from the steam-exploded wheat straw are converted into interconnected carbon sheet networks with hierarchical porous structures, and the precursor FeCl3·6H2O is converted into magnetic nanoparticles uniformly embedded in the porous carbon foams. The generated magnetic nanoparticles are benefit to enhance the interface polarization and magnetic loss ability to improve the efficient complementarities between the dielectric and magnetic loss, thus increasing the impedance matching. The obtained sample treated at 600 °C displays the best microwave absorption (MA) performance. It presents a minimal reflection loss (RL) of −43.6 dB at 7.1 GHz and the effective bandwidth (RL < −10 dB) is 3.3 GHz with the thickness of 4.7 mm. The 3D porous structure, multi-interfaces and the synergy of dielectric loss and magnetic loss make great contribution to the outstanding MA performance.

High-entropy alloy@air@Ni–NiO core-shell microspheres for electromagnetic absorption applications

Abstract: Core-shell microspheres with high-entropy alloy (HEA: FeCoNiCrCuAl0.3) as core and metal oxide (Ni–NiO) as shell have been successfully constructed via a two-step hydrothermal method. The chemical composition, microstructure, electromagnetic (EM) properties and EM wave absorption properties were characterized in detail. We find that the magnetic loss originated from high-entropy alloy and the dielectric loss caused by Ni–NiO can promote the consumption of EM energy through synergistic effect. The effective absorption bandwidth (fE, RL