High Electric Permittivity Research Articles

3D framework MXene Ti3C2/g-C3N4/Fe3Si magneto-dielectric foam unveiling superior microwave absorption and thermal management performance

In conjunction with the swift advancement of detection technologies, the challenge persists in developing advanced stealth materials. The focus of this work is on the straightforward synthesis of a hybrid magneto-dielectric nanocomposite material composed of MXene Ti3C2/Fe3Si/g-C3N4 within a three-dimensional melamine foam framework, designed to deliver effective stealth capabilities. The high electrical conductivity and considerable permittivity of Ti3C2 have imposed limitations on its effectiveness in electromagnetic wave absorbers. In this context, the utilization of this compound in combination with substances like g-C3N4 and Fe3Si to fine-tune impedance matching and fully exploit the intrinsic properties is suggested. Furthermore, the distinctive 3D porous frameworks of the melamine foam, combined with the accordion-like structure of the MXene compound, extend and elongate paths for wave propagation to enhance energy dissipation. Through the activation of various loss mechanisms, it was possible to achieve a minimum reflection loss of −44.3 dB using a 1.5 mm thickness with an effective absorption bandwidth of 1.9 GHz. The enhancement of stealth performance was achieved through the combination of heterojunction interfaces among hybrid components and a 3D interconnected continuous path within the structure.

Mean-field homogenization of liquid metal elastomer composites: comparative study and exact dilute solution of core–shell inclusion

Liquid metal-elastomer composites (LMECs) have gathered significant attention for their potential applications in various functional stretchable devices, with inclusion sizes ranging from micrometers to nanometers. These composites exhibit exceptional properties, such as high electric permittivity and thermal conductivity, surpassing those of the elastomer matrix, thus enabling a broader range of applications without compromising the material's stretchability. To investigate the diverse effective elastic and functional properties of LMECs, micromechanics-based homogenization method based on Eshelby's inclusion solution are invaluable. However, the extreme contrast in elastic constants among the phases in LMECs, particularly for nanosized inclusions where a considerable amount of stiff metal oxide forms around the inclusions, can lead to critical failure in predicting effective properties if inadequate homogenization approach is employed. In this study, we present multiple mean-field homogenization approaches applicable to LMECs with core-shell morphology, namely: (i) multi-phase, (ii) sequential, (iii) pseudo-grain, and (iv) direct approaches. We compare the accuracy of the models concerning effective elastic, thermal, and dielectric properties, evaluated against numerical homogenization results and compared with reported experimental data. Specifically, we highlight homogenization scheme utilizing exact field solutions of dilute core-shell inclusion, emphasizing the importance of accurately capturing the field in the micromechanics of LMECs. Furthermore, we demonstrate that widely utilized interphase model could not properly resolve the core-shell morphology and thus should be avoided. This comprehensive assessment provides critical insights into the proper homogenization strategies for designing advanced LMECs with precise prediction of effective properties.

Insights into a Defective Potassium Sulfido Cobaltate: Giant Magnetic Exchange Bias, Ionic Conductivity, and Electrical Permittivity

AbstractThe novel potassium sulfido cobaltate, K2[Co3S4] is introduced, with 25% vacancies of the cobalt positions within a layered anionic sublattice. The impedance and dielectric investigations indicate a remarkable ionic conductivity of 21.4 mS cm−1 at room temperature, which is in the range of highest ever reported values for potassium‐ions, as well as a high electrical permittivity of 2650 at 1 kHz, respectively. Magnetometry results indicate an antiferromagnetic structure with giant intrinsic exchange bias fields of 0.432 and 0.161 T at 3 and 20 K respectively, potentially induced by a combination of the interfacial effect of combined magnetic anionic and nonmagnetic cationic sublattices, as well as partial spin canting. The stability of the exchange bias behavior is confirmed by a training effect of less than 18% upon 10 hysteresis cycles. The semiconductivity of the material is determined, both experimentally and theoretically, with a bandgap energy of 1.68 eV. The findings render this material as a promising candidate for both, active electrode material in potassium‐ion batteries, and for spintronic applications.

Siloxane-Based Nanoporous Polymer Insulating Dielectrics With High Electrical Strength and Low Permittivity for Future Ultrahigh Voltage Pipeline Transmission

The operating gas-insulated transmission line (GIL) equipment is typically associated with some challenges, such as high insulation failure rate, severe greenhouse effect, and large space occupation. Thus, compact and environmentally friendly GIL equipment with high electrical performance is particularly desired for ultra-high voltage (UHV) pipeline transmission equipment. Nanocomposite technology, as a conventional method for improving the electrical performance of insulating materials, such as epoxy resin (EP), which is the base material used in basin-type insulators in GIL, has been proven nonviable because of the limited increases in the dielectric properties. Inspired by the singularity phenomenon recently reported that nanostructures inhibit electron multiplication transport in gas to enhance the breakdown field strength of dielectric, a siloxane-based nanoporous polymer insulating dielectric (SNPID) with nanoscale pore structure was developed, with high breakdown field strength 1111.34% greater than the surface flashover field strength of basin-type insulators in GIL. Specifically, the SNPID exhibits excellent dielectric properties, with low dielectric loss and a permittivity value of <2, which is significantly lower than those of existing insulating materials. Finally, to demonstrate the application prospects of the SNPID in a GIL, a SNPID filling-type GIL scaling model was designed, with an insulation level of 358.09% higher than that of basin-type insulators in GIL, which could significantly reduce greenhouse gas sulfur hexafluoride (SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ) emissions by markedly decreasing the pipeline volume. This discovery provides a new gas-solid composite insulation form based on super-insulating material with high breakdown field strength and low permittivity for improving the insulation of UHV pipeline transmission equipment in response to the greenhouse effect.

Metal and Nonmetal Ion Doping Effect on the Dielectric Relaxation of TiO2 Electrodes

Titanium dioxide (TiO2) is a highly stable, photosensitive, and nontoxic metal oxide. The physical and chemical properties of TiO2 electrodes have been explored extensively for the last few decades. However, a detailed and comparative study of the dielectric relaxation and carrier kinetics with the dopants is still lacking. Herein, the crystallinity of TiO2 electrodes decreased with the dopants is reported. The doping of copper (Cu) in TiO2 reduces its bandgap to 2.98 eV from 3.22 eV. The improved charge carrier conduction at high frequencies (ω = 103–106 radians s−1) with the doping is noticed. The charge transfer resistance (R ct) for the electrons is minimum for Cu–TiO2 (R ct = 34.11 Ω) and Cu, Zn, and N–TiO2 (R ct = 27.44 Ω) compared to pristine and Cu and Zn–TiO2. Further, the high electrical permittivity is associated with the polar nature of electrodes. The correlation analysis of impedance and modulus spectroscopy data provides a prodigious picture of the charge carrier relaxation and conduction mechanism. A shift in the dielectric relaxation process from Debye type to non‐Debye type is observed after doping due to defect‐mediated fast relaxation of polarization.

Mathematical and deep learning analysis based on tissue dielectric properties at low frequencies predict outcome in human breast cancer

BACKGROUND: The early detection of human breast cancer represents a great chance of survival. Malignant tissues have more water content and higher electrolytes concentration while they have lower fat content than the normal. These cancer biochemical characters provide malignant tissue with high electric permittivity (ε´) and conductivity (σ). OBJECTIVE: To examine if the dielectric behavior of normal and malignant tissues at low frequencies (α dispersion) will lead to the threshold (separating) line between them and find the threshold values of capacitance and resistance. These data are used as input for deep learning neural networks, and the outcomes are normal or malignant. METHODS: ε´ and σ in the range of 50 Hz to 100 KHz for 15 human malignant tissues and their corresponding normal ones have been measured. The separating line equation between the two classes is found by mathematical calculations and verified via support vector machine (SVM). Normal range and the threshold value of both normal capacitance and resistance are calculated. RESULTS: Deep learning analysis has an accuracy of 91.7%, 85.7% sensitivity, and 100% specificity for instant and automatic prediction of the type of breast tissue, either normal or malignant. CONCLUSIONS: These data can be used in both cancer diagnosis and prognosis follow-up.

Super Electrical Insulating Materials Based on Honeycomb‐Inspired Nanostructure: High Electrical Strength and Low Permittivity and Dielectric Loss (Adv. Electron. Mater. 4/2022)

Nanopore Structures In article number 2100979, Wenxia Sima and colleagues prepare a new type of porous material with excellent electrical performance, which brings new ideas for the development of super electric insulators. The nanopore structures of the materials divide the contained insulating fluid into nanounits, thereby significantly reducing the number of effective molecules and limits the head size of electron avalanches, which suppresses electron collision ionization and improve the electrical performance of the dielectrics.

Siloxane-Based Nanoporous Polymer Insulating Dielectrics with High Electrical Strength and Low Permittivity for Future Ultra-High Voltage Pipeline Transmission

Siloxane-Based Nanoporous Polymer Insulating Dielectrics with High Electrical Strength and Low Permittivity for Future Ultra-High Voltage Pipeline Transmission

Super Electrical Insulating Materials Based on Honeycomb‐Inspired Nanostructure: High Electrical Strength and Low Permittivity and Dielectric Loss

AbstractThe high breakdown field strength is the most important index to evaluate the performance of insulating materials. It is theoretically found that the breakdown field strength of dielectric samples can be significantly improved by up to 1–2 orders of magnitude by constructing nanopore structures. Thus, bridged silsesquioxane super electrical insulating materials (BSSEIM) are developed with nanosized pore structures and their extremely high electrical insulation performance is realized. The results indicate that the breakdown field strength of the BSSEIM is dramatically higher than aluminosilicate fiber insulating materials (ASFIM) by 570.5% for dry samples and 118.1% for oil‐impregnated samples. Specifically, the prepared BSSEIM samples have excellent dielectric performances with permittivity and dielectric losses that are only 51.3% and 1.1% of ASFIM, which are significantly lower than most existing insulating materials. Finally, the theoretical analysis indicates that the nanopore structures can effectively limit the scale of the head size for an electron avalanche and significantly reduce the number of effective gas molecules by dividing the gas into nanounits. This significantly inhibits the ionization of gas molecules and improves the breakdown field strength of samples. This discovery overturns previous understandings of traditional insulating materials and opens an avenue toward super electrical insulating materials.

Effect of an axial electric field on the breakup of a leaky-dielectric liquid filament

We study experimentally and numerically the thinning of Newtonian leaky-dielectric filaments subjected to an axial electric field. We consider moderately viscous liquids with high electrical permittivity. We analyze the influence of the electric field on the formation of satellite droplets from the breakup of the filaments in the experiments. The electric force delays the free surface pinching. Two electrified filaments with the same minimum radius are thin at the same speed regardless of when the voltage is applied. The numerical simulations show that the polarization stress is responsible for the pinching delay observed in the experiments. Asymptotically close to the pinching point, the filament pinching is dominated by the diverging hydrodynamic forces. The polarization stress becomes subdominant even if this stress also diverges at this finite-time singularity.

Mechanochemical Activation and Spark Plasma Sintering of the Lead-Free Ba(Fe1/2Nb1/2)O3 Ceramics.

This paper investigates the impact of the technological process (Mechanochemical Activation (MA) of the powder in combination with the Spark Plasma Sintering (SPS) method) on the final properties of lead-free Ba(Fe1/2Nb1/2)O3 (BFN) ceramic materials. The BFN powders were obtained for different MA duration times (x from 10 to 100 h). The mechanically activated BFN powders were used in the technological process of the BFN ceramics by the SPS method. The measurements of the BFNxMA ceramic samples included the following analysis: Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometry (EDS), DC electrical conductivity, and dielectric properties. X-ray diffractions (XRD) tests showed the appearance of the perovskite phase of BFN powders after 10 h of milling time. The longer milling time (up 20 h) causes the amount of the perovskite phase to gradually increase, and the diffraction peaks are more clearly visible. Short high energy milling times favor a large heterogeneity of the grain shape and size. Increasing the MA milling time to 40 h significantly improves the microstructure of BFN ceramics sintered in the SPS technology. The microstructure becomes fine-grained with clearly visible grain boundaries and higher grain size uniformity. Temperature measurements of the BFN ceramics show a number of interesting dielectric properties, i.e., high values of electric permittivity, relaxation properties with a diffusion phase transition, as well as negative values of dielectric properties occurring at high temperatures. The high electric permittivity values predestines the BFNxMA materials for energy storage applications e.g., high energy density batteries, while the negative values of dielectric properties can be used for shield elements against the electromagnetic radiation.

Improved whole-brain SNR with an integrated high-permittivity material in a head array at 7T.

To demonstrate that strategic use of materials with high electric permittivity along with integrated head-sized coil arrays can improve SNR in the entire brain. Numerical simulations were used to design a high-permittivity material (HPM) helmet for enhancing SNR throughout the brain in receive arrays of 8 and 28 channels. Then, two 30-channel head coils of identical geometry were constructed: one fitted with a prototype helmet-shaped ceramic HPM helmet, and the second with a helmet-shaped low-permittivity shell, each 8-mm thick. An eight-channel dipole array was used for excitation. In vivo maps of excitation flip angle and SNR were acquired. Simulation results showed improvement in transmit efficiency by up to 65% and in receive-side SNR by up to 47% on average through the head with use of an HPM helmet. Experimental results showed that experimental transmit efficiency was improved by approximately 56% at the center of brain, and experimental receive-side SNR (SNR normalized to flip angle) was improved by approximately 21% on average through orthogonal planes through the cerebrum, including at the center of the brain, with the HPM. Although HPM is used increasingly to improve transmit efficiency locally in situations in which the transmit coil and imaging volume are much larger than the HPM, here we demonstrate that HPM can also be used to improve transmit efficiency and receive-side SNR throughout the brain by improving performance of a head-sized receive array. This includes the center of the brain, where it is difficult to improve SNR by other means.

Tri-layer architectured epoxy composites with high electrical permittivity

In this work, epoxy composites filled with polypyrrole (ppy) coated paddy straw micro particles exhibiting high electrical permittivity were prepared. Oxidative vapour phase polymerization was used to obtain thin ppy coating over straw particles. These single layered epoxy composites exhibited high electrical permittivity and were further used to prepare tri-layer architectured composites in which an epoxy-graphene (−ve k) composite layer was stacked in-between two epoxy-ppy-straw (+ve k) composite layers. The layered composites displayed an even higher electrical permittivities, 124.2 and 227.7 (1 kHz) and suppressed tanδ 0.055 and 0.5 at 33 wt% and 38 wt% filler concentrations respectively. The tanδ showed strong frequency dependence and their minima shifted to higher frequencies. The thickness of +ve k layers were reduced progressively and corresponding permittivities were recorded which showed a linear increase as the thickness ratio of layers (−ve k/+ve k) increased.

Post-process porous silicon for 5G applications

The interest of 5G in centimeter and millimeter waves relies on large blocks of available spectra and thus increased bandwidth. At these frequencies, the dielectric and conductive losses of the substrate can greatly degrade the performances of RF circuits. With high electrical resistivity and low relative permittivity, porous silicon is an ideal candidate as a high-quality RF substrate. This paper presents an innovative technique of post device fabrication integration of porous silicon (POST-PSi) with the substrate. The frontside is not involved in porous layer growth and therefore the integrity of the RF circuitry is not impacted by the POST-PSi process. A comparison of the RF performances with benchmark trap-rich (TR) RF silicon substrate is presented. In addition to its compatibility with standard microfabrication processes and stable final structure, POST-PSi provides characteristics of low losses, high isolation and very high linearity, unmatched by any other silicon-based substrate. Finally, the substrate’s RF performance is evaluated at high temperature, and POST-PSi substrate linearity is shown to remain sufficiently high for RF and 5G applications up to 175 °C.

Influence of the charge ordering and quantum effects in heterovalent substituted hexaferrites on their microwave characteristics

M-type hexagonal ferrites with heterovalent substitutions (Nd3+-Zn2+ and Ti4+) were synthesized. X-Ray diffraction (XRD) powder patterns of Sr(Nd,Zn)xFe12-xO19 and BaFe12-xTixO19 (0.1 ≤ x ≤ 1.0) confirmed the single phase constitution of all investigated samples. High frequency magnetic (permeability), electrical (permittivity), and resonant properties were analyzed. Unexpected behavior in the permittivity and permeability as a function of frequency was observed. Appearance of two peaks for samples with x = 0.1 and 0.9 indicated mixed oxidation state for the Fe ions. Behavior for Sr(Nd,Zn)xFe12-xO19 (0.3 ≤ x ≤ 0.7) confirms the occurrence of the anomalous quantum effect, namely charge disproportionation. The permeability behavior of Ti-substituted samples with a double Fe oxidation state was theoretically discussed in terms of spin states crossover. The behavior of reflection losses for Sr(Nd,Zn)xFe12-xO19 and BaFe12-xTixO19 (0.1 ≤ x ≤ 1.0) samples was discussed in terms of the modalities of charge ordering in heterovalent substituted M-type hexaferrites.

Sculpting Extreme Electromagnetic Field Enhancement in Free Space for Molecule Sensing.

A strongly confined and enhanced electromagnetic (EM) field due to gap-plasmon resonance offers a promising pathway for ultrasensitive molecular detections. However, the maximum enhanced portion of the EM field is commonly concentrated within the dielectric gap medium that is inaccessible to external substances, making it extremely challenging for achieving single-molecular level detection sensitivity. Here, a new family of plasmonic nanostructure created through a unique process using nanoimprint lithography is introduced, which enables the precise tailoring of the gap plasmons to realize the enhanced field spilling to free space. The nanostructure features arrays of physically contacted nanofinger-pairs with a 2 nm tetrahedral amorphous carbon (ta-C) film as an ultrasmall dielectric gap. The high tunneling barrier offered by ta-C film due to its low electron affinity makes an ultranarrow gap and high enhancement factor possible at the same time. Additionally, its high electric permittivity leads to field redistribution and an abrupt increase across the ta-C/air boundary and thus extensive spill-out of the coupled EM field from the gap region with field enhancement in free space of over 103 . The multitude of benefits deriving from the unique nanostructure hence allows extremely high detection sensitivity at the single-molecular level to be realized as demonstrated through bianalyte surface-enhanced Raman scattering measurement.

High electric permittivity of polymer-modified cement due to the capacitance of the interface between polymer and cement

The electric permittivity is a material property that relates to the dielectric and electromagnetic behaviors. This work reports the effect of polymer admixtures on the permittivity (2 kHz) of cement paste. The permittivity is increased significantly by the addition of either methylcellulose (dissolved) or latex (styrene–butadiene, not dissolved), due to the capacitance of the interface between polymer and cement. The permittivity is effectively modeled by a material-level equivalent circuit model that comprises cement, polymer and cement/polymer interface in parallel. The series model is not effective. For both methylcellulose and latex, the cement and cement/polymer interface dominate the contributions to the permittivity, while the polymer contributes little. The contributions of polymer and cement/polymer interface increase monotonically with increasing polymer/cement ratio, while the contribution of cement decreases monotonically. Methylcellulose at the highest proportion of 1.4% by mass of cement gives permittivity 52, whereas latex at the highest solid latex proportion of 14% by mass of cement gives permittivity 43. For the same polymer/cement ratio, the permittivity is much higher for methylcellulose than latex. The difference between methylcellulose and latex is due to the much greater contribution of the cement/polymer interface to the permittivity for methylcellulose than latex, as caused by the nanoscale morphology of the methylcellulose and the consequent large cement/polymer interface area. At the same polymer/cement ratio, the fractional contribution from the cement/polymer interface is greater for methylcellulose than latex, though those from the polymer and cement are greater for latex than methylcellulose.

Miniaturised circularly‐polarised antenna with high‐constitutive parameter substrate

A two-dimensional (2D) high-constitutive parameter (TDHCP) substrate is designed using an artificial metamaterial with high-constitutive parameters. The planar TDHCP substrate is used for miniaturising of a circularly-polarised microstrip patch antenna. A 2D metamaterial unit cell is needed due to the fact that the electric and magnetic vectors are rotating in a circularly-polarised antenna. The proposed TDHCP substrate increases the constitutive parameters of the host substrate. It is composed of periodic split-ring resonators loop circuits embedded in a low dielectric host medium. The TDHCP substrate provides equal permittivity and permeability ( e r ≅ μ r ) at any frequency of interest, which compensates for the bandwidth reduction due to the increased permittivity. The size of the proposed TDHCP substrate antenna at 850 MHz is reduced up to about 72% compared to the conventional microstrip patch antenna. The bandwidth of the antenna is increased compared to high-electric permittivity substrates because of the increased the magnetic permeability. The proposed antenna is fabricated and measured. The simulated and measured results show a good agreement.

Maxwell–Wagner–Sillars mechanism in the frequency dependence of electrical conductivity and dielectric permittivity of graphene-polymer nanocomposites

The Maxwell–Wagner–Sillars (MWS) effects have been reported in various experiments of graphene-polymer nanocomposites under AC loading. It is considered to be the source of the observed high dielectric constant for this class of nanocomposites. But at present no theory seems to exist to provide a physical description of this mechanism, and to transform this effect into the reported high electrical conductivity and dielectric permittivity. In this work we start out from consideration of high disparity of electrical conductivity between graphene and polymer phases to present such a description, and then integrate it into an effective-medium theory to illustrate how it affects the overall properties of the nanocomposite. We model this mechanism with numerous nanocapacitors at the graphene-polymer interfaces, whose charge accumulation is taken to be directly proportional to the difference of conductivities of graphene fillers and polymer matrix. In the context of complex conductivity, this formulation gives rise to an added frequency-dependent conductivity and permittivity of the interface regions. We highlight this theory with an application to reduced graphene oxide/polypropylene (rGO/PP) nanocomposites, and demonstrate that the calculated conductivity and permittivity are in close agreement with experimental data over the frequency range from 103 to 107Hz. This study clearly demonstrates that the MWS mechanism is principally responsible for the frequency dependence of electrical conductivity and dielectric constant of graphene-polymer nanocomposites.

High-temperature electromagnetic interference shielding of layered Ti3AlC2 ceramics

The electromagnetic interference (EMI) shielding of dense Ti3AlC2 ceramics with distinct microstructures were investigated up to 800°C. Ti3AlC2 exhibits high EMI shielding effectiveness (SE) around 30dB which was mainly attributed to high electrical conductivity and complex permittivity. Besides, the EMI shielding were sensitive to the microstructure. Ti3AlC2 with high aspect ratio grains and certain degree of texture were preferred for high SE indicating that the typical layered structure also contributes to the high shielding capability. These results indicate that layered Ti3AlC2 ceramics could be considered as promising structural EMI shielding materials at high temperatures.