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The microwave properties of some of the low cost materials which can be used in high frequency applications with low transmission losses are investigated in this paper. One of the most accurate microwave characterization techniques, Split Post Dielectric Resonator technique (SPDR) is used for the experimental investigation. The dielectric constants of the 3 materials scrutinized at room temperature and at 10K are 3.65, 2.42, 3.61 and 3.58, 2.48, 3.59 respectively. The corresponding loss tangent values are 0.00370, 0.0015, 0.0042 and 0.0025, 0.0009, 0.0025. The high frequency transmission losses are comparable with many of the conventional materials used in low temperature electronics and hence these materials could be implemented in such applications.

We report the reflectivity of one-dimensional finite and semi-infinite photonic crystals, computed through the coupling to Bloch modes (BM) and through a transfer matrix method (TMM), and their comparison to the experimental spectral line shapes of porous silicon (PS) multilayer structures. Both methods reproduce a forbidden photonic bandgap (PBG), but slowly-converging oscillations are observed in the TMM as the number of layers increases to infinity, while a smooth converged behavior is presented with BM. The experimental reflectivity spectra is in good agreement with the TMM results for multilayer structures with a small number of periods. However, for structures with large amount of periods, the measured spectral line shapes exhibit better agreement with the smooth behavior predicted by BM.

Lead-free $x($Na${}_{0.5}$Bi${}_{0.5})$TiO₃–$(1-x)$Ba${}_{0.7}$Sr${}_{0.3}$Sn${}_{0.02}$Ti${}_{0.98}$O₃ (NBT–BSST) ceramics are prepared by a wet solid-phase reaction method. The effect of NBT/BSST ratio on phase structure, microstructure and dielectric properties has been investigated in detail. The X-ray diffraction (XRD) analysis illustrates that the composites are composed of tetragonal perovskite. With increasing NBT content, the ceramic capacitors display stronger temperature stability in its dielectric behavior. A great enhance of dielectric properties and other electric parameters is obtained in this system by properly modulating the compositions. For example, the composite ceramics with 30% NBT content possess a large dielectric constant $({𝜀}_{\mathrm{\text{r}}})$ of 3200 and a low dielectric loss $(tan\delta )$ of 0.09. The temperature coefficient of capacitance of NBT–BSST varies from −50% to 20% while the NBT content is 30% at the whole range of measured temperature. The results show that NBT–BSST ceramics are a good candidate of lead-free dielectric materials.

The ceramics with the composition of $x{\mathrm{\text{Na}}}_{0.5}{\mathrm{\text{Bi}}}_{0.5}{\mathrm{\text{TiO}}}_3$–$(1-x){\mathrm{\text{Ba}}}_{0.66}{\mathrm{\text{Mg}}}_{0.04}{\mathrm{\text{Sr}}}_{0.3}{\mathrm{\text{TiO}}}_3$ (NBT–BMST) in which $x$ = 0.2, 0.3, 0.4 and 0.5 were prepared successfully by the solid-state reaction method. The effects of NBT-doping on phase structure, morphology, temperature stability and dielectric properties had been investigated in detail. The XRD results show that the composites are composed of tetragonal perovskite. The phase structure of NBT–BMST is observed by scanning electron microscopy. The dielectric constant of $0.3{\mathrm{\text{Na}}}_{0.5}{\mathrm{\text{Bi}}}_{0.5}{\mathrm{\text{TiO}}}_3$–$0.7{\mathrm{\text{Ba}}}_{0.66}{\mathrm{\text{Mg}}}_{0.04}{\mathrm{\text{Sr}}}_{0.3}{\mathrm{\text{TiO}}}_3$ ceramic is $\sim$4100, the temperature coefficients of capacitance are −15%, 15% and 22% at −55${}^{\circ }$C, 60${}^{\circ }$C and 200${}^{\circ }$C, respectively. And the dielectric loss is less than 0.13, which is obviously superior to other compositions. The results of this work showed that the component of $0.3{\mathrm{\text{Na}}}_{0.5}{\mathrm{\text{Bi}}}_{0.5}{\mathrm{\text{TiO}}}_3$–$0.7{\mathrm{\text{Ba}}}_{0.66}{\mathrm{\text{Mg}}}_{0.04}{\mathrm{\text{Sr}}}_{0.3}{\mathrm{\text{TiO}}}_3$ is a promising candidate to high-temperature stable materials.

$x{\mathrm{\text{Na}}}_{0.5}{\mathrm{\text{Bi}}}_{0.5}{\mathrm{\text{TiO}}}_3@(1-x)[0.85{\mathrm{\text{BaTiO}}}_3-0.15\mathrm{\text{Bi}}({\mathrm{\text{Zn}}}_{2/3}{\mathrm{\text{Nb}}}_{1/3}){\mathrm{\text{O}}}_3]$ (NBT@BT–BZN) composite ceramic materials were prepared by wet solid-phase reaction method. The effects of ${\mathrm{\text{Na}}}_{0.5}{\mathrm{\text{Bi}}}_{0.5}{\mathrm{\text{TiO}}}_3$ (NBT) on the phase structure, morphology and dielectric properties of NBT@BT–BZN composites were studied in detail. All of the NBT@BT–BZN composites consist of BT–BZN and NBT phases. The dense microstructure was observed in all the NBT@BT–BZN samples. It is found that the introduction of NBT into BT–BZN leads to enhanced temperature stability in dielectric property. Samples with 40 mol.% NBT shows good dielectric property, in which the temperature change rate of the dielectric constant at $-55^{\circ }\mathrm{\text{C}}$ to $200^{\circ }\mathrm{\text{C}}$ is 1% to −15.20%, basically meeting the requirements of X9R. These results indicate that the 0.40NBT@0.60 (BT–BZN) is a promising candidate for high temperature stable materials.

A new characterization method based on impedance frequency response analysis at different temperatures has been developed to assess and identify the dielectric and semiconductor materials for organic field-effect transistors (OFET). This method can not only characterize simultaneously dielectric and conductive behaviors of materials but also distinguish individual contributions to electrical conduction or to polarization from layers such as dielectric layer, semiconductor layer, and interfaces in OFET. Two kinds of materials, Urathan and DuPont 5018A as dielectric materials have been used to make a multilayer organic capacitor. It has been observed that Urathan, due to its lower conductivity, non-metallic conduction behavior at high temperature, and lower interfacial resistance, is more suitable as dielectric layer for OFET. Urathan appears an enhancement in conductivity by heating following an Arrhenius law with an activation energy transition from 0.002 to 0.24 eV at ~307 K, which originates from band tail hopping that occurs around the Fermi edge. At ~314 K, a dielectric transition also occurs, which is interpreted as a combination of electron polarization associated to the band tail hopping. The materials were used to fabricate OEFT, which performance was in agreement with that obtained from impedance analysis of the organic capacitor.

A new series of multi-walled carbon nanotube reinforced polybenzoxazine (MWCNT/PBZ) nanocomposites was successfully designed and developed. Three different maleimido terminal benzoxazine monomers (MI-BZs) were synthesized using N-(4-hydroxyphenyl) maleimide (HPM) and formaldehyde solution through Mannich condensation reaction and were characterized by FT-IR and NMR spectroscopy. Varying weight percentages (0 wt.%, 0.5 wt.%, 1.0 wt.% and 1.5 wt.%) of glycidyl-MWCNT were then incorporated into benzoxazine matrices to prepare MWCNT/PBZ nanocomposites. The nanocomposites having higher weight percentage of MWCNT were found to possess excellent thermal properties than those of neat PBZs. The developed nanocomposites exhibited better flame retardancy and higher dielectric constant. The optical properties ascertained from the UV-Vis absorption bands at the region of 300–350 nm and strong fluorescent emissions were observed in the wavelength range of 300–550 nm from Photoluminescence analysis. The intensity of characteristic diffraction peaks corresponding to g-MWCNT confirmed the reinforcement of MWCNT in the benzoxazine matrices, which indicated the successful formation of nanocomposites. The morphological studies ascertain the compatibility and uniform dispersion of MWCNT in the PBZ network.

This study presents a numerical method based on parallel RC equivalent circuit model fitting methodology for analysis and modeling of dielectric materials. The proposed method employs gradient-descent optimization method (GDOM) to estimate parallel RC equivalent circuit model from current waveforms by minimizing sum of squared difference (SSD) error. Estimation of parallel RC equivalent circuit parameters from measured current waveforms provides a useful tool for identification, simulation and analysis of dielectric materials. Moreover, applications of the proposed method for time and frequency analyses of dielectric materials are demonstrated numerically. Numerical simulations were presented to discuss efficiency of the proposed method for modeling, analysis and monitoring of insulator materials.

Frequency selective surface (FSS) has been extensively studied due to its potential applications in radomes, antenna reflectors, high-impedance surfaces and absorbers. Recently, a new principle of designing FSS has been proposed and mainly studied in two levels. In the level of materials, dielectric materials instead of metallic patterns are capable of achieving more functional performance in FSS design. Moreover, FSSs made of dielectric materials can be used in different extreme environments, depending on their electrical, thermal or mechanical properties. In the level of design principle, the theory of metamaterial can be used to design FSS in a convenient and concise way. In this review paper, we provide a brief summary about the recent progress in all-dielectric metamaterial frequency selective surface (ADM-FSS). The basic principle of designing ADM-FSS is summarized. As significant tools, Mie theory and dielectric resonator (DR) theory are given which illustrate clearly how they are used in the FSS design. Then, several design cases including dielectric particle-based ADM-FSS and dielectric network-based ADM-FSS are introduced and reviewed. After a discussion of these two types of ADM-FSSs, we reviewed the existing fabrication techniques that are used in building the experiment samples. Finally, issues and challenges regarding the rapid fabrication techniques and further development aspects are discussed.

The polycrystalline samples of 0.8BiSm_xFe${}_{1-x}$O₃–0.2PbTiO₃ ($x=0.05,0.10,0.15$ and 0.20) were prepared by using the conventional solid-state reaction technique and sintered at high temperature (850${}^{\circ }$C). X-ray diffraction (XRD) confirms the distorted rhombohedral crystal structure for all the composites at room temperature. The surface morphology was checked by field-emission scanning electron microscope (FESEM) technique and homogeneous mixing of the components was confirmed by energy-dispersive analysis of X-ray (EDAX). The detailed study of dielectric properties of the composites reveals an increasing nature of dielectric constant (${\epsilon }_r$) and loss tangent (tan$\delta$) with the increase of temperature due to thermal activation. The Arrhenius plots of temperature dependence of AC conductivity yield the activation energy within the material at high-temperature range. The ferroelectric study shows that the remnant polarization decreases with the increase of Samarium (Sm) concentration.

Polymer/metal composites (PMC) comprising of polyvinylidene fluoride/nanocrystalline nickel with varying volume fractions of nickel ($f_{\mathrm{\text{con}}}$) prepared under cold press show an insulator to metal transition (IMT) at percolation threshold ($f_c=f_{\mathrm{\text{con}}}=0.27$). The two kinds of generalized Johnscher’s universal dielectric response (UDR) laws on both sides of IMT hold good, while for the percolative sample, none of the two laws hold good. Neither the concept of dipolar relaxation nor anomalous low frequency dispersion stands valid for $f_c=0.27$, while a completely different, neutral and competing electrical behavior is observed over the entire range of frequencies. The emerged third kind of Johnscher’s like UDR for $f_c$ is observed and the relaxation law has been formulated as the ratio of imaginary and real parts of dielectric constant remains constant over the entire range of frequency starting from dc to any higher frequency. The value of the constant is attributed to depend on the PMC, the dielectric constant of the polymer, the differences of conductivity and fractions of the components of the PMC and also on their connectivity arising due to the difference of their process conditions. The emerged unique dielectric relaxation consists of multiple relaxations arising due to the combination of other relaxations (arising due to the two different types of species) present in the sample, $f_{\mathrm{\text{con}}}=0.27$. This novel material may be suitable for certain specific applications in electrical and electronics engineering.

In this study, carbon black (CB) powder-loaded polyurethane (PU) composites (CB–PU composites) were prepared by melt mixing method with different volume percentages (45, 50, 55, 58 and 61 vol.%) of CB in the PU matrix. The prepared CB–PU composites had been further studied for surface morphology using the field-emission scanning electron microscopy (FESEM) technique. Dielectric properties in terms of real permittivity ($𝜀\prime )$ and imaginary permittivity ($𝜀\prime \prime )$ of the fabricated composites were computed using an Agilent E8364B vector network analyzer in the frequency range of 8–12 GHz ($X$-band). Dielectric loss factor of the prepared CB–PU composites was computed in terms of the dielectric loss tangent (tan ${\delta }_e$ = $𝜀\prime \prime$/$𝜀\prime )$. Microwave absorbing properties were appraised in terms of the reflection loss (RL) which in turn was calculated for varying thicknesses of the prepared composites from the measured real and imaginary permittivity data. The minimum RL was observed as −20.10 dB for the absorber with a thickness of 2.2 mm and the bandwidth achieved was 1.92 GHz for RL $\le -$10 dB. Based on the above results these CB–PU composites have potential use as effective microwave absorbers in 8–12-GHz ($X$-band) frequency range.

An organic nonlinear optical (NLO) crystal of Guanidinium carbonate (GUCT) was synthesized by the slow evaporation solution growth method using water as solvent. The GUCT crystalized in the tetragonal crystal system with non-centrosymmetric space group P4₃2₁2, which has been confirmed by single-crystal X-ray diffraction. The crystalline perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. The UV-Vis-NIR spectrum studies have been carried out to identify the optical transmittance, lower cut off wavelength and optical band gap energy of GUCT crystal. The luminescence spectrum of crystal contains a green emission band with λ_max, 545 nm. From thermo-gravimetric analysis (TGA), the thermal stability of the grown crystal is found to be 117°C. The dielectric tensor components ε₁₁ and ε₂₂ of the grown crystal were evaluated as a function of frequency at 40°C. The mechanical strength and its parameters of the grown crystals have been determined by Vickers' microhardness test. The Kurtz-powder technique reveals that the second harmonic generation (SHG) efficiency of the grown crystal is 5.2 times greater than that of KDP.