Auswahl der wissenschaftlichen Literatur zum Thema „Colossal equivalent relative permittivity“

Electron-pinned defect dipoles, in the form of highly stable triangle-diamond and/or triangle-linear dopant defect clusters with well defined relative positions for Ti reduction, are present in rutile In + Ta co-doped TiO₂ for the colossal permittivity and low loss.

(Nb5+, Si4+) co-doped TiO2 (NSTO) ceramics with the compositions (Nb0.5Si0.5)xTi1−xO2, x = 0, 0.025, 0.050 and 0.1 were prepared with a solid-state reaction technique. X-ray diffraction (XRD) patterns and Raman spectra confirmed that the tetragonal rutile is the main phase in all the ceramics. Additionally, XRD revealed the presence of a secondary phase of SiO2 in the co-doped ceramics. Impedance spectroscopy analysis showed two contributions, which correspond to the responses of grain and grain-boundary. All the (Nb, Si) co-doped TiO2 showed improved dielectric performance in the high frequency range (>103 Hz). The sample (Nb0.5Si0.5)0.025Ti0.975O2 showed the best dielectric performance in terms of higher relative permittivity (5.5 × 104) and lower dielectric loss (0.18), at 10 kHz and 300 K, compared to pure TiO2 (1.1 × 103, 0.34). The colossal permittivity of NSTO ceramics is attributed to an internal barrier layer capacitance (IBLC) effect, formed by insulating grain-boundaries and semiconductor grains in the ceramics.

Calcium copper titanate (CCTO) ceramics were successfully synthesized using a rapid laser reactive sintering method without conventional long heat treatment times. The microstructure, dielectric properties, and impedance spectroscopy results for CCTO sintered at laser power rates of 25–85 W were investigated in detail. The X-ray diffractometry results showed that prepared CCTO is polycrystalline in a cubic structure with high purity. Scanning electron microscopy showed that CCTO sintered at 85 W has a dense microstructure with an average grain size of 30 nm. The dielectric permittivity of CCTO ceramics increased with increasing laser power over the entire frequency range and achieved a value of almost 105 in the low-frequency region. The dielectric permittivity maintained almost constant values from 102 Hz to 107 Hz, with lower dielectric loss (~0.1) from 103 Hz to 106 Hz, demonstrating good frequency stability. The impedance spectroscopy study showed that grain and grain boundary resistance decreased with rising laser power based on two parallel Resistor-Capacitance (RC) equivalent circuits in series. The activation energies for the grain boundaries were calculated from the impedance using the slope of ln σ versus 1/T and were found to be in the range of 0.53–0.63 eV. CCTO synthesized by rapid laser reactive sintering is competitive for practical applications.

Purpose This paper aims to give a brief overview of dielectric properties, relative complex permittivity and its dependence on frequency. The significance of different approaches to complex permittivity is also discussed. Design/methodology/approach The different mechanisms of polarization are then presented. Dielectric measurements are given, and an RC parallel-equivalent circuit is used to simulate a parallel plate capacitor, and the way in which the impedance of the circuits is affected by frequency is illustrated in their respective diagrams. The way in which dielectric properties change with time is also discussed. Findings The goal of this paper is to give an overview of the characteristics of the dielectrics and how frequency affects the relative complex permittivity and to present different approaches to and equations for the relative complex permittivity, such as that of Debye, Cole–Cole, Cole–Davidson and Havriliak–Negami. In addition, three mechanisms of polarization, namely, electronic, atomic and bipolar, are presented. The most common dielectric characterization device, a capacitor with parallel plates between which the dielectric material under study is located, is also discussed. Ohmic and dielectric losses of a non-ideal capacitor are accounted for. Furthermore, this paper studies the equivalent circuits of a non-ideal parallel plate capacitor, those being a resistor and an ideal capacitor connected either in series or in parallel. Originality/value Finally, dielectric responses to both time and to stepwise excitation are given.

This paper aims to present an effective electromagnetic (EM) modelling approach for rectangular bundle of single-walled carbon nanotubes (RB-SWCNTs), based on the electrical conductivity, relative complex permittivity and linear distribution impedance by applying General Ohm’s law for this bundle. The equivalent single conductor material (ESCM) model for personification the RB-SWCNTs is present in this paper. The main target of this modeling approach is to estimate and investigate the EM properties of RB-SWCNTs using common EM engineering tool solver CST (MWS). For this purpose, the RB-SWCNTs and ESCM dipole antennas will be designed and implemented using CST (MWS). The equivalent conductivity model, relative complex permittivity and other parameters of the RB-SWCNTs will be derived in this paper and considered as an equivalent material parameters for the ESCM. This modeling technique is expected to provide new avenues for designing different antenna structures.

Complex permittivity is one of the most important parameters to characterize the interaction between microwave and medium, especially for microwave-excited plasma. It is convenient to study plasma’s dielectric properties and microwave propagation characteristics by measuring its complex permittivity. A dynamic measurement method of equivalent relative complex permittivity of microwave-excited plasma at atmospheric pressure is proposed in this paper. Firstly, a cavity based on WR-430 at a frequency of 2.45 GHz was specially designed in COMSOL. Then, the samples with different real parts of complex permittivity and loss tangent were simulated in the designed cavity to obtain their corresponding S parameters, and they were used to train the BP neural network until the error was lower than 0.001. A two-port network was built to excite the plasma. The input power, reflected power, and transmitted power could be measured by the transmission reflection method. Finally, the measured power values were converted into S parameters and used as inputs in the BP neural network. The plasma’s real parts of complex permittivity and loss tangent were obtained by inversion. The variation of plasma complex permittivity conforms to the interaction principles between microwave and plasma, which verifies the accuracy of the method.

This paper investigates the electrical properties in the microwave range of a contact made by graphene nanoplatelets. The final goal is that of estimating the range of values for the equivalent electrical complex permittivity of a contact obtained by integrating low-cost graphene in the form of nanoplatelets (GNPs) into a high-frequency electrical circuit. To this end, a microstrip-like circuit is designed and realized, where the graphene nanoplatelets are self-assembled into a gap between two copper electrodes. An experimental characterization is carried out, both to study the structural properties of the nanomaterials and of the realized devices, and to measure the electromagnetic scattering parameters in the microwave range by means of a microstrip technique. A full-wave electromagnetic model is also derived and used to investigate the relationship between the measured quantities and the physical and geometrical parameters. The combined use of the experimental and simulation results allows for retrieving the values of the equivalent complex permittivity. The equivalent electrical conductivity values are found to be well below the values expected for isolated graphene nanoplatelets. The real part of the electrical relative permittivity attains values comparable to those obtained with GNP nanocomposites.

An increasing interest is arising in developing miniaturized antennas in the microwave range. However, even when the adopted antennas dimensions are small compared with the wavelength, radiation performances have to be preserved to keep the system-operating conditions. For this purpose, magneto-dielectric materials are currently exploited as promising substrates, which allows us to reduce antenna dimensions by exploiting both relative permittivity and permeability. In this paper, we address generic antennas in resonant conditions and we develop a general theoretical approach, not based on simplified equivalent models, to establish topologies most suitable for exploiting high permeability and/or high-permittivity substrates, for miniaturization purposes. A novel definition of the region pertaining to the antenna near-field and of the associated field strength is proposed. It is then showed that radiation efficiency and bandwidth can be preserved only by a selected combinations of antenna topologies and substrate characteristics. Indeed, by the proposed independent approach, we confirm that non-dispersive magneto-dielectric materials with relative permeability greater than unit, can be efficiently adopted only by antennas that are mainly represented by equivalent magnetic sources. Conversely, if equivalent electric sources are involved, the antenna performances are significantly degraded. The theoretical results are validated by full-wave numerical simulations of reference topologies.

Ce manuscrit se focalise sur l’effet de divers matériaux composites sur les différentes problématiques de compatibilité électromagnétique dans un véhicule automobile. Les modèles surfaciques des matériaux diélectriques sont validés en confrontant des résultats de mesures et de simulation de leurs permittivités. Ceux des matériaux conducteurs le sont en confrontant le modèle d’impédance de surface à un modèle filaire et en effectuant des mesures des simulations de paramètres S sur une structure majoritairement constituée par un matériau de ce type. Dans les deux cas, la technique de modélisation donne de bons résultats. L’évaluation de l’effet de ces matériaux sur les problématiques de CEM au niveau d’un véhicule est faite sur un démonstrateur qui intègre les équipements et les faisceaux embarqués dans un véhicule en les représentants par des monopôles et des fils conducteurs. L’évaluation des effets des différents matériaux composites sur les problématiques CEM est faite par mesure et simulation des couplages électromagnétiques à l’intérieur du démonstrateur et entre le démonstrateur et une antenne test. L’analyse des couplages électromagnétiques confirme que le modèle d’impédance de surface reproduit assez bien les comportements des matériaux composites étudiés. Concernant l’effet des matériaux composites sur les problématiques CEM au niveau d’un véhicule, cette étude mène à deux résultats majeurs du point de vue de la compatibilité électromagnétique. Le premier concerne l’usage des matériaux diélectriques qui augmente globalement la plupart des couplages mesurés de 5 dB à 30 dB. Le second porte sur le matériau conducteur étudié qui n’a quasiment aucun effet sur les différents couplages analysés en comparaison de la structure en acier
The main concern of this thesis is the characterization of the impacts of some composite materials on the main electromagnetic compatibility issues in a vehicle. The surface models of the dielectric materials are validated by confronting their simulated and measured permittivity. The surface model of the studied conductive material is validated by confronting it to a wire model and by measuring and simulating the S parameters on a structure constituted by such a material. It appears in both cases of dielectric and conductive composite materials that the surface impedance modeling technique gives a good description of the materials. The analysis of the effects of these materials on the EMC issues within a vehicle is done by use of a demonstrator representing the car body. The different equipment and harnesses embedded in a vehicle are represented in the demonstrator by some wires and monopoles. The evaluation of the impact of the composite materials on the EMC issues is done by measuring and simulating the different couplings within the demonstrator and between the demonstrator and a test antenna. The analysis of the different couplings confirms that the surface impedance material modeling approach describes well the materials under test. Concerning the impact of the composite materials on the EMC issues at a vehicle level, this analysis fulfills two main results. The first one concerns the dielectric materials. Indeed the use of these materials increases the different coupling by a value varying between at least 5 dB to 30 dB. The second conclusion concerns the use of conductive composite materials. It appears that they have no effect on the different couplings in comparison to the full steel structure

The master’s thesis deals with the piezoelectric coefficients, the resonance frequency and especially the piezoelectric constants verification. With the assistance of several devices, for instance LCR-meter HIOKI 3532, impedance analyzer Agilent 4294A and LCR-meter Agilent E4980A, the resonance and the anti-resonance frequencies as well as impedance and capacitance of samples are measured. The paper opens with the theory of the piezoelectric phenomenon and the difference between direct and indirect piezoelectric phenomenon, it also describes the basic behaviour of a piezoelectric ceramic element during mechanical straining or applied voltage. Further, the paper concerns the description of various piezoelectric constants and their calculations. Subsequent part of the paper is devoted to the temperature dependence of the main piezoelectric parameters of PZT ceramics. The materials coefficients are delineated as a function of temperature of the piezoelectric charge coefficients dij, relative permittivity r, electromechanical coupling factor kij and frequency constants Ni. One of the chapters also determines the piezoelectric charge constant d33 of PZT ceramics by laser interferometer and compares it with the value measured by resonance methods. The surface displacement was measured by a single-beam interferometer Polytec OFV-5000. The results of measurements of piezoelectric charge coefficients d33 acquired by the first and the second method are identical. The last section of the paper is focused on different methods of experimental studies on the characteristics of heat transfer by diffusing heat through conduction between the silver-plated surface of cylinder made of PZT ceramics. The effect on the resonance and the anti-resonance frequencies is monitored. There after, the real heat, determined by thermo camera and the physical model of heat transfer created in program COMSOL Multiphysics, is analysed.

Abstract Thermal sprayed ceramic coatings are well used as the electrode of corona discharge treatment in order to modify the surface of many kinds of films and papers due to its superior durability and adaptability. Some kinds of Al2O3-TiO2 were sprayed by APS on the parallel plate electrodes, and output power of corona discharge generated by the electrodes was measured by using Sawyer-Tower circuit. In addition, discharge output power was calculated with an equivalent circuit of corona discharge. By comparing them, effects of the electrical property of the coating on discharge was researched. As a result, the electrostatic capacitance of the coatings influences the impedance of the whole circuit, and higher relative permittivity of the coating brought higher output power in a constant voltage.