Dielectric Frequency Research Articles

Optical properties of PVC composite modified during light exposure to give high absorption enhancement

Modified poly(vinyl chloride) (PVC) films have been synthesized with a simple superficial deposition by using solvent tetrahydrofuran (THF). These modified films were prepared by a casting method over a glass substrate. Different types of the amino group with a suitable aromatic aldehyde as an organic compound, which were reacted to prepare different PVC composite films. These films have been analyzed by UV-Visible spectra. The percentage of PVC was (0.25 g) with (0.05 g) amino group and aromatic aldehyde combinedly, then dissolved with (8 ml) of tetrahydrofuran (THF) at room temperature (300 K). The optical properties as absorption coefficient, reflectance, transmittance, skin depth, energy gap, refractive index, extinction coefficient, and urbach energy were studied. The transmittance value of the pure PVC film was 1.0 then declined gradually after dispersion with the compounds to the lowest value at 0.1, the reflectance also decreased. The energy gap for direct allowed decreased from (5.1 to 2.9 eV), and indirect transition decreased also from (5.0 to 2.8 eV), this behavior indicate that the modified films become work as semi-crystalline compounds toward the light. In tailoring, the optical properties, and urbach energy have been increased after mixed with PVC polymer. The scattering energy (Ed) and the effective single oscillator (Eo), were decreased. In a similar manner the dielectric constant high frequency (ε∞) and effective mass (Nm*), of dielectric constants were increased for PVC modified films. The PVC modified films are appropriate for anti-reflected coating while being good suitable in high refractive lenses and photovoltaic cells applications.

Highly luminescent nanocomposites of nematic liquid crystal and hybrid quantum dots CdSe/CdS with ZnS shell

This work is focused on synthesis of highly luminescent hybrid CdSe/CdS ”core/shell” quantum dots (QDs) with different core sizes and an additional ZnS shell. These quantum dots were doped into a nematic liquid crystal (NLC) phase to obtain new composites. According to the dielectric and femtosecond laser spectroscopy data, sizes of the QD cores and built-up additional ZnS shells are correlated with luminescence and dielectric characteristics of the ZhK-1282 and QD composites. With larger QD cores in the ZhK-1282, a decrease in dielectric relaxation frequency of the LC molecules rotating around their short axis is observed, same for the activation energy of this process. A shift to a shorter wavelength of the LC main luminescence peak and the strong luminescence quenching effect can be observed for the composites with the 2 nm QD cores. This effect is the result of nonradiative excitation energy transfer from LCs to QDs in the composite. The adhesion work values have been calculated for all the samples, alignment substances and substrates. Optimized homeotropic aligning layers with the best composite anchoring parameters have been selected both for normal glass and glass with a sputtered indium tin oxide (ITO) layer.

Measurement of Non-Invasive Blood Glucose Level by UWB Transceiver in Diabetic Patient Type-1-

Diabetes is a silent killer and a rapidly increasing global epidemic worldwide. The change in healthy diabetes diet and life-style is only therapy as no permanent treatment. The measuring of the amount of Blood Glucose Level (BGL) continuously is important for diabetes management. In general terms, two types of diabetes can be identified as Type-1- and Type-2-. Type-1- is the most dangerous type and affects (5-10 percent) of the diabetic population; they have to inject or pump insulin themselves. The common method of measuring is glucometer which the sample of blood is taken by clipping patient’s finger and analysis this sample. This invasive method is painful and discomfort for the patient. This article presents a microwave sensor with frequency falls in the range of Ultra-wideband (UWB) spectrum to determine blood glucose level non-invasively (i, e. without giving any sample of blood). Ultra-wideband technology for the Wireless Body Area Network (WBAN) is an important technology due to its advantages in sensing and communication for biomedical applications. The proposed system consists of a piece of microwave resonator that can be placed on the arm of the patient. Then, the first frequency resonance of the sensor is modifying because of many changes are calculated in dielectric blood permittivity and frequency value transferred from the sensor. Relationship between the frequency response and the changing in blood permittivity is observed. This may result in a measurement phase in which the Blood Glucose Level present has a relation with the frequency response value of the sensor. This system showed a clear and accurate outcome. Besides, it is easy to use by patient himself in any time with multiple use without exchanging any part of it, and safe because no taking any drop of blood just put the sensor in touch with patient’s skin without pains, and low cost compared with other methods that measure the glucose level.

Dielectric properties of edible fungi powder related to radio-frequency and microwave drying

Edible fungi are rich in nutrition, but they are susceptible to spoilage, and often prolonged by drying. RF and microwave energy drying have the advantages of short drying time, high energy efficiency and good process control. However, to develop an effective dielectric drying method, it is important to understand dielectric properties, the major factor characterizing the interaction between the electromagnetic energy and the food. At present, there is a lack of research on dielectric properties of edible fungi. In this study, a vector network analyzer and an open-ended coaxial-line probe were employed to measure the dielectric parameters. The dielectric parameters were observed at different temperatures (25–85 °C) for edible fungi powder with moisture content ranging from 5 to 30% wet basis over a frequency range of 1–3000 MHz. The relationship between the dielectric properties and frequency, temperature, and moisture content were obtained via regression analysis. Further, the dielectric penetration depth was calculated, and the effects of frequency, moisture content, and temperature on the penetration depth were also analyzed. The results showed that the dielectric properties of edible fungi powder increased with an increase in moisture content and temperature, while they decreased with increasing frequency. At high moisture content and temperature, the increase in dielectric properties was slightly larger than that at low moisture content and temperature. The dielectric properties changed more evidently at lower radio frequencies than at higher radio frequencies. The penetration depth decreased with an increase in temperature, moisture content, and frequency. It can be concluded that a large penetration depth at radio frequencies below 100 MHz could be used to dry edible fungi on a large scale, whereas microwave energy could be employed for drying edible fungi on a small scale.

Characteristics of Poly(vinyl Alcohol) (PVA) Based Composites Integrated with Green Synthesized Al3+-Metal Complex: Structural, Optical, and Localized Density of State Analysis.

The influence of dispersing Al-metal complex on the optical properties of PVA was investigated using UV–visible spectroscopy. Polymer composite films with various Al3+-complex amounts in the PVA matrix were arranged by solution casting technique by means of distilled water as a widespread solvent. The formation of Al3+-metal complex was verified through Ultraviolet–visible (UV-Vis) and Fourier-transform infrared spectroscopy (FTIR) examinations. The addition of Al-complex into the polymer matrix led to the recovery of the optical parameters such as dielectric constant (εr and εi) and refractive index (n). The variations of real and imaginary parts of complex dielectric constant as a function of photon wavelength were studied to calculate localized charge density values (N/m*), high-frequency dielectric constant, relaxation time, optical mobility, optical resistivity, and plasma angular frequency (ωp) of electrons. In proportion with Al3+-complex content, the N/m* values were amplified from 3.68 × 1055 kg−1 m−3 to 109 × 1055 kg−1 m−3. The study of optical parameters may find applications within optical instrument manufacturing. The optical band gap was determined from Tauc’s equation, and the type of electronic transition was specified. A remarkable drop in the optical band gap was observed. The dispersion of static refractive index (no) of the prepared composites was analyzed using the theoretical Wemple–DiDomenico single oscillator model. The average oscillator energy (Eo) and oscillator dispersion energy (Ed) parameters were estimated.

DIELECTROMETRIC STUDY OF RADIATION PROTECTION ABILITY OF ULTRA-DISPERSED NANODIAMONDS

Radiation protection ability of the ultra-disperse nanodiamonds (UDD) is studied based on the measurements of dielectric permittivity of red blood cells (RBC) affected by cancer. Wistar rats with Guerin's carcinoma were treated by X-ray 5.8 Gy. Some rats received UDD with food during 5 days prior to the X-ray. The groups with UDD, X-ray, and both UDD and X-ray treatments were compared to the control group. The complex dielectric permittivity of the RBC was measured by microwave dielectrometry. It was shown, tumor development leads to the increase in the dielectric permittivity and relaxation frequency. The irradiation promotes further growth of the parameters, while UDD uptake leads to insignificant changes in comparison to the control group. Therefore, UDD occur the radioprotective effect promoting repair, compensation and restoration of body tissues that is demonstrated by normalization of the dielectric parameters of RBC.

RELAXATION FREQUENCY SHIFT IN TRIGLYCINE SULFATE UNDER THE INFLUENCE OF SILICA NANOPARTICLES AT LOW FREQUENCIES

The present work is devoted to clarifying the influence of silica nanoparticles on dielectric relaxation frequencies of a classical ferroelectric – triglycine sulfate at low frequencies (102 – 107 Hz) from 20 ˚C to phase transition point for composite samples prepared at different composition weight ratios. Theresults indicated the reduction of relaxation frequency with increasing the silica content due to the intensified interaction between nanoparticles and tryglycine sulfate inclusion. The nature of this interaction was thoroughly discussed in this study.

Dielectric function of six elemental metals

We present an accurate first-principles study of the electronic structure and absorption spectrum of six elemental metals (aluminium, gold, silver, copper, palladium, platinum) using density functional theory in an all-electron full-potential framework. We calculate dielectric function spectra and plasma frequency, and compare with experimental data obtained from photo-emission, absorption, and electron energy loss spectra.

Dielectric and AC Breakdown Properties of SiO2/MMT/LDPE Micro–Nano Composites

Low-density polyethylene (LDPE) is an important thermoplastic material which can be made into films, containers, wires, cables, etc. It is highly valued in the fields of packaging, medicine, and health, as well as cables. The method of improving the dielectric property of materials by blending LDPE with inorganic particles as filler has been paid much attention by researchers. In this paper, low-density polyethylene is used as the matrix, and montmorillonite (MMT) particles and silica (SiO2) particles are selected as micro and nano fillers, respectively. In changing the order of adding two kinds of particles, a total of five composite materials were prepared. The crystallization behavior and crystallinity of five kinds of composites were observed, the εr and tanδ changes of each material were investigated with frequency and temperature, and the power frequency (50 Hz) AC breakdown performance of materials were measured. The differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results show that the crystallinity of the composites is higher than that of LDPE. Experimental data of dielectric frequency spectra show that the dielectric constants of micro–nano composites and composites with added MMT particles are lower than LDPE, the dielectric loss of composites can be improved by adding MMT particles. The experimental data of dielectric temperature spectra show that the permittivity of SiO2-MMT/LDPE is still at a low level under the condition of 20~100 °C. In terms of breakdown field strength, the SiO2/LDPE composite material increased by about 17% compared with the matrix LDPE, and the breakdown field strength of the materials SiO2-MMT/LDPE and MMT-SiO2/LDPE increased by about 6.8% and 4.6%, respectively.

Systematic characterization of THz dielectric properties of multi-component glasses using the unified oscillator model

A terahertz (THz) dielectric property characterization method based on a unified single oscillator model has been developed and applied to a variety of multi-component silicate oxide glasses. The experimental values of dielectric constant determined by THz time-domain spectroscopy (TDS) in the sub-THz region have been confirmed to agree well with the values calculated by the single oscillator model which incorporates the local field effects and the material’s ionicity. This has provided a unified formulation that enables systematic determination of the key physical parameters solely from the high-frequency (optical) and low-frequency (sub-THz) dielectric constants and characteristic resonance frequency in the (sub-)THz region. The low-frequency dielectric constant has been demonstrated to be fully determined by a single parameter of the microscopic total susceptibility. Also, the polarization ionicity, which is defined by the ionic fraction in the microscopic total susceptibility, has been found to be a good indicator to represent the ionic nature of the material. Through this analysis, an increasing trend of the effective ionic charge has been found in high-dielectric constant glasses such as oxyfluorosilicate glasses, and the physical mechanism of their dielectric constant enhancement has been discussed. The present method is expected to be applied to design and characterize dielectric properties of a wide range of multi-component glasses and other isotropic, insulating materials.

Correlation between enhanced lattice distortion and volume fraction of polar nanoregions in quenched Na1/2Bi1/2TiO3–BaTiO3 ceramics

Quenching has been established as a viable method to increase the depolarization temperature in (100-x) Na1/2Bi1/2TiO3–xBaTiO3 (NBT–xBT). The proposed hypothesis of a stabilized ferroelectric order would entail changes in the polarized volume. To this end, air-quenched and furnace cooled samples of four compositions of NBT–xBT with x = 3, 6, 9, and 12 mol. % BT were studied. Upon quenching, all the compositions demonstrate an increase in the ferroelectric to relaxor transition temperature, TF-R, by 23–44 °C and enhanced lattice distortion. Resonance frequency damping analysis was utilized to measure Young's modulus in the temperature range of 25 °C to 800 °C and to estimate the volume fraction of polar nanoregions using a composite model. Quenching leads to an 8% decrease in Young's modulus, but to an increase in the volume fraction of polar nanoregions by 12% at 300 °C for NBT-6BT. Transmission electron microscopy investigations of quenched NBT-6BT reveal a combination of lamellar domains and more homogenous areas with nanometer-sized domains. The existence of lamellar domains in quenched morphotropic phase boundary compositions together with enhanced lattice distortion and a decrease in dielectric frequency dispersion substantiate the premise of a stabilized ferroelectric order.

Linear and non-linear optical parameters of polycarbonate reinforced inorganic bismuth nitrate pentahydrate salt composite

The effect of dispersinga filler on the optical properties of polycarbonate (PC) was studied using UV–Visible spectroscopy. The composite films with different weights of bismuth nitrate pentahydrate (Bi (NO3)3·5H2O or BNP) in the PC matrix (from 0.1 wt% up to 5 wt%) were prepared by solution casting technique using dichloromethane (DCM) as the solvent of PC. Tauc's equation was used to obtain the optical band gap and the type of electronic transition occurring on absorption of a suitable photon of electromagnetic radiation. Significant decrease in the optical band gap was noticed for PC/BNP composite containing 0.75 wt% of BNP, when compared to pure PC. Important optical parameters like dielectric constant (ϵr and ϵi), refractive index (n) and optical conductivity (σ) of the PC/BNP composites are significantly improved with the addition of BNP in the PC matrix. Interestingly, the composite sample with filler level (FL) 5 wt % showed the highest optical conductivity (9.90 × 109 s-1) at 4.56 eV (incident photon energy) the prepared composite films. The theoretical Wemple-DiDomenico single oscillator model was used to estimate various dispersion parameters (average oscillator energy (Eo), oscillator dispersion energy (Ed), optical spectral moments (M-1 and M-3), static refractive index (no), and static dielectric constant (ϵs)) of the prepared composites. The average oscillator strength (So), average oscillator wavelength (λo) and high frequency dielectric constant (ϵ∞1) were determined by using the Sellmeier single oscillator model. Also, the ratio of free carriers to effective mass (N/m*), lattice dielectric constant (ϵL) and plasma frequency (ωp) have been calculated. The values of (N/m*) increased from 3.79 × 1037 kg−1 m-3 to 24.86 × 1037 kg−1 m-3 with increasing FL (from 0 wt % up to 2.5 wt %). The volume energy loss function (VELF) and surface energy loss function (SELF) were determined using real and imaginary part of dielectric constant. The non-linear third order optical susceptibility (χ(3)) and non-linear second order refractive index (n2) were determined using simple semiempirical relations. The photo-induced changes in the optical parameters are significant due to an interaction between the incident light and electrons of the composite, and thus, detailed analysis of these optical parameters of PC composites may find applications in optical devices.

Effect of carbonaceous oil palm leaf quantum dot dispersion in nematic liquid crystal on zeta potential, optical texture and dielectric properties

In the present work, the dispersion of oil palm leaf based carbonaceous quantum dots (OPL QDs) in nematic liquid crystal (NLC) E 48 eutectic mixture has been reported. The dispersed systems with concentrations 0.1, 0.2, and 0.3 wt% are designated respectively, as MIX 1, MIX 2, and MIX 3. The objective of this study is to analyze the results on the zeta potential, optical texture, dielectric constant, dielectric loss, conductivity, dielectric strength, relaxation frequency, specific power loss and total power loss of pure and OPL QDs dispersed nematic E 48 system. Zeta potential measurement has been performed in the solution state to ensure dispersion stability. The optical textures and dielectric results are recorded after filling the respective samples in sample cells. The core findings in the present study show that the zeta potential varies from − 23.43 mV to + 28.07 mV that signifies the stability of OPL QDs suspension in LCs. Specific power loss (SPL) and total power loss (TPL) are found to be least for MIX 1 which shows that the problem of high power consumption in LCDs can be resolved by dispersing a small weight percent concentration of OPL QDs in LC medium (MIX 1). Improved molecular alignment in the dispersed system has been observed from the textural study which finds its application in good contrast display devices. The color change in the aligned textures with temperature has been attributed to the birefringence change. The porous nature of carbonaceous OPL QDs has its application in supercapacitors. The benchmark results of this study highlight the effect of temperature and frequency on dielectric parameters for both planar and homeotropic state of E 48 LCs. OPL QDs dispersed system display increased conductivity for MIX 3. The decrease in the activation energy for OPL QDs dispersed system in comparison to pure LC material E 48 is a consequential result of the potential barrier change. The increment in the dielectric strength and relaxation frequency of OPL QDs dispersed system is noticed in comparison to pure E 48. These outcomes open the door for the applicability of present LCs in the field of both display and non-display devices like sensors, supercapacitors, low power consumption displays, energy conversion, and electrical storage devices as well as advanced smart systems.

A PCB Sensor for Detecting Icing Events

Ice formation can be problematic on surfaces, such as roads, bridges, wings, and sensitive plants. A simple low-cost sensor for detecting the formation of ice has been developed using standard low-cost commercial printed circuit board fabrication techniques. The sensor consists of a capacitive interdigitated electrode structure, realized in the top Cu layer of the circuit board and covered with a polymeric solder mask. The sensor's capacitance is measured at 1 and 64 kHz, and then, the ratio of the two capacitances is computed. The ratio is then compared with a threshold value of 2.0. Icing results in the capacitance ratio exceeding 2.0, whereas dry conditions or water result in a ratio of less than 2.0. This technique exploits the dielectric relaxation properties of ice, in which ice has a high dielectric constant below the relatively low dielectric relaxation frequency of ≤3 kHz and a low dielectric constant well above that frequency. The sensor was evaluated in air, water, and ice over a temperature range of −30 to 34 °C and successfully identified ice every time.

A theoretical proposal for a plasma density sensor based on the dielectric substrate antenna with high dielectric constant

ABSTRACT With the rapid development of industrial production and aerospace, how to measure the plasma density has also developed rapidly. So a radio-frequency plasma transducer based on a three-layer dielectric substrate antenna with a high dielectric constant is introduced. The top and bottom layers are dielectric plates, which protect the internal antenna structure and improve the equivalent permittivity of the antenna. The middle layer is the structure layer of the designed antenna. And the antenna size is 3.8 × 2 × 1.8 mm3. When the plasma frequency changes from 0.3 GHz to 7 GHz, the corresponding dielectric substrate antenna resonant frequency (RF) changes from 4.076 to 5.213 GHz. The minimum unit is 0.1 GHz, and all the measurement accuracy is more than 90%. The method based on the effective dielectric constant of plasma will change under different plasma frequencies, so the RF of the antenna is different. In this paper, the radio-frequency plasma transducer is studied theoretically and analyzed numerically.

Investigation of dielectric behavior in Ni0.7-xZn0.3MxFe2O4 (M=Mn/Co/Cu) ferrites by impedance spectroscopy

The electrical characteristics of the Mn/Co/Cu-substituted Ni–Zn ferrites prepared using the citrate technique have been explored in detail by ac impedance spectroscopy. Measurements between temperatures (373K–523 K) were observed over a broad frequency range of 100 Hz–1 MHz. Maxwell and Wagner's model was used to analyze the frequency dependence of dielectric parameters. Dielectric loss tangent versus frequency plots show relaxation peaks due to the coincidence of the frequency of charge hopping between the localized state and the outer field. The Cole-Cole curve was designed to investigate the complex impedance of the current systems. Two semicircles corresponding to the grain and grain boundary were observed. The investigation of the electrical modulus includes the electrical relaxation of the non-Debye form. The substitution of Ni ions by Mn/Co/Cu ions indicates a major improvement in the dielectric characteristics of Ni − Zn ferrite. The Ni–Zn–Cu ferrite series displays the best dielectric properties suggesting the capability of this series to be suitable for high-frequency devices.

Capacitance Measurement of Cerium Oxide Thin Film Capacitors

IntroductionCerium oxide (CeOx) is an attractive material for large volume on-chip decoupling capacitors, owing to its high dielectric constant (k) of 28. Commonly, a definite frequency dispersion in the small-signal capacitance measurement is observed in the frequency sweep, and larger capacitance values can be obtained at low frequency in the kHz range. The dielectric relaxation is reported to originate from the interface polarization between the polycrystalline grains in the films. In this work, the thickness-dependent polarization and the capacitance measurement under a DC voltage application are characterized.Fabrication processCeOx films with thicknesses from 8 to 20 nm were deposited by e-beam evaporation on an n+Si substrate with a W layer atop. Another W layer was deposited on CeOx layers and patterned to form electrodes. After the Al back contact formation, the samples are annealed at 420oC.ResultsFig. 1 shows the frequency dispersion of the capacitors with different CeOx thicknesses measured at 0 V. The dielectric relaxation frequency shifts to higher frequency while thinning the thickness, which is useful for capacitor application. The transient current upon 1 V application is shown in fig. 2. After a high charge current, one can observe a decay in the transient current, indicating the delay in the polarization. The capacitance of the samples can be obtained by taking the integral of the charge current and is shown in fig. 3. Comparable capacitance values were obtained with the small-signal measurements. 2 to 3 times higher capacitance values can be achieved with respect to the ionic polarization.ConclusionHigh capacitance values measured in the small-signal setup were confirmed by direct current measurement by DC voltage application. An even higher capacitance can be obtained with the thinner film.

Colossal permittivity of (Gd + Nb) co-doped TiO2 ceramics induced by interface effects and defect cluster

Material with high dielectric constant plays an important role in energy storage elements. (Gd + Nb) co-doped TiO2 (GNTO) ceramics with giant dielectric permittivity (>104), low dielectric loss, good temperature and frequency stability in broad range of 30–150 °C and 102–106 Hz have been systematically characterized. Especially, a low dielectric loss of 0.027 and a giant dielectric permittivity of 5.63 × 104 at 1 kHz are attained for the composition with x = 0.01. Results of complex impedance spectroscopy, I–V curve and frequency dependent dielectric constant under DC bias indicate that internal barrier layer capacitance (IBLC) effect, electrode effect and electron-pinned defect-dipole (EPDD) effect contribute to the colossal permittivity (CP) property simultaneously.

Structural, optical, and dielectric properties of Bi2O3-K2O-TiO2-P2O5 glasses and related glass-ceramics

ABSTRACT The glasses in the Bi2O3-K2O-TiO2-P2O5 system were elaborated by the conventional quenching method. Their structure was studied by Raman spectroscopy, and additional information is determined from density measurements and thermal analysis. The optical absorption of the glasses is investigated and it is found that the optical gap and the Urbach energy decrease and increase, respectively, with increasing Bi2O3 content. The crystallization of the glasses was performed under controlled heat treatments to develop glass-ceramics. Their dielectric constants are carried out by impedance spectroscopy. The variations of the permittivity (ϵr) and the dielectric loss (tanδ) versus frequency and temperature are determined. It is evidenced that the introduction of Bi2O3 in the glasses diminished the dispersion at low frequencies. The presence of bismuth oxide in the materials is also beneficial since it allowed the formation of glass-ceramics with high dielectric constant and low dielectric loss.

Rayleigh analysis and dielectric dispersion in polycrystalline 0.5(Ba0.7Ca0.3)TiO3–0.5Ba(Zr0.2Ti0.8)O3 ferroelectric thin films by domain-wall pinning element modeling

We use impedance spectroscopy to investigate the dielectric response in polycrystalline, lead-free 0.5(Ba0.7Ca0.3)TiO3–0.5Ba(Zr0.2Ti0.8)O3 (BCZT) ferroelectric thin films as a function of amplitude E0 and frequency f of an applied ac electric field. Impedance spectra from f=10 Hz to 1 MHz were collected at different E0 on polycrystalline BCZT capacitor stacks, grown by pulsed laser deposition on platinized Si substrates and covered with Au electrodes. Deconvolution of the spectra is achieved by fitting the measured impedance to the impedance of an equivalent-circuit model of the capacitor stacks, including a recently proposed domain-wall pinning element ZDW. From an extended data analysis, we quantify the coupling strength between dielectric nonlinearity and frequency dispersion in the BCZT thin films, and we obtain a schematic diagram of the different domain-wall-motion regimes. Our results indicate that the presence of grain boundaries in BCZT reduces the coupling strength and suppresses the motion of internal domain-wall segments and also the irreversible center-of-mass motion of the domain walls.