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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.

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.

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.

Finally, dielectric responses to both time and to stepwise excitation are given.

The purpose of this paper is to develop the models of the dielectric permittivity dispersion of heterogeneous systems based on semiconductors to a level that would allow to apply effectively the method of broadband dielectric spectroscopy for the study of electronic processes in ceramic and composite materials.

The new approach for determining the complex dielectric permittivity of heterogeneous systems with semiconductor particles is used. It includes finding the analytical expression of the effective dielectric permittivity of the separate semiconductor particle of spherical shape. This approach takes into account the polarization of the free charge carriers in this particle, including capturing to localized electron states. This enabled the authors to use the known equations for complex dielectric permittivity of two-component matrix systems and statistical mixtures.

The presented dispersion equations establish the relationship between the parameters of the dielectric spectrum and electronic processes in the structures like semiconductor particles in a dielectric matrix in a wide frequency range. Conditions of manifestation and location of the different dispersion regions of the complex dielectric heterogeneous systems based on semiconductors in the frequency axis and their features are established. The most high-frequency dispersion region corresponds to the separation of free charge carriers at polarization. After this region in the direction of reducing of the frequency, the dispersion regions caused by recharge bulk and/or surface localized states follow. The most low-frequency dispersion region is caused by recharging electron traps in the boundary layer of the dielectric matrix.

Dielectric dispersion models are developed that are associated with: electronic processes of separation of free charge carriers in the semiconductor component, recapture of free charge carriers in the localized electronic states in bulk and on the surface of the semiconductor and also boundary layers of the dielectric at the polarization. The authors have analyzed to situations that correspond applicable and promising materials: varistor ceramics and composite structure with conductive and semiconductor fillers. The modelling results correspond to the existing level of understanding of the electron phenomena in matrix systems and statistical mixtures based on semiconductors. It allows to raise efficiency of research and control properties of heterogeneous materials by dielectric spectroscopy.

To outline different versions of a novel method for accurate and efficient determining the dielectric properties of arbitrarily shaped materials.

Complex permittivity is found using an artificial neural network procedure designed to control a 3D FDTD computation of S‐parameters and to process their measurements. Network architectures are based on multilayer perceptron and radial basis function nets. The one‐port solution deals with the simulated and measured frequency responses of the reflection coefficient while the two‐port approach exploits the real and imaginary parts of the reflection and transmission coefficients at the frequency of interest.

High accuracy of permittivity reconstruction is demonstrated by numerical and experimental testing for dielectric samples of different configuration.

Dielectric constant and the loss factor of the studied material should be within the ranges of corresponding parameters associated with the database used for the network training. The computer model must be highly adequate to the employed experimental fixture.

The method is cavity‐independent and applicable to the sample/fixture of arbitrary configuration provided that the geometry is adequately represented in the model. The two‐port version is capable of handling frequency‐dependent media parameters. For materials which can take some predefined form computational cost of the method is very insignificant.

A full‐wave 3D FDTD modeling tool and the controlling neural network procedure involved in the proposed approach allow for much flexibility in practical implementation of the method.

The principle of microwave characterization of dielectric materials using open-ended coaxial line probe is to link the dielectric properties of the sample under test to the measurements of the probe admittance (Y(f) = G(f)+ jB(f )). The purpose of this paper is to develop an alternative inversion tool able to predict the evolution of the complex permittivity (ε = ε′ – jε″) on a broad band frequency (f from 1 MHz to 1.8 GHz).

The inverse problem is solved using adaptive network based fuzzy inference system (ANFIS) which needs the creation of a database for its learning. Unfortunately, train ANFIS using f, G and B as inputs has given unsatisfying results. Therefore, an inputs selection procedure is used to select the three optimal inputs from new inputs, created mathematically from original ones, using the Jang method.

Inversion results of measurements give, after training, in real time the complex permittivity of solid and liquid samples with a very good accuracy which prove the applicability of ANFIS to solve inverse problems in microwave characterization.

The originality of this paper consists on the use of ANFIS with input selection procedure based on the Jang method to solve the inverse problem where the three optimal inputs are selected from 26 new inputs created mathematically from original ones (f, G and B).

The purpose of the present work is to fabricate composite with strong absorbing nature and with more strength. The usage of wireless communication is increasing day by day, electromagnetic absorbing material is required to reduce this pollution. In the present experimental investigation, composites were fabricated for zero and 45° fiber orientation and as a filler material of Multiwall Carbon Nanotubes (MWCNTs) for the proposed percentage in the composites. Microwave absorbing properties were investigated for both perfect electric conductor (PEC)-backed composites and without PEC-backed composites.

The electromagnetic absorbing performance was analyzed based on complex permeability, complex permittivity, dielectric tangent and magnetic tangent losses. The experimentation was done by Vector Network Analyzer in the frequency range of 8.2 to 12.4 GHz by X-band. The surface morphological study was done. The mechanical and thermal properties are also investigated for these composites.

By investigating the experimental values, the induced percentage of MWCNTs and PEC of composites affects the electromagnetic and microwave absorption properties of the composites. The microwave absorption properties improved when the composites were able to absorb wide bandwidth and low reflection loss. The best results are obtained for PEC-backed composites for 5%, which is about −43.56 dB at 11.1 GHz compared to without PEC-backed composites. The reflection loss is developed by the dielectric loss initiated from MWCNTs and by PEC.

To the best of the authors’ knowledge, no work was reported on hand lay-up method and PEC-backed composites in electromagnetic absorption properties with regression analysis.

The dielectric properties of materials (complex permittivity) can be deduced from the admittance measured at the discontinuity plane of a coaxial open‐ended probe. This implies the implementation of an inversion procedure. The purpose of this paper is to develop a new non‐iterative inversion methodology in the field of microwave characterization allowing reducing the computation cost comparatively to iterative procedures.

The inversion methodology combines the support vector machine (SVM) technique and the finite element method (FEM). The SVM are used as inverse models. They show good approximation and generalization capabilities. FEM allows the generation of the data sets required by the SVM parameter adjustment. A data set is constituted of input (complex admittance and frequency) and output (complex permittivity) pairs.

The results show the applicability of SVM to solve microwave inverse problems instead of using traditional iterative inversion methods which can be very time‐consuming. The experimental results demonstrate the accuracy which can be provided by the SVM technique.

The paper allows extending the capability of microwave characterization cells developed at Laboratoire de Génie Électrique de Paris.

A new inversion method is developed and applied to microwave characterization. This new concept introduces SVM in the context of microwave characterization. SVM results and iterative inversion procedure results are compared in order to evaluate the effectiveness of the developed technique.

The purpose of this paper is to develop new knowledge in experimental characterization of contaminants in engine lubricants, using surface plasmon resonance (SPR) sensing that can be applicable for on‐line condition monitoring of lubricant quality and engine component performance.

The effect of change in optical properties (e.g. transparency, absorption, and refractive index) of engine lubricants caused by the introduction of contaminants, such as gasoline, coolant, and water, on the surface plasmon resonance characteristics is analyzed experimentally. In SPR measurement, variations in both the refractive index and absorption cause changes in the SPR curve, which is the dependence of reflectivity vs incidence angle. The SPR characteristics (e.g. refractivity) of engine lubricant contaminated by gasoline, water and coolant at different concentration are measured as a function of resonance angle and analyzed with respect to different concentration (1%‐10%) of contaminants. Also, pattern recognition analysis between fresh and used engine lubricants is performed, to show applicability of Bayesian classification methodology for on‐line monitoring and predicting engine lubricant condition.

It was shown experimentally that attenuation of surface plasmons due to introduction of contaminants to the engine lubricant leads to a noticeable change in resonance angle and reflectivity minimum of the SPR curve due to an increase in the dielectric permittivity. In addition, the changes in the SPR characteristics were observed between fresh and used engine lubricant, causing resonance angle and reflectivity minimum of the SPR curve to shift.

The knowledge generated in this study lays the informational basis to further develop an on‐line system for engine lubricant condition monitoring using miniaturized SPR sensors fully suitable for on board applications.

SPR characterization is originally applied for analysis of optical properties of engine lubricants caused by the introduction of contaminants, such as gasoline, coolant, and water.

A review of the dielectric measurement techniques that are currently available for the characterization of thick film and LTCC materials at microwave and millimeter wave frequencies is presented. The intention is to show the relative advantages and limitations of the various methods, and to provide some practical guide to the particular technique that is most suitable for a given type of material, for use in a particular application. In addition, a novel slit cavity resonator method is proposed to enable substrate parameters to be more easily measured, whilst retaining high measurement accuracy. Measured data on materials from a variety of manufacturers are presented to show the validity and usefulness of this method.

This paper aims to report on fabrication procedure and presents microstructure and dielectric behaviour of LiZn_0.92Cu_0.08PO₄ ceramic material with Li₂CO₃ as a sintering aid.

Substrates based on LiZn_0.92Cu_0.08PO₄ with Li₂CO₃ addition were prepared via solid-state synthesis, doping, milling, pressing and sintering. Characterization of the composition, microstructure and dielectric properties was performed using X-ray diffractometry, energy dispersive spectroscopy, scanning electron microscopy, impedance spectroscopy in the 100 Hz to 2 MHz range and time-domain spectroscopy in the 0.1–3 THz range.

Doped LiZnPO₄ ceramic, which exhibits a low dielectric constant of 5.9 at 1 THz and low sintering temperature of 800 °C, suitable for low temperature co-fired ceramics (LTCC) technology, was successfully prepared. However, further studies are needed to lower dielectric losses by optimising the doping level, synthesis and sintering conditions.

Search for new low dielectric constant materials applicable in LTCC technology and optimization of processing are essential tasks for developing modern microwave circuits. The dielectric characterization of doped LiZnPO₄ ceramic in the terahertz range, which was performed for the first time, is crucial for potential millimetre-wave applications of this substrate material.

An improved analytical model is presented to investigate the scattering properties of high T_c superconducting triangular antennas in multilayered configuration. The spectral method is used to study the scattering properties of superconducting triangular antennas. Galerkin method is used in the resolution of the electric field integral equation. The boundary condition for the electric field was used to derive an integral equation for the electric current. To validate the theoretical results, a study has been performed for perfectly conducting triangular patch on a single layer, with air gap, and cover layer. The computed data are found to be in good agreement. The paper aims to discuss these issues.

A spectral domain approach has been used for the numerical calculation of the characteristics of a high T_c superconducting microstrip antenna with an air gap and cover layer. Initially, the authors use an integral method of moment which enabled them to exploit the spectral tensor of green. The resolution of the integral equations of the electric field by the procedure of Galerkin makes it possible to lead to a system of equations homogenous. The authors have calculated the frequency of resonance and the radiation pattern of antenna.

The properties of the HTSTMA structure were stable at temperatures slightly lower than the critical temperature. Also computations show that the air separation can be adjusted to have the maximum operating frequency of the superconducting microstrip antenna. On the other hand, the bandwidth increases monotonically with increasing the air gap width. Therefore, HTS materials do offer efficiency improvements for antenna systems that can accommodate the added constraints of the superconducting environment. The calculated results have been compared with measured one available in the literature and excellent agreement has been found.

To the best of the authors' knowledge, this subject has not been reported in the open literature; the only published results on the analysis of perfectly conducting triangular microstrip antennas.