Strong and Flexible Carbon Fiber Fabric Reinforced Thermoplastic Polyurethane Composites for High‐Performance EMI Shielding Applications

Electromagnetic shielding materials play a significant role in solving the increasing environmental problem of electromagnetic pollutions. The commonly used metal‐based electromagnetic materials suffer from high density, poor corrosion resistance, and high processing cost. Polymer composites exhibit unique combined properties of lightweight, good shock absorption, and corrosion resistance. In this study, a novel high angle sensitive composite is fabricated by combining carbon fiber (CF) fabric with thermoplastic polyurethane elastomer (TPU). The effect of stacking angle of CF fabric on EMI shielding performance of composite is studied. When the stacking angle of CF fabric changed, the electromagnetic interference (EMI) shielding effectiveness (SE) of CF fabric/TPU composite can reach a maximum of 73 dB, and the tensile strength can reach 168 MPa. In addition, the composite has anisotropic conductivity, which is conductive along the plane direction and nonconductive along the thickness direction. Moreover, the CF fabric/TPU composite manifests exceptional EMI‐SE/density/thickness value of 383 dB cm² g^?1, which is higher than most of current EMI shielding composites reported in literature. In summary, CF fabric/TPU composite is an excellent EMI shielding material that is lightweight, highly flexible, and mechanically robust, which can be applied to the field of aerospace and some intelligent electronic devices.     

Material and geometry factors in joint design of electronic equipment to minimize electromagnetic interference

Reducing electromagnetic interference in electronic equipments is of great importance. This is normally accomplished by increasing the shielding effectiveness of the enclosure. In this study, shielding effectiveness is examined against enclosure material, joint geometry, and operating frequency. An experimental apparatus is designed and manufactured to aid in finding the suitable joint configurations and materials with high shielding effectiveness. Three groups of material, namely, metallic, filled polymers, and metalized filled polymers, are investigated. In addition to the choices of material, effect of joint configurations on shielding behavior are examined. Based on the experimental results, empirical relations are developed that relate shielding effectiveness to effective length, shape factor, and aperture dimensions of the joint structure. Finally, the best material and joint geometry among the investigated cases are presented. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1667–1679, 1997     

Intrinsic Size Effects in a Barium Titanate Glass-Ceramic

A series of glass ceramics have been synthesized to produce bulk materials with nanometer-sized barium titanate (BaTiO₃) crystals grown in a residue glass matrix. Structure-property relations have been made to determine the size distribution and the dielectric temperature dependence of the ceramics. Through dielectric and density mixing laws, it has been inferred that depolarization fields limit the dielectric polarizability of the particles and influence the transition temperature. The transition temperature, dielectric anomaly broadening, and peak dielectric constant all scale systematically with the mean size of the BaTiO₃ crystals, which is consistent with an intrinsic size effect. In addition, scaling the transition temperature with the Ishikawa relation predicts a critical size of 17 nm, for which BaTiO₃ cannot support a ferroelectric transition. These results are discussed in relation to other size studies on ferroelectric materials.     

Polarization and strain behaviors of 0.74BiNaTiO3–0.26SrTiO3/Bi0.5(Na0.8K0.2)0.5TiO3 ceramic composite

We investigated the temperature- and frequency-dependent polarization and strain of two bismuth-based perovskite materials, a matrix material and a seed material, with which we formed a composite whose properties we likewise investigated. The chosen matrix material is 0.74Bi_0.5Na_0.5TiO₃–0.26SrTiO₃ (BNT-ST) which has a transition point of ~65 °C, from the relaxor to the ferroelectric phase (T_R-F). The seed material was Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ (BNKT), which possesses a T_R-F of 120 °C. Different polarization and strain behaviors were observed in the BNT-ST/BNKT composite at different test temperatures. At T=25 °C (<T_R-F of the relaxor BNT-ST), the composite exhibited a hysteretic polarization loop and parabolic strain curves which involve an ergodic relaxor-to-normal ferroelectric phase transition with application of an external electric field and the reverse ferroelectric-to relaxor phase transition with removal of the field. When T=80 and 100 °C (>T_R-F °f the relaxor BNT-ST and <T_R-F of the ferroelectric BNKT), the BNT-ST/BNKT has a slim polarization loop and strain magnitudes that are slightly increased from those of pure BNT-ST. When T=120 °C (~T_R-F of the ferroelectric BNKT), the composite has a very slim polarization loop and strain behavior with values that are almost same as those of pure BNT-ST. In addition, the P-S relation for the BNT-ST/BNKT is identical to that of BNT-ST as the operating frequency increases up to 100 Hz. This may be because the polarization of BNT-ST is lower than that of BNKT. The electric field-induced polarization and strain of the BNT-ST/BNKT composite with respect to the temperature and frequency are related to the thermal stability of the ferroelectric seed and the degree of the phase transition in the relaxor matrix.     

Synchronous improvement of piezoelectric property and temperature stability in PSN-PMN-PT ceramics by forming composites with ZnO

Relaxor ferroelectric materials with high piezoelectric properties always suffer from low phase transition temperature, making them difficult to satisfy the demands for high-temperature environment applications. In this work, we proposed a composite approach to improve the piezoelectricity and temperature stability of PSN-PMN-PT ceramics at the same time. The ZnO nanoparticles as a second phase were introduced into the PSN-PMN-PT matrix to form composite ceramics. When the ZnO content reaches 5 mol%, the piezoelectric constant d₃₃ increases from 529 pC/N for pure PSN-PMN-PT ceramic to 590 pC/N. Meanwhile, the retained d₃₃ after annealing at 200 °C keeps 92% of the value before annealing, indicating the thermal depolarization behavior is suppressed by the composite method. The synchronous improvement of the d₃₃ and thermal depolarization behavior for PSN-PMN-PT/ZnO composite ceramics is related to the local electric field and stress field caused by the addition of ZnO particles. Our results pave a simple and effective way to develop next-generation PT-based relaxor ferroelectric ceramics.     

Waste cotton Fabric/MXene composite aerogel with heat generation and insulation for efficient electromagnetic interference shielding

Electromagnetic interference (EMI) shielding materials have become more and more indispensable due to serious electromagnetic-radiation pollution. Herein, waste cotton cellulose aerogels were prepared by dissolving waste cotton fabrics (WCF) in NaOH/urea aqueous solution, and MXene nanosheets were subsequently deposited on the cellulose aerogels by a facile dip coating method to obtain WCF/MXene composite aerogels. The WCF/MXene composite aerogels with highly porous network structure show remarkable electrical conductivity (8.2 Ω/sq of surface resistance), high EMI shielding effectiveness (EMI SE) in the range of 2–18 GHz (39.3–48.1 dB). The WCF/MXene aerogel possesses high SSE and SSE/t of 677.94–829.74 dB cm³ g^?1 and 3512.62–4299.17 dB cm² g^?1, respectively (2–18 GHz). In addition, the heating temperature of WCF/MXene composite aerogels reaches 199 °C when 3 V positive voltage is applied on them. The WCF/MXene composite aerogels possess excellent electromagnetic shielding effectiveness, heat generation property and insulation, which can be potentially used as multifunctional materials for EMI shielding, electrical-heating and high temperature protection.     

电磁屏蔽复合材料包装箱的研究

采用复合材料树脂传递模塑（RTM）工艺，利用一层含不锈钢纤维的导电布为屏蔽材料，制备了具有电磁屏蔽效能的玻璃纤维增强树脂基复合材料包装箱，该包装箱材料在1．0～4．0GHz电磁波范围内，电磁屏蔽效能最高可高达36dB左右，且与未含导电布的相同体系的复合材料相比，力学性能基本保持不变。     

Vermicular Ni@RL-CS: Preparation,characterization and its applications in electromagnetic shielding

One-dimensional conductive materials are of great significance to the construction of conductive network in the polymer matrix due to their large aspect ratio. In this work, a nickel-plated rod-like calcium silicate composite (Ni@RL-CS) with unique vermicular structure was successfully fabricated by an electroless plating method. The structure and property of as-prepared Ni@RL-CS were characterized, and its electromagnetic shielding ability was evaluated through mixing with thermoplastic polyurethane (TPU). Results indicate that the Ni@RL-CS shows good electrical conductivity, magnetic property and strong dielectric loss ability. The Ni@RL-CS with a one-dimensional vermicular structure is easier to construct a continuous conductive network in TPU matrix, which greatly improves the electromagnetic shielding effectiveness of the TPU resin. TPU/Ni@RL-CS binary composite with 20 vol% Ni@RL-CS achieves ultrahigh specific EMI SE/thickness of 92.6 dB/mm in the frequency of X-band. By further hybridizing Ni@RL-CS with GNPs, the TPU/Ni@RL-CS/GNPs trinary composite exhibits excellent electromagnetic shielding performance. When the contents of Ni@RL-CS and GNPs are 10 vol% and 1.5 vol%, respectively, the specific EMI SE/thickness of the corresponding trinary composite reaches 74.6 dB/mm in the X-band owe to the dense conductive network, which is 56.5% higher than that of the binary TPU/Ni@RL-CS composite with the same content of 10 vol% Ni@RL-CS.. The synergistic effects of dielectric loss, magnetic loss, and the interfacial polarization loss are the main shielding mechanism. This work provides a strategy to prepare a functional filler based on an insulating inorganic material for electromagnetic shielding. The as-prepared Ni@RL-CS with the unique vermicular structure and outstanding electromagnetic shielding performance can serves as a functional filler to modify polymers for electromagnetic shielding applications.     

Effect of microstructure induced by microcellular injection molding on electromagnetic interference shielding properties

Preparing lightweight and versatile products is the unremitting goal of industry to save resources and energy. Lightweight carbon fiber reinforced polypropylene (CF/PP) composite foams with high-performance electromagnetic interference (EMI) shielding materials were fabricated by microcellular injection molding (MIM) technology. The average length and distribution of CF in CF/PP composite foams were examined. Thanks to the introduction of foaming process, the average CF length of composite foams was 33.98% longer than that of solids, which effectively enhanced the electrical conductivity and EMI shielding properties. The effect of shot size, gas content, and injection rate on the electrical conductivity and EMI properties was investigated. With melt shot size of 2/3 of the cavity volume, gas content of 0.5 wt% N₂ and injection rate of 100 mm/s, optimal cellular structure of the composite material was obtained. The EMI shielding effectiveness (SE) reaches 36.94 dB, which is the highest value achieved by using MIM technology to the best of the authors' knowledge. In addition, the mechanical properties of cellular structure can still maintain good values, with the tensile strength and impact strength improved by 15.3% and 14.03%, respectively.     

Can the addition of a dielectric improve the figure of merit of a tunable material?

The influence of addition of a low-loss linear dielectric material to a tunable ferroelectric material has been investigated in terms of the electrostatic consideration. The calculations of the dielectric loss and dielectric non-linearity of ferroelectric-dielectric composites have been performed by using three different models. On the basis of results obtained, the figure of merit of the composite material has been evaluated. No improvement of the figure of merit of composite material compared to the pure ferroelectric has been observed for the considered models.     

Tuning the electrocaloric effect in 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics by relaxor phase blending

The pseudo-first-order phase transition in 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ ceramics leads to a sharp increase in temperature change (ΔT) in the vicinity of the ferroelectric-to-relaxor transition temperature T_FR (~100 °C) [Appl. Phys. Lett. 110 (2017) 182904]. In this study, we add the 0.78Bi_0.5Na_0.5TiO₃-0.06BaTiO₃-0.16(Sr_0.7Bi_0.2)TiO₃ relaxor phase to the 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ ferroelectric matrix to tune its electrocaloric effect. The results show that the addition of the relaxor phase plays a vital role in phase and local-structure evolution. A transition occurs between the ferroelectric and ergodic relaxor phases when the mass fraction of the latter increases to 30% (x = 0.3), as verified by X-ray diffraction analysis, Raman spectroscopy, and polarization-electric field (P-E) hysteresis loops. Furthermore, addition of the relaxor phase reduces the T_FR from 76 °C at x = 0.1–55 °C at x = 0.2; however, this transition disappears at x = 0.3 and 0.4 composite. In-situ piezo-force microscopy (PFM) images illustrate that domains can be written into x = 0.1 and 0.2 ceramics with a valley in the piezoresponse curves. Increasing the temperature agitates the domain arrangement and decreases the contrast for PFM images; this indicates a gradual phase transition in the composite. The temperature corresponding to maximum ΔT exhibits a downward shift (0.58 K at 80 °C for x = 0.1 and 0.5 K at 65 °C for x = 0.2), while the temperature-ΔT curves are flat when x = 0.3 and 0.4. Moreover, the maximum ΔT shows a decrease with an increase in the relaxor phase content; this is believed to be related to a decrease in the latent heat due to a pseudo-first-order to second-order transition. Thus, we suggest that the incorporation of a relaxor phase into ferroelectric matrices is an effective technique to tune their electrocaloric effect and improve the thermal stability of ceramic composites.     

High electromagnetic interference shielding effectiveness in MgO composites reinforced by aligned graphene platelets

Graphene has been considered as an excellent filler to reinforce ceramics with enhanced properties. However, the uniform dispersion and controlled orientation of graphene sheets in a ceramic matrix have become major challenges toward higher performance. In this paper, we prepared MgO matrix composites with parallel graphene layers through the intercalation of the precursor into expandable graphite. We obtained a high electromagnetic interference (EMI) shielding effectiveness of ~30 dB, due to the multiple reflections and absorptance of electromagnetic waves between the parallel graphene layers. The hardness and strength of the MgO composite were also increased by introducing parallel graphene layers. All these properties suggest that the graphene/MgO composite represents a promising electromagnetic shielding material.     

Multifunctional Shape-Stabilized Phase Change Materials with Enhanced Thermal Conductivity and Electromagnetic Interference Shielding Effectiveness for Electronic Devices

A paraffin-based shape-stabilized composite phase change material (CPCM) is fabricated with dramatically enhanced thermal conductivity and excellent electromagnetic interference (EMI) shielding capacity. The as-prepared CPCMs are supported by graphene-based frameworks with many bubble-like micropores that are prepared by the addition of polystyrene microspheres into graphene oxide hydrogel as hard templates. These bubble-like micropores can encapsulate paraffin wax (PW) due to the strong capillary force between the graphene-based framework and PW and leading to enhanced shape stability of the as-prepared CPCMs. Moreover, the continuous thermally and electrically conductive network formed by graphene nanoplatelets endows the as-prepared CPCMs with a high thermal conductivity and an excellent EMI shielding effectiveness. When the ratio of graphene-based framework is 23.0 wt%, the thermal conductivity and latent heat of CPCM reaches 28.7 W m⁻¹ k⁻¹ and 175.8 J g⁻¹, respectively, and the EMI shielding effectiveness is higher than 45 dB in the frequency of 8.2–12.4 GHz. Their outstanding thermal and EMI shielding performance makes the as-prepared CPCMs promising candidates for use in thermal management and EMI shielding of electronic devices.     

Electromagnetic interference shielding effectiveness of hybrid multifunctional Fe3O4/carbon nanofiber composite

Electromagnetic interference shielding effectiveness (EMI SE) of multifunctional Fe₃O₄/carbon nanofiber composites in the X-band region (8.2–12.4 GHz) is studied. Here, we examine the contributing effects of various parameters such as Fe₃O₄ content, carbonization temperature and thickness on total shielding efficiency (SE_total) of different samples. The maximum EMI SE of 67.9 dB is obtained for composite of 5 wt.% Fe₃O₄ (0.7 mm thick) with the dominant shielding by absorption (SE_A) of electromagnetic radiation. The enhanced electromagnetic shielding performance of Fe₃O₄/carbon nanofiber composites is attributed to the increment of both magnetic and dielectric losses due to the incorporation of magnetite nanofiller (Fe₃O₄) in electrically conducting carbon nanofiber matrix as well as the specific nanofibrous structure of carbon nanofiber mats, which forms a higher aspect ratio structure with randomly aligned nanofibers. Furthermore, we prove that the addition of elastomeric polydimethylsiloxane (PDMS) as a coating for carbon nanofiber composite strengthens the composite structure without interfering with its electromagnetic shielding efficiency.     

Highly Uniform and Stable Transparent Electromagnetic Interference Shielding Film Based on Silver Nanowire–PEDOT:PSS Composite for High Power Microwave Shielding

Electromagnetic interference (EMI) shielding materials, especially ones with excellent shielding effectiveness (SE), high optical transmittance, long-term stability as well as high uniformity, are urgently desired to meet the requirements of many applications. Herein, an extremely transparent, stable and uniform silver nanowire (Ag NW)–poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composite film as an EMI shielding material is prepared, which possess excellent shielding capability to both small signal and high power microwaves (HPM). The composite film exhibits SE of 30.5 dB in the frequency range of 1–12 GHz (small signal) and simultaneously has an optical transmittance of 91.0%. The SE continuously increases to 41.4 dB, while the optical transmittance still maintains at 81.1%. The composite film is very uniform, and its SE is almost unchanged even when exposed in air for a year. The SE of this composite film under the excitation of HPM is also thoroughly investigated. The HPM SE is much larger than that of small signal. As the power density of HPM is increased, the SE firstly remains unchanged, then continuously increases, and finally saturates. The SE exceeds 50 dB with the excitation power density of 40 W. More interestingly, the SE is saturated at a fixed HPM power density.     

Electromagnetic interference properties of carbon nanofiber–reinforced acrylonitrile–styrene–acrylate/natural graphite composites

Acrylonitrile–styrene–acrylate/natural graphite/carbon nanofiber composites (ASA/NG/CNF) were prepared using a melting blending method. The effects of CNFs on the morphology, rheological properties, dynamical mechanical properties, electrical resistivity, and electromagnetic interference shielding effectiveness (EMI SE) were studied using a scanning electron microscope, a rotational rheometer, and dynamic mechanical analysis (DMA). The addition of CNFs changed the oriented and laminated structure of the ASA/NG composite. The flexural strength of the ASA composite reached a maximum at 6% CNF, and then it began to decrease. The addition of CNFs did not alter the glass‐transition temperature of ASA, but it largely increased the storage modulus of the composite in DMA tests. In the rheological measurements, the complex viscosity and storage modulus of the composite increased as CNF content increased, and the resistance to creep of the composites was significantly increased by the addition of CNFs. The electrical resistivity of the ASA composites decreased from 49.8 Ω cm to 2.3 Ω cm as the CNF content was increased from 0 to 12%. At the same time, the EMI properties of the composites rose from 15 dB to 30 dB in the frequency range 30–1500 MHz. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45455.     

Improved Electromagnetic Interference Shielding Properties of MWCNT–PMMA Composites Using Layered Structures

Electromagnetic interference (EMI) shielding effectiveness (SE) of multi-walled carbon nanotubes–polymethyl methacrylate (MWCNT–PMMA) composites prepared by two different techniques was measured. EMI SE up to 40 dB in the frequency range 8.2–12.4 GHz (X-band) was achieved by stacking seven layers of 0.3-mm thick MWCNT–PMMA composite films compared with 30 dB achieved by stacking two layers of 1.1-mm thick MWCNT–PMMA bulk composite. The characteristic EMI SE graphs of the composites and the mechanism of shielding have been discussed. SE in this frequency range is found to be dominated by absorption. The mechanical properties (tensile, flexural strength and modulus) of the composites were found to be comparable or better than the pure polymer. The studies therefore show that the composite can be used as structurally strong EMI shielding material.     

Dielectric and Pyroelectric Properties of Cadmium Niobate Ceramics

The low-temperature dielectric and pyroelectric properties of pyrochlore Cd₂Nb₂O₇ ceramics have been investigated over the temperature range from 10 to 300 K. Dielectric data confirmed that two ferroelectric transitions occurred in the Cd₂Nb₂O₇ ceramics at temperatures near 80 and 192 K. The higher-temperature ferroelectric transition is complex, with evidence for three separate transitions occurring within a narrow temperature range. The temperature and frequency dependencies of the dielectric constant were consistent with both second-order (diffuse) and improper ferroelectric (ferroelastic) effects. Pyroelectric data also confirmed the multiple-transition behavior, with anomalies in the pyroelectric coefficient at temperatures corresponding to the onset of the diffuse ferroelectric transition and the ferroelastic effect. Dielectric loss data (analyzed by both Arrhenius and Cole-Cole formalisms) indicated the presence of three separate relaxation-type dielectric loss mechanisms in this temperature range. Unambiguous explanations for the observed dielectric and pyroelectric phenomena could not be made, but domain effects are believed to be responsible for at least part of the complex nature of the ferroelectric transitions in this material.     

Electromagnetic Shielding Particleboard with Nickel-Plated Wood Particles

We investigated the production of wooden materials with electrical and effective electromagnetic shielding properties. Wood particles metallized by electroless plating were suitable as a raw material for the manufacture of particleboard. The specific gravity of the particleboard was about half that of plastic composite materials. We observed a correlation between the surface resistivity of the metallized wood particles and the volume resistivity and shielding effectiveness of the particleboard. The shielding effectiveness of the particleboard was improved by increasing the quantity of metallized wood particles and the applied pressure.     

TPMS多孔铝-石蜡复合相变材料蓄热过程数值模拟及实验

传统相变材料受限于自身热导率小,其相变蓄热效率难以提升,通过在相变材料中添加具有高热导率的金属多孔结构是强化传热的重要手段之一。本文建立了三周期极小曲面（triply periodic minimal surface,TPMS）多孔铝-石蜡复合相变材料的三维、瞬态包含自然对流的相变蓄热模型,利用数值仿真结合实验的方法研究了TPMS多孔铝-石蜡复合相变材料在蓄热过程中的固液相界面演变规律、实时温度变化、热传输特性以及蓄热性能。结果表明,在纯石蜡中添加primitive杆状（primitive sheet,PS）、primitive壳状（primitive network,PN）两种TPMS多孔铝结构后,石蜡相变温度范围内出现明显的相变温度平台,PS-石蜡、PN-石蜡复合相变材料的相变起始时间较纯石蜡分别减少了74.1%与91.4%,竖直方向上的最大温度梯度由纯石蜡的1605.7℃/m分别下降至PS-石蜡、PN-石蜡复合相变材料的840℃/m、943.8℃/m,蓄热速率较纯石蜡分别提高3.10倍、4.69倍。最后,通过选区激光熔化（selective laser melting,SLM）技...