Significant Dielectric Loss Research Articles

Lignin-Derived Lightweight Carbon Aerogels for Tunable Epsilon-Negative Response.

Electromagnetic (EM) metamaterials have garnered considerable attention due to their capacity to achieve negative parameters, significantly influencing the integration of natural materials with artificially structural media. The emergence of carbon aerogels (CAs) offers an opportunity to create lightweight EM metamaterials, notable for their promising EM shielding or absorption effects. This paper introduces an efficient, low-cost method for fabricating CAs without requiring stringent drying conditions. By finely tuning the ZnCl2/lignin ratio, the porosity is controlled in CAs. This control leads to an epsilon-negative response in the radio-frequency region, driven by the intrinsic plasmonic state of the 3D carbon network, as opposed to traditional periodic building blocks. This approach yields a tunable and weakly epsilon-negative response, reaching an order of magnitude of -103 under MHz frequencies. Equivalent circuit analysis highlights the inductive characteristics of CAs, correlating their significant dielectric loss at low frequencies. Additionally, EM simulations are performed to evaluate the distribution of the electric field vector in epsilon-negative CAs, showcasing their potential for effective EM shielding. The lignin-derived, lightweight CAs with their tunable epsilon-negative response hold promise for pioneering new directions in EM metamaterials and broadening their application in diverse extreme conditions.

Giant dielectric tunability in ferroelectric ceramics with ultralow loss by ion substitution design

Due to their responsiveness to modulation by external direct current fields, dielectric tunable materials are extensively utilized in integrated components, such as ferroelectric phase shifters. Barium strontium titanate ceramics have been considered the most potential tunable materials for a long time. However, the significant dielectric loss and high voltage drive have limited their further applications. Recently, Bi6Ti5WO22 ceramic has regained attention for its high dielectric tunability with low loss. In this study, we judiciously introduce Nb5+ with a larger ionic radius, replacing Ti4+ and W6+. This successful substitution enables the modulation of the phase transition temperature of Bi6Ti5WO22 ceramics to room temperature, resulting in superior tunable properties. Specifically, the 0.7Bi6Ti5WO22−0.3Bi6Ti4Nb2O22 ceramics exhibit giant tunability (~75.6%) with ultralow loss (<0.002) under a low electric field (1.5 kV/mm). This tunability is twice that of barium strontium titanate ceramics with a similar dielectric constant and only one-tenth of the loss. Neutron powder diffraction and transmission-electron-microscopy illustrate the nanodomains and micro-strains influenced by ion substitution. Density functional theory simulation calculations reveal the contribution of ion substitution to polarization. The research provides an ideal substitute for tunable material and a general strategy for adjusting phase transition temperature to improve dielectric properties.

Enhanced microwave absorption properties of conducting polymer@graphene composite to counteract electromagnetic radiation pollution: green EMI shielding.

Conducting polymers have been thoroughly investigated and found to have extensive applications in the fields of microwave absorption and electromagnetic (EM) shielding owing to their distinctive characteristics and adaptability. In the present work, conducting polymer (PEDOT and polyaniline) and graphene composites were prepared via an in situ chemical polymerization technique. Further, these composite materials were characterized to determine their potential to address the issue of EM radiation pollution in the microwave frequency (12.4 GHz to 18 GHz). The PEDOT/graphene composites exhibited significant shielding effectiveness of up to 46.53 dB, achieving a green index (gs) of 1.17. Also, absorption was observed to be the dominant shielding mechanism in all the samples owing to significant dielectric losses (ε''/ε' ≈ 1.9-3.1) and microwave conductivity (σs = 19.9-73.6 S m-1) in the samples at 18 GHz. Both dielectric loss and conduction loss occurred because of the strong interactions involving polarization, charge propagation, and the creation of conductive routes through the incorporation of graphene in the polymer matrix. These properties/shielding results indicate the potential of the composites to be used as lightweight EM shielding materials. These materials are suitable shield materials for electronic devices to protect them from harmful electromagnetic radiation, making them vital in various applications.

Relationship between the characteristic temperature and terahertz permittivity of different rank coals considering FeS2 content

In this study, the characteristic temperatures and terahertz permittivity of lignite with varying pyrite content were determined using a synchronous thermal analyzer and terahertz time-domain spectroscopy. A mathematical relationship between these two parameters was established by combining experimental data. The results indicate that within the range of 0–9% pyrite content, there is a trend where pyrite initially enhances and then weakens the promotion effect on coal spontaneous combustion. A quadratic polynomial can describe this relationship, with the extremum occurring at 6%. Regarding permittivity, as the pyrite content increases from 0% to 9%, the real part of permittivity exhibits irregular variations, while the imaginary part shows a well-defined linear increase. This behavior is attributed to enhanced relaxation polarization, leading to more significant dielectric losses. Furthermore, through the combination of experimental data, a robust quadratic relationship is observed between characteristic temperature and terahertz permittivity. The credibility of this relationship is validated by comparing it with experimental results. These findings contribute to the advancement of the theoretical understanding of coal's permittivity and spontaneous combustion characteristics, and provide a theoretical possibility for the rapid estimation of spontaneous combustion characteristics in pyrite-bearing coal seams using electromagnetic methods.

Constructing honeycomb-like hierarchical foam via electromagnetic cooperation strategy for broadband microwave absorption

The application of wireless electronic devices inevitably leads to electromagnetic pollution. Three-dimensional porous foam structures have been shown to be an effective strategy to construct high-performance microwave absorbers. Herein, the honeycomb-like hierarchical foams were fabricated via melamine-formaldehyde (MF) foam as substrate coupled with flaky carbonyl iron (CI)-MXene lamellae. Inside the synthesized composite foam, flaky CI is interlaced into MXene nanosheets to form hierarchical structures, which effectively alleviates the originally self-stacking phenomenon and provides numerous heterogeneous interfaces, resulting in the optimization of impedance matching. In addition, owing to the construction of consecutive electromagnetic networks, the CI-MXene/MF foams exhibit significant dielectric loss and magnetic loss capability. Moreover, the honeycomb-like structure offers multiple reflections/scattering for electromagnetic waves, which effectively prolongs the transmission paths, further improving the microwave attenuation ability. Hence, the synthesized composite foam exhibits superior microwave absorption performance with a minimum refection loss of −61.4 dB and a maximum effective absorption band of 7.18 GHz. The construction of unique microstructure and regulation of electromagnetic components is demonstrated to be feasible strategies for the design of efficient microwave absorbers in future.

Honeycomb-like bamboo powders-derived porous carbon with low filler loading, high-performance microwave absorption

Nowadays, the problem posed by electromagnetic wave pollution to electronic devices and biological systems is of serious concern. To create a microwave absorber, component and structural modulation is crucial. Biomass-derived porous carbon is a potential material for microwave absorption applications due to the characteristics of lightweight, high specific surface area, and significant dielectric loss. In this study, by examining the impact of various KOH concentrations on the pore structure, bamboo powders with an 80-mesh size were used as a raw material to create honeycomb-like bamboo powders-derived porous carbon (BPDPC) materials. The activation mechanism of the BPDPC material is also explained. Based on the electromagnetic parameters, the sample BPDPC-4 impregnated with 4 mol/L KOH has a maximum effective absorption bandwidth (RL ≤ −10 dB) of 4.76 GHz at a matching thickness of 2.0 mm, covering 11.54–16.30 GHz and a minimum reflection loss (RLmin) of −40.99 dB at a matching thickness of 2.2 mm at 5 wt% ultra-low filler loading. Due to polarization loss, conduction loss, and the mutually beneficial effects of multiple electromagnetic wave reflection and scattering, the superior wave absorption performance is explained. This work also serves as a reference for investigating porous carbon generated from biomass.

Exhibition of Dielectric Property Based on Soil Class and Moisture Presence for Bengaluru District

This research examined the dielectric characteristics of soils by utilizing four types of soil (clay-loam, loam, clay, and Frank) in a vector network analyzer (VNA) in the 600–8000 MHz microwave frequency range at ambient temperature (25°C ± 3°C). In this experiment, three observations were performed on the basis of soil moisture contents (dry, 33%, 66%, and 100% field capacities (CC)). Both actual (dielectric constant) and fictional (loss factor) parts of the dielectric characteristics improved with increasing soil moisture; however, the responses were not linear. It was observed that dry soil dielectric characteristics were deficient when compared to wet soil. In conclusion, the dielectric behavior of soil mainly was resolute by the moisture in the soil. Frank soil had considerably lower dielectric characteristics, while the Jain University (JU) clay soil had a far more significant dielectric loss factor.

In-situ growth of bamboo-shaped carbon nanotubes and helical carbon nanofibers on Ti3C2Tx MXene at ultra-low temperature for enhanced electromagnetic wave absorption properties

The potential of two-dimensional layered MXenes in electromagnetic wave (EMW) absorption needs further development. Herein, we carried out the in situ growth of carbon nanotubes (CNTs) on the surface of Ti3C2Tx MXene at ultra-low temperature via chemical vapor deposition. The obtained CNTs exhibited a bamboo-like structure and were accompanied by helical carbon nanofibers. The ultra-low temperature solved the problem that the high temperature required in the traditional CNT growth process would destroy the structural integrity of MXene. The lush CNT forest cross-linked the MXene layers, transforming the two-dimensional layered structure into a three-dimensional conductive network, providing abundant conductive channels for carriers, optimizing the impedance matching of the CNT/MXene hybrid, and resulting in a significant dielectric loss. The as-prepared CNT/MXene hybrid exhibited a minimal reflection loss of −52.56 dB (99.9994% EMW absorption) in the X-band. This work proposes a new idea to enhance the EMW absorption properties of Ti3C2Tx MXene and fabricate high-performance MXene-based EMW absorbers.

Process intensification on co-pyrolysis of polyethylene terephthalate wastes and biomass via microwave energy: Synergetic effect and roles of microwave susceptor

The present study employs microwave (MW) energy to enhance the co-pyrolysis of polyethylene terephthalate (PET) wastes and biomass. Based on the characterization of raw materials as well as gas and liquid products, we propose a pyrolysis mechanism of PET and biomass during microwave-assisted pyrolysis (MAP). The MAP of PET-biomass blends shows a synergetic effect that the interaction between PET and biomass promotes the yields of value-added products (e.g. aromatic acids and phenols) and suppresses the generation of biphenyls and polycyclic aromatic hydrocarbons, compared to the MAP of individual biomass or plastics. Besides, the blending ratio of PET-biomass has significant effect on the formation of major liquid products. The liquid product from the MAP of PET-biomass 4:1 blends contains above 30 wt.% chain hydrocarbon that can be used as gasoline and kerosene. Moreover, we evaluate the roles of three typical MW absorbing materials during MAP, including carbon powder, ferroferric oxide (Fe3O4) and calcium oxide (CaO). Carbon powder can enlarge the yield of main products from plastics pyrolysis due to its significant dielectric loss. Apart from the MW-absorbing ability, Fe3O4 can accelerate the esterification and decarboxylation reaction; CaO can convert acids into ketones and hydrocarbons through neutralization and catalytic cracking reactions.

Dielectric behavior of dehydrated homoionic alkali-cations-exchanged montmorillonite

The dielectric properties of a series of montmorillonite clays, namely, Li+, Na+, K+, Rb+ and Cs+-montmorillonite in dry state have been measured by means of complex impedance spectroscopy. These measurements are performed between 173 K and 473 K at frequencies ranging from 10−2 to 106 Hz. The objective of this study was to correlate the dielectric properties with the temperature and the nature of exchanged cations. The real and imaginary parts of the complex dielectric permittivity for the alkali-exchanged montmorillonites, show at fixed temperatures a decrease with increasing frequency, and on the other hand show an increase with increasing temperature. Furthermore, by considering the activation energy of cations, at a fixed temperature, the frequency dependence of the real and imaginary parts seemed to follow the polarizing power of the cations. The frequency dependence reveals significant dielectric losses in the low frequency range where the appearance of resonance peaks in the loss tangent is due to dielectric relaxation processes of this material.

Relaxation peaks of ZnO varistors and their correlations with electrical properties

Many dielectrics exhibit a (polarization) relaxation response when a time-varying electric field is applied. In some frequency bands, the amplitude of the polarization changes rapidly, with a significant dielectric loss; the maxima in the change rate are referred to as relaxation peaks. ZnO varistors exhibit a dielectric response with several relaxation peaks, but the relationship between the relaxation peaks and electrical properties has not been established. To understand this relationship, dielectric spectroscopy measurements of ZnO varistors were conducted in the temperature range of −110 °C to 200 °C in the frequency range of 10−1–106 Hz. By changing two important dopants of Bi2O3 and Sb2O3, four relaxation peaks, named Peak A, Peak B, Peak C, and Peak D, were detected. It was found that peaks A, B, and D are indispensable for higher nonlinearity and lower leakage current density. The detection of all four peaks implies that ZnO varistors possess excellent electrical properties, that is, a high breakdown field (235.2 V mm−1), nonlinear coefficient (76.2), and low leakage current density (0.065 μA cm−2).

Effect of organoclay loading on the dielectric properties and charge dynamics of a PP‐rubber nanocomposite

The addition of organoclay to a polypropylene-rubber (PP-rubber) blend, primarily introduced to compatibilise the immiscible polymer blend, invokes contrasting dielectric and charge dynamic behaviour depending on the filler loading level. The authors report that at 0.5 wt.% loading, the organoclay decreases the DC conductivity, causes no significant dielectric losses, makes no significant difference to the space charge results compared to the unfilled system, and increases the reproducibility of the breakdown strength results, and hence the reliability of the material. These somewhat surprising results, contrasted by measurements of samples with 2.5 and 5 wt.%, lead us to conclude that trace amounts of organoclay improve the otherwise immiscible polymer blend making organoclay a suitable additive for HVDC applications.

Primary measuring transducer of moisture content for grain quality control

The main task of the research is the development of the primary capacitive measuring transducer that can perform testing influences on the material under research, applied for automatic “type uncertainty” method error compensation, that takes place because of the method of measurement imperfection. To estimate the relevant level of testing influences a group of different materials with 2, 2.5, 3 and 3.5 dielectric permittivity values was taken for 0, 10, 20, 30 and 40% of moisture content control points. The primary measuring transducer of moisture content is organized with an electrode system in a form of V-type plates, which is fixed on the internal surface of two dielectric rings. Testing influences on the substance are reproduced directly in the capacitive primary transducer by simple metallic plates with fixed thickness introduction into the space between separate electrodes of an electrode system. A prototype product of the primary measuring transducer had been experimentally tested together with the new method of moisture measurement, which includes two additive, two multiplicative and two complementary testing influences on the material under research. Moisture content with nominal values 0, 10, 20 and 30% was reproduced by certain group of grains with different dielectric permittivity values. Experimental setup of an adaptive moisture meter was assembled using the substitution method of measurement to provide good accuracy for the conditions of capacitance measurement in substances with significant dielectric losses. The accuracy of moisture measurement was defined as discrepancy between average measured and nominal moisture content and as an uncertainty of this discrepancy in a form of type A uncertainty.

Facile synthesis of LaNiO3 microspheres with efficient broad band microwave absorption performance

Here, we synthesized LaNiO3 microspheres by a simple hydrothermal synthesis and subsequent annealing process. The LaNiO3 microspheres are characterized by TG-DSC, XRD, FESEM, TEM and VAN. Noticeably, owing to the effective synergism between significant dielectric loss and optimum impedance match, LaNiO3 microspheres exhibit significantly remarkable attenuation capability and wide-band respond. Therefore, the possible mechanism of microwave absorption enhancement is carefully investigated. A minimum reflection loss intensity −30.6 dB of LaNiO3 microspheres can be achieved and a broad effective absorbing bandwidth (reflection loss reaches −10.0 dB) of 4.72 GHz (8.16–12.88 GHz) at the thickness of 2.0 mm. Furthermore, the overall effective bandwidth is obtained up to 14.5 GHz from 3.5 GHz to 18 GHz, covering more than 90% of the measured frequency range. It is expected that the LaNiO3 microspheres could be used to design efficient microwave absorption materials.

Strain engineering of dischargeable energy density of ferroelectric thin-film capacitors

Abstract Ferroelectric oxide thin-film capacitors find applications in microelectronic systems, mobile platforms, and miniaturized power devices. They can withstand higher electric fields and display significantly larger energy densities than their bulk counterparts and exhibit higher maximum operating temperatures and better thermal stabilities than polymer-based dielectric capacitors. However, ferroelectric oxide thin films typically possess large remanent polarization and exhibit significant dielectric loss, thereby limiting their dischargeable energy densities. Here we demonstrate, using phase-field simulations, that strain can be utilized to modify the polarization response to electric field and thus optimize the energy-storage performance of ferroelectric thin-film capacitors. For example, an in-plane tensile strain can significantly narrow hysteresis loops by reducing the remanent polarization without significantly decreasing the out-of-plane saturated polarization. As a result, both the dischargeable energy density and charge-discharge efficiency can be significantly enhanced. We analysed the domain structures and energy surfaces to understand the underlying mechanisms for the enhancements. We also propose a bending strategy to further improve the dischargeable energy density, which can be achieved, e.g., by growing ferroelectric thin films on a flexible substrate (e.g., mica). This work provides a general strategy to optimize the energy-storage performance of ferroelectric thin-film capacitors for high-energy/power-density storage applications.

Tunable dielectric properties of niobium (Nb) doped CaCu3Ti4O12 nanocubes synthesized via facile molten salt route

Doping induced tuning of dielectric constant of nanomaterials has huge technological importance, but its realization is limited by lack of synthetic protocols for uniform dielectric nanostructures, with controlled doping. Here, nanocubes of niobium doped calcium copper titanate (Nb-doped CCTO) is realized through molten salt route and the effect of Nb doping on tunability of dielectric behavior is reported. Particular focus is to minimize the significant dielectric loss which is practical concern of CCTO based giant dielectric materials. The structural and compositional properties of as synthesized powders and sintered pellets are analyzed by X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. XRD analysis carried out on the samples confirmed single phase formation and indicated overall increase in lattice constant. The surface morphology of the molten salt derived product shows nanocubes with size in the range of 250–280 nm. Energy dispersive X-ray spectroscopy pattern confirmed the presence of Nb in doped samples. The dielectric response of sintered CaCu3Ti4−xNbxO12 samples studied by precision LCR meter suggest that although Nb substitution in CCTO reduces the dielectric constant but dielectric loss had lower values than those of undoped CCTO.

Air-Filled Substrate Integrated Waveguide Fed Magneto-Electric Dipole Antenna Array for Millimeter-Wave Applications

A substrate integrated magneto-electric (ME) dipole antenna array with an improved radiation efficiency is presented in the 28-GHz band. A novel full-corporate air-filled substrate integrated waveguide (SIW) feed network with low losses is designed and realized by utilizing the low-cost printed circuit board (PCB) facilities. Different from most previous millimeter-wave planar arrays consisting of 2 × 2 subarrays, an SIW fed sub-array with a larger size of 2 × 4 is investigated to simplify the configuration of the major portion of the array feed network, which is of importance to the successful realization of the air-filled SIW feed network. An 8×8 array prototype with a four-layered geometry is fabricated and measured to verify the design. The array has an impedance bandwidth of 25.9%, a gain up to 26 dBi and stable radiation patterns over the operating band. Benefitted from the absence of the significant dielectric loss in the feed network, a high antenna efficiency of 80% is also achieved. The proposed design provides an effective method to improve the achievable gain and efficiency characteristics of the substrate integrated arrays with a large size that are attractive for millimeter-wave wireless applications.

Flat-On Secondary Crystals as Effective Blocks To Reduce Ionic Conduction Loss in Polysulfone/Poly(vinylidene fluoride) Multilayer Dielectric Films

Recently, poly(vinylidene fluoride) (PVDF)-based multilayer films have demonstrated good potential as high energy density, high temperature, and low loss polymer dielectrics for advanced electrical and power applications. However, impurity ion conduction in the PVDF layers can cause significant dielectric loss at high temperatures. In this study, we discovered a facile melt-recrystallization method to suppress ionic conduction loss in polysulfone (PSF)/PVDF 50/50 (v/v) 33-layer films. By use of combined differential scanning calorimetry, broadband dielectric spectroscopy, and simultaneous small-angle X-ray scattering/wide-angle X-ray diffraction techniques, the underlying mechanism for the suppression of ionic conduction was unraveled. Basically, the growth and hierarchical organization of primary and secondary PVDF crystals confined in 400 nm layers played an important role. When the cooling rate during melt-recrystallization was high (e.g., ≥500 °C/min), small and poorly oriented secondary crystals betw...

Porous Fe3O4/C microspheres for efficient broadband electromagnetic wave absorption

Porous Fe3O4/C microspheres, which were Fe3O4 nanocrystals (～8 nm) embedded in an open nanostructured carbon network, were successfully synthesized via a facile hydrothermal process. The porous Fe3O4/C microspheres possessed many distinct attributes that facilitate efficient broadband electromagnetic wave absorption (EMWA). EMWs were attenuated through multiple reflections and absorption in the 3D interconnected porous structure of the microspheres; these processes collectively improved the interaction between the EMWs and the absorber. Additionally, the carbon network and embedded Fe3O4 nanoparticles caused significant dielectric losses and magnetic losses, respectively, which also enhanced EMWA. The EMWA characteristics of the microspheres could be precisely tuned via changing the carbon content to achieve optimized impedance matching. Porous Fe3O4/C microspheres with a 71.5 wt% carbon content displayed particularly impressive EMWA properties: a maximum reflection loss (RL) value of − 31.75 across broad band frequencies in the range of 7.76–12.88 GHz (RL < −10 dB) at an absorber thickness of 3.0 mm. These excellent EMWA properties may be attributed to both dielectric loss (carbon) and magnetic loss (Fe3O4). Additionally, the 3D interconnected porous structure of the Fe3O4/C microspheres is especially favorable for impedance matching.

Magnetic graphene enabled tunable microwave absorber via thermal control

By synthesizing nitrogen-doped graphene (NG) via a facile thermal annealing method, a fine control of the amount and location of doped nitrogen as well as the oxygen-containing functional groups is achieved with varying annealing temperature. The favorable magnetic properties have been achieved for N-doped rGO samples obtained at two temperatures of all NG samples, i.e., 500 °C and 900 °C with saturation magnetization of 0.63 emu g−1 and 0.67 emu g−1 at 2 K, respectively. This is attributed to the optimized competition of the N-doping and reduction process at 500 °C and the dominated reduction process at 900 °C. NG obtained at 300 °C affords the best overall absorbing performance: when the absorber thickness is 3.0 mm, the maximum absorption was −24.6 dB at 8.51 GHz, and the absorption bandwidth was 4.89 GHz (7.55–12.44 GHz) below −10 dB. It owes its large absorbing intensity to the good impedance match and significant dielectric loss. The broad absorption bandwidth benefits from local fluctuations of dielectric responses contributed by competing mechanisms. Despite the significant contribution from materials loss to the absorption, the one quarter-wavelength model is found to be responsible for the reflection loss peak positions. Of particular significance is that an appropriate set of electromagnetic parameters associated with reasonable reduction is readily accessible by convenient control of annealing temperature to modulate the microwave absorbing features of graphene. Thus, NG prepared by thermal annealing promises to be a highly efficient microwave absorbent.