Dielectric percolative composites with high dielectric constant and low dielectric loss based on sulfonated poly(aryl ether ketone) and a-MWCNTs coated with polyaniline

Acidified multi-walled carbon nanotubes (a-MWCNTs) coated with polyaniline (PANI) (a-MWCNTs@PANI) nanofiller were prepared by in situ polymerization. Novel dielectric percolative composites, sulfonated poly(aryl ether ketone) (SPAEK)/a-MWCNTs@PANI, with high dielectric constant and low dielectric loss were fabricated using simple solution blending technique. A SPAEK/a-MWCNTs@PANI composite prepared in this fashion exhibited a high dielectric constant above 800, a dielectric loss tangent less than 1.1 at 10 kHz and room temperature. The morphological study of composites by SEM suggested that the in situ polymerization method of preparing a-MWCNTs@PANI nanofillers was useful to achieve good dispersion of fillers in SPAEK matrix.

A unique strategy towards high dielectric constant and low loss with multiwall carbon nanotubes anchored onto graphene oxide sheets

Multiwall carbon nanotubes (MWNTs) were anchored onto graphene oxide sheets (GOs) via diazonium and C-C coupling reactions and characterized by spectroscopic and electron microscopic techniques. The thus synthesized MWNT-GO hybrid was then melt mixed with 50/50 polyamide6-maleic anhydride-modified acrylonitrile-butadiene-styrene (PA6-mABS) blend to design materials with high dielectric constant (30) and low dielectric loss. The phase morphology was studied by SEM and it was observed that the MWNT-GO hybrid was selectively localized in the PA6 phase of the blend. The 30 scales with the concentration of MWNT-GO in the blends, which interestingly showed a very low dielectric loss (< 0.2) making them potential candidate for capacitors. In addition, the dynamic storage modulus scales with the fraction of MWNT-GO in the blends, demonstrating their reinforcing capability as well.

Characterization of low dielectric constant polyaniline thin film synthesized by ac plasma polymerization technique

Polyaniline thin films were prepared by ac plasma polymerization technique. Capacitance, dielectric loss, dielectric constant and ac conductivity of these films were investigated in the frequency range from 100 Hz to 1MHz and in the temperature range from 300 to 373 K. Capacitance and dielectric loss decreased with frequency and increased with temperature. This type of behaviour was found to be in good agreement with an existing model. The ac conductivity σ(ω) was found to vary as ωs with the index s 1. Annealing of polyaniline thin films in high vacuum at 373K for 1 h was found to reduce the dielectric loss. FTIR studies reveal that the aromatic ring is retained in the polyaniline thin films, which enhances the thermal stability of the polymer films

Dielectric loss and phase transition of sodium potassium niobate ceramic investigated by impedance spectroscopy

The dielectric permittivity of Na0.80K0.20NbO3 ceramic was investigated by impedance spectroscopy. The dielectric characterization was performed from room temperature to 800 degreesC, in the frequency range 5 Hz-13 MHz. The bulk permittivity was derived by the variation of the imaginary part of the impedance as a function of reciprocal angular frequency. The permittivity values as a function of temperature showed two maxima. The first maximum is very similar at 200degreesC and the second one positioned at around 400degreesC, which was associated to Curie's temperature. The evolution of the complex permittivity as a function of frequency and temperature was investigated. At low frequency dispersion was investigated in terms of dielectric loss. The Na0.80K0.20NbO3 showed a dissipation factor between 5 and 40 over a frequency range from 1 to 10(2) kHz. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Low fat loss response after medium-term supervised exercise in obese is associated with exercise-induced increase in food reward

Objective: To examine exercise-induced changes in the reward value of food during medium-term supervised exercise in obese individuals. ---------- Subjects/Methods: The study was a 12-week supervised exercise intervention prescribed to expend 500 kcal/day, 5 d/week. 34 sedentary obese males and females were identified as responders (R) or non-responders (NR) to the intervention according to changes in body composition relative to measured energy expended during exercise. Food reward (ratings of liking and wanting, and relative preference by forced choice pairs) for an array of food images was assessed before and after an acute exercise bout. ---------- Results. 20 responders and 14 non-responders were identified. R lost 5.2 kg±2.4 of total fat mass and NR lost 1.7 kg±1.4. After acute exercise, liking for all foods increased in NR compared to no change in R. Furthermore, NR showed an increase in wanting and relative preference for high-fat sweet foods. These differences were independent of 12-weeks regular exercise and weight loss. ---------- Conclusion. Individuals who showed an immediate post-exercise increase in liking and increased wanting and preference for high-fat sweet foods displayed a smaller reduction in fat mass with exercise. For some individuals, exercise increases the reward value of food and diminishes the impact of exercise on fat loss.

An investigation of structural, magnetic and dielectric properties of R2NiMnO6 (R = rare earth, Y)

We have investigated the structure, magnetic and dielectric properties of the double perovskite oxides, R2NiMnO6 (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho and Y). We could refine powder X-ray diffraction patterns of all the phases on the basis of monoclinic (P2(1)/n) double perovskite structure where Ni and Mn atoms are ordered at 2c and 2d sites, respectively. All the phases are ferromagnetic insulators exhibiting relatively low dielectric loss and dielectric constants in the range 15-25. The ferromagnetic ordering temperature of the R2NiMnO6 series seems to correlate better with the radius of R3+ atoms than with the average Ni-O-Mn angle (phi) in the double perovskite structure. These results are consistent with all samples having Mn4+ and Ni2+ With minimal antisite disorder.

Dielectric Studies of laser ablated Ca doped BaTiO3 thin films

Recently, there has been growing interest in Ca modified BaTiO3 structures due to their larger electro-optic coefficients for their use in optical storage of information over conventional BaTiO3 crystals. Barium Calcium Titanate (BCT) shows promising applications in advanced laser systems, optical interconnects and optical storage devices. BaTiO3 thin films of varied Ca (3 at. % - 15 at. %) doping were deposited using pulsed laser ablation (KrF excimer laser) technique over Pt/Si substrates. The stoichiometric and the compositional analysis were carried out using EDAX and SIMS. The dielectric studies were done at the frequency regime of 40 Hz to 100 kHz at different ambient temperatures from 200 K to 600 K. The BCT thin films exhibited diffuse phase transition, which was of a typical non lead relaxor behavior and had high dielectric constant and low dielectric loss. The phase transition for the different compositions of BCT thin films was near the room temperature, showing a marked departure from the bulk phase transition. The C - V and the hysteresis behavior confirmed the ferroelectric nature below the phase transition and paraelectric at the room temperature.

Effect of Pb Volatilization on Dielectric Properties of 0.77PbMg1/3(Nb0.9Ta0.1)2/3O3-0.23PbTiO3

Lead magnesium niobate-lead titanate (PMN-PT) is an intriguing candidate for applications in many electronic devices such as multi-layer capacitors, electro-mechanical transducers etc. because of its high dielectric constant, low dielectric loss and high strain near the Curie temperature. As an extension of our previous work on Ta-doped PMNT-PT aimed at optimizing the performance and reducing the cost, this paper focuses on the effect of Pb volatilization on the dielectric properties of 0.77Pb(Mg1/3(Nb0.9Ta0.1)2/3)O3-0.23PbTiO3. The dielectric constant and loss of the samples are measured at different frequencies and different temperatures. The phase purity of this compound is determined by X-ray diffraction pattern. It is found that the volatilization during sintering does influence the phase formation and dielectric properties. The best condition is sintering with 0.5 g extra PbO around a 4 g PMNT-PT sample.

Rearrangeable nonblocking SOI waveguide thermooptic 4x4 switch matrix with low insertion loss and fast response

A rearrangeable nonblocking 4 x 4 thermooptic silicon-on-insulator waveguide switch matrix at 1.55-mu m integrated spot size converters is designed and fabricated for the first time. The insertion losses and polarization-dependent losses of the four channels are less than 10 and 0.8 dB, respectively. The extinction ratios are larger than 20 dB. The response times are 4.6 mu s for rising edge and 1.9 mu s for failing edge.

A silicon-on-insulator-based thermo-optic waveguide switch with low insertion loss and fast response

A silicon-on-insulator-based thermo-optic waveguide switch integrated with spot size converters is designed and fabricated by inductively coupled plasma reactive ion etching. The device shows good characteristics, including low, insertion loss of 8 +/- 1 dB for wavelength 1530-1580 nm and fast response times of 4.6 As for rising edge and 1.9 mu s for failing edge. The extinction ratios of the two channels are 19.1 and 18 dB, respectively.

Design and Fabrication of Low-microwave loss Coplannar Waveguide and precise V groove on Silicon Substrate for Optoelectronic Packaging - art. no. 601938

Optoelectronic packaging has become a most important factor that influences the final performance and cost of the module. In this paper, low microwave loss coplanar waveguide(CPW) on high resistivity silicon(HRS) and precise V groove in silicon substrate were successfully fabricated. The microwave attenuation of the CPW made on HRS with the simple process is lower than 2 dB/cm in the frequency range of 0 similar to 26GHz, and V groove has the accuracy in micro level and smooth surface. These two techniques built a good foundation for high frequency packaging and passive coupling of the optoelectronic devices. Based on these two techniques, a simple high resistivity silicon substrate that integrated V groove and CPW for flip-chip packaging of lasers was completed. It set a good example for more complicate optoelectronic packaging.

Low-Microwave Loss Coplanar Waveguides Fabricated on High-Resistivity Silicon Substrate

Three kinds of coplanar waveguides （CPWs） are designed and fabricated on different silicon substrates---common low-resistivity silicon substrate （LRS）, LRS with a 3μm-thick silicon oxide interlayer, and high-resistivity silicon （HRS） substrate. The results show that the microwave loss of a CPW on LRS is too high to be used, but it can be greatly reduced by adding a thick interlayer of silicon oxide between the CPW transmission lines and the LRS.A CPW directly on HRS shows a loss lower than 2dB/cm in the range of 0-26GHz and the process is simple,so HRS is a more suitable CPW substrate.

Design of Topas photonic bandgap fiber with high birefringence and low confinement loss

A highly birefringent hollow-core photonic bandgap fiber based on Topas cyclic olefin copolymer is designed. The rhombic hollow-core with rounded corners is formed by omitting four central air holes of the cladding structure. The guided modes, birefringence and confinement loss of the fiber are investigated by using the full-vector finite element method. A high phase birefringence of the order of 10(-3), a group birefringence of the order of 10(-2) and confinement loss less than 0.1 dB/km are obtained at the central wavelength (1.55 mu m) range of the bandgap for fiber with seven rings of air holes in the cladding region. (C) 2010 Elsevier B.V. All rights reserved.