Average Dielectric Constants Research Articles

Ice Thickness Assessment of Non-Freshwater Lakes in the Qinghai–Tibetan Plateau Based on Unmanned Aerial Vehicle-Borne Ice-Penetrating Radar: A Case Study of Qinghai Lake and Gahai Lake

Ice thickness has a significant effect on the physical and biogeochemical processes of a lake, and it is an integral focus of research in the field of ice engineering. The Qinghai–Tibetan Plateau, known as the Third Pole of the world, contains numerous lakes. Compared with some information, such as the area, water level, and ice phenology of its lakes, the ice thickness of these lakes remains poorly understood. In this study, we used an unmanned aerial vehicle (UAV) with a 400/900 MHz ice-penetrating radar to detect the ice thickness of Qinghai Lake and Gahai Lake. Two observation fields were established on the western side of Qinghai Lake and Gahai Lake in January 2019 and January 2021, respectively. Based on the in situ ice thickness and the propagation time of the radar, the accuracy of the ice thickness measurements of these two non-freshwater lakes was comprehensively assessed. The results indicate that pre-processed echo images from the UAV-borne ice-penetrating radar identified non-freshwater lake ice, and we were thus able to accurately calculate the propagation time of radar waves through the ice. The average dielectric constants of Qinghai Lake and Gahai Lake were 4.3 and 4.6, respectively. This means that the speed of the radar waves that propagated through the ice of the non-freshwater lake was lower than that of the radio waves that propagated through the freshwater lake. The antenna frequency of the radar also had an impact on the accuracy of ice thickness modeling. The RMSEs were 0.034 m using the 400 MHz radar and 0.010 m using the 900 MHz radar. The radar with a higher antenna frequency was shown to provide greater accuracy in ice thickness monitoring, but the control of the UAV’s altitude and speed should be addressed.

Effect of cosolvents on the phase separation of polyelectrolyte complexes.

Evidence is shown that cosolvent mixtures control the coacervation of mixtures of oppositely charged polyelectrolytes. Binary and ternary solvent mixtures lead to non-monotonic solubility as a function of the average dielectric constants of the solvent mixtures. These data are rationalized by considering both electrostatic-driven phase separation and solvophobic-driven phase separation using group contribution effects on solubility parameters. These estimates are introduced into an effective Flory-Huggins interaction parameter within the framework of Voorn-Overbeek theory with variable dielectric constants and temperature dependences. Despite its simplicity, the model recovers salient experimental observations not only on their coacervate stabilities, but also on their lower critical solution temperature behaviors. These observations highlight the importance of weak van der Waals interactions in determining the phase behaviors of polyelectrolyte complexes relative to electrostatic correlations.

The difference in microwave loss mechanism between nano- and micron-sized Ag particles

Separated E/H-field heating in microwave cavities enables us to examine the microwave loss mechanisms. We prepared mixtures of SiO2 particles (having almost no microwave loss) and Ag particles with micrometer- and nano-sizes. Their average impedance and dielectric constants were measured. Electric conductivity exhibited percolation behavior at a specific threshold of Ag fraction. When the mixtures were heated in the separated fields, H-field heating was dominant in all the fraction ranges for the micrometer-sized Ag mixture. However, E-field heating was dominant below the percolation threshold for the nano-sized Ag mixture, and above the threshold, the H-field became dominant. This change in heating rates indicates the change in the energy loss mechanism. According to the size dependence of the induction current loss in a metallic sphere, the loss becomes less effective below the size of skin depth, namely, in the nano-size region. The permittivity of nano-sized Ag particles was estimated by an approximated Lindhard’s equation, which was input into the Maxwell–Garnett mixing model for predicting the effective complex permittivity of the mixture. It was possible to interpret the measured permittivity dependence on the Ag fraction.

A molecular contact theory for simulating polarization: application to dielectric constant prediction.

Microscopic polarization in liquids, which is challenging to account for intuitively and quantitatively, can impact the behavior of liquids in numerous ways and thus is ubiquitous in a broad range of domains and applications. To overcome this challenge, in this work, a molecular contact theory was proposed as a proxy to simulate microscopic polarization in liquids. In particular, molecular surfaces from implicit solvation models were used to predict both the dipole moment of individual molecules and mutual orientations arising from contacts between molecules. Then, the calculated dipole moments and orientations were combined in an analytical coupling, which allowed for the prediction of effective (polarized) dipole moments for all distinct species in the liquid. As a proof-of-concept, the model focused on predicting the dielectric constant and was tested on 420 pure liquids, 269 binary organic mixtures (3792 individual compositions) and 46 aqueous mixtures (704 individual compositions). The model proved to be flexible enough to reach an unprecedented satisfactory mean relative error of about 16-22% and a classification accuracy of 84-90% within four meaningful classes of weak, low average, high average and strong dielectric constants. The method also proved to be computationally very efficient, with calculation times ranging from a few seconds to about ten minutes on a personal computer with a single CPU. This success demonstrates that much of the microscopic polarization concept can be satisfactorily described based on a simple molecular contact theory. Moreover, the new model for dielectric constants provides a useful alternative to computationally expensive molecular dynamics simulations for large scale virtual screenings in chemical engineering and material sciences.

Chemical Composition-Microstructure-Dielectric Constant Relations of Mg-Doped Calcium Titanate Synthesized by Solid State Reaction Technique

It has been generally accepted that doping of dielectric materials could significantly contribute to compositional and microstructural evolution, which consequently lead to alteration in dielectric properties. In this study, the effects of adding magnesium (Mg) at 5,10 and 20at% on the chemical composition, microstructure and dielectric constant of calcium titanate (CaTiO3) synthesized by solid state reaction was assessed. Chemical composition analysis using an X-ray diffraction technique CaTiO3 doped with 5 at% Mg has been found to contain a single phase whereas samples doped with 10 and 20 at% Mg both exhibited apparent secondary phase (MgO). Microstructural examination however, revealed that no significant variation in particle size, grain size and density were evident among the samples of different Mg contents. Average dielectric constants obtained from the entire samples ranged from 245.9 to 387.6 (at 1 MHz) and the sample with the highest dielectric constant was that doped with 5 at% Mg. Enhancement of dielectric constant in the samples with the lowest level of Mg doping has been attributed largely to the homogeneity of its chemical composition.

Fabrication of lanthanum doped BaTiO3 fine-grained ceramics with a high dielectric constant and temperature-stable dielectric properties using hydro-phase method at atmospheric pressure

Lanthanum doped BaTiO3 powders were synthesized by the hydro-phase method at atmospheric pressure, which controls the uniformity and particle size of the ceramic powders. The effects of La3+ ions concentration on the microstructure and dielectric properties of BaTiO3 ceramics were studied. The results suggested that both the average grain size and dielectric constants (εr and εmax) of the ceramics decreased as the concentration of La3+ increased. The ceramic met the X8R specifications: La3+ ions concentration of 3mol%, a permittivity of 2322, low dielectric loss of less than 0.6% at room temperature, and average grain size of about 260nm.

Influences of B-site Cations on Intrinsic Dielectric Properties of Ba(B′1/3B′′2/3)O3 Materials

Effects of B-site cations on polar phonon frequencies, mode effective charges, and lattice dielectric response of 1:2 ordered Ba(Mg1/3Ta2/3)O3, Ba(Mg1/3Nb2/3)O3, and Ba(Zn1/3Nb2/3)O3 microwave dielectrics are studied using first-principles calculations. The calculated optical phonon frequencies and the average dielectric constants are found to be in excellent agreement with experiments. Replacing Ta (Mg) with Nb (Zn) is found to significantly affect frequency, oscillator strength, and mode effective charges of the dominant polar phonons. Dielectric contributions from O anions are dominant and strongly B-site dependent. Furthermore, we demonstrate that the greater the dielectric contribution from O anions, the smaller the measured microwave Q × f-factor.

A new method to estimate the average dielectric constants of aged power cables

A new method to estimate the average dielectric constants of cable sections that have undergone aging is proposed. By comparing the experimental Joint Time-Frequency Domain Reflectometry waveform signatures from a new and an aged cable of the same type, it is demonstrated that the change in the average dielectric constant of the insulation material due to aging can be estimated. For example, for a cable containing Cross-Linked Polyethylene insulation, accelerated aging tests based on the modified Arrhenius equation that simulate 120 years of aging at 50 °C operating temperature show that the dielectric constant of the insulation decreases by more than 34.5%. The same tests performed on another cable containing Ethylene-Propylene Rubber insulation show that the average dielectric constant of the insulation decreases by 10.4%. The efficacy of the method is further demonstrated by estimating the increase in the average dielectric constant of a wedge section of a cable that contained water intrusion.

Electronic, dielectric, and optical properties of the B phase of niobium pentoxide and tantalum pentoxide by first‐principles calculations

AbstractWe report a theoretical study of the electronic structure and optical properties of the B phase of niobium pentoxide (B‐Nb2O5) and tantalum pentoxide (B‐Ta2O5) by means of first‐principle calculations. We have used density functional theory along with the revised Perdew–Burke–Ernzerhof (PBEsol) exchange‐correlation functional and the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional. It has been found that these compounds are indirect wide‐gap semiconductors, the calculated gaps for B‐Nb2O5 (B‐Ta2O5) are and eV. We have also calculated the frequency‐dependent and static dielectric tensor, the refraction index and the transmittance. The calculated average static dielectric constants of B‐Nb2O5 (B‐Ta2O5) are 33.7 (30.9), in good agreement with the available experimental data.

Structural and dielectric behavior of pulsed laser ablated Sr 0.6Ca 0.4TiO 3 thin film and asymmetric multilayer of SrTiO 3 and CaTiO 3

Homogeneous thin films of Sr 0.6Ca 0.4TiO 3 (SCT40) and asymmetric multilayer of SrTiO 3 (STO) and CaTiO 3 (CTO) were fabricated on Pt/Ti/SiO 2/Si substrates by using pulsed laser deposition technique. The electrical behavior of films was observed within a temperature range of 153 K–373 K. A feeble dielectric peak of SCT40 thin film at 273 K is justified as paraelectric to antiferroelectric phase transition. Moreover, the Curie–Weiss temperature, determined from the ε′( T) data above the transition temperature is found to be negative. Using Landau theory, the negative Curie–Weiss temperature is interpreted in terms of an antiferroelectric transition. The asymmetric multilayer exhibits a broad dielectric peak at 273 K, and is attributed to interdiffusion at several interfaces of multilayer. The average dielectric constants for homogeneous Sr 0.6Ca 0.4TiO 3 films (∼650) and asymmetric multilayered films (∼350) at room temperature are recognized as a consequence of grain size effect. Small frequency dispersion in the real part of the dielectric constants and relatively low dielectric losses for both cases ensure high quality of the films applicable for next generation integrated devices.

WET Sensor Performance in Organic and Inorganic Media with Heterogeneous Moisture Distribution

Interest in electronic monitoring of soil water has grown as increased demand for water creates a greater need for effective water management. Relatively inexpensive commercial soil water sensors that use measured soil dielectric properties to calculate soil water content have been developed to address this need but have received little independent testing of critical calibration procedures and parameters. The WET sensor (Delta‐T Devices, Cambridge, UK) is one such sensor. The two primary objectives in this study were to: (i) determine appropriate calibration parameters for a variety of inorganic soils and organic media; and (ii) determine how WET sensor readings are affected in media with strongly contrasting water contents. We found that the two‐point calibrations suggested by the manufacturer yielded parameters that were not significantly different (α = 0.05) from those suggested by the manufacturer and yielded values consistent with well‐established oven‐dry values. For the organic media, we found that accurate, media‐specific calibration could be obtained for all media tested and that the general form of the calibration equation used for soils applies to organic media. Experiments in a variety of layered media showed that, in contrast to time domain reflectometry results, the WET‐measured dielectric value is the arithmetic average of the two contrasting layers. In soils, the linear correlation between measured and arithmetic average dielectric constants was very high (R2 > 0.99) for all four soils tested. This indicates that the upward infiltration calibration technique is generally inappropriate for the WET sensor.

On the Monolayer Adsorption of Thiol‐Terminated Dendritic Oligothiophenes onto Gold Surfaces

AbstractThe self‐assembled monolayer formation of a series of thiophene dendron thiols with different generations and alkyl chain lengths onto gold surfaces is studied. Average film thicknesses and dielectric constants were calculated from SPR using a two‐subphase differential method. The in situ adsorption of the thiophene dendron thiols was monitored by SPR kinetics measurements and fitted using an empirical three‐step model. Electrochemical redox molecular probing experiments provided additional insight into surface coverage, which showed different abilities to block electron transfer at the monolayer/electrode interfaces. The surface coverage of the films was also estimated by QCM measurements and supported by static WCA measurements. magnified image

Investigation of Electronic Structures of Titanium Nitride Layers on TiNi Substrate

The electronic structure of titanium nitride layers formed on the TiNi substrates is examined by Auger electron spectroscopy and electron emission distribution methods. Spectral analysis shows that the on-top carbon layer has a graphite structure and the neighbouring layer is constituted of titanium nitride. The shape of the main valence spectra was explained by the Hubbard model. From the comparison of experiment and theory the model parameters were estimated. Besides, the existence of surface and internal plasmons verifies the layered structures with average dielectric constants.

Pure-silica zeolite thin films by vapor phase transport of fluoride for low-k applications

A new method to synthesize pure-silica zeolite films is presented. Specifically, this method uses fluoride-mediated syntheses that involve the vapor phase transport of the mineralizing agent, fluoride, to crystallize a precursor film deposited by dip-coating techniques to obtain thin films of pure-silica zeolites with LTA, CHA, and ITW topologies. The films are characterized by a combination of X-ray diffraction, field emission scanning electron microscopy, and X-ray energy dispersive analyses. The films are polycrystalline, intergrown, continuous and well-adhered to their substrates. The usefulness of these thin films as low-k materials, that are needed to reduce cross-talk noise and energy dissipation between transistors in an integrated circuit, is demonstrated via evaluation of the pure-silica LTA film. The LTA topology has the lowest framework density (FD=14.2) of the 19 known pure-silica zeolites, and theoretically could have the lowest dielectric constant. The average dielectric constants of the LTA films are calculated from capacitance measurements at a frequency of 1MHz with metal–insulator–metal structures on low-resistivity silicon substrates, and yield an average k=1.69, well within the ultra low-k material requirements (k between 2.3 and 2.6).

Morphological characteristics of mechanically processed ZnO and MnO 2 powder mixtures

The evolution of structural–morphological characteristics of ZnO + 1 wt.% MnO 2 and ZnO + 10 wt.% MnO 2 samples during prolonged mechanical treatment (MT) was investigated by X-ray, AFM, LPS, SEM and IR methods. Changes in crystallite size due to mechanical activation were determined from X-ray measurements. These results were correlated with changes in particle size followed by SEM and AFM. Particle and aggregate size distributions were determined from LPS measurements. Interpretation of the evolution of IR-absorption peaks during mechanical activation using the theory of average dielectric constants enabled analysis of changes of particle and agglomerate shapes. All these results enabled establishment of a relationship between crystallites, particles, aggregates of particles, and superficial processes that occur during mechanical activation.

Synthesis of (Ba1−xSrx)(Ti0.5Zr0.5)O3 ceramics and effect of Sr content on room temperature dielectric properties

The compositions in the system (Ba1−xSrx)(Ti0.5Zr0.5)O3 with different Sr (x) content, were synthesized through solid oxide reaction route. The phase formation behaviors in the system were investigated by XRD. The room temperature dielectric properties of the compositions were investigated in the frequency range 10 Hz to 13 MHz. The solid solution system Ba1−xSrxTi0.5Zr0.5O3 remains as cubic perovskite up to x 0.6. Composition with x = 0.6 contains a mixture of cubic and tetragonal phases with broadened diffraction pattern. It is observed that the increasing of Sr substitution results in the decreasing of bulk density, average grain size and dielectric constants etc. in the composition system. The AC dielectric conductivity of the ceramics also decreases with the increase in Sr-substitution due to decrease in loss as well as grain size with that substitution.

In situ real-time spectroscopic ellipsometry study of HfO2 thin films grown by using the pulsed-source metal-organic chemical-vapor deposition

The HfO2 thin-film growth process is investigated by using in situ real-time spectroscopic ellipsometry (SE) technique combined with the first-principles molecular-orbital (MO) calculations of the electronic states. The HfO2 films are grown on the silicon substrate by using the pulsed-source metal-organic chemical-vapor deposition method. Particular attention is paid to the formation of an interfacial layer at the early stage of the growth process by monitoring energy-dependent dielectric constants of the film. The energy dependence of the electronic polarizabilities and dielectric constants is calculated for the amorphous HfO2, SiO2, and HfSiO4 films based on the electronic states and density of states obtained using the discrete-variational Xα MO method with the unit cluster model. The measured SE spectra show that the average dielectric constants of the film vary gradually from those for SiO2 to those for HfO2 when the number of deposition cycles increases. By comparing the varied dielectric constants during the film growth with the calculated results, we find that the HfO2 film growth process can be divided into two stages with different growth mechanisms: SiO2 and HfxSiyOz layers are grown at the first stage, which are regarded as the interfacial layers, and the HfO2 layer formation becomes predominant at the second stage.

Ab initio calculations for large dielectric matrices of confined systems.

Calculations for optical excitations in confined systems require knowledge of the inverse screening dielectric function epsilon(-1)(r,r(')), which plays a crucial role in determining exciton binding energies. We present a new efficient real-space method of inverting and storing large ab initio dielectric matrices of confined systems, which relies on the separability of epsilon matrix in r and r('). The method has allowed, for the first time, full ab initio calculation of epsilon(-1)(r,r(')) of dimension N approximately 270 000, and for quantum dots as large as Si35H36. The effective screening in Si quantum dots up to 1.1 nm in diameter is found to be very ineffective with average dielectric constants ranging from 1.1 to 1.4.

Study of second-phases in Ba(Mg1/3Ta2/3)O3 materials by microwave near-field microscopy

Abstract A three-dimensional (3D) finite element simulation was performed to model the behavior of the measuring resonator in an evanescent microwave probe (EMP). A calibration curve was derived using the frequency shift data as standards. The EMP measuring techniques was applied to measure the dielectric properties of Ba(Mg 1/3 Ta 2/3 )O 3 , BMT, materials. The average dielectric constants for these BMT materials ( e r =26–30) are consistent with the dielectric properties measured by conventional cavity method. The EMP mapping indicates clearly the presence of higher or lower dielectric constant inclusions in the one-step processed BMT materials, which contain a large proportion of secondary phases. The measurements demonstrate that the EMP method is capable of mapping the distribution of dielectric constant at very high spatial resolution.

Measurement of Complex Permittivity of Asphalt Pavement Materials

To facilitate applications of road penetration radar and other nondestructive testing technologies on roads, an apparatus was developed for the measurement of complex permittivity of construction materials. The system consists of an automatic network analyzer, a sample holder, coaxial cable connections, and data processing software. The sample holder can accommodate either laboratory-prepared or field-drilled asphalt and concrete samples with maximum aggregate sizes up to 19 mm and lengths up to 400 mm. A computer program is used to convert the parameters measured by the automatic network analyzer into the real and imaginary parts of the complex permittivity. The dielectric constants of 43 laboratory-prepared asphalt samples of fairly consistent bulk densities were measured over the frequency domain of 0.1 MHz to 1.5 GHz. The average dielectric constants were 6.0 ± 0.15 for dry specimens and 6.52 ± 0.99 for soaked samples over the frequency range of 8–900 MHz. A linear relationship was observed between the gravimetric moisture content and dielectric constant up to a moisture content of 1%, with dielectric constant increasing by 0.62 for every 1% increase of moisture content. The results indicate that the asphalt content and mix type did not significantly affect the dielectric constants, whereas the moisture content was identified as the predominant factor. The results provide much needed information on the dielectric properties of asphalt pavement materials.