Decrease In Permittivity Research Articles

Study of the Complex Permittivity of a Polyurethane Matrix Modified by Nanoparticles

This study presents the influence of various types of nanoparticle (NP) fillers incorporated into a polyurethane (PU) (VUKOL 022) matrix and its subsequent changes in complex permittivity. Two types of surface modification of SiO2 fillers were investigated. The frequency dependence of the real and imaginary parts of complex permittivity was measured within the frequency range of 1 mHz to 1 MHz using the capacitance method. The 1 wt.% NPs in PU caused an increase (MgO, TiO2, n-SiO2, and f-SiO2) or a decrease (d-SiO2) in the real permittivity. The $\alpha $ -relaxation and intermediate dipolar effect were observed at the temperature dependence of the imaginary permittivity. The change in permittivity by various surface modifications of SiO2 and other nanofillers was discussed based on the multi-core model. Moreover, the NPs caused a shift in the local maximum of the permittivity, which was a result of the interfacial polarisation and a charge multiplication of the $\alpha $ -relaxation process.

Application of superheated water as a soil remediation media: a review

Water is a unique solvent cause its highly hydrogen-bonded structure, and at room temperature it has a high boiling point for its mass, a high dielectric constant and high polarity. At the higher temperatures, its permittivity, viscosity and surface tension decreases, but diffusion rate increases. Superheated water is a general term to denote the region of the condensed phase between 100°C and the critical point. Liquid water at elevated temperatures above its boiling point has been used for many years as an industrial solvent and cleaning agent in applications ranging from enhancing the extraction of oil shale, the extraction of sulphur from ore bodies in the Frasch process, to degreasing. In recent years, there has been an interest in using superheated water for soil remediation. In this paper, a review on this area of application has been performed.

TRIGLYCINE SULPHATE DYNAMICS OF DOMAINS IN RELATION WITH TEMPERATURE AND BIAS FIELD

Triglycine sulphate crystal (TGS) is a hybrid organic-inorganic ferroelectric crystal with a large electronic band-gap, transparent in visible spectra. It has large applications in electronics, as thermal IR detector. Pure and doped TGS crystals of 3-5 cm linear dimensions were grown at constant temperature in the paraelectric phase (52 oC), by slow solvent evaporation. Pure TGS samples show non-reproducible values of permittivity and losses in the ferroelectric phase after the “excursion” in the paraelectric phase. Walking up and down the crystal temperature, using a special program, the permitivity and losses were automatically recorded and analyzed. There is a continuous decrease of permittivity towards an equilibrium value during a long period of time. Previous AFM measurements from the literature have revealed peculiar aspects of domain dynamics. The relaxation process of permittivity was considered according to the equation er = A - B exp(-t/t). However, surprisingly, there is not a unique relaxation time t. For the first 500 sec (or so), the relaxation time is t » 7 minutes, while between the next time decades 1.000 - 10.000 - 100.000 sec, it is approximately 1 hour and 8 h respectively. The process is related with the ferroelectric domain’s dynamics, which are more or less strongly pined by dislocations or some other lattice defects.

Pressure effects on the metallization and dielectric properties of GaP.

In situ impedance measurement, resistivity measurements and first-principles calculations have been performed to investigate the effect of high pressure (up to 30.2 GPa) on the metallization and dielectric properties of GaP. It is found that the carrier transport process changes from mixed grain and grain boundary conduction to pure grain conduction at 5.8 GPa, and due to pressure-induced structural phase transition, the resistance drops drastically by three orders of magnitude at 25.5 GPa. Temperature dependence of resistivity measurements and band structure calculations suggest the occurrence of a semiconductor-metal transition. Combining differential charge density and dielectric analysis, it is observed that the electron localization is weakened, which leads to increased polarization and larger relative permittivity in the zb structure. After the phase transition, both the polarization and the relative permittivity decrease. Pressure increases the complex dielectric constant and dielectric loss factor, due to the increase in relaxation polarization and the scattering effect of carriers. Moreover, by comparing the high-pressure behavior of GaP, GaAs and GaSb, the changes in the electronic structure and electric transport process caused by the phase transition can be understood, which can enable us to better understand the metallization behavior and dielectric properties of Ga-based III-V family semiconductors under pressure, and stimulate the design and modification of other related group III-V semiconductors for optoelectronic devices and sensors.

Complex permittivity of FeSiAl/Al2O3 ceramic composite at X-band frequencies

The objective of this paper is to extract and study the complex permittivity of the FeSiAl/Al2O3 ceramic composite at X-band frequencies. We studied by simulation the complex permittivity of four composites with FeSiAl content varying from 0% to 15% by volume in the alumina matrix. The influence of the FeSiAl content on the complex permittivity of the FeSiAl / Al2O3 composite was also studied. The results obtained show on the one hand that the complex permittivity depends on the frequency. Indeed, the values of the real and imaginary parts of the complex permittivity decrease with the increase in frequency over the entire frequency range in the X band. On the other hand, the high FeSiAl content has a significant impact on the values of the real and imaginary parts of complex permittivity. Higher values were obtained for composites with a high inclusion content. In this work, we obtained a good agreement between the simulation results and the published experimental results. These results indicate that the FeSiAl / Al2O3 composite can be used in applications as an electromagnetic wave absorbing material.

Permittivity of SiC ceramic matrix compositesin Ku band

The objective of this work is to determine the dielectric permittivity of two SiC ceramic matrix composites. These composites are reinforced with NicalonSiCfibers and SCS6SiC fibers (SiCf / SiC) and have different volume fractions. The results obtained show that the dielectric property depends on the volume fraction and the frequency. Composites with high volume fractions have better dielectric properties than others. The values of the real and imaginary part of the complex permittivity decrease with frequency increase in the Ku-band. Moreover, the imaginary part takes negative values.

Investigation of dielectric and optical properties of pure and diamond nanoparticles dispersed nematic liquid-crystal PCH5

ABSTRACT In the present work, we have dispersed diamond nanoparticles (DNPs) in nematic liquid crystal 4-(Trans-4ʹ-n-Pentylcyclohexyl) Benzonitrile (PCH5) and studied the dielectric and optical properties of pure and DNPs dispersed nematic systems. We have investigated the effect of dispersion of DNPs (concentrations 0.5 and 1.0 wt%) in nematic liquid crystals (NLC) PCH5 on the dielectric permittivity, dielectric loss, dielectric anisotropy, photoluminescence, UV-Vis absorbance. It has been found that these properties are influenced by the dispersion of DNPs in nematic PCH5 system and applied electric field. Due to the dispersion of DNPs (1.0 wt% concentration) in PCH5, a significant decrease in the relative permittivity occurs. The relaxation peaks of dielectric loss shifts towards higher frequency side for NLC-DNPs composites. The dielectric anisotropy has been found to decrease with the dispersion of DNPs into pure NLC. The PL emission and UV-Vis absorbance for the dispersed systems have been decreased. An effort has been made to explain the observed results on the basis of interaction between nematic molecules and diamond NPs. The possible applications have also been suggested for the dispersed systems in this study.

Structural and dielectric studies of three-phase composite containing multiwalled carbon nanotubes, nanodispersed silica and KDP

ABSTRACT The study provides experimental results for clarifying the influence of a conductive filler of multiwalled carbon nanotubes (MWCNT) and a dielectric inclusion of nanodispersed silica (nSiO2) on dielectric properties of a classical ferroelectric of KH2PO4 (KDP) in composites containing these substances. Wits increasing nSiO2 content, the phase transition point of KDP was shifted toward higher temperatures along with a decrease in dielectric permittivity. Meanwhile, MWCNT composition did not affect phase transition, but enhanced dielectric permittivity that reached highest values at MWCNT:nSiO2:KDP mass ratio of 0.096:1:1. The thrshod of MWCNT in the composite was also determined. The conductive nature of MWCNT and the interaction between nSiO2 with KDP in the presence of residual water was figured out as the main reason for these anomalies.

Dielectric properties of polymer/clay nanocomposites

Intercalated and exfoliated nanocomposites of insulating polymers poly methyl methacrylate and acrylonitrile butadiene styrene with organically modified montmorillonite (OMMT) was prepared by solution casting method. Formation of polymer nanocomposites was confirmed by X-Ray Diffraction. Fourier transform infrared spectroscopy confirmed the interaction between polymers and cations on the surface of OMMT layers. Dielectric properties of these nanocomposites were examined at room temperature in the frequency range of 100 Hz–1 MHz. The findings of dielectric measurements exhibited higher real and imaginary dielectric permittivity values for exfoliated nanocomposites and lesser real and imaginary dielectric permittivity values for intercalated nanocomposites as compared with pure polymers in the same frequency range. The increase in the permittivity values is attributed to Maxwell Wagner polarization in exfoliated nanocomposites because of increased interfacial area between polymer and the clay layers. Decrease in dielectric permittivity in intercalated polymer nanocomposites is attributed to restricted mobility of polymer chains due to nanoscopic confinement of the polymer with the silicate layers.

Growth and impedance analysis of pure TGAc and dye doped TGAc crystals-enhanced dielectric permittivity for energy-storage devices

Herein, we delineate the enhancement of the dielectric properties of an anionic dye doped triglycine acetate crystal for the first time. Single crystals of pure triglycine acetate (TGAc) and reactive orange 16 (RO16) dye-doped (0.01, 0.03 mol%) triglycine acetate were synthesized with an intention to enhance the strengths of pure TGAc crystal using slow evaporation process. The crystalline structure and phase purity of the grown crystals were analyzed using Powder XRD studies. The frequency dependence of real and imaginary part of dielectric constant, loss tangent, real and imaginary part of impedance, electrical modulus and ac electrical conductivity have been investigated. The dielectric constant and dielectric loss for the grown crystals, have been found to decrease with increasing frequency. The decrease in permittivity and dielectric loss with an increase in applied field frequency is as per Maxwell–Wagner theory. The Cole–Cole plot implies that the mechanism of conduction is mainly due to bulk resistance. The enhanced dielectric constant of the doped crystals confirms the appropriateness of the developed crystals for energy storage capacitor applications.

Dielectric properties and in vitro hemocompatibility of Nd:YAG laser-irradiated polyethylene terephthalate.

Surface properties and morphology of the biomaterial play an essential role in the polymer-material interaction. In this work, laser surface modification of polyethylene terephthalate as a polymer with distinguished mechanical properties was carried out using (neodymium-doped yttrium aluminum garnet) Nd:YAG laser (1.064µm) with different output power (0.3, 3, and 6W). The structural, surface, and dielectric properties of PET before and after laser irradiation have been studied using attenuation total reflection-Fourier transform infrared (ATR-FTIR), dielectric spectroscopy (DS), scanning electron microscope (SEM), and contact angle measurements. Moreover, the anticoagulant properties of the laser-irradiated PET was determined through measuring the prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR). In vitro platelet adhesion test was used to assess the platelets adhered to the surface of the samples; in addition to hematological study. It was found that contact angle (θ) measurements of laser-irradiated PET samples decreased compared to the unirradiated PET. The irradiated samples at 0.3W have the lowest contact angle which is a clear indication that surface treatment with Nd:YAG laser brought about improving the wettability of the polymer. From the dielectric measurements, both values of permittivity and dielectric loss decrease by increasing the laser power. The electrical conductivity decreases with increasing laser power, but still in the same order 10-14S/cm. The decrease in electrical conductivity σ may be due to the cross-linking of the polymeric matrix which led to a decrease in the total polarity and consequently decrease in electrical conductivity. The magnitude of σ obtained is highly recommended to be used for insulator purposes in addition to the main purpose that is blood contact.

Lead-free Na0.4K0.1Bi0.5TiO3 ceramic: Poling effect and enhancement in electromechanical and piezoelectric voltage coefficient

The effect of electric poling on the piezoelectric properties of the sintered Na0.4K0.1Bi0.5TiO3 is studied with varying poling field and temperature. An optimized poling condition (EP =50 kVcm, TP =110 °C) exhibited a high piezoelectric voltage (g33∼ 85 mV m/N) and charge coefficients (d33∼193pC/N). A combination of electric field induced irreversible transformation from polar nano regions embedded in a non-polar relaxor state to a long-range ordered ferroelectric state and increase in the structural ordering are responsible for the observed high piezoelectric properties. A mechanism is discussed to reveal the origin of high voltage coefficient due to poling, where the decrease of dielectric permittivity can facilitate high g33. This investigation provides an approach for designing the high performance Na0.4K0.1Bi0.5TiO3based materials suitable for sensors and energy harvesting applications.

Effect of ZnO nanoparticles doping on structural, dielectric and interfacial behavior of polyoxyethylene (20) sorbitan/ethylene glycol lyotropic phases

ABSTRACT We are reporting on the interaction of zinc oxide (ZnO) nanoparticles (NPs) with the lyotropic phase comprises of Polyoxyethylene (20) sorbitan monolaurate and protic solvent ethylene glycol. The concentration of the NPs has been varying from 0.05 to 0.5 wt%. Multiwall lamellar and inverse phases have been observed at lower and higher concentration of ZnO NPs doping. Interestingly, the organization of ZnO NPs on the periphery and inside the periphery of ring-like structures has been observed at lower and higher concentration of the dopant, respectively. Such organization of the NPs can be explained considering interfacial interaction amid host and dopant and may also attribute to the adsorption mechanisms of surfactant. Effects of NPs doping on the dielectric dynamics has also been examined. About 32.6% decrease in the dielectric permittivity has been noticed at higher NPs doping. Such decrement in permittivity could be a result of the screening of the ZnO NPs dipole moment by the adsorption of surfactant molecules on their surface. Relaxation and optical parameters of the non-doped and doped mixtures have also been discussed.

Assessing the Role of a Semiconductor’s Anisotropic Permittivity in Hafnium Disulfide Monolayer Field-Effect Transistors

2-D semiconductors show great promise to serve as channel materials in next-generation field-effect transistors (FETs). The permittivity of many 2-D semiconductors is anisotropic, though many recent simulation works studying 2-D FETs have treated these materials as though they have isotropic permittivities. Because there have been no works that investigate the role of each element of a semiconductor’s anisotropic permittivity on a device’s performance, the impact that this isotropic approximation has on a simulation’s accuracy is unknown. Furthermore, the impact of a semiconductor’s anisotropic permittivity on a device’s performance cannot be explained using existing theory. In this simulation study, we investigate, for the first time, the impact of a semiconductor’s anisotropic permittivity on the performance of FETs. Our main findings are that the isotropic approximation becomes inaccurate as the channel lengths of FETs are scaled down and that short-channel effects become less significant when the semiconductor’s in-plane permittivity decreases or its out-of-plane permittivity increases. We also find that the capacitance of the semiconductor in the out-of-plane direction (i.e., the capacitance associated with the out-of-plane permittivity) more significantly influences a device’s gate capacitance when equivalent oxide thickness (EOT) decreases. Therefore, EOT alone cannot be used to assess total gate control in aggressively scaled 2-D devices.

Dispersion characteristics of terahertz transverse electric mode in a smooth-wall cylindrical waveguide with a degenerate plasma layer

The propagation of transverse electric mode in a cylindrical metallic smooth-wall waveguide contains a dielectric rod and a cold collisionless unmagnetized degenerate plasma layer is analytically investigated in the terahertz frequency region. The dispersion relations of fast and slow waves for this mode are derived and solved numerically. The effects of geometrical and physical parameters such as dielectric, plasma and metal radii, and dielectric permittivity on the dispersion characteristics of terahertz transverse electric mode and its frequency spectrum are studied. It is shown that the decrease of dielectric permittivity and metal radius, and the increase of degenerate plasma radius leads to higher frequency fast waves. It is also indicated that an increase in the dielectric radius results in a decrease in the frequency of fast waves. In addition, it is found that by reducing the dielectric rod radius and with increasing metal radius, the frequency is increased in the slow waves. Finally, it is shown that the increase in dielectric permittivity causes a decrease in the frequency of both fast and slow waves.

The Effect of Carbon Coatings on the Electrochemical Performance of Composite Electrodes

This work focuses on the effects of sample preparation and particle size on the dielectric properties of polymer nanocomposites. A comparison between the dielectric permittivity and dielectric loss of Polymethyl methacrylate (PMMA) samples, prepared by solution casting and compression molding, has been achieved. A Time Domain Spectrometer and an Agilant (HP) 4284A LCR precision meter, were furbished and used to measure the dielectric properties of insulating nanocomposite materials. The cast samples have shown different dielectric responses from the melt-pressed samples. These differences diminish with lengthening the dry time of the cast samples under vacuum. In addition, nanocomposite and microcomposite samples were prepared by solution casting of PMMA solution and Titanium dioxide (TiO2) particles. The dielectric properties of the nanocomposites were different from the polymer samples where a decrease in the dielectric permittivity of the nanocomposite has been observed. These differences in the dielectric response of the PMMA sample and the nano/micro composite samples might be due to many issues such as, sample preparation or the aggregation of the TiO2 nanoparticles in the polymer matrix. Furthermore, polymer-blends samples of PEO and PMMA have been prepared by solution casting method. The results reported in this work show similar trend compared to those reported in the literature.

Quantifying Fluorogenic Dye Hydration in an Epoxy Resin by Noncontact Microwave Dielectric Spectroscopy.

We investigated a chemically modified rhodamine B dye as a sensor of local water content in dye-modified epoxy resins, where these measurements were combined with dielectric measurements to estimate the dye-water association ratio in the material. In particular, the water-sensitive fluorogenic dye was covalently attached to the epoxy resin backbone. This dye becomes fluorescent only upon photoactivation by ultraviolet light and its protonation in the presence of water. High-resolution noncontact microwave cavity dielectric measurements on these materials indicate a decrease of the dielectric permittivity upon photoactivation. We utilize this effect to determine the average extent of hydration of the activated dye molecules. Our results suggest that fluorogenic dyes are promising for the quantification of the local water content in polymer materials, such as the technologically important problem of interfacial water in epoxy materials.

Compression strength, dielectric and magnetic properties of new aluminium matrix hybrid nanocomposites

Nanocomposites are materials fabricated from two or more materials with different mechanical and electrical properties. Combining these materials produces a new designed material with new and better properties compared to the individual components. In recent years nanocomposites have been developed and employed almost in all industries. The current study deals with fabricating a hybrid nanocomposite ( when there are a minimum of three materials, the composite is called as hybrid composite). Pure aluminium as the base matrix. Iron oxide Fe2O3 (alpha) and aluminium oxide Al2O3 (alpha alumina). Fe2O3 weight percentage (wt.%) is varied (1.5, 2.5 and 5 % by weight) and the wt % of Al2O3 is held constant (2 wt.%). The new designed nanocomposite was produced using Powder Metallurgy (P/M) method. This method has been widely used for fabricating aluminium matrix nanocomposites (AMNCs), due to it is low costs and gives high accuracy as well as the ease of using. The matrix used was aluminium powder with an average particle size of (60µm) with 99.6% purity and Fe2O3 (99% purity and 30 nm particle size) and Al2O3 with (99.5% purity and 14-20 nm particle size ). The experimental results revealed that the microstructure images of composites showed uniformly distributed of Fe2O3 and Al2O3 in aluminium matrix. The maximum compressive strength is 152 MPa in nanocomposite containing (1.5 Fe2O3 + 2 Al2O3) wt.%. The improvement percentage was recorded to be 30% for CS. The real and imaginary components of relative permittivity decrease with increase of frequency. The hysteresis curve of nanocomposites showed that the magnetic properties were improved for all the nanocomposites but the better response of magnetic properties was found with the nanocomposite of (1.5% Fe2O3 + 2% Al2O3) content.

A simple and accurate FDTD based technique to determine equivalent complex permittivity of the multi-layered human tissue in MICS band

Abstract This paper proposes a methodology to determine the equivalent electrical properties of multilayered human tissue using the Finite Difference Time Domain (FDTD) method for dispersive media. In addition, the impact of fat layer thickness on the equivalent dielectric properties has also been critically analyzed. The effect of moisture content present in the skin layer has also been studied. The main advantage of the proposed method is that it can be used for any thickness and any number of layers of human tissue. The multilayer reflection and transmission coefficients of the human tissue are first calculated using the FDTD method and then the permittivity and conductivity are extracted using the Nicholson Ross Weir (NRW) Method. The results are validated analytically using the concept of transmission line analogy for plane wave propagation. The tool used is MATLAB. In this paper, a three-layered software model of the human chest for pacemaker applications has been analyzed in the Medical Implants Communication Service band (MICS). At the frequency of 403.5 MHz in the MICS band, the equivalent permittivity of 3 layered human tissue is approximately 43 and its conductivity is 0.41 s / m . Moreover, the effective permittivity, conductivity and tan delta loss decrease with the increase in fat layer thickness. These results form the basis for the development of phantom mixtures used for designing, testing and evaluation of implantable antenna and SAR measurements. The choice of using FDTD is because it is a very powerful tool for creating a numerical mixture.

A theory of frequency dependence and sustained high dielectric constant in functionalized graphene-polymer nanocomposites

Functionalized graphene/polymer composites are currently under extensive investigation due to their excellent mechanical and functional properties. Within the framework of electrical properties, many experiments have shown that their electrical conductivity and dielectric permittivity are strongly dependent on the frequency of the applied electric field and the volume concentration of graphene fillers. In this paper we first apply Dyre's hopping function and Debye's relaxation function to build the constitutive equations for the graphene fillers, polymer matrix, and the interface regions. In addition, Cauchy's cumulative probabilistic function is also introduced to account for the drastic increase of electron tunneling and the rapid build-up of Maxwell-Wagner-Sillars polarization at the interface. These functions are then integrated into an effective-medium framework in the complex domain to establish a complete theory for the frequency dependence of these two effective properties as a function of graphene loading. The developed theory is highlighted by a direct comparison with the experimental data of reduced graphene oxide/polypropylene (rGO/PP) nanocomposites. The results show that both the theory and experiment display a general increase of conductivity but a decrease of permittivity as frequency increases, and that, with the graphene loading of 0.2 vol%, there is a sustained, high level of dielectric constant beyond 1,000 covering the frequency range up to 104 Hz. This remarkable feature can be of particular significance to energy storage and conversion.