High Conduction Loss Research Articles

Ultralight SiO2 Nanofiber-Reinforced Graphene Aerogels for Multifunctional Electromagnetic Wave Absorber.

The high-efficiency utilization of two-dimensional (2D) graphene layers for developing durable multifunctional electromagnetic wave (EMW) absorbing aerogels is highly demanded yet remains challenging. Here, renewable, low-density, high-strength, and large-aspect-ratio ceramic silicon dioxide (SiO2) nanofibers were efficiently prepared to assist in the preparation of ultralight yet robust, highly elastic, and hydrophobic graphene aerogels using facile, scalable freeze-drying followed by a carbonization approach. The ceramic nanofibers efficiently prevent the agglomeration of graphene and enhance interfacial interactions, significantly promoting mechanical strength. In addition to the high conduction loss capability derived from the interconnected graphene network, high interfacial polarization derived by abundant heterogeneous interfaces is accomplished for the three-dimensional (3D) hybrid aerogels. The hybrid aerogels thus showcase excellent EMW absorption performance, involving a minimum reflection loss of -74.5 dB at 1.8 mm and an effective absorption bandwidth of 5.7 GHz, comparable to those of the best EMW absorbers. Furthermore, the integration of one-dimensional SiO2 and 2D graphene into 3D hybrid aerogels enables remarkable photothermal antibacterial, photothermal oil absorption, and thermal insulation performances. This work thus provides a type of ultralight ceramic/graphene aerogel with a high-efficiency utilization of graphene for accomplishing high-performance multifunctional applications.

Sulfidation and reassembly strategy enables yolk-shell metal sulfide/alloy nanoparticles @carbon with efficient electromagnetic wave absorption

Constructing hybrid metal-organic frameworks (MOFs) demonstrates significant potential to improve electromagnetic wave (EMW) absorption performance by leveraging synergistic effects between composition and structure, addressing challenges in tuning electromagnetic parameters of single-composition MOFs. This study proposes a sophisticated strategy involving sulfidation-interface growth-reassembly: sulfide nanoparticles form by sulfidating the core (CoFe-MIL-88A), and then ZIF-67 guests grow and reassemble on the sulfided host MOF, resulting in a layered EMW absorption material. The composite material integrates synergistic effects, which include high conductive loss and defect/interface/dipole polarization induced by N and S atom doping. The CFSNC composite material outperforms previously published values, achieving a minimum reflection loss (RLmin) of −65.96 dB and an effective absorption bandwidth (EAB) of 6.15 GHz with a thickness of merely 2 mm. Simulation calculations of the real far-field radar cross-section (RCS) further validate its practical application potential. This work introduces novel ideas and methods for designing and preparing high-performance EMW absorption materials, offering both theoretical insights and practical applications.

Graphene/carbon nanotube aerogels with ultralow filling ratio through perfect cross-linking interface for efficient microwave absorption

Utilizing high-efficiency electrostatic assembly and a scalable freeze-drying technique followed by carbonization, we have developed a series of unique, lightweight, hierarchically porous 1D+2D aerogels containing carbon nanotubes (CNTs) and reduced graphene oxide (rGO). By manipulating the interaction between CNTs and graphene oxide perjurer in cellulose nanofiber (CNF), CNTs can uniformly distribute along the graphene cell walls via an exceptional cross-linking interface in the resultant rGO/CNT aerogels. This arrangement enables abundant heterogeneous interfaces, endowing the aerogels with high conductivity and polarization loss capacity. Moreover, the 1D+2D microstructure of CNT/rGO and the hierarchical pore architecture of the aerogels facilitate multiple scattering, further enhancing their loss capacity toward electromagnetic wave absorption (EMW). Coupled with the optimized impedance matching derived from the adjustable dielectric properties, the aerogels exhibit outstanding EMW absorption with a filling ratio of merely 2 wt%. Specifically, a minimum reflection loss (RLmin) of −49.61 dB and an effective absorption bandwidth (EAB) of 4.16 GHz are achieved. With a filling ratio of 3 wt%, the RLmin reaches −77.51 dB, accompanied by an EAB of 3.84 GHz, surpassing the reported carbon or graphene-based aerogel EMW absorbers. In this work, the ultra-low filling ratio resulting from high conductivity confers a practical design for fabricating lightweight carbon-based aerogels suitable for high-efficiency EMW absorption, manifesting multiple applications in electromagnetic compatibility and aerospace contexts.

Engineering multifunctionality graphene-based nanocomposites with epoxy-silane functionalized cardanol for next-generation microwave absorber

As technology advances, the demand for effective microwave-absorbing materials (MAM) to mitigate electromagnetic wave interference is growing. Two-dimensional (2D) materials are increasingly favored across various fields for their high specific surface area, electrical conductivity, low density, and dielectric loss properties. This study presents lightweight nanocomposites composed of graphene nanoplatelets blended with epoxy resin (ER) and cardanol with silane-functionalized (SFC) as a toughening agent. The resulting nanocomposites exhibit a high surface roughness of 130 nm and an enhanced hydrophobicity, as evidenced by a high contact angle. Notably, the ER/SFC/GNP sample at 3 wt% (0.075 g) achieves a minimum reflection loss value of −18 dB at a thickness of 10 mm, indicating improved impedance matching and enhanced dielectric loss capability. The increasing damping factor ratio to approximately 0.95 further augments the reflection loss performance. The research aims to develop cost-effective, efficient, lightweight graphene-based nanocomposite absorbers.

Sintering behavior, zinc volatilization, microstructure and microwave dielectric properties of ZnxSiO2+x ceramics

In this paper, the evolution of the microstructure for the zinc silicate ceramics with different Zn/Si ratios was revealed, and the factors influencing their dielectric properties were discussed. Our results demonstrate that Zn volatilization plays an important role on the defect structure of the samples. Low relative density, high conductivity loss caused by volatilization, and the presence of ZnO phase collectively result in low quality factor (Qf) of Zn2.0SiO4.0. By using the powder embedded sintering method, the loss could be reduced owing to the suppression of volatilization. As the Zn/Si ratio decreases, the ZnO disappears, while the Si-rich phase emerges and increases. The formation of a liquid phase results in a dense microstructure of the non-stoichiometric samples. Moreover, these samples exhibit a minor degree of Zn loss, probably because the presence of liquid phase constraints the volatilization during sintering. The samples with x = 1.8 display desirable properties, including a relative dielectric constant (εr) of 6.5, a Qf of 100,800 GHz, and a temperature coefficient of resonant frequency (τf) of −21.3 ppm/°C, due to their high degree of densification, slight zinc loss, and the elimination of the ZnO phase.

Highly Anisotropic Thermally Conductive Dielectric Polymer/Boron Nitride Nanotube Composites for Directional Heat Dissipation.

An ideal dielectric material for microelectronic devices requires a combination of high anisotropic thermal conductivity and low dielectric constant (ɛ') and loss (tan δ). Polymer composites of boron nitride nanotubes (BNNTs), which offer excellent thermal and dielectric properties, show promise for developing these dielectric polymer composites. Herein, a simple method for fabricating polymer/BNNT composites with high directional thermal conductivity and excellent dielectric properties is presented. The nanocomposites with directionally aligned BNNTs are fabricated through melt-compounding and in situ fibrillation, followed by sintering the fibrous nanocomposites. The fabricated nanocomposites show a significant enhancement in thermal properties, with an in-plane thermal conductivity (K‖) of 1.8 Wm-1K-1-a 450% increase-yielding a high anisotropy ratio (K‖/K⊥) of 36, a 1700% improvement over isotropic samples containing only 7.2 vol% BNNT. These samples exhibit a 120% faster in-plane heat dissipation compared to the through-plane within 2 s. Additionally, they display low ɛ'of ≈3.2 and extremely low tan δ of ≈0.014 at 1kHz. These results indicate that this method provides a new avenue for designing and creating polymer composites with enhanced directional heat dissipation properties along with high K‖, suitable for thermal management applications in electronic packaging, thermal interface materials, and passive cooling systems.

Synthesis of Mo2C/C nanoclusters attached on rGO nanosheets for high-Efficiency electromagnetic wave absorption

It is an effective strategy that constructing composites with a multi-dimensional structure synergistically enhance their electromagnetic (EM) wave absorbing performance. Herein, a high-efficiency EM wave absorber of Mo2C/C nanoclusters uniformly encapsulated in rGO nanosheets (Mo2C/C-rGO) was prepared by a combination of the directing freeze-dry and subsequently carbothermal reaction method. Mo2C/C was in-situ induced from spherical phosphomolybdic acid/polypyrrole (PMo12/PPy) to result in a unique cluster-like microstructure. Abundant heterogeneous interfaces endowed the Mo2C/C-rGO composites with excellent EM wave absorption performance at a low filling ratio of 5 wt%. The minimum reflection loss (RL) value was −49.3 dB at 1.38 mm and the maximum effective absorption bandwidth (EAB, RL<-10 dB) was 5.12 GHz at 1.60 mm. The excellent performance was owing to the lamellar structure and abundant heterogeneous interfaces in Mo2C/C-rGO, lengthening the transmission path of the incident wave, as well as resulting in high conduction loss and interfacial polarization loss. This universal strategy would be extended to other absorbers with multi-interface structures for lightweight and broadband EM wave absorption.

Analysis of cubic perovskite oxide AgNbO3 under stress conditions: Potential for photovoltaic and high-temperature applications - A DFT study

In the family of perovskite materials, perovskite oxide gained considerable attention from researchers in diverse fields, due to their flexible chemistry. Here, cubic perovskite oxide AgNbO3 was studied using DFT via CASTEP code, to explore the key properties under varying stress conditions ranging from 0 to 100 GPa. Phase stability was confirmed by XRD analysis. Electronic properties confirmed the increasing trend in the band gap from 1.422 eV to 1.722 eV, with increasing stress. Optical characteristics reveal high absorption, conductivity, and lower loss function. Significantly, the elastic constants (C11, C12, and C44) satisfy the Born-stability criteria, ensuring the mechanical stability of the considered compound. Moreover, the Poisson ratio, Pugh's ratio (B/G), Frantsevich ratio, Cauchy pressure (PC), and anisotropic factor ensure the ductile nature as well as an anisotropic character over the entire stress range. The positive trajectory in phonon density confirms the thermal stability. Thermodynamically, the studied material shows high-temperature stability with a higher value of applied stress as confirmed by Debye temperature (θD). Furthermore, an inverse association of enthalpy and total entropy with free energy was observed. Based on these findings, confidently suggested that the considered cubic perovskite oxide, AgNbO3, can be efficiently used for photovoltaic and high-temperature applications.

Rapid preparation of Si3N4 ceramics with high thermal conductivity and low dielectric loss by fast hot-pressing (FHP) sintering

A series of Si3N4 ceramics with MgO and Y2O3 as sintering additives were successfully prepared by fast hot-pressing (FHP) sintering at the sintering temperature of 1700 °C, with the hold time of only 10 min and the whole sintering process of 36 min. The sintering behavior, densification process, microstructure, crystalline phase composition, bond composition, thermal conductivity and dielectric properties were systematically investigated. FHP reduces the sintering temperature and sintering time of Si3N4 ceramic compared to traditional solid-state method. The results of a series of tests have shown that the densification of Si3N4 ceramics and the phase transition from α-Si3N4 to β-Si3N4 can be facilitated by appropriate levels of additives, resulting in a dense, homogeneous and non-porous microstructure. Additionally, based on test results in this work, Si3N4 -4 wt.% Y2O3 -2 wt.% MgO exhibit the highest thermal conductivity of 78.16 W/mK, the dielectric constant of 8.50 and the dielectric loss of 5.52 × 10−4. The Si3N4 ceramics investigated in this work exhibit excellent properties for use of power semiconductor device packages, microwave devices, and power electronics. And also demonstrate the potential of FHP in laying the foundation for the further preparation of higher performance Si3N4 ceramics.

High thermal conductivity and low dielectric loss of three-dimensional boron nitride nanosheets/epoxy composites

Electronic power devices are moving towards high frequency, high integration, and high power, which urgently needs to develop high thermal conductive encapsulating insulation materials to improve the heat dissipation of electronic devices. Herein, we propose to modify the commercialized encapsulating materials of epoxy resin (EP) by incorporating three-dimensional hydroxylated boron nitride nanosheets (3D-BNNSs). The cryogel and vacuum freeze-drying techniques are employed to prepare the 3D-BNNSs using agarose. The results show that the constructed high thermal conductive structure of 3D-BNNSs can effectively enhance the thermal conductivity of EP and reduce the interfacial thermal resistance between BNNSs fillers. The thermal conductivity of 3D-BNNSs/EP composites with 33.03 wt% BNNSs reach 2.54 W/(m·K), which is 13.11 times higher than that of EP (0.18 W/(m·K)). Meanwhile, the resultant composites remain outstanding electrical insulation and dielectric properties. Because agarose contains numerous hydroxyl groups that can form hydrogen bonds with the hydroxyl groups on the surface-functionalized BNNSs, hydrogen bonding can lead to strong intermolecular interactions, which is conductive to accelarate phonon transport. Additionally, agarose can cross-link with the molecular chains of epoxy, impeding the movement of molecular chain segments and resulting in composites with low dielectric loss at high frequencies. This study demonstrates that the 3D-BNNSs/EP composites have great potential for application in thermal management of electronic components.

Itaconic anhydride functionalized cyanoethyl cellulose with crosslinked structure enabled improved dielectric properties

AbstractAs a type of cellulose ether, cyanoethyl cellulose (CEC) is considered to be a promising candidate for polymer dielectrics due to its sustainable nature and high dielectric constant induced by the cyano groups. However, the relatively high conduction loss of CEC arising from the charge motion across the polymer degrades its dielectric properties. In this work, we designed and synthesized an all‐organic polymer composite of CEC/itaconic anhydride (ITA) to improve dielectric properties. The CEC matrix was graft functionalized by ITA via an esterification reaction between the anhydride groups of ITA and hydroxyl groups of CEC. Meanwhile, crosslinking structure was also established in the composite by the generation of diester. Significantly improved dielectric constant (εr), elevated breakdown strength (Eb), restrained dielectric loss (tan δ) and decreased conductivity (σ) were observed in the composites compared with unmodified CEC. The εr increased from 17 for pure CEC to 32 for CEC/ITA at 1 kHz, and Eb also soared from 145 MV m−1 for CEC to 226 MV m−1 for the composite. The tan δ reduced from 0.24 for pure CEC to about 0.05 for the composite at 100 Hz. This should be attributed to the molecule trapping centers arising from the high electron affinity ITA and the formation of crosslinked networks as well as hydrogen bonding, which impeded the electric conduction. It also provided additional advantages of better dielectric properties for the CEC/ITA composites than pure CEC at high temperatures, which may offer inspiration for the design and preparation of bio‐based dielectrics for high temperatures. © 2024 Society of Chemical Industry.

Crystal Structure and Spectroscopic Characterization of a New Hybrid Compound, (C12H17N2)2[CdBr4], for Energy Storage Applications.

Organic-inorganic hybrid materials have recently found a vast variety of applications in the fields of energy storage and microelectronics due to their outstanding electric and dielectric characteristics, including high dielectric constant, low conductivity, and low dielectric loss. However, despite the promising properties of these materials, there remains a need to explore novel compounds with improved performance for practical applications. In this research paper, the focus is on addressing this scientific challenge by synthesizing and characterizing the new-centrosymmetric (C12H17N2)2[CdBr4] crystal. This compound offers potential advancements in energy storage technologies and microelectronics due to its unique structural and electronic properties. The chemical mentioned above crystallizes in the monoclinic system, and its protonated amine (C12H17N2)+ and isolated anion [CdBr4]2- are bound by C-H···π and N-H···Br hydrogen bonds to form its zero-dimensional structure. Through optical absorption analysis, the semiconductor nature of the material is verified, showcasing a band gap of around 2.9 eV. Furthermore, an in-depth examination of Nyquist plots reveals the material's electrical characteristics' sensitivity to frequency and temperature variations. By applying Jonscher's power law to analyze ac conductivity plots, it is observed that the variation in the exponent "s" accurately characterizes the conduction mechanism, aligning with CBH models. The compound exhibits low dielectric loss values and a high permittivity value (ε ∼ 105), making it a promising candidate for energy storage applications. By managing the scientific challenge of improving material performance for energy storage and microelectronics, this research contributes to advancing the field and opens avenues for further exploration and application of organic-inorganic hybrid materials.

Room temperature deprotonation engineering for large-scale preparation of MIL-88B-like for efficient electromagnetic wave absorption

Metal-organic frameworks (MOFs)-derived electromagnetic functional materials are a hot research trend in the field of microwave absorption (MA). However, there is a lack of high-yield strategies to drive high-performance MOFs-derived MA absorbers out of the laboratory. Herein, we prepared MIL-88B-like using a simple room-temperature liquid-phase method with more than 75 times the yield of the solvothermal method. The obtained MOFs were pyrolyzed to form C/FeO/FeN0.0324/Fe quaternary composite materials. Under suitable graphitizing conditions, the moderate conductivity of derivative material of M1 precursor carbonized at 700 °C (M1-700) not only meets the requirement of impedance matching but also provides high conduction loss. Meanwhile, the multiple polarization loss mechanisms from defect-induced polarization, dipole polarization, heterogeneous interfaces, and magnetic loss mechanism synergize with each other, resulting in an effective absorption bandwidth (EAB) of 6.71 GHz and a reflection loss (RL) value of −62.57 dB at 22.5 wt% filler, which is a 6-fold increase in the RL compared with that of the conventional MIL-88B-derived wave absorber. In conclusion, this work provides a feasible solution for practical absorbers and an excellent reference value for high MA performance materials for applications.

Ultra-low dielectric loss and high thermal conductivity of PTFE composites improved by schistose and globular alumina

Polytetrafluoroethylene (PTFE) based microwave dielectric composite has been widely used because of its adjustable dielectric constant and low dielectric loss, but its low thermal conductivity can not meet the heat dissipation requirements of high-power microwave devices. Therefore, it is of great significance to develop microwave dielectric composites with high thermal conductivity and low loss. In order to obtain microwave composite materials with high thermal conductivity and low losses, schistose Al2O3/PTFE (S-A/PTFE) composites and globular Al2O3/PTFE (G-A/PTFE) composites were successfully prepared. It is compared whether S-A can combine with PTFE more fully than G-A, which can promote the dielectric properties and thermal conductivity of Al2O3/PTFE composites. Surprisingly, the S-A/PTFE composites demonstrate higher thermal conductivity, lower thermal expansion and hygroscopic properties. The S-A/PTFE composites can deliver a high thermal conductivity of 0.986 W/m K. Composite substrates with 53 wt% S-A filler exhibits excellent performance, which specifically show credible dielectric constant (εr = 4.01) and admissible dielectric loss (tanδ = 0.0014 at 10 GHz). Furthermore, the composite substrate shows a similar thermal expansion coefficient to copper, and lower water absorption rate (0.05 %). The relationship between dielectric constant of composite and filler was predicted by different theoretical modeling methods.

Co-Doped Porous Carbon/Carbon Nanotube Heterostructures Derived from ZIF-L@ZIF-67 for Efficient Microwave Absorption.

Carbon-based magnetic metal composites derived from metal-organic frameworks (MOFs) are promising materials for the preparation of broadband microwave absorbers. In this work, the leaf-like co-doped porous carbon/carbon nanotube heterostructure was obtained using ZIF-L@ZIF-67 as precursor. The number of carbon nanotubes can be controlled by varying the amount of ZIF-67, thus regulating the dielectric constant of the sample. An optimum reflection loss of -42.2 dB is attained when ZIF-67 is added at 2 mmol. An effective absorption bandwidth (EAB) of 4.8 GHz is achieved with a thickness of 2.2 mm and a filler weight of 12%. The excellent microwave absorption (MA) ability is generated from the mesopore structure, uniform heterogeneous interfaces, and high conduction loss. The work offers useful guidelines to devise and prepare such nanostructured materials for MA materials.

Sustainable chitosan derived 3D hierarchically porous carbon aerogel toward advanced infrared-radar compatibility

Simultaneously achieving infrared-radar compatibility in one material is an important challenge for multi-spectral compatible stealth technology. Chitosan-derived three-dimensional (3D) hierarchically porous carbon aerogel can effectively solve the problem. Inspired by floors-pillars concept, this work elaborately designed and successfully fabricated 3D skeletons consisted of two-dimensional (2D) sheets and one-dimensional (1D) struts. Benefiting from esterification and directional freeze drying method, the entire network could provide sufficient space for reducing thermal conductivity and motivating dipole polarization sites. Thanks to the facile calcination process, conductive components could be obtained, which guarantee low infrared (IR) emissivity and high conduction loss performance. In this work, the as-prepared carbon aerogel with ultra-low density of 0.005 g cm−3 exhibits superb infrared stealth property. It shows a low thermal conductivity coefficient of only 0.0933 W m−1 K−1. In addition, the heating rate of the upper surface is slow when placed on a heating platform of 60 °C. The relevant IR emissivity value is as low as 0.563 in 3–5 μm band and 0.432 in 8–14 μm band. Under relatively thin thicknesses, the prominent radar stealth performance including the optimum reflection loss value of −75.90 dB, the maximum effective bandwidth of 3.93 GHz, and the simulated radar cross section reduction value of 27.66 dB m2, can be obtained. This study not only introduces innovative design ideas but also offers technical approaches, facilitating further development in the realm of infrared-radar compatible stealth.

Novel high-voltage GaN CAVET with high threshold voltage and low reverse conduction loss

A novel GaN current-aperture vertical electron transistor (CAVET) with an energy band pinning (EBP) structure (EBP-CAVET) is proposed and investigated by simulations. The EBP-CAVET is featured with hybrid contacts on the p-GaN layer, locally having Ohmic contact combined with Schottky gate metals in the longitudinal direction. The Ohmic contact is shorted to the source electrode and the Schottky gate metals are shorted to the gate electrode. The conduction band (Ec) in the gate region is modulated by the alternately arranged contacts. In the Ohmic contact region, Ec remains a fixed value, which acts as an energy band pinning and suppresses the variation of the Ec in the gate region. In the on-state (VGS > 0 V) and blocking-state with high VDS, the EBP structure inhibits the Ec shifting downwards in the gate region to achieve a high threshold voltage (Vth), a low leakage current density (Jdss), and a high breakdown voltage (BV). In the reverse conduction state (VDS < 0 V &VGS ≤ 0 V), the EBP structure suppresses the Ec shifting upwards to achieve a low and independent of gate bias reverse turn-on voltage (VRT). The proposed EBP-CAVET achieves a high Vth of 2.10 V, a VRT of 0.69 V, a low Jdss of 3.1 × 10−11 A/cm2 at VDS = 1000 V, a high BV of 1660 V. Compared with an integrated Schottky barrier diode or fin diode in a field effect transistor (FET), the EBP structure occupies a much smaller chip area. Thus, the EBP-CAVET achieves a low specific ON-resistance (Ron,sp) of 1.19 mΩ cm2 and an extremely high power-figure-of-merit (PFOM) up to 2.32 GW/cm2. Consequently, the proposed structure presents a new design concept and enhances the application potential for GaN CAVET with high Vth and low reverse conduction loss.

In-situ exfoliation of hexagonal boron nitride during the forced flow of highly elastic polylactide to fabricate electrospun fibrous film with high thermal conductivity and low dielectric loss

Boron nitride nanosheets (BNNS) have promising applications in thermal management materials, due to their high thermal conductivity and low dielectric loss. However, it is still challenging to fabricate BNNS with large lateral size and structural integrity via solvent-free methods. Here, we report a novel processing method for in-situ exfoliation of hexagonal boron nitride (h-BN) to fabricate BNNS with an average lateral size of 1.45 μm, average thickness of 4.88 nm and few lattice defects during the forced flow of polylactide (PLA) in a highly elastic state. We further fabricate flexible and bio-degradable PLA/BNNS electrospun fibrous film for electronic devices to replace petroleum-based composites. The PLA/BNNS fibrous film exhibits an in-plane thermal conductivity of 4.9 W/(m·K) at the BNNS loading of 20 wt%. Moreover, the fibrous film also has a low dielectric loss (0.007 at 1 kHz) and good electrical insulation. The in-situ exfoliation strategy is simple, economical and environmentally friendly, providing an effective route to design thermal management materials with high thermal conductivity and low dielectric loss in the future of electronic devices.

A Novel Mixture-Devices-Based Submodule for MMC by Using Low on-State Voltage IGCT and High di/dt Ability IGBT

At present, insulated-gate bipolar transistor (IGBT) is widely used as the converter component in the submodule of modular multilevel converter (MMC) for its excellent performance in driving circuit and switching speed, but the further application is restricted by its high conduction loss and cost rate. Integrated gate-commutated thyristor (IGCT) is another converter device used in MMC with low conduction loss and cost. However, the d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> /d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> capability of IGCT is limited so that a snubber circuit is required in the submodule for protection, which generates unwanted power loss for MMC. For better performance and reliability, this paper proposes a mixture-devices-based submodule (MS) for MMC based on the cooperation of parallel IGCT and IGBT devices. Double-pulse switching experiments for the MS are conducted to verify its effectiveness, and to get the data for the follow-up switching power loss calculation. The power loss of MMC based on IGBT, IGCT and mixture devices are calculated based on the model established in this paper. Furthermore, the comprehensive comparison for power loss among IGBT-based, IGCT-based and mixture-device-based MMCs are performed, proving the effectiveness of the mixture topology in terms of power loss reduction. Meanwhile, the proposed MS is cost-competitive.

Regulating surface energy and establishing covalent bonds to enhance interface interaction between m‐BN and polyphenylene oxide for 5G applications

AbstractIncorporation of boron nitride (BN) into polymers is a promising method to obtain composites with high thermal conductivity, low dielectric constant (Dk), and dielectric loss (Df), while the practical applications are limited by the poor interface between BN and polymer because of surface energy mismatch and absence of covalent bond connection between them. Herein, polydopamine (PDA) with good adhesion is deposited onto the BN. Then, a different amount of silane coupling agent containing vinyl reactive groups is grafted onto PDA‐coated BN. In this way, the surface energy of modified BN (m‐BN) can be adjusted to ensure BN contacts well with polymers. Moreover, reactive groups were introduced on BN for further reaction. Subsequently, covalent bonds between the m‐BN and the polyphenylene oxide (PPO) were established in situ during the curing process. The effects of the m‐BN surface energy on interface quality and thermal conductivity of composites are investigated. The m‐BN/PPO composite achieves a through‐plane thermal conductivity of 5.87 W/m·K and a low Df value of 1.53 × 10−3, as well as a low coefficient of thermal expansion (CTE) value (7.8 ppm/K) when the m‐BN loading is 32.6 vol%. This research provides a simple and efficient strategy for fabricating high‐performance composites for high‐frequency applications.Highlights Hexagonal boron nitride was modified successfully by combining non‐covalent and covalent modifications. Regulating surface energy and establishing covalent bonds enhances interface interaction between BN and polyphenylene oxide. Modified BN/polyphenylene oxide composites display improvements in thermal conductivity and dimensional stability as well as dielectric loss. Provides a feasible strategy for designing polymer composites with high thermal conductivity, dimensional stability, and low dielectric loss for 5G applications.