Real Permittivity Research Articles

Laboratory study of the electrical properties of Lutetian limestones in the 100 Hz to 10 MHz frequency range

ABSTRACTLutetian limestones have been widely used in historical monuments within the Paris Basin during the course of the medieval and modern periods. Among the physical properties that can be used to assess the evolution of the limestonesin situin the buildings and their present health, the complex effective permittivity in the 10–100 kHz frequency range is easy to measure and reflects the internal structure of the stone along with the dependence on the water content. To improve our knowledge about this property, a laboratory study on four samples collected in the relevant quarries has been undertaken using measurements in the 100 Hz–10 MHz frequency range. Except close to zero water content, the observed results exhibit a quasi‐absence of variation of the real effective permittivity with the water content. The frequency variation fits fairly well with a model taking into account a Jonscher's decrease, a direct current conductivity, a high‐frequency dielectric permittivity and losses, and a relaxation phenomenon. When fitted by a Cole–Cole model, the magnitude of the corresponding relative permittivity change always stays close to 30, but the time constant varies from 1.0 μs to 0.1 μs as the water content increases.

Effects of crystallization kinetics on the dielectric and electrical properties of BiFeO3films

BiFeO3 thin films were prepared using the chemical solution route on Pt/TiO2/SiO2/Si(100) substrates under different crystallization kinetics. The crystallization kinetic effects on the dielectric and electrical properties have been investigated. These properties included dielectric permittivity, electric modulus, electrical conductivity measurements as a function of the temperature (300–525 K) and frequency (102–106 Hz), and leakage current measurements electric field range ± 30 kV/cm at room temperature. The differences observed in conductivity and current density of the BiFeO3 films were discussed in terms of possible defects induced by the crystallization kinetic. An anomalous relaxor-like dielectric behavior characterized by a broad maximum in the real dielectric permittivity as a function of temperature and the low-frequency dielectric dispersion has been observed. The nonexpected peaks in the real permittivity were accompanied by increasing at least four orders in the conductivity’s magnitude at high temperatures. The origin of the relaxor-like dielectric anomalies is discussed, suggesting that the dielectric permittivity peaks are artifacts due to carrier migration correlated to the onset of the Maxwell–Wagner effect.

Preparation, Characterization, and Microwave Absorption Properties of Cobalt-Doped SrFe12O19 Nanoparticles

Ferrite is the major absorbing components of conventional radar absorbing materials (RAM). However, conventional RAM made of the single-absorbing components cannot meet the comprehensive requirements of “thin, wide, light, and strong.” To overcome this limitation, a composite compound of cobalt-doped SrFe12O19 nanoparticles is currently exploited to improve absorbing ability. SrFe12−xCoxO19 (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25) composite ferrites were prepared using the sol-gel method. Results show that the powders obtained are pure lead-magnetite ferrite, and the properties of the samples are improved evidently after Co substitution. At room temperature, the samples substituted using Co exhibit typical permanent magnetism. When x = 0.2, the maximum saturation magnetization and coercivity of the powders are 55.8 A·2/kg and 302.4 kA/m, respectively. The real complex permittivity part of SrFe12−xCoxO19 first increases and then decreases with the increase in x and has a maximum value of x = 0.2. The complex imaginary permittivity part fluctuates with the increase in x; it first decreases, then increases, and finally decreases. With the increase in x, the complex permeability real part of the sample does not change much between 2 GHz to 16 GHz but first increases and then decreases in the range of 16-18 GHz. The imaginary part of the complex permeability first increases and then decreases, reaching its maximum at x = 0.2. The attenuation constants and absorbing properties of the samples before and after substitution were analyzed. The matching thickness of strontium ferrite (SrFe12O19) is 5.2 mm, the matching thickness of SrFe11,8Co0.2O19 (x = 0.2) is reduced to 2.4 mm, the minimum reflectivity is −24.7 dB (13.8 GHz), and the microwave absorption bandwidth lower than −10 dB is 4.7 GHz (11.6-16.3 GHz). These results indicate that an appropriate amount of Co substitution could greatly improve the absorbing performance of SrFe12O19. This study provides a simple method for the preparation of Co doped strontium ferrite. The microwave absorbing properties of the composite powders are excellent and have potential engineering application value.

Inverse-design of non-Hermitian potentials for on-demand asymmetric reflectivity.

We propose a genetic algorithm-assisted inverse design approach to achieve 'on- demand' light transport in periodic and non-periodic planar structures containing dielectric and gain-loss layers. The optimization algorithm efficiently produces non-Hermitian potentials from any arbitrarily given real (or imaginary) permittivity distribution for the desired frequency selective and broadband asymmetric reflectivity. Indeed, we show that the asymmetric response is directly related to the area occupied by the obtained permittivity distribution in the complex plane. In particular, unidirectional light reflection can be designed in such a way that it switches from left to right (or vice versa) depending on the operating frequency. Moreover, such controllable unidirectional reflectivity is realized using a stack of dielectric layers while keeping the refractive index and gain-loss within realistic values. We believe this proposal will benefit the integrated photonics with frequency selective one-way communication.

Tuning the microwave electromagnetic properties of biochar-based composites by annealing

We report on the effects of thermal treatment of biochar embedded in epoxy-based composites on their microwave electrical properties, linking such properties to the material structure investigated by Raman, X-ray photoelectron spectroscopy, and X-ray diffraction. Annealing temperatures in the range 900–1500 °C and biochar concentrations in the epoxy matrix in the range from 5 to 25 wt.% were investigated. The microwave analysis, in the range from 250 MHz to 6 GHz, allowed us to determine the complex permittivity of composites and, through a proper deconvolution technique, to determine the contribution of biochar inclusions alone. High values of real permittivity (up to 220) and conductivity (up to 17 S/m) were evaluated for the biochar particles at 5 GHz, after the 1500 °C thermal treatment. A clear correlation between electrical properties and the biochar microstructure emerged from the dataset, with real permittivity and conductivity increasing as carbon inclusions transform from amorphous to nanocrystalline graphite. Conversely, the percentage of aromatic carbon has a weaker influence on the microwave properties. This study opens to the possibility of tailoring the high-frequency properties of biochar and biochar composites through proper thermal treatments.

The Structure, Morphology, and Complex Permittivity of Epoxy Nanodielectrics with In Situ Synthesized Surface-Functionalized SiO2.

Epoxy nanocomposites have demonstrated promising properties for high-voltage insulation applications. An in situ approach to the synthesis of epoxy-SiO2 nanocomposites was employed, where surface-functionalized SiO2 (up to 5 wt.%) is synthesized directly in the epoxy. The dispersion of SiO2 was found to be affected by both the pH and the coupling agent used in the synthesis. Hierarchical clusters of SiO2 (10–60 nm) formed with free-space lengths of 53–105 nm (increasing with pH or SiO2 content), exhibiting both mass and surface-fractal structures. Reducing the amount of coupling agent resulted in an increase in the cluster size (~110 nm) and the free-space length (205 nm). At room temperature, nanocomposites prepared at pH 7 exhibited up to a 4% increase in the real relative permittivity with increasing SiO2 content, whereas those prepared at pH 11 showed up to a 5% decrease with increasing SiO2 content. Above the glass transition, all the materials exhibited low-frequency dispersion effect resulting in electrode polarization, which was amplified in the nanocomposites. Improvements in the dielectric properties were found to be not only dependent on the state of dispersion, but also the structure and morphology of the inorganic nanoparticles.

(Bi13Co11)Co2O40–Co3O4 nanocomposites: Synthesis, characterization and application as substrate for microstrip patch antenna

The sillenite-cobaltite nanocomposites with chemical formula (Bi13Co11)Co2O40–Co3O4 were synthetized and characterized for application as substrate in a microstrip patch antenna. To prepare the sample, the combustion method using urea as fuel was applied. The structural and vibrational characterizations were done through X-ray diffraction and infrared spectroscopy. The morphology of the sample was studied through FESEM images. The magnetization as a function of magnetic field recorded at 300 K confirmed the paramagnetic character of the sample. Electric characterization was performed from 1.0 GHz to 8.5 GHz aiming a wide frequency spectrum data, presenting steady real relative permittivity around 7, with low losses as results. A microstrip patch antenna was designed by cavity method with the nanocomposite as substrate for application in X-band communication services. Reflection coefficient measurements displayed a good agreement with simulations, achieving only 0.39% error in resonance frequency, validating the performed morphological and electrical characterizations, as antenna design. Simulated radiation pattern is also presented, with coherent results for a directive device.

A Modified SIW Re-Entrant Microfluidic Microwave Sensor for Characterizing Complex Permittivity of Liquids

In this paper, a modified substrate integrated waveguide (SIW) re-entrant microwave sensor is implemented by an annular slot loaded SIW re-entrant cavity resonator (RECR) to evaluate complex permittivity of liquid under test (LUT). The fringe electric field (E-Field) around metal post of the SIW RECR is suppressed by loading the plane disk. And then, by loading a narrow annular slot, the corresponding fringe non-linear capacitor is transferred as an annular capacitor which has linear response to real permittivity of LUT and is connected in parallel with the gap parallel plate capacitor of the RECR, and then the corresponding physical equivalent circuit model is accurately established. The dependence of the sensitivity of the proposed sensor on the dimension of the annular slot is discussed. The unique quantitative function relationship, instead of a mathematical fitted one, between the resonant frequency and the real permittivity of LUT is obtained to characterize the real permittivity predictive model by reasonably neglecting the ratio term of annular-slot capacitance to LUT effective capacitance. Additionally, an improved algorithm for more accurately extracting imaginary permittivity is proposed. A prototype of the proposed sensor is fabricated and measured. The predictive model of the complex permittivity is calibrated by using of methanol-water mixtures with known complex permittivity and is further verified by ethanol-water mixtures. The result of experiment verification, with the maximum measurement errors of real and imaginary permittivity of 4.07% and 7.79%, demonstrates that the complex permittivity of the liquid can be accurately characterized by using the proposed sensor.

120 MeV Au+9 swift heavy ion irradiation of pulsed laser deposited BaM/LSMO bilayers

In the present study, we report the structural and electrical properties of pulsed laser deposited (PLD) bilayers of BaFe12O19 (BaM) and La0.67Sr0.33MnO3 (LSMO) thin films deposited on platinized silica substrate. Structural and electrical variation arising due to irradiation of 120 MeV Au+9 ion in these bilayers were studied with different fluences. X-ray diffraction (XRD) shows co-existence of phase pure BaM and LSMO throughout the measurement range. Scanning electron micrographs reveals the influence of irradiation on grains and its density. Frequency dependent real permittivity, imaginary permittivity, tangent loss and AC conductivity are highly affected by irradiation. Well established theoretical models like Maxwell-Wagner polarization, Relaxation mechanism, Universal dielectric response and Jonscher's power law have been employed to explain irradiation induced discrepancies in electrical properties. Magnetic field dependent magnetodielectric properties have been investigated for ion beam assisted modifications in the presently studied samples.

An evaluation and characterization study of knitted fabrics for use as telecommunication device substrate

This work aims to characterize and evaluate the textiles and electrical properties that have a vital impact on weft knitted for use as substrates applied to telecommunications devices. There are several applications where flexible devices are required, for example when devices are contained in technical uniforms or technical textiles garments. So, to understand the characteristics of the substrate for use in antennas, therefore, it is necessary to characterize the different types of blended knitted (100% Cotton, 50% Cotton/50% Polyester, 50% Cotton/50% Spandex and 50% Cotton/50% Polyamide) to indicate the composition of blended Jersey structures that exhibited significantly better properties for application in E-textiles. Although the knitted fabrics studied in this article are developed for conventional applications, their real permittivity and loss tangent are satisfactory for use in applications as a substrate and the differences between values in each knitted fabric can be linked to the composition (CO, CO + PES, CO + PUE and CO + PA) studied.

Negative permittivity behavior in Ti3AlC2-polyimide composites and the regulation mechanism

With the rapid development of metamaterials, percolating composites with negative dielectric constant have become a research hotspot in recent years. In this work, Ti3AlC2-polyimide percolating composites were prepared by mechanical mixing and pressure forming, and their microstructure and dielectric properties were investigated in detail. By controlling the Ti3AlC2 content, an electrical percolation phenomenon appears with the formation of Ti3AlC2 conductive network. The conductive mechanism changed from hoping conduction to metal-like conduction. Above the percolation threshold (68%–72%), real permittivity changes from positive to negative and mainly due to the damped motion of the free electrons. The Drude model analysis showed that the negative permittivity resulted from the plasma-like oscillation of free electrons. The equivalent circuit analysis indicated that the generation of negative permittivity was closely related to the appearance of inductance. This work provided a simple and effective strategy for regulating negative permittivity and promoted its application.

Determining the Dielectric Tensor of Microtextured Organic Thin Films by Imaging Mueller Matrix Ellipsometry.

Polycrystalline textured thin films with distinct pleochroism and birefringence comprising oriented rotational domains of the orthorhombic polymorph of an anilino squaraine with isobutyl side chains (SQIB) are analyzed by imaging Mueller matrix ellipsometry to obtain the biaxial dielectric tensor. Simultaneous fitting of transmission and oblique incidence reflection Mueller matrix scans combined with the spatial resolution of an optical microscope allows to accurately determine the full biaxial dielectric tensor from a single crystallographic sample orientation. Oscillator dispersion relations model well the dielectric tensor components. Strong intermolecular interactions cause the real permittivity for all three directions to become strongly negative near the excitonic resonances, which is appealing for nanophotonic applications.

Terahertz Permittivity of Pressed ZnO and CuO Powder in Polyethylene Pellets: Effect of Porosity

Terahertz (THz) spectroscopy is used to measure permittivity (100 GHz-2.5 THz) of ZnO and CuO powders with low fill factor pressed into pellets in a polyethylene binder. We show that porosity (air) of such pressed pellets has a large effect on effective pellet permittivity (~10%) and on the extracted permittivity of the oxide constituent (~150%). We explore a two-step analysis based on sequential application of different effective medium models, first to account for the air, and subsequently to extract the oxide's dielectric properties. We show that the combination of Vegard's law and the Maxwell-Garnett model is the best combination to account, respectively, for the air and the oxide powders. In this regard, the capacity that this approach has to adapt to each phase's physical characteristics by using multiple EMMs is an advantage. The resulting oxide permittivities are significantly larger than previously reported for such pellets as a consequence of the porosity. We find for the real relative permittivities of CuO and ZnO ~12.1 and ~8.9, respectively, in the THz range.

MgO nanoparticles dispersion effects in electro optical parameters of 5CB nematic liquid crystal

MgO nanoparticles (NPs) have been dispersed in pure 5CB in three various concentrations. It was found that by incrementing NPs concentration, dielectric permittivities (ε ∥ and ε ⊥) and dielectric anisotropy (Δε) continuously decrease. Real dielectric permittivities of pure and doped liquid crystals in terms of frequency in the range 50–500Hz were obtained. The influence of nano doping on physical and optical parameters, i.e. threshold voltage, ac electric conductivity, phase transition temperature, light transmission, splay elastic constant and refractive index anisotropy was investigated. The temperature-dependent dielectric properties have been improved in the frame of a novel six-parameter dielectric permittivity model.

Dielectric Properties of the Medusae Fossae Formation and Implications for Ice Content

AbstractThe extensive Medusae Fossae Formation (MFF) along the dichotomy boundary on Mars has geologic features indicative of wind erosion of low‐density material. There is evidence suggesting a water ice component, but with considerable uncertainty linked to the unknown MFF porosity and compaction behavior. We use SHARAD radar sounder data to estimate the real permittivity and loss tangent of MFF deposits, and compare these to a model for sediment compaction and to the properties of ice in mid‐latitude glaciers. In areas along the margins of Eumenides Dorsum, between Gordii Dorsum and Amazonis Mensa, and in northwest Zephyria Planum, the loss tangent is about 0.001 at 170 m and plateaus at about 0.003 for 310–550 m thickness. The real dielectric constant across the study areas ranges from 2 to 3. We propose that the MFF is a two‐layer deposit, with 300–600 m of fine‐grained, self‐compacting material above up to 2 km of minimally compacting, low‐loss material. The lower unit could be ice‐free and very coarse‐grained, but we see no evidence of extensive sand exposed by erosion. The lower layer might instead be ice‐rich and protected from sublimation by the dry cover. The volume of cover relative to a high ice content in the lower layer implies hybrid MFF formation as glacial or polar layered deposits capped by a dry, perhaps pyroclastic ash, component.

Advantages of a Multi‐Frequency Experiment for Determining the Dielectric Constant of a Layer in a Rectangular Waveguide and Free Space

AbstractAn inverse problem of reconstructing real permittivity of a plane‐parallel layer in a perfectly conducting rectangular waveguide or in free space from experimental data using an explicit expression for the scattering matrix is considered. In general, this problem is improperly posed and may be unsolvable due to inaccuracy of the experimental data, and for a perfect noiseless experiment the solution may be not unique because the scattering coefficients curve has self‐intersection points. It is shown that the traditional multi‐frequency method of measurements applied in vector network analyzers can be justified. The following facts are rigorously proved in the paper: nonuniqueness of the solution can be removed if the frequency resolution is sufficiently small; and an algorithm for processing measurement results using least squares provides an approximate solution to the problem that converges to the exact one when the quality of the experiment improves, the convergence rate depends on the number of frequencies used in the experiment.

Poles, physical bounds, and optimal materials predicted with approximated Mie coefficients

Resonant electromagnetic scattering with particles is a fundamental problem in electromagnetism that has been thoroughly investigated through the excitation of localized surface plasmon resonances (LSPR) in metallic particles or Mie resonances in high refractive index dielectrics. The interaction strength between electromagnetic waves and scatterers is limited by maximum and minimum physical bounds. Predicting the material composition of a scatterer that will maximize or minimize this interaction is an important objective, but its analytical treatment is challenged by the complexity of the functions appearing in the multipolar Mie theory. Here, we combine different kinds of expansions adapted to the different functions appearing in Mie scattering coefficients to derive simple and accurate expressions of the scattering electric and magnetic Mie coefficients in the form of rational functions. We demonstrate the accuracy of these expressions for metallic and dielectric homogeneous particles before deriving the analytical expressions of the complex eigen-frequencies (poles) for both cases. Approximate Mie coefficients can be used to derive simple but accurate expressions for determining complex dielectric permittivities that lead to poles of the dipolar Mie coefficient and ideal absorption conditions. The same expressions also predict the real dielectric permittivities that maximize (unitary limit) or minimize (anapole) electromagnetic scattering.

Dielectric Responses of Polyurethane/Zinc Oxide Blends for Dry-Type Cast Cold-Curing Resin Transformers.

The influence of different concentrations (0.5, 1.0, and 2.0 wt.%) of Zinc Oxide (ZnO) filler on the dielectric properties of the cold-curing polyurethane (PU) resin is presented in this study. For this purpose, the direct DC conductivity and the broadband dielectric spectroscopy measurements were used to describe the changes in dielectric responses of PU/ZnO nanocomposites over the frequency and temperature range, respectively. It can be stated that, the 1.0 wt.% nanoparticles and lower caused a decrease in the real relative permittivity compared to the pure PU resin, while the higher concentration of nanoparticles for frequencies above 1 Hz had the opposite effect. The presence of nanoparticles in the polyurethane resin affected the segmental dynamics of the polymer chain and changed a charge distribution in the given system. These changes caused a shift of local relaxation peaks in the spectra of imaginary permittivity and dissipation factor of nanocomposites. It is suggested that the temperature-dependent transition of the electric properties in the nano-composite is closely associated with the -relaxation and intermediate dipolar effects (IDE).

The effect of an AC electric field on the dielectric properties of Pb(Mg1/3Nb2/3)O3 ceramic

The dynamic dielectric response of Pb(Mg1/3Nb2/3 )O3 ceramic was experimentally studied as a function of the EAC amplitude field. An increase in real dielectric permittivity was obtained by increasing the applied electrical field within the investigated temperature range for frequencies below 10 kHz. The temperature of maximum dielectric permittivity and freezing temperature decreased with an increase in E AC. Nonlinear permittivity was studied and found to behave similarly to freezing temperature. A statistical model was used to fit the dielectric dispersion of real dielectric permittivity with temperature and frequency. The results are discussed in terms of different factors’ contributions to dielectric permittivity under different EAC field conditions.

Analysis of Forward Model, Data Type, and Prior Information in Probabilistic Inversion of Crosshole GPR Data

The crosshole ground penetrating radar (GPR) is a widely used tool to map subsurface properties, and inversion methods are used to derive electrical parameters from crosshole GPR data. In this paper, a probabilistic inversion algorithm that uses Markov chain Monte Carlo (MCMC) simulations within the Bayesian framework is implemented to infer the posterior distribution of the relative permittivity of the subsurface medium. Close attention is paid to the critical elements of this method, including the forward model, data type and prior information, and their influence on the inversion results are investigated. First, a uniform prior distribution is used to reflect the lack of prior knowledge of model parameters, and inversions are performed using the straight-ray model with first-arrival traveltime data, the finite-difference time-domain (FDTD) model with first-arrival traveltime data, and the FDTD model with waveform data, respectively. The cases using first-arrival traveltime data require an unreasonable number of model evaluations to converge, yet are not able to recover the real relative permittivity field. In contrast, the inversion using the FDTD model with waveform data successfully infers the correct model parameters. Then, the smooth constraint of model parameters is employed as the prior distribution. The inversion results demonstrate that the prior information barely affects the inversion results using the FDTD model with waveform data, but significantly improves the inversion results using first-arrival traveltime data by decreasing the computing time and reducing uncertainties of the posterior distribution of model parameters.