Imaginary Parts Of Complex Permittivity Research Articles

A study on the complex dielectric (ε*)/electric-modulus (M*)/impedance (Z*), tangent-loss (tanδ), and ac conductivity (σac) of the Al/(S:DLC)/p-Si/Au (MIS)-type Schottky structures in a wide range of frequency and voltage at room temperature (RT)

In this work, the Al/(S:DLC)/p-Si/Au Schottky structures were fabricated, and the real and imaginary parts of complex-permittivity (ε*), complex electric-modulus (M*), complex-impedance (Z*), loss-tangent (δ), electrical-conductivity (σac), and phase-angle (θ) were investigated in the wide-frequency-range of 2 kHz-2 MHz between −3.0V/4.0V. All these-factors were found to be heavily dependent on frequency and voltage because of the surface states (Nss), Maxwell-Wagner polarization, and interlayer. The voltage-dependent profile of tanδ and M″ exhibits a significant shift in peak location towards forward-bias voltages as frequency increases due to the relaxation process of the Nss and dipole polarization. The ε′ was found to be 571.81 (at 2 kHz) and 59.72 (at 1 MHz). The value of ε′, even at 2 kHz, is about 151.5 times higher than the maximum value of traditional SiO2 (3.8) insulators, and hence, it can be successfully used instead of insulators to store more electric charges or energy.

Fabrication and microwave absorption properties of BaTiO3 -SrTiO3-Ni0.5Zn0.5Fe2O4 polymer nanocomposites

In this present work, barium titanate (BaTiO3), strontium titanate (SrTiO3) and nickel zinc ferrite (Ni0.5Zn0.5Fe2O4) were used to prepare electromagnetic wave absorption composite. Homogeneous polymer composites containing of BaTiO3 -SrTiO3 – Ni0.5Zn0.5Fe2O4 was produced by the physical mixing method. Surface morphology of polymer composites was characterized by scanning electron microscopy (SEM). Microwave absorbing and electromagnetic parameters were recorded by vector network analyzer (VNA).The influence of the ratio of nickel-zinc magnetic particles into the dielectric materials was studied. Microwave absorption properties of polymer composites were determined by complex permittivity measurement and the effects of the barium titanate, strontium titanate and nickel-zinc magnetic particles on the microwave absorption properties were examined in the frequency range of 2–16 GHz. Real and imaginary parts of complex permittivity and permeability were determined by reflection/transmission technique. The dielectric interactions between two different dielectric materials were investigated and the role of Ni0.5Zn0.5Fe2O4 ferrite in the composite has been explored. Results showed that The RL of absorber composites with thickness of 3.0 mm reached a maximum value of −9.47 dB in the frequency range from 2.00 to 16.00 GHz and demonstrated that the nanocomposites could be use as electromagnetic absorber.

Achieving absorption-type electromagnetic shielding performance in silver micro-tubes/barium Ferrites/Poly(lactic acid) composites via enhancing impedance matching and electric-magnetic synergism

High conductivity can give materials excellent electromagnetic shielding performance, but it leads to serious impedance mismatching and causes inevitable secondary pollution. Developing materials with both excellent microwave absorption and microwave shielding performance remains a formidable challenge. Herein, absorption-type electromagnetic shielding materials with high electromagnetic shielding effectiveness (EMW SE) values were successfully prepared by combining hollow silver micro-tubes and magnetic nano-barium ferrites. The electromagnetic parameters and impedance matching of the composites could be easily regulated by changing the ratio of silver micro-tubes (C) and nano-barium ferrites (M). Thanks to micro-tube structure and the electric-magnetic synergism of the fillers, the composites with the C:M ratio of 9:1 exhibited a high absorption coefficient (A) value of ∼0.77 and a high EMW SE value of ∼100 dB, simultaneously. The absorption-type shielding mechanism of the composites was also evaluated via discussing real and imaginary parts of complex permittivity, real and imaginary parts of complex permeability, and Cole-Cole curves. Furthermore, the composites with the C:M ratio of 3:7 exhibited excellent microwave adsorption performance with the minimum reflection loss of −46.3 dB at thickness of 3.0 mm and a maximum effective absorption band-width of 6.13 GHz.

Magnetic properties of CCTO doped with GeO2

The high dielectric constant presented by CaCu3Ti4O12 (CCTO) makes this material promising for industrial applications, in particular for electronic devices. Nevertheless, the preparation method and the doping by oxides has a great influence on the microstructure, and consequently in the dielectric properties. In this work we prepared and studied CCTO doped by germanium oxide, in concentrations up to 10% by weight. X-ray diffraction shows the presence of nanocristals. The grains and the grain boundaries compositions have been characterized by scanning electron microscopy with energy dispersive X-ray spectrometry mapping. The magnetization measurements show an antiferromagnetic behaviour with a Néel temperature TN=25 K, independent of the GeO2 doping (up to 6%). Analyses of the high temperature dependence of the magnetic susceptibility show that the increase of the GeO2 doping decreases the paramagnetic temperature. Dielectric spectroscopy measurements, in the frequency range from 75 kHz to 30 MHz, at room temperature, have been carried out. Cole-Cole model of dielectric relaxation adjusts correctly the data. The results, obtained with the different techniques, indicate that there is the increase of samples grain size up to 6% of germanium oxide, which causes an increase of the real and imaginary parts of complex permittivity.

Combined microwave dielectrometry and molecular dynamic study of aqueous solutions of human serum albumin with additives

We combined the microwave dielectrometry method for the complex permittivity experimental study of aqueous Human Serum Albumin (HSA) solutions and a molecular dynamics simulation of similar modelling aqueous solutions. Using microwave dielectrometry we obtained that the real and imaginary parts of complex permittivity of all studied solutions (HSA water solutions, HSA water solutions with NaCl or glucose) decrease at the HSA concentration growing. The molecular dynamics simulation of HSA aqueous solutions showed that the increase of the HSA concentration causes the number of H-bound increase between water and protein molecules and leads to complex permittivity value decrease for the tested solutions. Thus, the molecular dynamics simulation results are in good agreement with microwave dielectrometry experimental data for HSA aqueous solutions with the addition of NaCl and glucose. Our study can be applied in the ecological investigations of wastewater samples owing to demonstrated sensitivity of complex permittivity parameters measured to the small changes of the concentration in the solutions.

Influence of Quartz Fiber on Electromagnetic Wave Transmission Properties of High-Alumina Cement Paste

In this paper, the effects of quartz fibers on the resistivity, complex permittivity, complex permeability, and S-parameters of high-alumina cement pastes are investigated. Meanwhile, the change of microstructure after adding quartz fibers were analyzed by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM). The results show that with the increase the content of quartz fiber, the real part of complex permittivity decreases, while the imaginary part of complex permittivity, dielectric loss tangent, and resistivity increased. At the same time, there are more small pores, and the interface situation is more complicated after adding quartz fiber. Therefore, the reflectivity decreases and the absorptivity increases, but the scope of increase in the absorptivity is smaller than the decrease in the reflectivity, resulting in an increase in the transmittivity. When the content of quartz fiber is 0.15, 0.30, 0.45, and 0.60%, the average transmittance of high-alumina cement paste is increased by 3.69, 6.18, 15.51, and 21.03% respectively. It is indicated that the quartz fibers can improve the wave transmission properties of the high-alumina cement paste.

Research on the electromagnetic wave absorption properties of GNPs/EMD cement composite

Electromagnetic wave pollution has been paid more and more attention with the improvement of human ecological awareness. Hence urban construction materials with electromagnetic wave absorption properties will be demanded widely in the future. In this paper, the electromagnetic wave absorption properties of cement composites with various dosage graphene nanoplates (GNPs) and electrolytic MnO2 (EMD) are investigated and the electromagnetic reflectivity loss, electromagnetic parameter of cement composites are tested and discussed in frequency range of 2–18 GHz. The effect of GNPs and EMD on complex permittivity, complex permeability of cement composites is analyzed, and further mechanism analysis are discussed combined with XRD and SEM micrographs. Experimental results show that cement composites with 1.0% GNPs and 10.0% EMD exhibit lower electromagnetic reflectivity loss curves, which is the optimal dosages. Lowest electromagnetic reflectivity loss curve is achieved when 1.0% GNPs and 10.0% EMD incorporated together and the effective absorption frequency width (lower than −10 dB) is 5.8 GHz, of which more than 90% EMWs energy is translated to thermal energy and absorbed by matrix, reaching similar EWMs absorption effect of absorption coating materials. Besides, the imaginary part of complex permittivity and dielectric loss tangent of cement composites increases when GNPs and EMD added, indicating better EMWs absorption performance.

Characterization of Complex Dielectric Permittivity of Concrete by GPR Numerical Simulation and Spectral Analysis

In this paper, we present a numerical finite-difference time-domain (FDTD) simulation procedure developed to quantify the frequency-dependent ground penetrating radar (GPR) spectral responses occurring in four on-site scenarios involving concrete that is dry, half-saturated, saturated and chloride- contaminated. The responses are (1) numerically simulated by making use of the real and imaginary parts of complex permittivity derived from the GPR signal’s two-way travel time and rebar reflection amplitude, respectively; then (2) characterized using Nyquist and Bode plots, and (3) compared to the wavelets obtained from authentic concrete specimens. The characterization shows good correspondence with the well-established Debye’s models. Experimental validation shows that the simulated dispersion model is compatible with authentic concrete specimens when an optimal centre frequency is used. The method demonstrated in this paper can be used to convert GPR into a spectral analyser for predicting the on-site variability in material properties, the expected depth ranges of targets, and levels of attenuation and scattering before actual GPR survey.

Effective dielectric properties of Cement/Ba0.06(Na0.5Bi0.5)0.94TiO3 composites: A comparative approach

Lead-free ceramic powder of a morphotropic phase boundary composition Ba0.06(Na0.5Bi0.5)0.94TiO3 (BNBT) was prepared from a solid-state synthesis route. The cement-ceramic (1−ϕ)cement/ϕBNBT; 0 ≤ ϕ 1.0 composites were fabricated. The filler concentration-dependent values of the bulk density and real part of complex permittivity showed an increasing trend of variation while the apparent porosity and imaginary part of complex permittivity followed a decreasing trend. In order to test the acceptability of dielectric mixture equations of the inclusion material in the mixture, five such equations have been chosen. The Bruggeman, and Rother-Lichtenecker equations showed their coherence with minimal deviation from the experimental results of the real part of complex permittivity for the entire measurement range of volume fractions. Also, a first-order exponential growth/decay type of mathematical model was suggested which could fit the experimental data excellently well (r2 > 0.97).

Linear optical properties of 2d assembly of interacting gold nanoparticles: analytical approach in dipole approximation

Using a Drude-like model for the conduction electrons of Metal Nanoparticles (MNPs) assembled in a periodic two-dimensional (2D) array, considering dipole-dipole interactions of adjacent particles, an analytical expression is achieved for the MNP permittivity where the functionality of interaction term on the different geometric and physical parameters is evident. A numerical analysis is carried out for a gold NP array for two different sizes of NPs and two different host media of water and glass. It is shown that, interaction of NPs leads to a substantial increase in the extinction cross section, the red-shift of the Surface Plasmon Resonance (SPR) wavelength and decrease in the full width at half maximum (FWHM) of cross section. The absolute values of the real and imaginary parts of complex permittivity of each MNP decrease in comparison with the single particle case.

Low frequency AC conduction and dielectric spectroscopy investigations on graphene oxide using dielectric modulus approach

Graphene oxide (GO) was chemically synthesized by improved Hummer's method. The synthesis was confirmed by Raman and FT-IR spectroscopy. The dielectric relaxation studies of graphene oxide (GO) in the frequency range of 100 Hz - 1 MHz and in the temperature range of 77 - 475 K are reported here. At lower temperatures (<250 K), the measured ac conductivity shows linear variation with frequency. Whereas, at higher temperatures, it is almost independent of frequency as dc conductivity predominates in this region. In the dielectric measurement studies, it is observed that dielectric constant increases rapidly with temperature up to 300 K. Broad loss peaks are observed in the temperature region where the measured ac conductivity approaches dc conductivity. The behaviour of both high values of real as well as imaginary part of complex permittivity has been thoroughly investigated in the light of dielectric modulus formalism and is attributed to the interfacial polarization between insulating sp3 region and conducting sp2 domains. The material exhibits great potential towards giant dielectric constant applications.

Linear optical properties of a linear chain of interacting gold nanoparticles

In a Drude-like model for the conduction electrons of metal nanoparticles (MNPs) in a periodic linear chain, considering dipole-dipole interactions of adjacent particles, an analytical expression is derived for each particle permittivity for two different polarizations of incident light: parallel with and perpendicular to the chain line. A numerical analysis is carried out for a chain including 10 identical gold nanoparticles (NPs) for two different sizes of NPs and two different host media: air and glass. It is shown that in the parallel case of polarization, interaction of NPs leads to a substantial increase in the extinction cross section and the redshift of the surface plasmon resonance (SPR) wavelength. In comparison with the linear properties of a single NP, the second and penultimate particles have the most increase in the extinction cross section and SPR wavelength displacement while the first and last particles experience the least variations due to the mutual interactions. For the perpendicular polarization, inversely, the dipolar coupling causes a decrease in extinction cross section of all particles and the blue-shift of SPR wavelength. For the parallel polarization, the absolute values of the real and imaginary parts of complex permittivity of each MNP decrease in comparison with the single particle case while they increase for the perpendicular state of polarization.

Research on electromagnetic properties and microwave deicing performance of carbon fiber modified concrete

The electromagnetic properties of concrete have an important effect on the microwave deicing performance of concrete road. In this paper, the carbon fiber was added into the concrete matrix to prepare carbon fiber modified concrete (CMFC), aiming to improve the concrete’s microwave absorbing performance and enhance the efficiency of road microwave deicing. Moreover, a rectangular waveguide transmission/reflection method was used to test the electromagnetic properties of concrete, and a self-developed microwave deicing test system was employed to test the microwave deicing performance. The electromagnetic characteristics tests show that with the increase of carbon fiber content, the microwave energy storage performance of CFMC is firstly increased and then decreased, its performance of microwave energy loss increases gradually, and its reflection of microwave enhances gradually as well. When the microwave frequency is in the vicinity of 2.45 GHz, the real part of complex permittivity of CFMC with a carbon fiber content of 1‰ (CFMC-1), 3‰ (CFMC-2) and 5‰ (CFMC-3) are 1.59 times, 1.69 times and 0.94 times of that of plain concrete (PC), respectively. As for the imaginary part of complex permittivity, the ratios are 4.42 times, 36.38 times and 37.74 times, respectively. As for the reflection properties, CFMC-1 has the lowest reflectivity, which is −6.21 dB. In addition, the microwave deicing tests show that CFMC-3 has the fastest heating rate, which is 1.680 ℃/s, 4.46 times that of PC. However, considering the mechanical properties, deicing effect and economic cost, CFMC-1 has the best application prospects, whose heating rate is 1.289 ℃/s, 3.42 times that of PC. Above all, it can be concluded that the efficiency of concrete road microwave deicing can be effectively improved by adding carbon fiber, and the research in this paper can provide theoretical guidance for the road microwave deicing operations in some sense.

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.

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.

Enhanced microwave absorption properties of Zn-substituted SrW-type hexaferrite composites in the Ku-band

Enhanced microwave absorption properties were successfully achievable from SrFe2-xZnxFe16O27 (SrFe2-xZnxW; x = 0.0, 0.5, 1.0, and 2.0) hexaferrite filler-epoxy resin matrix composites. The composite samples were fabricated with the filler volume fractions (Vf) of 30, 50, 70, and 90%. Compared with fully Zn-substituted SrZn2W composite (x = 2.0), unsubstituted and partially Zn-substituted SrFe2-xZnxW (x = 0.0, 0.5, and 1.0) composites exhibited much higher real and imaginary parts of complex permittivity (εr), which is attributable to higher electron hopping between Fe2+ and Fe3+ ions, and also slightly higher real and imaginary parts of complex permeability (μr) due to higher saturation magnetization (Ms). Among all samples, a 2.8 mm-thick SrFe1·5Zn0·5W (x = 0.5) composite with the Vf of 90% exhibited the most appropriate for application in the region of 3.4–3.8 GHz, having the minimum reflection loss (RLmin) of −46 dB at 3.6 GHz with the bandwidth of 0.43 GHz (3.38–3.81 GHz) below −10 dB, while a 2.15 mm-thick SrFeZnW (x = 1.0) composite with the Vf of 70% showed the most appropriate for application in the region of 5.9–7.1 GHz, possessing the RLmin value of −23.7 dB at 6.6 GHz with the bandwidth of 1.38 GHz (5.85–7.23 GHz) below −10 dB. Consequently, partially Zn-substituted SrW-type hexaferrites are very promising microwave absorbers for 5G mobile communications in the Ku band (0.5–18 GHz).

Effect of Gallium and Boron doping on dielectric and conductivity properties of ZnO sintered from nanoparticles of different morphology in THz region

ZnO nanoparticles with different morphology and doping levels of B or Ga within the interval 0.5 mol % – 20 mol % respective to zinc were prepared using spray-assisted co-precipitation synthesis. The frequency dependent dielectric properties were studied using THz time domain spectroscopy, and the real and imaginary parts of complex permittivity ε′ and ε′′ were obtained. Materials prepared from pseudohexagonal ZnO doped with boron showed higher ε′ (8.56–9.64) than materials of the same composition having nanoparticles with elongated morphology (6.56–7.20). In the case of gallium doping, pseudohexagonal morphology showed higher ε′ (7.94–9.58) than nanoparticles with elongated spindle-like morphology (6.59–7.20). The frequency behavior of the real and imaginary parts of complex optical conductivity showed that boron and gallium cause comparable changes in complex optical conductivity but the absolute values were higher for gallium doping. Particle morphology have significant effects on the dielectric and conductivity properties.

Naturally derived FeTiO3 nanoparticles: analysis of optical properties

Eco-friendly metal titanates, which are abundant in nature, are widely used in our day-to-life in a variety of areas. This work is focused on the optical properties of FeTiO3 (FT) nanoparticles prepared by acid extraction method from ilmenite sand. The prepared FeTiO3 nanoparticles were analyzed by ultraviolet (UV) spectroscopy. Various linear optical parameters such as refractive index, extinction coefficient, absorption coefficient, real and imaginary parts of dielectric constant, loss tangent, optical conductivity, electron energy loss, and dielectric relaxation time were calculated in 1.5–6 eV energy range and discussed as a function of photon energy. The calculated values of the real part of complex permittivity and volume energy loss were higher than those of the imaginary part of complex permittivity and surface energy loss, respectively. The discussed results showed that the prepared FeTiO3 nanoparticles are suitable for the photocatalytic activity and optoelectronic device applications due to their hybridization orbital.

Rubber-ceramic composites applicable in flexible antennas

Abstract Glass ceramics from the CaO–P2O5–SiO2 system were synthesized. They were characterized by XRD, SEM and EDX methods. It was found that they contain two crystalline [Whitlockite, Ca3 (PO4)2 and Hydroxylapatite, Ca5 (PO4)3 (OH)] and one residual amorphous phase. The ceramics are composed of porous aggregates of fine particles with predominant macro- and mesopores in it. The ceramics were used as a functional filler in natural rubber based composites, as the filling is in the range of 5–50 phr. The influence of the chemical nature and structure of the ceramics and the degree of filling on the vulcanization characteristics, physicomechanical parameters, dielectric and dynamic properties, the coefficient of thermal conductivity and the volume resistivity, including external pressure or bending on the specimens were investigated. An influence of the filler and the degree of filling on all studied properties was found. All tested composites have dielectric parameters (ε′, real part of complex permittivity; ε′′, imaginary part of complex permittivity; σ, conductivity; tanδ ɛ, tangent from dielectric loss angle) suitable for use as substrates and insulating layers of flexible antennas. Particularly impressive are composites containing 30 and 50 phr fillers, which have the lowest tangent from dielectric loss angle values.

Mechanical and microwave absorption properties of Ti-filled SiCf/SiC composites via precursor infiltration and pyrolysis

SiC fiber reinforced SiC ceramic matrix composite is a kind of promising high-temperature structure absorbing integrated material because of its good temperature resistance and high-temperature stability. However, the mechanical properties of the composites are poor and it is difficult to adjust the electromagnetic parameters. In this study, Ti powders were used as active fillers to improve the mechanical and microwave absorption properties of SiCf/SiC composites fabricated by polymer infiltration and pyrolysis (PIP) process. The compositions of SiC matrix derived from polycarbosilane (PCS) precursor modified by various content Ti powders were investigated by XRD and Raman spectroscopy. With the incorporation of Ti powders, free carbon decomposed from PCS was consumed due to the formation of TiC phase. The effect of Ti fillers on the mechanical and dielectric properties of SiC/SiC composites was also investigated. The flexural strength of SiCf/SiC composite was gradually improved with increasing Ti content owing to the improved density and TiC particle strengthening. Besides, consumption of free carbon in SiC matrix may impair the conductive network of free carbon, leading to decreased conductivity and the imaginary part of complex permittivity of the composite. Therefore, an optimum microwave absorption performance of SiCf/SiC composite with an RLm value of − 37 dB at 10.51 GHz and an effective absorption bandwidth of 3.28 GHz was obtained at the thickness of 2.5 mm and the Ti content of 5 wt%. The Ti-filled SiCf/SiC composite with superior microwave absorption property is a promising candidate in the high-temperature structure absorbing field.