Dielectric Shielding Research Articles

Effects of TiO2 nanoparticles on the dielectric and electromagnetic shielding performance of PVA/POM hybrid nanocomposites

ABSTRACT Metal oxide-infused polymer composites with higher dielectric constants are emerging as compelling solutions for effective Electromagnetic Interference shielding (EMIS) applications. In this work, hybrid polymer blends were made of polyoxy methane (POM) and polyvinyl alcohol (PVA), using the conventional solution casting method. This study investigated the dielectric properties of the polymer blend by adding different concentrations (1 to 4 wt.%) of titanium dioxide (TiO2) nanofillers that are synthesized via combustion technique with egg albumen. It is evident from the crystallite size of the TiO2 nanoparticles that the egg albumen not only acted as a fuel but also acted as a capping agent in preventing the agglomeration of the particles thereby controlling the size. Increased nanofiller decreased the crystallinity of the polymer blend. The composite with 3 wt.% TiO2 exhibits the highest dielectric constant (1385) and electromagnetic shielding effectiveness. Further, the developed hybrid nanocomposites exhibit excellent shielding effectiveness in the frequency range of 8 to 12 GHz. The uniqueness of this study lies in the cost-effective preparation of nanocomposites with a very less concentration of TiO2 nanoparticles. These nanocomposite films could be a potential replacement for films infused with carbon black, multiwalled carbon nanotubes, graphene oxide and nickel oxide nanofillers, etc.

Ce3+ doped zinc manganese ferrite nanoparticles: Tuned mechanical, dielectric and radiation shielding characteristics

In this paper, the impact of cerium (Ce) additives on the structural, electrical and radiation attenuation characteristics of cerium zinc (Zn)- manganese (Mn)-based spinel nanoferrite, named ZMCeF-nanoferrite was investigated. Our investigation involved a thorough examination of the morphology and distribution of the ZMCeF-nanoferrite utilizing HR-TEM analysis, which revealed showcasing the distinctive spherical morphology of the nanoparticles along with observations of their aggregation tendencies. These findings are ascribed to the heightened magnetic interactions between the ZMCeF-ferrite nanoparticles. The ZMCeF5 nanoferrite demonstrates an optimal dielectric constant value compared to the free Ce ferrite composition, exhibiting an enhancement ratio of 109 %. Additionally, it showcases optimal conductivity, with an upgrading ratio of 780 %, and minimal loss, with an enhancing ratio of 3.5 %. Moreover, the elastic moduli of the ZMCeF5 sample exhibited a marked increase as the Ce content increased. Upon examining the mass attenuation coefficient (MAC) of ZMCeF-nanoferrite across three energy regions, we note a trend of increased MAC values corresponding to higher Ce additions. In contrast, the half-value layer (HVL) values decrease as Ce additions increase. Comparing the HVL values of the current ZMCeF-nanoferrite with those of selected radiation shielding material, we find that HVL of the ZMCeF-nanoferrite exhibits smaller values. These findings present promising prospects for optimizing spinel nanomaterials for use in radiation shielding applications.

A monolithic numerical model to predict the EMI shielding performance of lossy dielectric polymer nanocomposite shields in a rectangular waveguide: Design of an absorption-based sawtooth-shaped layer

A three-dimensional numerical model is constructed to predict the EMI shielding performance of a polymer nanocomposite shield in a rectangular waveguide. The Helmholtz wave equation for the electric field is implemented in component form and the set of coupled equations is solved via the finite element approach. Mesh convergence and model verification is performed by comparing free space model predictions for a flat, uniform layer to benchmark solutions calculated via transfer matrix theory. The capability of the model is showcased by exploring the role of geometry on the shielding performance of a sawtooth-shaped composite layer in a rectangular waveguide. Increasing the inclusion angle of the sawtooth, which is proportional to the ratio of the sawtooth amplitude and repeat unit width, reduces the transmitted power through the shield and increases the ratio of absorption to reflection of wave power by the shield. Thus, a rational design of this sawtooth geometry allows to overcome the typical trade-off between total shielding effectiveness and wave absorption contribution, thereby resulting in highly performant absorption-dominated shields.

Synthesis and characterization of FMWCNTs/ZnO doped PVDF nanocomposites for enhanced mechanical, dielectric, and radiation shielding properties

This study investigates the enhancement of radiation shielding properties of polyvinylidene fluoride (PVDF) through the incorporation of functionalized multi-walled carbon nanotubes (FMWCNTs) and zinc oxide nanoparticles (ZnONPs), aiming to develop a lightweight, effective, and environmentally friendly shielding material. PVDF-based nanocomposites with varying concentrations of FMWCNTs@ZnO (0.0, 0.5, 1.0, 1.5, and 3.0 wt%) were synthesized using a solution casting method. Morphological analysis via high-resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) confirmed the uniform dispersion of FMWCNTs@ZnO within the PVDF matrix. X-ray diffraction (XRD) studies revealed an increase in the β-phase crystallinity of PVDF at 1 wt% FMWCNTs@ZnO concentration, with a notable peak shift indicating enhanced polar group development. Vickers microhardness tests showed a significant improvement, with hardness values increasing from 342.5 kg/mm2 for pure PVDF to 391.2 kg/mm2 for nanocomposites containing 3 % FMWCNTs@ZnO. Dielectric analyses demonstrated increased permittivity and a dynamic relaxation behavior indicative of improved charge carrier density and interfacial polarization. Gamma shielding efficiency, assessed through linear attenuation coefficients (GLAC) and mass attenuation coefficients (GMAC), exhibited superior performance at lower photon energies (80 keV), with the highest GLAC and GMAC values observed for the 3 wt% FMWCNTs@ZnO doped samples. These findings underscore the potential of FMWCNTs@ZnO doped PVDF nanocomposites as promising materials for radiation shielding applications, offering a synergistic approach to enhancing mechanical, dielectric, and protective properties against ionizing radiation.

Structural, morphological, and EMI shielding evaluations of Sm-Mn co-doped Sr-based M-type hexaferrite for Ku band applications

High-performance, thin, and lightweight EMI (Electromagnetic interference) materials with outstanding shielding effectiveness were explored over the last years to solve the problems in electronic devices. Magnetic absorbing materials have extensive bandwidth, good impedance matching, and excellent absorption features. In the present study, Sm-Mn Sr-doped M hexaferrites with Sr1-xSmxFe12-yMnyO19 whereas (x= 0.00, 0.025, 0.05, 0.075, y = 0.00, 0.25, 0.5, 0.75) were prepared by the chemical route. XRD, FESEM, HRTEM, FTIR, VSM, and VNA are used to evaluate the properties of the Sm-Mn doped Sr-based M-type hexagonal ferrite. The XRD (X-ray diffraction) results revealed the presence of a hexagonal phase in the prepared samples. Rietveld refinement also confirmed the phase purity for the Sm-Mn doped Sr-based M-type hexagonal ferrites. The FESEM (Field emission scanning electron microscopy) and HRTEM (High-resolution transmission electron microscopy) images revealed the hexagon-type shapes of the particles in the Sm-Mn doped Sr-based M-type hexagonal ferrites. The FTIR (Fourier transform infrared spectroscopy) spectra showed the 446–620 cm-1 lines, confirming the presence of the tetrahedral and octahedral phases of hexagonal ferrites. Dielectric and electromagnetic shielding effectiveness (SE) parameters are evaluated for Sm-Mn doped Sr-based M-type hexagonal ferrite. The electromagnetic parameters, such as complex refractive index, absorption and impedance, are also investigated for the Sm-Mn doped Sr-based hexagonal ferrite powder with x=0.075, y=0.75 having epoxy resin with 20 wt%, 30 wt% and 50 wt% samples, respectively. SE parameters are higher at more extensive filler loading. The green shielding index was found higher for Sm-Mn doped Sr-based hexagonal ferrite powder with x=0.075, y=0.75 having 20 wt% epoxy resin and decreased with filler loading. It is found the epoxy/Sm-Mn doped Sr-based M-type hexagonal ferrites-based composites are excellent absorbers in the Ku band. The investigated absorbers could be the best candidates for next-generation EMI green shielding absorbing devices and applications.

Sm3+ doping-adjusted mechanical, dielectric, and radiation shielding properties of cobalt copper nanoferrites

The scarcity of research on the shielding properties of spinel ferrites underscores the necessity for more rigorous investigations. Consequently, this study introduces a facile synthesis method for Co, Cu, and Sm spinel nanoferrites (referred to as CCS nanoferrites) using the citrate combustion technique. The investigation focuses on their mechanical, dielectric, and gamma-ray shielding parameters. Gamma-ray shielding features are obtained theoretically via the Phy-X database. The particle size, nature, and distribution of the present CCS nanoferrites were analyzed using HR-TEM microscopy. HR-TEM results reveal both the spherical shapes and the aggregation of nanoparticles. These observations can be attributed to the interplay of high surface energy and magnetic interactions among the components of the CCS nanoferrites. The Co0.5Cu0.5Sm0.15Fe1.85O4 nanoferrite exhibits an optimal dielectric constant value of 4587, with an enhanced ratio of 1618% compared to the pristine CCS0 sample. Additionally, it demonstrates an optimal conductivity of 38.59 μ (Ω·m)−1, with an enhanced ratio of 1105%. Furthermore, the loss is reduced to 2.65, showing an improvement ratio of 54% compared to the pristine nanoferrite at room temperature and 50 Hz. Moreover, the longitudinal modulus, shear modulus, Young's modulus, and bulk modulus of the nanoferrite Co0.5Cu0.5Sm0.15Fe1.85O4 were increased from 1.79 to 4.96 GPa, 0.32–0.93 GPa, 0.88–2.56 GPa, and 1.37–3.73 GPa, respectively, when compared to the pristine sample. The comparative study of half-value layers at 0.662 MeV revealed that CCS nanoferrites exhibit smaller half-value layers than common radiation shielding materials. Additionally, the study highlighted the enhanced radiation shielding performance of the nanoferrites. Concerning the dielectric, mechanical, and ionizing radiation shielding properties of the CCS spinel nanoferrites, the CCS5 (with the highest Sm content) has the optimum ionizing radiation shielding ability with the highest dielectric and mechanical parameters compared to the other samples. The implications of these findings extend to potential applications in biomedicine, radiation protection, and the optimization of electronic devices operating in radiation fields.

Temperature-dependent conduction mechanism of NiO@Carbon@Polypyrrole nanomaterial with EMI shielding characteristics

A simple hydrothermal technique and in-situ chemical oxidative polymerization of pyrrole monomer yield the functionalized NiO@C@PPy nanomaterial for electromagnetic shielding applications. The crystal structure, morphology, dielectric and electromagnetic shielding (EMI) performance in the X-band (8.2–12.4 GHz) is thoroughly studied. Impedance spectroscopy is utilized to study the electrical response of a NiO@C@PPy pellet. This study focuses on the modulations of relaxation time with frequency at different temperatures. In the NiO@C@PPy composite, a semiconductor-to-metal transition (SMT) is observed, at 328 K. The conduction mechanism of NiO@C@PPy is explained based on the carrier hopping transport model in Ni2+ and Ni3+ ions. It is evident from the activation energy value (Ea ≈ 0.32 eV) determined from impedance, conductivity, and dielectric data that the relaxation and conduction processes correspond to the same electro-active region. Using the variable range hopping (VRH) model localization length of the carrier is calculated to be 1.56 Å. The NiO@C@PPy sample demonstrated enhanced conductivity and low dielectric values which are vital in EMI shielding applications. Consequently, the electromagnetic interference shielding effectiveness is found to be 21.9 dB of NiO@C@PPy in the X-band frequency range. This composite material is a good candidate for high frequency shielding applications.

Electrostatic Contribution to 19F Chemical Shifts in Fluorotryptophans in Proteins.

DFT calculations indicate that the 19F chemical shifts of aromatic rings containing single fluorine substituents are sensitive to the electric fields and electric field gradients at the position of the fluorine atom. The present work explores whether long-range structure restraints can be gained from changes in 19F chemical shifts following mutations of charged to uncharged residues. 19F chemical shifts of fluorotryptophan residues were measured in two different proteins, GB1 and the NT* domain, following mutations of single asparagine residues to aspartic acid. Four different versions of fluorotryptophan were investigated, including 4-, 5-, 6-, and 7-fluorotryptophan, which were simultaneously installed by cell-free protein synthesis using 4-, 5-, 6-, and 7-fluoroindole as precursors for the tryptophan synthase present in the S30 extract. For comparison, the 1H chemical shifts of the corresponding nonfluorinated protein mutants produced with 13C-labeled tryptophan were also measured. The results show that the 19F chemical shifts respond more sensitively to the charge mutations than the 1H chemical shifts in the nonfluorinated references, but the chemical shift changes were much smaller than predicted by DFT calculations of fluoroindoles in the electric field of a partial charge in vacuum, indicating comprehensive dielectric shielding by water and protein. No straightforward correlation with the location of the charge mutation could be established.

Effect of sintering temperature on impedance and EMI shielding of carbon modified CoFe2O4 nanofibers via electrospinning

The electrospinning technique is employed for the synthesized cobalt ferrite/carbon nanofibers, utilizing iso-propanol as the solvent. The nanofibers prepared are subjected to sintering at three different temperatures. A comprehensive analysis is carried out on the structural, morphological, dielectric, impedance, and electromagnetic shielding effectiveness within the X-band frequency range (8.2–12.4 GHz). The application of the Debye-Scherer formula yielded an estimated crystallite size of 22 nm. The electrical response of cobalt ferrite/carbon nanofibers pellet is characterized by employing impedance spectroscopy. Variations in impedance plane plots are discussed based on frequency dependent relaxation time modulations. The impact of sintering temperature is observed in terms of increased impedance values and modifications in the conduction mechanism. These changes are contributed to distinct hopping carriers’ linkages between Fe3+-Fe2+ and Co3+-Co2+ ions. Dielectric studies are elucidated considering cation polarizability, colossal resistivity, and tangent loss. This study revealed notable characteristics of CoFe2O4/C nanofibers, including colossal resistivity (8.45 × 108 Ωcm), a dielectric constant of 22, and colossal tangent loss. The CoFe2O4/C nanofibers exhibit a characteristic electromagnetic interference (EMI) shielding performance of 30–35 dB. This remarkable shielding performance is observed in nanofibers with a 3 mm thickness, specifically in sample S1 that underwent sintering at a low temperature. The shielding effectiveness is demonstrated within the X-band frequency range.

Molecular Ferroelectric with Directional Polarization Field for Efficient Tin‐Based Perovskite Solar Cells

AbstractDue to the relatively inferior dielectric constant, Sn‐based perovskites exhibit lower defect tolerance and insufficient dielectric shielding effect compared with Pb‐perovskites. Upgrading built‐in electric field (BEF) in Sn‐based perovskite solar cells (PSCs) can be effective to reduce large voltage deficit and improve poor performance caused by the low defect tolerance resulting from the intrinsic inferior dielectric of Sn‐based perovskites. Herein, 2‐methylbenzimidazole (MBI) molecular ferroelectric with low coercive field and high Curie‐temperature is introduced to construct an additional ferroelectric field in FASnI3‐based PSCs. The ferroelectric effect of MBI can promote exciton dissociation, enhance carrier population, and suppress the adverse effect of the residual defects on carriers, and the directional polarization of MBI in FASnI3 film can be driven by the BEF in PSCs to broaden the width of depletion region. Additionally, the MBI molecules with amine functional groups effectively regulate perovskite crystallization, passivate Sn‐related defects, and enhance the oxidation barrier. Profiting from the above advantages, the MBI‐modified device achieves a champion power conversion efficiency (PCE) of 12.91%, keeping over 94% average PCE after 1056 h in N2 glovebox for the unencapsulated device. This study highlights the significant role of molecular ferroelectrics in perovskite photovoltaics.

Dielectric, thermal and gamma shielding characteristics of PbO–TeO2–V2O5–CoO glasses

For the first time the lead vanado-tellurite glasses with varied concentrations of CoO were prepared and investigated for dielectric, thermal and gamma shielding properties. Density found increased and molar volume decreased, glass transition temperature and thermal stability increased with increase of CoO mole fractions. Dielectric and impedance spectra have been studied for temperature range 300K–500K and frequency range 50 Hz - 20 MHz. Dielectric constant is found to vary in the range from 10.10 × 102 to 5.56 × 102 and dielectric loss 1.42–1.55 × 104. With increase of frequency, both dielectric constant and loss decreased, and increased with increase of temperature. A single semiconducting phase is revealed by cole-cole plots. The dc conductivity deduced form impedance data and its activation energy is found increased with CoO content. Dielectric relaxation period and thermal activation energy for impedance and modulus were determined. These results are in close agreement with one another. Electric moduli master curves revealed temperature independent relaxation mechanism. Utilizing Phy-X/PSD software γ-radiation attenuation characteristics were determined. Mass and linear attenuation coefficients are found to be greater and, half and tenth value layer values smaller than those reported for several commercial glasses and rocks. Exposure build up factor and energy absorption build up factor were found to be smaller and fast neutron removal cross section values greater than those reported for various concretes, glasses and rocks in the literature. Present glasses through the evaluated characteristics, showed better gamma and neutron shielding efficiency compared to various systems quoted in the literature.

Designing improved electromagnetic shielding efficacy of poly(3‐hydroxybutyrate‐co‐3hydroxyvalerate) nanocomposites foam using carbon nanotubes and graphene nanoplatelets

AbstractNowadays, one of the design direction of bio‐derived and biodegradable polymer foams with multi‐functionalization is how to attain superior electromagnetic interference (EMI) shielding property, which has become a hot topic. Herein, bio‐based poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) foams filled with carbon nanotubes (CNTs) and/or graphene nanoplatelets (GNPs) were fabricated by supercritical carbon dioxide. As observed by optical microscope and scanning electron microscope, the CNTs and GNPs in PHBV matrix might gradually construct three kinds of network structures (CNTs‐CNTs, GNPs‐GNPs and GNPs‐CNTs network structures), which would improve the melt viscoelasticity, crystallization, electrical, dielectric and EMI shielding properties of PHBV. The complex viscosity and storage modulus of PHBV nanocomposites with the ratio of CNTs/GNPs as 1:1 rose nearly three orders of magnitudes than those of pure PHBV, in addition, its crystallization temperature and crystallinity increased remarkably to 122°C and 62%, individually. When the CNTs/GNPs ratio was 1:1 at a low total content of 3 wt%, PHBV nanocomposite and its foam implemented the high dielectric properties. Furthermore, the EMI specific shielding effectiveness of obtained PHBV was blend with 1.5 wt% CNTs and 1.5 wt% GNPs nanocomposite foam was the highest, reaching 19.3 dB cm3/g. This work paved a feasible way to the production of eco‐friendly PHBV nanocomposite foams for the application of electronics and aerospace industries.Highlights PHBV/CNTs/GNPs foams were prepared using a scCO2‐assisted foaming method. Dispersion of carbon fillers in PHBV was the best as CNTs/GNPs ratio was 1:1. G' of PHBV/C1.5/G1.5 specimens were increased by three orders of magnitude. EMI specific shielding effectiveness of PHBV/C1.5/G1.5 nanocomposite foam could reach 19.3 dB cm3/g.

Electromagnetic Interference Shielding Performances of Carbon-Fiber-Reinforced PA11/PLA Composites in the X-Band Frequency Range.

To solve the problem of increasing electromagnetic pollution, it is crucial to develop electromagnetic interference (EMI) shielding materials. Using lightweight, inexpensive polymeric composites instead of currently used metal shielding materials is promising. Therefore, bio-based polyamide 11/poly(lactic acid) composites with various carbon fiber (CF) amounts were prepared using commercial extrusion and injection/compression molding methods. The prepared composites' morphological, thermal, electrical conductivity, dielectric, and EMI shielding characteristics were investigated. The strong adhesion between the matrix and CF is confirmed by scanning electron microscopy. The addition of CF led to an increase in thermal stability. As CFs formed a conductive network in the matrix, direct current (DC) and alternative current (AC) conductivities of the matrix increased. Dielectric spectroscopy measurements showed an increase in the dielectric permittivity/energy-storage capability of the composites. Thus, the EMI shielding effectiveness (EMI SE) has also increased with the inclusion of CF. The EMI SE of the matrix increased to 15, 23, and 28 dB, respectively, with the addition of 10-20-30 wt % CF at 10 GHz, and these values are comparable or higher than other CF-reinforced polymer composites. Further analysis revealed that shielding was primarily accomplished by the reflection mechanism similar to the literature data. As a result, an EMI shielding material has been developed that can be used in commercially practical applications in the X-band region.

Electric, Dielectric, Mechanical and Emi Shielding Study of Fiber Reinforced Polymer Based Nanocomposites with the Incorporation of Graphene/Cnts

Objective: Glass fiber reinforced composites with epoxy were prepared using thermally reduced graphene oxide (TRGO) and multiwall carbon nanotubes (CNTs) as electrically conductive nano filler. Electrical, mechanical, dielectric and electromagnetic interference (EMI) shielding properties were analyzed and compared. Methods: TRGO was prepared by modified hummers method and X-ray diffraction spectra showed the carbon hexagonal structure with 6-8nm of thickness. Tensile, flexural and impact strength of these composites was comparable and increase with increasing filler content. The effect of TRGO and CNTs on AC & DC conductivity of composites was also compared, which showed that increasing the TRGO content increased the electrical conductivity little better than that of CNTs filled composite. Results: The dielectric properties also improved better for composite incorporating TRGO than with the CNTs, at higher frequency (5MHz). With addition of 2.0% TRGO and CNTs, the maximum SET observed was 32dB at lower frequency, with TRGO-based composite manage to maintain its performance even at higher frequency whereas, this value dropped to 24dB for CNT-based composite at 5MHz of frequency. Conclusion: The dispersion state, the composition of the fillers, and their interaction with matrix are the most important factors in these polymeric composites for the development in EMI shielding effectiveness.

Superior mechanical, electrical, dielectric, and EMI shielding properties of ethylene propylene diene monomer (EPDM) based carbon black composites.

In this study, the mechanical, electrical, dielectric, and electromagnetic interference (EMI) shielding properties of ethylene propylene diene monomer (EPDM) based carbon black composites, namely high abrasion furnace (HAF) and conductive Printex blacks, were investigated and their effectiveness compared. The results show that Printex black filled composites exhibited superior properties in all aspects compared to HAF filled composites. The electrical percolation threshold value of Printex black filled composites was approximately 1/2 to 1/3 lower compared to HAF black filled composites based on classical theory and the Sigmoidal model. Moreover, the tensile modulus, dielectric permittivity, and EMI shielding efficiency (SE) of the Printex black filled composites were 4.6 times, in the order of 106 at 1 kHz, and 6.65 times improved compared to HAF black filled composites at their 40 phr loadings, respectively. The Printex black filled 40 phr loaded composite showed an EMI SE of 49.94 dB that is 99.999% the attenuation of EM radiation. These properties can be attributed to the high structure of Printex black, which facilitates the ease of formation of the conductive channel through the polymer matrix, higher reinforcement, higher interfacial polarization, and high absorption of radiation. These properties were compared with some published literature on carbon black filled composites and it was found that the results of the Printex black filled composites are highly competitive with the published work. The results show that these composites are highly effective for load bearing materials, supercapacitors, and EM radiation protection.

Water dopant control of structural stability and charge recombination of perovskite solar cells: A first-principles study

Humidity is a key factor in affecting the long-term stability of perovskite solar cells. However, how water interacts with the perovskite film and influences the individual energy conversion process in perovskite solar cells remains virtually unexplored. By using ab initio molecular dynamics and nonadiabatic molecular dynamics, we reveal that the MAX-terminated surface is more susceptible to water erosion. The intrusion of water brings in severe lattice distortion, whose degree follows the law of MAPbI3 > MAPbBr3 > MAPbCl3, thereby leading to attenuation in optical absorbance. Unexpectedly, the carrier lifetimes of hydrated MAX-terminated systems are prolonged, while the PbX-terminated surfaces are largely unaffected. This is due to the dielectric shielding effect of invading water molecules, hindering electron-hole recombination. Our results shed light on a comprehensive understanding of the complex effect of humidity on the perovskite performance, rationalize the contradictory experimental observations, and provide novel insights for further optimization of renewable energy devices.

FEM simulation‐based development of a new tunable non‐magnetic RF high voltage capacitor for the new generation of MRI

Using Radio Frequency (RF) waves, magnetic resonance imaging (MRI) systems can make detailed images of human organs for accurate diagnostic processes and disease detection. The overhaul of certain electronic components has become necessary to keep up with the progress of MRI systems. Among the components responsible for image quality, the adjustable non-magnetic capacitors, also called trimmers, are of great importance. The purpose of this paper is to suggest a new design of a trimmer using non-magnetic materials, able to hold a high voltage ( >3 kV) and reach a resonance frequency above 100 MHz. Constructional analysis performed on existing commercial trimmers, combined with the electrical Finite Element Method, were carried out to propose a prototype matching the desired specifications. A dielectric shield surrounding the electrodes was sized to ensure voltage withstand. Moreover, the rotor and the worm-and-gear set were joined together to combat the vibrations generated by the MRI system. The present study includes the modelling step of the component by numerical simulation, the manufacturing, the electrical performance characterization, and the mechanical solution for tuning capacitance. The final prototype combines electrical performance corresponding to the required specifications in particular a high breakdown voltage (39.7 kV) and a resonance frequency (130 MHz).

(Invited) Large Carrier Mobility in Graphene with Enhanced Shubnikov–De Haas Quantum Oscillations

Graphene devices are susceptible to the surrounding environment1-4. For example, the substrate in contact with graphene influences the device performance because the carriers are confined in two-dimensional (2D) atomic thickness. However, 2D van der Waals dielectric materials used as an interface modifier can provide a path to improve the device quality. In this paper, we report an enhanced mobility of 35000 cm2 V-1 s-1 in a CrOCl-coated monolayer graphene on the SiO2/Si substrate through a dielectric shielding effect. When monolayer graphene is sandwiched between two layers of 2D CrOCl insulator, the enhanced mobility can be 70000 cm2 V-1 s-1. Because of the enhanced mobility, the Shubnikov-de Haas (SdH) quantum oscillation is also observed with the amplitude linearly decreasing with increasing temperature, consistent with the standard Lifshitz-Kosevich theory, and the effect persists at temperatures up to 100 K. Our work paves a way to improve graphene mobility and realize nontrivial quantum states at high temperature for the exploration of potential applications in electronics.

The Mechanical, Dielectric, and EMI Shielding Properties of Nickel Ferrite (NiF)/Graphene (Gr)-Doped Epoxy Composites

The Mechanical, Dielectric, and EMI Shielding Properties of Nickel Ferrite (NiF)/Graphene (Gr)-Doped Epoxy Composites

Dielectric, magnetic and electromagnetic shielding properties of Poly-(3,4ethylenedioxythiophene)-maghnite associated with different fillers with any non-canonical shape

A new inverse measuring technique that corrects non-desired sample displacements and can handle any kind of sample shapes is presented. It is applied to the estimation of permittivity and permeability of Poly-(3,4ethylenedioxythiophene)-maghnite (PEDOT-Mag) associated with different additives such as iron, copper, and hydrogen. This electromagnetic characterization has been performed over the 9 to 11 GHz frequency range by comparing the simulated and measured scattering parameters of a partially filled WR-90 waveguide. Additionally, the reflection, absorption multiple reflection losses and the shielding effectiveness of these materials have been calculated. Results show higher values of dielectric constant and loss factor for PEDOT-Mag-copper, than those compounds associated with hydrogen or iron. As expected, the highest permeability values are achieved by PEDOT-Mag-iron. The composite PEDOT-Mag-copper exhibits higher attenuation constant, absorption loss, multiple reflection loss and shielding efficiency values than composites associated with iron or hydrogen. PEDOT-Mag-hydrogen, however, shows the highest reflection loss values.