Showing papers on "Dielectric loss published in 2011"

Hierarchical Dendrite-Like Magnetic Materials of Fe3O4, γ-Fe2O3, and Fe with High Performance of Microwave Absorption

Abstract: Iron-based microstructured or nanostructured materials, including Fe, γ-Fe2O3, and Fe3O4, are highly desirable for magnetic applications because of their high magnetization and a wide range of magnetic anisotropy. An important application of these materials is use as an electromagnetic wave absorber to absorb radar waves in the centimeter wave (2−18 GHz). Dendrite-like microstructures were achieved with the phase transformation from dendritic α-Fe2O3 to Fe3O4, Fe by partial and full reduction, and γ-Fe2O3 by a reduction−oxidation process, while still preserving the dendritic morphology. The investigation of the magnetic properties and microwave absorbability reveals that the three hierarchical microstructures are typical ferromagnets and exhibit excellent microwave absorbability. In addition, this also confirms that the microwave absorption properties are ascribed to the dielectric loss for Fe and the combination of dielectric loss and magnetic loss for Fe3O4 and γ-Fe2O3.

Core-shell structured poly(methyl methacrylate)/BaTiO3 nanocomposites prepared by in situ atom transfer radical polymerization: a route to high dielectric constant materials with the inherent low loss of the base polymer

Abstract: Core-shell structured BaTiO3/poly(methyl methacrylate) (PMMA) nanocomposites were successfully prepared by in situ atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) from the surface of BaTiO3 nanoparticles. A broadband dielectric spectrometer was used to investigate the temperature dependence of the dielectric properties of the nanocomposites in a frequency range from 0.1 Hz to 1 MHz. It was found that the nanocomposites not only showed a significantly increased dielectric constant when compared with pure PMMA, but also showed the inherent low loss of the base polymer in a wide range of frequencies. Only in the very low frequency/high temperature range, can a higher dielectric loss can be observed in the nanocomposites. It was also found that the effective dielectric constant of the core-shell structured hybrid nanoparticles can be tailored by varying the polymer shell thickness. The dielectric response of beta relaxation of PMMA was also studied and the results showed that the nanoparticles had no influence upon the relaxation activation energy. Fourier-transform infrared spectroscopy (FTIR) and 1H NMR spectra confirmed the chemical structure of the PMMA shell on the surface of the BaTiO3 nanoparticles. Transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) results revealed that the PMMA shell thickness could be well controlled by tuning the feed ratio of MMA to BaTiO3.

Study of loss in superconducting coplanar waveguide resonators

Abstract: Superconducting coplanar waveguide (SCPW) resonators have a wide range of applications due to the combination of their planar geometry and high quality factors relative to normal metals. However, their performance is sensitive to both the details of their geometry and the materials and processes that are used in their fabrication. In this paper, we study the dependence of SCPW resonator performance on materials and geometry as a function of temperature and excitation power. We measure quality factors greater than 2 × 106 at high excitation power and 6 × 105 at a power comparable to that generated by a single microwave photon circulating in the resonator. We examine the limits to the high excitation power performance of the resonators and find it to be consistent with a model of radiation loss. We further observe that while in all cases the quality factors are degraded as the temperature and power are reduced due to dielectric loss, the size of this effect is dependent on resonator materials and geometry. Finally, we demonstrate that the dielectric loss can be controlled in principle using a separate excitation near the resonance frequencies of the resonator.

Carbon Nanotube Array/Polymer Core/Shell Structured Composites with High Dielectric Permittivity, Low Dielectric Loss, and Large Energy Density

Abstract: Polymer-based composites have been found to be widely attractive in the past few years because of their great potential in various fi elds. [ 1–7 ] Exploring polymer-based dielectrics with high energy density ( J = κ 0 κ E 2 /2), i.e., high dielectric permittivity (highκ ), high breakdown electric fi eld (highE ), and low dielectric loss (low tan δ ), has recently aroused considerable interest. [ 1 , 8 , 9 ] However, the relative dielectric permittivity of polymers is very low ( κ < 5) while the breakdown electric fi eld ( E > 200 kV mm − 1 ) remains high. [ 1 , 4 , 5 ] Thus, a key issue is to enhance dielectric permittivity of polymers while retaining other excellent performances. One common approach is to add highκ ceramic fi llers (e.g., BaTiO 3 , Pb(Zr,Ti)O 3 , CaCu 3 Ti 4 O 12 , etc) into polymers, which can increase κ by about ten times relative to the polymer matrix. [ 10–14 ] However, high loading of the ceramic fi llers (usually over 50 vol%) dramatically decreases the mechanical properties of the polymer matrix. Another strategy is to fabricate percolative composite capacitors by adding conductive fi llers (e.g., metal particles and carbon nanotubes) into polymers. [ 4 , 5 , 15 , 17 ] As the volume fraction of the fi llers increases to the percolation threshold, κ of the composites can be dramatically enhanced. However, the dielectric loss of these percolative composites is usually quite high due to the insulator–conductor transition near the percolation threshold. Among these conductive fi llers in polymer-based composites, carbon nanotubes (CNTs) have a large aspect ratio and present unique mechanical properties, showing high electrical and thermal conductivity values. [ 16–18 ] CNT/polymer composites have been pursued with the hope of delivering CNT properties to a processable and synergistic host. [ 19–21 ] With respect to the electrical properties of CNT/polymer composites, the dielectric properties of CNT/polymer composites were reported, and it was found that these materials showed different dielectric properties depending on the polymer matrix and dispersion of CNTs in the composites. [ 16 , 17 , 21 , 22 ] Several methods have been

Two Level System Loss in Superconducting Microwave Resonators

Abstract: High quality factor, i.e. low loss, microwave resonators are important for quantum information storage and addressing. In this work we study the resonance frequency and loss in superconducting coplanar waveguide resonators as a function of power and temperature. We find that there is increased loss at low power and low temperature. The increased loss is attributed to the existence of two-level systems (TLS) at the surfaces, interfaces, and in the bulk of insulators deposited on the structures. We show that both the temperature dependence of the resonant frequency and the power dependence of the loss can be used to find the TLS contribution to the loss. The TLS intrinsic loss tangent derived from the frequency shift data at high power is shown to agree well with the direct loss measurement at low power. The former allows for a relatively fast measurement of the TLS loss. As an example, we measure the properties of amorphous AlOX deposited on the resonators and find a TLS loss tangent of 1 × 10-3.

Development of polymer-based 0{3 composites with high dielectric constant

Abstract: Composites have been extensively studied for dielectric and related applications. This is a review of polymer based 0–3 composites that exhibit a high dielectric constant. These composites are classified into two types: Dielectric–dielectric composite and conductor–dielectric composite. The physical principles and related models are presented with associated assumptions and approximations. In general, a dielectric–dielectric composite needs a higher concentration of the fillers to reach a high dielectric constant than a conductor–dielectric composite. The high dielectric constant observed in the conductor–dielectric composites is usually associated with a high dielectric loss and a low electric breakdown field. The experimental results are summarized to illustrate the principles for, and the achievements in, the development of these composites. The challenges facing the fundamental understanding and the further development of these composites for different applications are discussed.

Morphology-controllable graphene–TiO2 nanorod hybrid nanostructures for polymer composites with high dielectric performance

Abstract: High permittivity polymer-based materials are highly desirable due to their inherent advantages of being easy to process, flexible and light weight. Herein, a new strategy for the development of polymer composites with high permittivity and low dielectric loss has been proposed based on morphology-controllable graphene–TiO2 nanorod hybrid nanostructures. These hybrid nanostructures possess large aspect ratio, high surface area and high electric conductivity graphene sheets, which provide ideal electrodes in the construction of microcapacitors. In addition, the morphology-controllable TiO2 nanorod decoration effectively prevents direct contact between the graphene sheets in the composite, which give advantages for forming a large microcapacitor network and suppressing the leakage current. As a consequence, a polystyrene composite with 10.9 vol% graphene–TiO2 nanorod sheets exhibits a very high permittivity of 1741 at 102 Hz, which is 643 times higher than the value for pure polystyrene (2.7), and low dielectric loss (tanα) of only 0.39. The permittivity of the composites can be controlled by controlling the amount of nanorod decoration on the graphene substrates, which provides a new pathway for tuning the permittivity of polymer composites. We expect that our strategy of controlling filler interface will be applied to acquire more polymer composites with high permittivity and low dielectric loss.

Rietveld analysis, dielectric and magnetic properties of Sr and Ti codoped BiFeO3 multiferroic

Abstract: Polycrystalline Bi0.8Sr0.2Fe1 − xTixO3 (x = 0.0, 0.1, 0.2) multiferroics were synthesized via the conventional solid state reaction method. The structure, dielectric relaxation, and magnetic properties of as prepared samples were investigated. The crystal structure examined via XRD and Rietveld analysis confirmed a single phase rhombohedral (space group R3c no. 161) structure. In the Rietveld refinement, good agreement between the observed and calculated pattern was observed. The dielectric response of these multiferroics was analyzed in the frequency range of 10 Hz to 5 MHz at different temperatures. All the samples showed dispersion in dielectric constant (έ) and dielectric loss factor (tan δ) values. The temperature dependence of έ and tan δ showed broad peaks. A reduction in the values of έ and tan δ was observed upon the incorporation of Ti. Magnetic measurements were carried out at room temperature up to a field of 20 kOe. Magnetic hysteresis loops revealed a significant increase in magnetization with Ti substitution. A remnant magnetization (Mr) of 33.428 memu/g and a coercive field (Hc) of 1.724 kOe were observed in the sample with x = 0.2.

Dielectric studies on hybridised PVDF–ZnO nanocomposites

Abstract: Nanocomposites of polyvinylidene fluoride (PVDF) and nano-ZnO were prepared using the solution casting method for different concentrations of nano-ZnO and were characterised by X-ray diffraction and atomic force microscopy. Optical properties of these nanocomposites were determined by using UV-Vis absorption spectroscopy and Fourier transform infrared analysis. The variation of dielectric properties such as dielectric constant, dielectric loss and electric modulus of the hybrid films based on the content of ZnO studied for various microwave frequencies at room temperature showed that the dielectric constant of PVDF–ZnO hybrid films increased with increasing ZnO content at room temperature.

Elastic block copolymer nanocomposites with controlled interfacial interactions for artificial muscles with direct voltage control

Abstract: Soft, physically crosslinking, block copolymer elastomers were filled with surface-treated nanoparticles, in order to evaluate the possibility for improvement of their properties when used as soft dielectric actuators The nanoparticles led to improvements in dielectric properties, however they also reinforced the elastomer matrix Comparing dielectric spectra of composites with untreated and surface-treated particles showed a measurable influence of the surface on the dielectric loss behaviour for high filler amounts, strongly indicating an improved host–guest interaction for the surface-treated particles Breakdown strength was measured using a test bench and was found to be in good agreement with the results from the actuation measurements Actuation responses predicted by a model for prestrained actuators agreed well with measurements up to a filler amount of 20%vol Strong improvements in actuation behaviour were observed, with an optimum near 15%volnanoparticles, corresponding to a reduction in electrical field of 27% for identical actuation strains The use of physically crosslinking elastomer ensured the mechanical properties of the matrix elastomer were unchanged by nanoparticles effecting the crosslinking reaction, contrary to similar experiments performed with chemically crosslinking elastomers This allows for a firm conclusion about the positive effects of surface-treated nanoparticles on actuation behavior

Functionalised graphene sheets as effective high dielectric constant fillers

Abstract: A new functionalised graphene sheet (FGS) filled poly(dimethyl)siloxane insulator nanocomposite has been developed with high dielectric constant, making it well suited for applications in flexible electronics. The dielectric permittivity increased tenfold at 10 Hz and 2 wt.% FGS, while preserving low dielectric losses and good mechanical properties. The presence of functional groups on the graphene sheet surface improved the compatibility nanofiller/polymer at the interface, reducing the polarisation process. This study demonstrates that functionalised graphene sheets are ideal nanofillers for the development of new polymer composites with high dielectric constant values. PACS: 78.20.Ci, 72.80.Tm, 62.23.Kn

The enhanced microwave absorption property of CoFe(2)O(4) nanoparticles coated with a Co(3)Fe(7)-Co nanoshell by thermal reduction.

Abstract: CoFe2O4 nanoparticles were fabricated by a sol–gel method and then were coated with Co3Fe7–Co by means of a simple reduction process at different temperatures under 2% H2 with the protection of argon to generate the dielectric-core/metallic-shell structure. The optimum reflection loss (RL) calculated from permittivity and permeability of the 80 wt% CoFe2O4/Co3Fe7–Co and 20 wt% epoxy resin composites reached − 34.4 dB, which was much lower than that of unreduced CoFe2O4 and epoxy resin composites, at 2.4 GHz with a matching thickness of 4.0 mm. Moreover the RL exceeding − 10 dB in the maximum frequency range of 2.2–16 GHz was achieved for a thickness of composites of 1.0–4.5 mm with 600 °C thermal reduction process. The improved microwave absorption properties are a consequence of a proper electromagnetic match and the enhanced magnetic loss besides its dielectric loss due to the existence of the core/shell structure in CoFe2O4 composites. Thus, the reductive CoFe2O4 nanoparticles have great potential for being a highly efficient microwave absorber.

Dopant induced hollow BaTiO3 nanostructures for application in high performance capacitors

Abstract: In this work, large-scale single crystalline Nd-doped BaTiO3 hollow nanoparticles have been synthesized via a simple hydrothermal method without the assistance of a surfactant or high temperature sintering. With unique hollow structures, the nanoparticles not only exhibit excellent compatibility with poly(vinylidene fluoride) (PVDF), but significantly enhanced the dielectric properties of the nanocomposites. We demonstrated that the dielectric constant of the nanocomposite reached up to 480.3 with dielectric loss of 0.6 at 102 Hz. Design and optimization of the synthesis method have been achieved through a systematic study of the effect of reaction conditions on the size and morphology evolution of the hollow nanoparticles. The formation of hollow nanostructures is proposed to follow a Kirkendall induced hollowing mechanism which is governed by the differences in diffusion rates of dopant ions, water molecules and core ions during the synthesis reaction.

Poly(vinylidene fluoride)-graft-poly(2-hydroxyethyl methacrylate): a novel material for high energy density capacitors

Abstract: We report the graft copolymerization synthesis of novel high dielectric constant HEMA (2-hydroxyethylmethacrylate)-graft-poly(vinylidene fluoride) (PVDF) copolymers for potential applications in high energy density capacitors. In the present study the graft copolymerization reaction was introduced by irradiation (electron beam) treatment of the PVDF polymer powder. The chemical changes in the PVDF polymers after HEMA grafting were monitored and the results were evaluated by FTIR, DSC, TGA and contact angle measurement. An analysis is presented on the effectiveness of this approach as a function of electron beam operating variables including radiation dose, reaction time, reaction temperature, monomer concentration and effect of solvent. The PHEMA-g-PVDF copolymers demonstrate improved dielectric properties such as high dielectric constant, lower leakage and low dielectric loss as compared to pristine PVDF. Correlation of dielectric properties with the graft copolymerization reaction mechanism was discussed.

Nonferroelectric contributions to the hysteresis cycles in manganite thin films: A comparative study of measurement techniques

Abstract: Several experimental methods to measure ferroelectric hysteresis loops and to extract polarization values are compared for thin films with significant losses and different magnitudes of polarization. The analysis allows the determination of the most appropriate frequency range and technique to extract reliable values of the remanent polarization in materials with low polarization and high leakage. Examples include multiferroic YMnO3 and Bi0.9La0.1NiMnO6 thin films.

Electrical and switching properties of NiAlxFe2−xO4 ferrites synthesized by chemical method

Abstract: Nickel-aluminum ferrite system NiAlxFe2−xO4 has been synthesized by wet chemical co-precipitation method. The samples were studied by means of X-ray diffraction, d.c. electrical resistivity, a.c. electrical resistivity, a.c. conductivity and switching properties. The XRD patterns confirm the cubic spinel structure for all the synthesized samples. The crystallite size calculated from XRD data which confirm the nano-size dimension of the prepared samples. Electrical properties such as a.c. and d.c. resistivities as function of temperature were studied for various Al substitution in nickel ferrite. The dielectric constant and dielectric loss tangent were also studied as a function of frequency. The dielectric constant follows the Maxwell–Wagner interfacial polarization. A.C. conductivity increases with increase in applied frequency. The d.c. resistivity decreases as temperature increases, which indicate that the sample have semi-conducting nature. Verwey hoping mechanism explains the observed variation in resistivity. The activation energy is derived from the temperature variation of resistivity. Electrical switching properties were studied as I–V measurements. The current controlled negative resistance type switching is observed in all the samples. The Al substitution in nickel ferrite decreases the required switching field.

Loss determination methodology for a piezoelectric ceramic: new phenomenological theory and experimental proposals

Abstract: The key factor to the miniaturization of piezoelectric devices is power density, which is limited by the heat generation or loss mechanisms. There are three loss components in general in piezoelectric vibrators/resonators, i.e., dielectric, elastic and piezoelectric losses. The mechanical quality factor, determined by these three factors, is the Figure Of Merit (FOM) in the sense of loss or heat generation. In this paper, we introduce a new loss phenomenology and innovative measuring methods based on the theory. First, quality factors at resonance and antiresonance for the k31, k33, kt and k15 vibration modes are derived theoretically, and the methodology for determining loss factors in various orientations (i.e., loss anisotropy) is provided. For simplicity, we focus on materials with ∞ mm (equivalent to 6 mm) crystal symmetry for deriving the loss factors of a polycrystalline ceramic, and 14 different loss factors among 20 in total can be obtained from the measurements. Second, we propose the experimental methods for measuring both mechanical quality factors QA and QB at the resonance and antiresonance modes: a continuous admittance/impedance spectrum measuring method (traditional with temperature rise) and a burst mode (to circumvent the temperature effect).

Influence of crystalline properties on the dielectric and energy storage properties of poly(vinylidene fluoride)

Abstract: Poly(vinylidene fluoride) (PVDF) films with various crystal phases (α, β, and γ phases) and varied crystallinities were fabricated via different processes. The influence of the crystalline properties, such as the crystallinity and crystal phases, on the breakdown strength and dielectric and energy storage properties of the films were studied. Under low electric field, the dielectric constant was governed by the crystallinities of the films, and the dielectric loss was more related to the polarity of their crystal phases. Under high electric field, the high polarity of the crystal phases favored high-maximum, remnant, and irreversible polarization of the films. The lower crystallinity of the films with the same crystal phases led to a higher maximum and remnant polarization but a lower irreversible polarization. Under direct-current electric field, the discharged energy efficiency was mainly dominated by the polar nature of crystal phases. Under an electric field below 300 MV/m, the discharged energy density and energy loss of the three kinds of films were rather close, regardless of the phase transition. When the electric field was over 300 MV/m, the overall discharged energy density was dominated by the practical breakdown strength. γ-PVDF with a proper crystallinity and crystal grain size is expected to realize an energy density over 10 J/cm3 under an electric field over 400 MV/m. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Dielectric Properties of Vegetable Oils

Abstract: In search of PCB (polychlorinated biphenyl) free mineral oil used in transformer, we have carried out the detailed study on dielectric properties of some vegetable oils, such as corn oil and cottonseed oil. Dielectric constant, dielectric loss factor have been determined for corn oil, cotton seed oil, and PCB free mineral transformer oil having International Electrotechnical Commission number IEC-60296 in the frequency range 330 Hz to 3 MHz and in temperature range 25 0 C to 70 0 C. The dielectric data of the vegetable oils is critically compared with that of the transformer oil and appropriate causes for similarities and differences have been discussed. Owing to comparable results in the vegetable oils and transformer oil studied, it is suggested that vegetable oils may also be used as transformer oil. Keywords : dielectric constant; dielectric loss; dielectric relaxation; polarization. © 2011 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. doi:103329/jsr.v3i3.7049 J. Sci. Res. 3(3), 491-502 (2011)

The measurement of very low conductivity and dielectric loss in XLPE cables: a possible method to detect degradation due to thermal aging

Abstract: The dielectric response of crosslinked polyethylene (XLPE) insulated, miniature power cables, extruded with inner and outer semicons, was measured over the frequency range 10-4 to 104 Hz at temperatures from 20 to 100 °C. A dielectric spectrometer was used for the frequency range 10-4 to 10-2 Hz. A bespoke noise-free power supply was constructed and used to measure the dc conductivity and, using a Fourier transform technique, it was also used to measure the very low dielectric tanδ losses encountered at frequencies of 1 to 100 Hz. Tanδ measurements of <;10-5 were found in this frequency range and attributed to a β-mode dielectric relaxation lying above 100 Hz due to motion of chain segments in the amorphous region and an β-mode relaxation lying below 1 Hz window due to twists of chains in the crystal lamellae. The dc conductivity measurements were consistent with those of the dielectric spectrometer and indicate lower dc conductivities in vacuum degassed cables than have been previously reported for XLPE (less than 10-17 S.m-1). The conduction process is thermally activated with an activation energy of approximately 1.1 eV. Higher conductivities were found for non-degassed cables. A transformer ratio bridge was used for measurements in the range 1 to 10 kHz; loss in this region was shown to be due to the series resistance of the semicon layers. Thermal ageing of the cables at 135 °C for 60 days caused significant increases in the conductivity and tanδ and it is considered that such measurements may be a sensitive way of measuring electrical degradation due to thermal aging.