Showing papers on "Dielectric loss published in 2008"
TL;DR: In this paper, the dielectric properties of epoxy nanocomposites with insulating nano-fillers, viz., TiO2, ZnO and AI2O3 were investigated at low filler concentrations by weight.
Abstract: The dielectric properties of epoxy nanocomposites with insulating nano-fillers, viz., TiO2, ZnO and AI2O3 were investigated at low filler concentrations by weight. Epoxy nanocomposite samples with a good dispersion of nanoparticles in the epoxy matrix were prepared and experiments were performed to measure the dielectric permittivity and tan delta (400 Hz-1 MHz), dc volume resistivity and ac dielectric strength. At very low nanoparticle loadings, results demonstrate some interesting dielectric behaviors for nanocomposites and some of the electrical properties are found to be unique and advantageous for use in several existing and potential electrical systems. The nanocomposite dielectric properties are analyzed in detail with respect to different experimental parameters like frequency (for permittivity/tan delta), filler size, filler concentration and filler permittivity. In addition, epoxy microcomposites for the same systems were synthesized and their dielectric properties were compared to the results already obtained for nanocomposites. The interesting dielectric characteristics for epoxy based nanodielectric systems are attributed to the large volume fraction of interfaces in the bulk of the material and the ensuing interactions between the charged nanoparticle surface and the epoxy chains.
566 citations
TL;DR: In this article, the authors present the loss tangents of some common amorphous and crystalline dielectrics, measured at low temperatures (T < 100mK) with near single-photon excitation energies, using both coplanar waveguide and lumped LC resonators.
Abstract: The microwave performance of amorphous dielectric materials at very low temperatures and very low excitation strengths displays significant excess loss. Here, we present the loss tangents of some common amorphous and crystalline dielectrics, measured at low temperatures (T<100mK) with near single-photon excitation energies, E∕ℏω0∼1, using both coplanar waveguide and lumped LC resonators. The loss can be understood using a two-level state defect model. A circuit analysis of the half-wavelength resonators we used is outlined, and the energy dissipation of such a resonator on a multilayered dielectric substrate is theoretically considered.
329 citations
TL;DR: In this paper, the effect of porous structure on microwave absorption property of the carbon/Co nanocomposite was also discussed and the maximum reflection loss of the porous C(Co) nanocompositionite can reach 40dB at 4.2GHz with 5mm in thickness and the primary microwave absorptive mechanism is ascribed to the dielectric loss.
Abstract: Porous carbon/Co nanocomposites were fabricated by a sol-gel method. The electromagnetic parameters were measured in the 2–18GHz range. Compared with porous carbon composite, porous carbon/Co nanocomposite has larger dielectric loss due to the enhanced interfacial polarization relaxation loss and Ohmic loss. The maximum reflection loss of the porous C(Co) nanocomposite can reach 40dB at 4.2GHz with 5mm in thickness and the primary microwave absorptive mechanism is ascribed to the dielectric loss. The effect of porous structure on microwave absorption property of the carbon/Co nanocomposite was also discussed.
327 citations
TL;DR: In this paper, the microstructure of core/shell (metal/metal oxide) in nanoparticle formed after in situ passivation process was measured in the frequency range of 2-18 GHz.
267 citations
TL;DR: In this paper, a dielectric loss spectra showed the presence of one relaxation for all compositions, which is associated with the motions of the Li ion coordinated polymer segments, and the relaxation has been characterized by the empirical Havriliak-Negami (H-N) equation.
250 citations
TL;DR: In this paper, the magnetic and electrical properties of hexaferrite nanoparticles were investigated using the chemical co-precipitation method, where five samples were synthesized by the Chemical Co-PrecIP method.
212 citations
TL;DR: In this article, a conducting polymer nanocomposites of polyphenyl amine with barium ferrite nanoparticles (50-70nm) was synthesized via emulsion polymerization and the complex permittivity, permeability and microwave absorption properties of the composite were studied in the 12.4-18GHz (Ku band) frequency range.
Abstract: Conducting polymer nanocomposites of polyphenyl amine with barium ferrite nanoparticles (50–70nm) have been synthesized via emulsion polymerization. The complex permittivity, permeability, and microwave absorption properties of the composite were studied in the 12.4–18GHz (Ku band) frequency range. The composite has shown high shielding effectiveness due to absorption (SEA) of 28.9dB (∼99.9%), which strongly depends on dielectric loss, magnetic permeability, and volume fraction of barium ferrite nanoparticles. The high value of SEA suggests that these composites can be used as a promising radar absorbing materials.
180 citations
TL;DR: In this article, the authors measured real and imaginary dielectric parameters of manganese ferrite in the frequency range of 100 kHz-8 MHz at different temperatures. And they found that the dispersion and roadening properties of the vanishes of the dielectrics suggest the possibility of a distribution of relaxation time and the existence of multiple equilibrium states in manganized ferrite.
Abstract: Nanoparticles of manganese ferrite were prepared by the chemical co-precipitation technique. The dielectric parameters, namely, real and imaginary dielectric permittivity ($\varepsilon'$ and $\varepsilon"$), ac conductivity $(\sigma_{ac})$ and dielectric loss tangent $(tan \delta)$, were measured in the frequency range of 100 kHz–8 MHz at different temperatures. The variations of dielectric dispersion $(\varepsilon')$ and dielectric absorption $(\varepsilon")$ with frequency and temperature were also investigated. The variation of dielectric permittivity with frequency and temperature followed the Maxwell–Wagner model based on interfacial polarization in consonance with Koops phenomenological theory. The dielectric loss tangent and hence $\varepsilon"$ exhibited a relaxation at certain frequencies and at relatively higher temperatures. The dispersion of dielectric permittivity and roadening of the dielectric absorption suggest the possibility of a distribution of relaxation time and the existence of multiple equilibrium states in manganese ferrite. The activation energy estimated from the dielectric relaxation is found to be high and is characteristic of polaron conduction in the nanosized manganese ferrite. The ac conductivity followed a power law dependence $\sigma_{ac} = B\omega^n$ typical of charge transport assisted by a hopping or tunnelling process. The observed minimum in the temperature dependence of the frequency exponent n strongly suggests that tunnelling of the large polarons is the dominant transport process.
169 citations
TL;DR: In this paper, the authors report the trends of dielectric permittivities and tan delta (loss tangent) of epoxy nanocomposites with single nano-fillers of Al2O3 and TiO2 at low filler concentrations over a frequency range of 1 MHz-1 GHz.
Abstract: To achieve a compact and reliable design of electrical equipment for the present day requirements, there is an urgent need for better and smart insulating materials and in this respect, the reported enhancements in dielectric properties obtained for polymer nanocomposites seems to be very encouraging. To further understand the dielectric behavior of polymer nanocomposites, this experimental work reports the trends of dielectric permittivities and tan delta (loss tangent) of epoxy nanocomposites with single nano-fillers of Al2O3 and TiO2at low filler concentrations (0.1%, 0.5%, 1% & 5%) over a frequency range of 1 MHz-1 GHz. Results show that the nanocomposites demonstrate some very different dielectric characteristics when compared to those for polymer microcomposites. Unlike the usual expectations of increasing permittivity with increasing filler concentration in polymer microcomposites, it has been seen that up to a certain nano-filler concentration and depending on the permittivity of the nano-filler, the permittivities of the epoxy nanocomposites are less than that of the unfilled epoxy at all the measured frequencies. This suggests that there is a very strong dependence of the filler concentration and nano-filler permittivity on the final permittivity of the nanocomposites at all these frequencies. But, in the case of tan delta behavior in nanocomposites, significant effects of filler concentrations were not observed with both Al2O3 and TiO2 fillers. Tan delta values in nanocomposites with Al2O3 fillers are found to be marginally lower at all filler concentrations when compared with the value for unfilled epoxy. But, in TiO2Oepoxy nanocomposites, although the variations in tan delta are not significant with respect to unfilled epoxy, some interesting trends are observed with respect to the frequencies of measurement.
163 citations
TL;DR: In this article, the authors present the modeling of lossy substrate integrated waveguide interconnects and components by using the boundary integral-resonant mode expansion method, which is extended to account for conductor, dielectric and radiation losses.
Abstract: This paper presents the modeling of lossy substrate integrated waveguide interconnects and components by using the boundary integral-resonant mode expansion method. The extension of the numerical technique to account for conductor, dielectric and radiation losses is discussed. Moreover, a systematic investigation of the different contributions of loss and their dependence on some geometrical parameters is performed in the case of interconnects and components, aiming at minimizing the losses. The physical explanation of the different effects is also provided. Finally, the validity of the equivalent waveguide concept is extended to the case of lossy interconnects and components.
157 citations
TL;DR: In this paper, spherical alumina (Al2O3) nanoparticles were incorporated into diglycidyl ether of bisphenol A (DGEBA) epoxy resin.
Abstract: Spherical alumina (Al2O3) nanoparticles were incorporated into diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The objective of this study is to investigate the effect of water absorption on the mechanical and dielectric properties of the Al2O3/epoxy nanocomposites. The results from tensile tests indicate that the incorporation of the Al2O3 nanoparticles into the epoxy can improve the stiffness of the matrix. DMA results show that the stiffness improvement is more pronounced at the rubbery state of the matrix. The Al2O3 nanoparticles can increase the dielectric constant of the epoxy resin due to the increase in the total interfacial area. Upon water absorption, the mechanical properties of the Al2O3/epoxy nanocomposites decrease evidently, because of the damage of water on the epoxy resin. However, the ductility can be improved by the water absorption process. In addition, both dielectric constant and dielectric loss of the Al2O3/epoxy nanocomposites increases greatly after water absorption treatment.
TL;DR: A wide variety of high dielectric constant (k) composite materials which have been developed and evaluated for embedded capacitor application are reviewed in this paper, where new insights into the effect of unique properties of the nanoparticle filler, filler modification and the dispersion between filler and polymer matrix on the dielectrics of the nanocomposites are discussed in details.
Abstract: In this paper, a wide variety of high dielectric constant (k) composite materials which have been developed and evaluated for embedded capacitor application are reviewed. Current research efforts toward achieving high dielectric performance including high-k and low dielectric loss for polymer composites are presented. New insights into the effect of unique properties of the nanoparticle filler, filler modification and the dispersion between filler and polymer matrix on the dielectric properties of the nanocomposites are discussed in details.
TL;DR: In this article, the dielectric properties and conductivity of carbon nanofibers (CNF)/semi-crystalline polymer nanocomposites are studied.
TL;DR: In this paper, the dielectric properties of the CdS∕α-Fe2O3 heterostructure nanocomposites have been investigated and the equivalent circuit model of the same structure was established, which reasonably explained the nonlinear resonance behavior.
Abstract: CdS∕α-Fe2O3 heterostructures, where the CdS nanorods grow irregularly on the side surface of α-Fe2O3 nanorods, were synthesized via a three-step process The dielectric properties of the CdS∕α-Fe2O3 heterostructure nanocomposites have been investigated The equivalent circuit model of the CdS∕α-Fe2O3 heterostructures was established, which reasonably explained the nonlinear dielectric resonant behavior of the CdS∕α-Fe2O3 heterostructure nanocomposites in the range of 5–15GHz The high dielectric loss is mainly attributed to the conductance loss and the dipole relaxation loss in the CdS∕α-Fe2O3 heterostructures
TL;DR: In this article, the dielectric behavior of polyvinylidene fluoride (PVDF), nanocrystalline nickel (nc-Ni) composites has been investigated over a broad frequency range of 40Hz-10MHz.
Abstract: The dielectric behavior of polyvinylidene fluoride (PVDF), nanocrystalline nickel (nc-Ni) composites has been investigated over a broad frequency range of 40Hz–10MHz. High effective dielectric constant (eeff=2050) and low loss (tanδ=10) at 100Hz have been observed near the percolation threshold. To the best of our knowledge, this is the highest eeff value reported to date among the PVDF based metal-polymer composites. The dielectric properties have been explained by using boundary layer capacitor effect and percolation theory while the dielectric anomalies are attributed to process of fabrication leading to thick insulating layer between the filler particles forming a gap in effective tunneling range of two filler particles and also making a difficulty in probability of higher order tunneling.
TL;DR: In this paper, the physical, magnetic and dielectric properties of Cu-substituted Mg-Zn ferrites having the general formula of Mg0.55−xCuxZn0.45O(Fe2O3)0.97 prepared by standard double sintering ceramic technique were studied.
Abstract: We report remarkable multiferroic effects in polycrystalline Bi2Fe4O9. High-resolution x-ray diffraction shows that this compound has orthorhombic structure. Magnetic measurements confirm an antiferromagnetic transition around 260K. A pronounced inverse S-shape anomaly in the loss tangent of dielectric measurement is observed near the Neel temperature. This feature shifts with the application of magnetic field. These anomalies are indicative of substantial coupling between the electric and magnetic orders in this compound.
TL;DR: In this article, two-dimensional multilayer and three-dimensional random powders were designed for high frequency applications using Spark Plasminer Sintering (SPS) to obtain highly densified ferroelectric-dielectric ceramic composites.
Abstract: Spark plasma sintering (SPS) is an efficient tool to obtain highly densified ferroelectric-dielectric ceramic composites with clean interfaces and tunable properties. Dielectric MgO and ferroelectric Ba0.6Sr0.4TiO3 (BST) were combined in two-dimensional multilayer and three-dimensional random powders design. Their unmodified BST Curie temperature proves the suppression of interdiffusion while dielectric losses are below 0.5% and the tunability is 40% at room temperature. The composites and pure BST with similar densities (>95%) were obtained, owing reliable comparison of their dielectric properties. Such SPS ceramics can be used as experimental input for simulation and are potential candidates for high frequency applications.
TL;DR: In this paper, the effect of acceptor doping on the dielectric and piezoelectric properties of MnO2-based polycrystalline materials was investigated.
Abstract: The effect of MnO2 addition on the dielectric and piezoelectric properties of 0.4Pb(Mg1∕3Nb2∕3)O3–0.25PbZrO3–0.35PbTiO3 single crystals was investigated. Analogous to acceptor doping in “hard” Pb(Zr,Ti)O3 based polycrystalline materials, the Mn doped crystals exhibited enhanced mechanical Q (∼1050) with low dielectric loss (∼0.2%), while maintaining ultrahigh electromechanical coupling k33>90%, inherent in domain engineered single crystals. The effect of acceptor doping was also evident in the build-up of an internal bias (Ei∼1.6kV∕cm), shown by a horizontal offset in the polarization-field behavior. Together with the relatively high usage temperature (TR-T∼140°C), the Mn doped crystals are promising candidates for high power and broad bandwidth transducers.
TL;DR: Gd-doped BiFeO 3 polycrystalline ceramics were synthesized by solid-state reaction method and their dielectric and magnetic properties were investigated as discussed by the authors.
TL;DR: In this article, the dielectric properties of compressed chickpea flour samples were determined using an open-ended coaxial-line probe with an impedance analyzer over the frequency range from 10 to 1800 MHz, moisture contents from 7.9% to 20% w.b., and temperatures from 20 to 90°C.
TL;DR: In this paper, a three-phase composite with multiwall carbon nanotube (MWNT) and BaTiO3 particles embedded into polyvinylidene fluoride (PVDF) was prepared.
Abstract: A three-phase composite with multiwall carbon nanotube (MWNT) and BaTiO3 particles embedded into polyvinylidene fluoride (PVDF) was prepared. The uniform dispersion of fillers was realized, and the dielectric constant was as high as 151 at 102Hz when the volume fraction of MWNT and BaTiO3 were 0.01 and 0.15, respectively. The BaTiO3-MWNT/PVDF composite with high dielectric constant displayed relatively low dielectric loss and good flexibility due to the low concentrations of MWNT and BaTiO3. The results can be explained by the space charge polarization at the interfaces between the conductor and the insulator and the evolutions of conductive pathway and microcapacitance structure.
TL;DR: In this article, it was observed that the energy loss remains very small under low and medium electric fields but dramatically increases at high field which is believed to be due to tunneling current.
Abstract: In several low loss dielectric materials, it was observed that the energy loss remains very small under low and medium electric fields but dramatically increases at high field which is believed to be due to tunneling current. The increase of tunneling current at high field is due to the decrease of barrier width and height and is a universal phenomenon in all dielectric materials. Due to the requirement of high energy efficiency, high field conduction places a limit for the maximum operation field, which could be lower than the breakdown field and act as the limiting factor of energy density.
TL;DR: Capacitive humidity sensors were fabricated using countersunk interdigitated electrodes coated with amorphous nanostructured TiO2, SiO2 and Al2O3 thin films grown by glancing angle deposition.
Abstract: Capacitive humidity sensors were fabricated using countersunk interdigitated electrodes coated with amorphous nanostructured TiO2, SiO2, and Al2O3 thin films grown by glancing angle deposition. The capacitive response and response times for each sensor were measured. The sensor utilizing TiO2 exhibited the largest change in capacitance, increasing exponentially from ~ 1 nF to ~ 1muF for an increase in relative humidity from 2% to 92%. Adsorption and desorption response times were measured using flow rates of 2.5 l/min and were between 90 ms and 300 ms for the sensors studied here. A simple model of the capacitive response of the devices has been developed and used to calculate the dielectric constant of the combined system of our films and adsorbed water. The obtained dielectric constants are found to be much higher than bulk or literature values for similar systems.
TL;DR: In this paper, lead-free piezoelectric ceramics derived from the solid solution of (1−x)(Na05Bi05)TiO3-xBiAlO3 (NBT-BA) have been synthesized by solid state reactions.
Abstract: Lead-free piezoelectric ceramics derived from the solid solution of (1−x)(Na05Bi05)TiO3–xBiAlO3 (NBT-BA) (x=0–010) have been synthesized by solid state reactions A pure perovskite phase was formed for x≤008 The temperature dependence of dielectric constant indicates an increased broadness of the dielectric peak as the amount of BA increases The large dielectric loss of NBT ceramics at low frequency and high temperature has been significantly reduced by the substitution of BA The high coercive field is decreased and ferroelectric hysteresis loops were displayed at room temperature The NBT-BA ceramics exhibit improved ferroelectric and piezoelectric properties compared to pure NBT ceramics, with Pr=52 μC/cm2, Ec=44 kV/cm, d33=130 pC/N, and kp=023 for 092NBT–008BA
TL;DR: 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) as discussed by the authors.
TL;DR: In this article, the preparation and characterization of SrTiO3 filled PEEK composite for microwave substrate applications is discussed, and the effect of particle size on the dielectric as well as mechanical properties of the composite system is also studied by incorporating micronsize and nanosize fillers.
TL;DR: In this article, six glasses with different molar ratios of CaO/B2O3/SiO2 (designed as CBS-3, CBS-5 and CBS-6) were prepared and pulverized, and they were sintered at different temperatures to reach maximum densification.
TL;DR: In this paper, a silver (Ag)-polymer nanocomposite has been developed by in-situ formation of metal nanoparticles within the polymer matrix and utilized as a high-dielectric constant (k) polymer matrix to enhance the dielectric properties of high-k composite materials.
Abstract: A silver (Ag)-polymer nanocomposite has been developed by in-situ formation of metal nanoparticles within the polymer matrix and utilized as a high-dielectric constant (k) polymer matrix to enhance the dielectric properties of high-k composite materials. By using an in-situ photochemical reduction method, uniformly dispersed Ag nanoparticles of size of around 10 nm were generated in polymer matrices. Self-passivated aluminium (Al) particles were incorporated into this Ag-epoxy matrix and the dielectric properties of the as-prepared composite materials were investigated. The composites showed more than 50% increase in k values as compared with an Al/neat epoxy composite with the same filler loading of Al. The dielectric loss tangent of the Al/Ag-epoxy composites was below 0.1, which meets the requirement for embedded decoupling capacitors. These results suggest that the Ag-epoxy high-kpolymer matrix effectively enhances the dielectric constant while maintaining the low dielectric loss of the high-k composites. In addition, detailed dielectric property measurements revealed that the dielectric properties and their frequency dispersion as well as the breakdown behaviors of the Al/Ag-epoxy composites were related to the incorporation and concentration of Ag nanoparticles in the high-kpolymer matrix.
TL;DR: In this article, the substitution of the aliovalent dopant Cr2O3 on the Ti site was investigated in terms of the effects on the dielectric properties at doping levels ranging from 0.1 to 1.0%.