Dielectric Constant Of Composites Research Articles

Microwave electromagnetic and absorption properties of SmN/α-Fe/Sm2Fe17N3 composites in 0.5–18 GHz range

SmN/α-Fe/Sm2Fe17N3 composites were prepared in situ by heating of Sm2Fe17N3 powders, and their electromagnetic wave absorption properties were measured in the frequency range of 0.5–18GHz. The result shows that saturation magnetization and coercivity of as-heated powder with 23.7wt% SmN, 58.5wt% α-Fe and 17.8wt% Sm2Fe17N3 are 130.82emu/g and 750Oe, respectively. The dielectric constant of composites was low over the frequency range of 0.5–18GHz, and their resonance frequencies were at a high frequency range. The effective electromagnetic wave absorption (RL<−20dB) of the compact sample with thickness of 0.7–3.2mm prepared with the SmN/α-Fe/Sm2Fe17N3 and resin was obtained in a frequency range of 5.5–16GHz. A minimum reflection loss of −33dB of the samples was observed at 5.5GHz with an absorber thickness of 3.2mm.

Temperature dependence of the dielectric permittivity of poly(methyl methacrylate) filled with metal nanoparticles

The temperature dependence of the dielectric constant of composites based on a dielectric poly(methyl methacrylate) (PMMA) matrix containing stabilized nanoparticles of silver has been studied. The Cole-Cole diagrams of PMMA-Ag composites at various temperatures have been constructed and analyzed.

Investigation on magnetoelectric and dielectric properties of Co0.9Mn0.3Fe1.8O4–Sr0.5Ba0.5Nb2O6 composites

The present paper reports the dielectric and magnetoelectric properties of Mn substituted yCo1.2−xMnxFe1.8O4 (CMFO) and (1 − y) Sr0.5Ba0.5Nb2O6 (SBN) ME composites. The composites are formed with three weight percent of Bi2O3 as sintering aid. The Co1.2−xMnxFe1.8O4 is initially studied for variation of electrical resistivity ρ, saturation magnetization Ms, permeability μ, coercive field Hc and coefficient of magnetostriction λ to determine a composition suitable to form a ME composite. Here x = 0.3 is observed to posses optimal value of ρ, Ms, μ, Hc and λ, therefore the composites are formed using Co0.9Mn0.3Fe1.8O4. The composites y MSBN = y CMFO + (1 − y) SBN are synthesized and investigated for their structural, dielectric and magnetoelectric properties. The dielectric constant of composites is observed to exhibit contribution due to interfacial polarization as well as a contribution due to the SBN phase. The variation of linear magnetoelectric coefficient α and quadratic magneto electric coefficient β for varies compositions are reported in this paper. The paper also repots the effect of sintering temperature and variation of frequency on the magnitude of α and β. It is observed that the use of sintering aid increases the magnetoelectric output of the MSBN composites. The samples with y = 0.4 is observed to show sufficiently large and useful magnitude of magnetoelectric coefficients.

High dielectric constant and superparamagnetic polymer‐based nanocomposites induced by percolation effect

AbstractTo obtain the high dielectric constant and superparamagnetic composites for application in dielectric energy storage capacitors and other electromagnetic devices, the Fe3O4 nanoparticles have been embedded into polyvinylidene fluoride (PVDF) polymer. As expectation, a distinct percolation effect has been found in these composites, because of the good conductivity of Fe3O4 nanoparticles. The composites exhibit great increase of the dielectric constants and conductivities near the percolation threshold. The maximum of dielectric constant is up to 5240 at 100 Hz, which is the highest value reported to date among the PVDF based percolative composites. Meanwhile, the dielectric loss is controlled in the range of 0–2.2. These composites also exhibit superparamagnetic with the presence of Fe3O4 nanoparticles. The maximum of saturation magnetization is 30.8 emu/g. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Studies of dielectric constant measurements at microwave frequency using mixing equations-The analyses on five rules

The microwave dielectric constants of ceramic dispersions in the polyethylene matrix are studied by five well-known mixture equations in this article. Three ceramic powders of fillers with various dielectric constants at 10 GHz are investigated. The experimental dielectric constant values of the mixtures are compared to the theoretical curves of the five mixing rules. The dielectric constants of pure ceramics are then estimated by these mixing laws from the dielectric constants of composites of various filler concentrations. The theoretical errors of estimations of rules are derived and analyzed. The most adequate mixture law(s) for measuring the dielectric constants of ceramic fillers will be recommended. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2481–2485, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26357

Study on Properties of Epoxy Resins Modified by Nano-Silica

Organic precursor of EP/PU was prepared by epoxy resin which was polyurethane toughened, and then modified epoxy resin adhesive was synthesized using nano-silica as modifier. Microstructure of composite materials was observed by scanning electron microscopy (SEM), the results showed that the inorganic phase had good compatibility in polymer matrix, and polyurethane in epoxy resin have formed the "island structure". The mechanical properties, thermal stability and dielectric loss, dielectric constant of composites were investigated. The results indicated that doping of appropriate amount of nano-silica could improve mechanical property, shear strength and impact strength of 2wt% SiO2/EP-PU were increased 173% and 106.67%, than that of pre-doping of composite, respectively. Thermal decomposition temperature (Td) was increased, Tdof 2wt%SiO2/EP-PU was increased 8.1°C than that of pre-doped of material. Dielectric constant (ε) was as follows: was decreased with the increase of frequency, but increased with the increase of inorganic component, dielectric loss (tanδ) was increased with the increase of frequency and inorganic doping.

Thermal and dielectric properties of the aluminum particle reinforced linear low‐density polyethylene composites

AbstractThe possibility of obtaining relatively high thermal conductivity and dielectric constant but low dielectric loss polymeric composites by incorporating the core‐shell‐structured aluminum (Al) particles in a linear low‐density polyethylene (LLDPE) by melt mixing and hot pressing was demonstrated in this study. The morphology, thermal and dielectric properties of the composites were characterized using X‐ray diffractions, thermal analysis, scanning electron microscope, and dielectric analyzer. The Al particle decreases the degree of crystallinity and has no appreciable influence on the melting temperature of LLDPE. The thermal conductivity, dielectric constant and loss factor of the composites increase with an increase in Al content at all the frequencies (1 ∼ 106 Hz). The thermal conductivity and dielectric constant of the 70 wt% flaky Al particles filled LLDPE are 1.63 W/mK and 50, much higher than those of the spherical Al reinforced one. Moreover, the surface treatment of Al particles with γ‐Aminopropyltriethoxysilane silane coupler improves the thermal conductivity. The dielectric loss factors of the composites still remain at relatively low levels in the measured frequency range. Further, the dielectric permittivity frequency independence in the measured frequency range was observed due to the nanoscale‐Al‐oxide insulating shell of Al. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Study on Novel Carbon-Nanotube/Sulfonated Poly(Aryl Ether Ketone) Composites with High Dielectric Constant at Low Percolation Threshold

Nanocomposites of Sulfonated Poly(Aryl ether ketone) (SPAEK) and functional multiwall carbon nanotubes (a-MWNTs) were fabricated by a solution method. The results showed that the composites exhibited a higher dielectric constant that was near 600 when the volume fraction of carbon-nanotubes was 0.07 (7 vol%) at 103 Hz. The percolation threshold of the a-MWNTs/SPAEK composites was only 3 vol% of a-MWNTs, and the dielectric constant could reach 210. The dielectric constant of composites changed little with frequency increase when the content of carbon nanotubes was more than 3 vol%, and the composites could keep high dielectric constant at high-frequency (>200, at 106 Hz).

Towards industrial utilization of oil palm fibre: Physical and dielectric characterization of linear low density polyethylene composites and comparison with other fibre sources

The physical, chemical and thermal properties of oil palm fibre (OPF) were characterised and compared with flax and hemp fibres. The effect of fibre size, fibre loading and fibre treatment on physical and dielectric properties of compression-moulded OPF–LLDPE (linear low density polyethylene) composites was studied. Composite density and dielectric constant were predicted from the individual values of fibre and matrix using different models. Analysis of fibre morphology indicated that the OPF surface is porous and fibre is constituted of vessel elements. The true density of OPF is found to be 1503 kg m−3. The OPFs obtained from the field contained nearly 25% impurities, and it was found that the equilibrium moisture content of fibres nearly doubled with 25% increase in relative humidity. The dielectric constant of OPF was in the range of 7.76–8.31. Thermograms of OPF had two endothermic peaks and three exothermic peaks with the first degradation temperature at 301.71 °C. Alkali treatment reduced first degradation temperature to 297.1 °C. The specific heat capacity of OPF varied from 1.083 J g−1 oC−1 to 3.317 J g−1 °C−1 in the temperature range of 20 °C–150 °C. True density of OPF–LLDPE composites were in the range of 967–1177 kg m−3, whereas the bulk density ranged from 942 to 1122 kg m−3. The dielectric constant of the composite was in the range of 3.22–6.73. The L∗, a∗ and b∗ values of OPF–LLDPE composites were respectively in the range of 42.25–59.69, 5.85–6.30, 15.65–22.06. Predicted values of true density of composites were in good agreement with measured values.

New composites with high thermal conductivity and low dielectric constant for microelectronic packaging

AbstractThree composites based on cyanate (CE) resin, aluminum nitride (AlN), surface‐treated aluminum nitride [AlN(KH560)], and silicon dioxide (SiO2) for microelectronic packaging, coded as AlN/CE, AlN(KH560)‐SiO2(KH560)/CE, and AlN‐SiO2/CE composite, respectively, were developed for the first time. The thermal conductivity and dielectric constant of all composites were investigated in detail. Results show that properties of fillers in composites have great influence on the thermal conductivity and dielectric constant of composites. Surface treatment of fillers is beneficial to increase the thermal conductivity or reduce dielectric constant of the composites. Comparing with binary composite, when the filler content is high, ternary composites possess lower thermal conductivity and dielectric constant. The reasons leading to these outcomes are discussed intensively. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

THE EFFECT OF REDUCED GATE LEAKAGE ON IMPROVED RETENTION TIME OF METAL-FERROELECTRIC (PbZr0.53Ti0.47O3)-INSULATOR (ZrO2)-SEMICONDUCTOR CAPACITORS

ABSTRACT Al/ Pb (Zr0.53, Ti0.47) O3 (PZT) /ZrO2/Si metal-ferroelectric-insulator semiconductor (MFIS) capacitors were fabricated. The wafers were given a H2O2 pre-treatment before ZrO2 deposition and a HCl treatment after deposition. The interface states were reduced from 5.62 × 1013/cm2 to 4.0 × 1012/cm2 and the composite dielectric constant of ZrO2 film plus interfacial layer was increased from 5.54 to 7.3. The leakage current density was 5.4 × 10−6 A/cm2 at a sweep voltage of 5 V. The retention time of Al/PZT/ZrO2/Si capacitors after these surface treatments was increased from 13.3 hours to 17.1 days. The improved retention time is attributed to the reduced gate leakage current.

High dielectric constant polyaniline/poly(acrylic acid) composites prepared by in situ polymerization

An ultra-high dielectric constant composite of polyaniline, PANI–DBSA/PAA, was synthesized using in situ polymerization of aniline in an aqueous dispersion of poly-acrylic acid (PAA) in the presence of dodecylbenzene sulfonate (DBSA). The water-soluble PAA served as a polymeric stabilizer, protecting the PANI particles from macroscopic aggregation. A very high dielectric constant of ca. 2.0 × 10 5 (at 1 kHz) was obtained for the composite containing 30% PANI by weight. The influence of the PANI content on the morphological, dielectric and electrical properties of the composites was investigated. The frequency dependence of dielectric permittivity, dielectric loss, loss tangent and electric modulus were analyzed in the frequency range from 0.5 kHz to 10 MHz. SEM micrograph revealed that composites with high PANI content (i.e., 20 wt%) consisted of numerous nano-scale PANI particles that were evenly distributed within the PAA matrix. The high dielectric constants of these composites were attributed to the sum of the small capacitors of the PANI particles.

SIMULATION AND FABRICATION OF EMBEDDED CAPACITORS FOR ORGANIC-BASED RF SYSTEM ON PACKAGE APPLICATIONS

ABSTRACT Embedded capacitor technology is one of the effective packing technologies for small size, high reliability, high performance and low cost of electric packaging systems. In this paper, the embedded capacitors were simulated and fabricated in the 8-layered printed circuit board employing standard PCB processes for RF SOP (System on package) applications. Usually, to reduce the size of embedded capacitors, high dielectric constant composites materials were employed. The composites of barium titanante (BaTiO3) powder and epoxy resin were employed in the dielectric materials for embedded capacitor applications. Theoretical considerations regarding the embedded capacitors have been paid to understand the frequency dependent impedance behavior. Frequency dependent impedance of fabricated embedded capacitors was investigated. Parasitic inductance was developed mainly through via holes and it has almost same value for all capacitors. Frequency dependent capacitance values of fabricated embedded capacitors were well matched with those of simulated embedded capacitors. Temperature dependent capacitance and loss tangent of fabricated embedded capacitor were presented.

Low loss flexible SrTiO3/POE dielectric composites for microwave application

Flexible, high dielectric constant and low dielectric loss composites for microwave application fabricated with SrTiO3 (STO) ceramic filler dispersed inside a thermoplastic polyolefin elastomer (POE) polymer matrix have been studied in this paper. The dielectric property and the mechanical property of STO/POE composites filled with different volume fraction of ceramic filler were investigated. The results indicated that with the increase volume fraction of ceramic filler, both the permittivity and the dielectric loss of composites increased. Good frequency stability within a wide range was observed in all the samples. For the composites containing 40 vol% STO, the composites has a tensile strength of 2.75 MPa with an elongation of about 90% at break value. The permittivity and the dielectric loss of the composites were 11.0 and 0.01 in microwave frequency, respectively. A microstrip transmission line on the composites containing 40 vol% STO as a microwave substrate is designed and measured after bending at different angles, meanwhile the transmission coefficients of the microstrip transmission line were unchanged when bending angle is less than 60°. This indicates that the STO/POE composites have the promising characteristics for potential applications in microwave substrate, flexible dielectric waveguide and related flexible microwave devices.

Modeling and experimental verification of dielectric constants for three-dimensional woven composites

In order to determine the dielectric constants of 3D orthogonal woven single fiber type (SFT) and hybrid composites from their component dielectric properties, a theoretical model is proposed based on the rule of binary mixtures. The model shows that with the same fiber volume fraction, a component with a larger cross-sectional area perpendicular to the electric field has a greater contribution to the composite dielectric constant. For experimental verification, SFT basalt/epoxy and aramid (Kevlar 129)/epoxy as well as interply and intraply basalt/aramid/epoxy 3D orthogonal woven hybrid composites were fabricated and their dielectric properties were measured using the waveguide method at a frequency range of 8–12 GHz. At 10 GHz, the experimental results agreed well with the calculated results from the model for the SFT composites, while a positive hybrid effect on the dielectric constant was observed for the two hybrid composites.

PVDF‐PZT‐5H composites prepared by hot press and tape casting techniques

AbstractPiezoelectric polymer–ceramic composites are promising materials for transducer applications, and they are widely used in underwater hydrophones, biomedical imaging with ultrasound, and nondestructive testing applications. The critical factor in the 0–3 composite is to ensure homogeneous distribution of the filler in the matrix. To ensure this objective, PVDF‐PZT composite was prepared by two different routes: hot press and tape casting techniques. Loss on ignition and scanning electron microscopy studies were conducted to find out the uniformity of the composites prepared. It is found that hot press technique gives better uniformity compared to tape casting technique. PZT concentration was varied from 20 to 60 vol %. Physical and dielectric properties were studied. FT‐IR, DSC, and XRD characterization studies of PVDF were also recorded. Density of the composites was 2.74 to 5.13 g/cm3 as PZT concentration increased from 20 to 60 volume fractions. The dielectric constant of composites at 1 MHz varied from 16.74 to 98.48 as PZT concentration increased from 20 to 60 volume fractions. Hot press technique that combines solution and melt processing was found to be the better method for the preparation of 0–3 composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Effect of dehydroxylation of hydrothermal barium titanate on dielectric properties in polystyrene composite

AbstractIn today's world, technology for capacitors has grown significantly with its requirements in the direction of better dielectric properties. Developing an ideal composite material (polymer and ceramic) for satisfying the processing parameters is of great interest for capacitor industry. In this study, chemically treated barium titanate (BT) nanocrystals were prepared and used to make ceramic–polystyrene (PS) composites. A unique methodology was used in processing these materials. Effects of the chemically treated BT, filler loading, and frequency on the dielectric properties of these composites were examined, and compared with untreated BT–PS composites. Composite dielectric constant was proportional to the volume ratio of the BT filler and remained stable at different frequencies. The experimental data show that the dielectric constant of composites made with treated BT powders can attain values 2.5 times higher than that of untreated BT–PS composites. In addition, the composite shows consistency in dielectric constant values measured at different frequencies. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

Dielectric enhancement in polymer-nanoparticle composites through interphase polarizability

Dielectric measurements on polyimide-oxide nanoparticle composite thin films show a composite dielectric constant (εcomposite) that increased monotonically with increasing oxide content well above the value predicted by Maxwell’s rule for dielectric mixtures below the percolation threshold. Above certain volume fractions, the measured εcomposite values were found to exceed the corresponding nanoparticle ε such that εpolymer&amp;lt;εparticle&amp;lt;εcomposite contrasted to conventional composites where εpolymer&amp;lt;εcomposite&amp;lt;εparticle. The εcomposite was independent of frequency to 10MHz with dielectric loss of &amp;lt;0.005 throughout this range, indicating that the observed enhancement in ε does not originate from space-charge related contributions and hence should be due to dipolar contributions. The observed ε enhancement (εcomposite−εMaxwell) showed a correlation with the total surface area of the nanoparticles. The dielectric model of Vo and Shi [Microelectron. J. 33, 409 (2002), and references therein] showed that the enhanced dielectric behavior originates from significant interfacial nanoparticle-polymer interactions and the critical role of additional contributions to polarizability through specific physicochemical interactions within the interphase region. An interphase εint considerably higher than that of the nanoparticle and a high interface interaction constant of 3.24 for the nanocomposite suggest a strong interaction between the functional groups of the polymer and the nanoparticle surface. Although modeling suggests a maximum of ε∼65vol%, loss in micromechanical stability occurred above 20% due to incomplete polymer wetting films arising from the high nanoparticle surface areas.

Evaluation of the time-domain reflectometry (TDR)-measured composite dielectric constant of root-mixed soils for estimating soil-water content and root density

The effects of dense plant roots on the time-domain reflectometry (TDR)-measured composite dielectric constant, ε c, and soil-water content, θ TDR, were investigated by laboratory experiments with root-mixed sand and loam soil. TDR overestimates ε c in the root-mixed sand while it underestimates ε c in the root-mixed loam soil. The TDR-measured water contents, θ TDR, in these two root-mixed soils provide neither the actual soil-water content, θ (excluding volume occupied by the roots and water within the roots), nor the bulk soil-water content, θ b (neglecting water in the roots, but including the root-occupied volume in the bulk volume), or the bulk total water content, θ t (water in the soil plus that in the roots comprises the total water) (please see nomenclature for definitions). The effects of the roots on TDR measurement are more pronounced at low soil-water content than at high soil-water contents. A 4-phase dielectric mixture model, consisting of the volume fractions of the soil minerals, roots, water, and air, describes the composite dielectric constant ε c well. The dielectric mixture model can estimate the actual soil-water content θ and the root density, v r (volume fraction), from ε c. This model also estimates the dielectric constant of the soil minerals, ε s, and the root density v r simultaneously provided that the bulk soil-water content is known. The exponent of the dielectric mixture model, α, and the root density are moderately sensitive to the dielectric constant of the soil minerals. An accurate estimate of ε s is therefore preferred for evaluating the composite dielectric constant in the root-mixed soils. The root density is relatively insensitive to α. The dielectric mixture model also accurately estimates the root density and bulk soil-water content simultaneously. The actual water content, θ, in the root-mixed soil is calculated by [ θ=( θ b/(1− v r))].

Dielectric properties of three ceramic/epoxy composites

Three ceramic/epoxy composites were under investigation. The ceramic fillers include self-synthesized BaTiO 3 and commercial BaTiO 3 and Pb(Mg 1/3Nb 2/3)O 3. Effects of the filler ratio and testing temperature and frequency on the dielectric properties of these three composites were discussed. The self-synthesized BaTiO 3/epoxy composite had the best dielectric property. Its 40%-filler composite had a dielectric constant of 44, which was higher than those of 27 and 24 for the commercial BaTiO 3 and Pb(Mg 1/3Nb 2/3)O 3 composites, respectively. The large ceramic aggregates formed in epoxy are the reason for the self-synthesized BaTiO 3/epoxy composite having a higher dielectric constant of 44. Composite dielectric constant was proportional to the volume ratio of the ceramic filler and remained constant at different test temperatures and frequencies. For the BaTiO 3/epoxy composites, the fabrication process of slurry-casting or screen-printing can have an effect on their porosity. The composites with a low porosity lead to a low dielectric loss tangent.