Dielectric properties and EMI shielding efficiency of polyaniline and ethylene 1-octene based semi-conducting composites

The preparation of polyaniline (PAni) was carried out by the oxidative emulsion polymerization of aniline and the semi-conducting composites were prepared by mixing it with a polyolefinic thermoplastic elastomer ethylene 1-octene copolymer (EN). Different electrical properties and electromagnetic interference shielding efficiency (EMI SE) of these composites were measured. The results revealed that the incorporation of PAni in EN increases the conductivity, dielectric constant, dielectric loss and EMI SE. These composites exhibit pressure dependent dielectric properties and may act as pressure sensor. There are increase in AC conductivity and decrease in dielectric constant with the increase in applied pressure on composites. A model correlation between EMI SE and AC conductivity at same frequency for the composites having maximum 40% of PAni was obtained through extrapolation and linear regression analysis, which shows that EMI SE has linear relationship with AC conductivity. Because of their semi-conductive behavior these composites can find application as antistatic materials and electromagnetic interference (EMI) shielding material.     

Bioinspired mineral MXene hydrogels for tensile strain sensing and radionuclide adsorption applications

MXene-based hydrogels have drawn considerable attention as flexible and wearable sensors. However, the application of MXene-based hydrogels after sensing failure has rarely been investigated, which is of great significance for expanding their engineering application. In this work, multifunctional mineral MXene hydrogels (MMHs) were synthesized via a simple method inspired by biomineralization. The prepared MMHs were stretchable, self-healable and conductive, and can be used to fabricate wearable tensile strain sensors showing a super-wide sensing range with excellent sensitivity. MMHs-based strain sensors were designed to be directly attached to the skin surface to detect tiny and large human motions. In addition, with the advantages of a large specific area, excellent hydrophilicity and abundant active adsorption sites for MXene nanosheets and hydrogels, dehydrated MMHs were used as highly efficient adsorbents for the removal of strontium ions from aqueous solutions. This work shows the great potential of MXene in promoting the development of next-generation functional materials.     

Optical microstrip patch antennas design and analysis

This paper has presented transparent conductor oxide materials (TCOMs) based microstrip patch antennas with glass substrate and copper ground plane, which have been deeply analyzed in the visible spectrum region in comparison with the practical patch antenna model of indium tin oxide patch with glass substrate and different TCOMs based ground plane. As well as the study have investigated the effect of transparent oxide materials on patch antenna design instead of perfect conductor materials such as copper that has low cost and weight. The tradeoff between optical transparency and electrical conductivity will be evaluated for a range of visible regions. Microstrip transmission line feed method is used to predict the skin effects on a patch antenna and their impact on antenna efficiency, resonance frequency and optical transmission are also described. This study have discussed assessment of these tradeoffs and effect of TCOMs parameters on antenna design.     

Electrical conductivity and electromagnetic interference shielding characteristics of multiwalled carbon nanotube filled polyacrylate composite films

Multiwalled carbon nanotubes (MWCNTs) were homogeneously dispersed in pure acrylic emulsion by ultrasonication to prepare MWCNT/polyacrylate composites applied on building interior wall for electromagnetic interference (EMI) shielding applications. The structure and surface morphology of the MWCNTs and MWCNT/polyacrylate composites were studied by field emission scanning microscopy (FESEM) and transmission electron microscopy (TEM). The electrical conductivity at room temperature and EMI shielding effectiveness (SE) of the composite films on concrete substrate with different MWCNT loadings were investigated and the measurement of EMI SE was carried out in two different frequency ranges of 100-1000 MHz (radio frequency range) and 8.2-12.4 GHz (X-band). The experimental results show that a low mass concentration of MWCNTs could achieve a high conductivity and the EMI SE of the MWCNT/polyacrylate composite films has a strong dependence on MWCNTs content in both two frequency ranges. The SE is higher in X-band than that in radio frequency range. For the composite films with 10 wt.% MWCNTs, the EMI SE of experiment agrees well with that of theoretical prediction in far field.     

Beta-manganese dioxide nanorods for sufficient high-temperature electromagnetic interference shielding in X-band

As the development of electronic and communication technology, electromagnetic interference (EMI) shielding and attenuation is an effective strategy to ensure the operation of the electronic devices. Among the materials for high-performance shielding in aerospace industry and related high-temperature working environment, the thermally stable metal oxide semiconductors with narrow band gap are promising candidates. In this work, beta-manganese dioxide (β-MnO₂) nanorods were synthesized by a hydrothermal method. The bulk materials of the β-MnO₂ were fabricated to evaluate the EMI shielding performance in the temperature range of 20–500 °C between 8.2 and 12.4 GHz (X-band). To understand the mechanisms of high-temperature EMI shielding, the contribution of reflection and absorption to EMI shielding was discussed based on temperature-dependent electrical properties and complex permittivity. Highly sufficient shielding effectiveness greater than 20 dB was observed over all the investigated range, suggesting β-MnO₂ nanorods as promising candidates for high-temperature EMI shielding. The results have also established a platform to develop high-temperature EMI shielding materials based on nanoscale semiconductors.     

Crystallization and annealing effects of sputtered tin alloy films on electromagnetic interference shielding

Sn, Al and Cu not only possess electromagnetic interference (EMI) shield efficiency, but also have acceptable costs. In this study, sputtered Sn-Al thin films and Sn-Cu thin films were used to investigate the effect of the crystallization mechanism and film thickness on the electromagnetic interference (EMI) characteristics. The results show that Sn-xAl film increased the electromagnetic interference (EMI) shielding after annealing. For as-sputtered Sn-xCu films with higher Cu atomic concentration, the low frequency EMI shielding could not be improved. After annealing, the Sn-Cu thin film with lower Cu content possessed excellent EMI shielding at lower frequencies, but had an inverse tendency at higher frequencies. For both the Sn-xAl and Sn-xCu thin films after crystallization treatment, the sputtered films had higher electrical conductivity, however the EMI shielding was not enhanced significantly.     

Designing of multiwalled carbon nanotubes reinforced low density polyethylene nanocomposites for suppression of electromagnetic radiation

High aspect ratio multi-walled carbon nanotubes (MWCNTs) reinforced low density polyethylene (LDPE) composites were prepared by solvent casting followed by compression molding technique. Electromagnetic interference (EMI) shielding effectiveness (SE) of these composites was investigated in the frequency range of 12.4?C18 GHz (Ku-band) for the first time. The experimental results indicate that the EMI-SE of these composites is sensitive to the MWCNT loading. The average value of EMI-SE reaches 22.4 dB for 10 wt% MWCNT-LDPE composites, indicating the usefulness of this material for EMI shielding in the Ku-band. The main reason for improved SE has been attributed to significant improvement in the electrical conductivity of the composites by 20 orders of magnitude, i.e., from 10^?20 for pure LDPE to 0.63 S/cm for MWCNT-LDPE, which is three order of magnitude higher than the previous reports for MWCNT-LDPE composites. Differential scanning calorimetry of the MWCNT-LDPE composites showed around 37% improvement in the crystalline contents over pure LDPE samples which resulted into enhanced thermal stability of the composites. The thermal decomposition temperature of LDPE is shifted by 40 °C on addition of 5 wt% MWCNT. The studies therefore show that these composite can be used as light weight, thermally stable EMI shielding, and antistatic material.     

Facile synthesis of Ag-reduced graphene oxide hybrids and their application in electromagnetic interference shielding

A fast and environmentally friendly method was proposed toward one-pot synthesis of Ag-reduced graphene oxide (Ag-RGO) hybrids by a chemical reduction method assisted by microwave irradiation treatment with the use of sodium citrate as green reductant. The as-synthesized samples were characterized systematically, and the results indicated the successful synthesis of Ag-RGO. Ag-RGO was further applied as filler in polymethyl methacrylate (PMMA) matrix polymer composites, and their electromagnetic interference (EMI) shielding performance was investigated. The prepared Ag-RGO/PMMA composites with 3.0 vol% Ag-RGO exhibited an excellent EMI shielding effectiveness (EMI SE) of average 26.8 dB in the 8–12 GHz X-band range, which outperformed the RGO/PMMA composites (18.4 dB) with bare RGO as fillers.     

Flexible and ultrathin dopamine modified MXene and cellulose nanofiber composite films with alternating multilayer structure for superior electromagnetic interference shielding performance

With the development of modern electronics, especially the next generation of wearable electromagnetic interference (EMI) shielding materials requires flexibility, ultrathin, lightweight and robustness to protect electronic devices from radiation pollution. In this work, the flexible and ultrathin dopamine modified MXene@cellulose nanofiber (DM@CNF) composite films with alternate multilayer structure have been developed by a facile vacuum filtration induced self-assembly approach. The multilayered DM@CNF composite films exhibit improved mechanical properties compared with the homogeneous DM/CNF film. By adjusting the layer number, the multilayered DM3@CNF2 composite film exhibits a tensile strength of 48.14 MPa and a toughness of 5.28 MJ·m⁻³ with a thickness about 19 μm. Interestingly that, the DM@CNF film with annealing treatment achieves significant improvement in conductivity (up to 17264 S·m⁻¹) and EMI properties (SE of 41.90 dB and SSE/t of 10169 dB·cm²·g⁻¹), which still maintains relatively high mechanical properties. It is highlighted that the ultrathin multilayered DM@CNF film exhibits superior EMI shielding performance compared with most of the metal-based, carbon-based and MXene-based shielding materials reported in the literature. These results will offer an appealing strategy to develop the ultrathin and flexible MXene-based materials with excellent EMI shielding performance for the next generation intelligent protection devices.     

Effect of heat treatment on ZrO2-embedded electrospun carbon fibers used for efficient electromagnetic interference shielding

ZrO₂-embedded carbon fibers were prepared for use as an electromagnetic interference (EMI) shielding material by electrospinning and heat treatment methods. Structural changes were observed in the ZrO₂ and in the carbon structures by XRD and Raman spectroscopy, respectively. During heat treatment, XRD analysis results revealed a transition from a monoclinic structure to a tetragonal structure in ZrO₂ and a graphitization in the structural formation of carbon fibers was observed by Raman spectroscopy. It was observed that these structural changes in the ZrO₂ and the carbon fibers improved the real and imaginary permittivities by a factor of more than 3.5. The EMI shielding efficiency (SE) improved along with the permittivity with higher treatment temperatures and greater amounts of embedded ZrO₂; the highest average EMI SE achieved was 31.79 dB in 800-8500 MHz. The heat treatment played an important role in the improvements in the permittivity and in the EMI SE because of the heat-induced structural changes of the ZrO₂-embedded electrospun carbon fibers. We suggest that the EMI shielding of the fibers is primarily due to the absorption of electromagnetic waves, which prevents secondary EMI by reflection of electromagnetic waves.     

Ultra-thin single-layer transparent geometrical phase gradient metasurface and its application to high-gain circularly-polarized lens antenna

A new method to design an ultra-thin high-gain circularly-polarized antenna system with high efficiency is proposed based on the geometrical phase gradient metasurface(GPGM).With an accuracy control of the transmission phase and also the high transmission amplitude,the GPGM is capable of manipulating an electromagnetic wave arbitrarily.A focusing transmission lens working at Ku band is well optimized with the F /D of 0.32.A good focusing effect is demonstrated clearly by theoretical calculation and electromagnetic simulation.For further application,an ultra-thin single-layer transmissive lens antenna based on the proposed focusing metasurface operating at 13 GHz is implemented and launched by an original patch antenna from the perspective of high integration,simple structure,and low cost.Numerical and experimental results coincide well,indicating the advantages of the antenna system,such as a high gain of 17.6 d B,the axis ratio better than 2 d B,a high aperture efficiency of 41%,and also a simple fabrication process based on the convenient print circuit board technology.The good performance of the proposed antenna indicates promising applications in portable communication systems.     

EMI shielding effectiveness of graphene decorated with graphene quantum dots and silver nanoparticles reinforced PVDF nanocomposites

Graphene decorated with graphene quantum dots (G-D-GQDs) have been successfully synthesized using solvothermal cutting of graphene oxide. The incorporation of G-D-GQDs in polyvinyledene fluoride (PVDF) matrix shows the total EMI shielding effectiveness (SE_T) of 31 dB at 8 GHz. The main mechanism of high EMI shielding effectiveness is reflection and absorption of EM radiation. The high absorption of EM radiation is due to tunneling of electrons from GQDs. Further, decoration of G-D-GQDs with conducting Ag nanoparticles (G-D-GQDsAg) enhances the SE_T value to 43 dB at 8 GHz of PVDF/G-D-GQDsAg nanocomposite, due to increase in electrical conductivity of PVDF/G-D-GQDsAg nanocomposite and enhanced dispersion of G-D-GQDsAg in PVDF matrix. The incorporation of G-D-GQDs and G-D-GQDsAg in PVDF matrix also increases the thermal stability and crystallinity of PVDF. The increase in thermal stability and crystallinity are more for PVDF/G-D-GQDsAg nanocomposite as compare to PVDF/G-D-GQDs nanocomposite, due to better dispersion of G-D-GQDsAg in PVDF matrix. Thus, PVDF/G-D-GQDsAg nanocomposite having high SE_T value can shield 99.9% of electromagnetic radiation in X-band range, which make it suitable for EMI shielding application for consumer electronic equipment’s.     

脉冲电场屏蔽效能测试系统及测试方法

 自主研制了一套小型脉冲电场屏蔽效能测试系统，该系统由脉冲电场发射设备和脉冲电场测试设备构成。脉冲电场发射设备的天线口面前60 cm处可产生峰值达7.5 kV/m的脉冲电场，测试设备的动态测试范围达97 dB。系统采用光纤测量设备，在测量工作中能有效抑制强电磁场干扰。采用Matlab编写自动测量及数据处理程序，实现了数据采集与处理自动化。实验测量了金属桥架、控制柜、屏蔽帐篷、导电水泥混凝土房的脉冲电场屏蔽效能，其脉冲电场峰值衰减量分别为52,64,66,30 dB。实验表明可用脉冲电场的峰值衰减量来评估屏蔽体的脉冲电场屏蔽效能。     

一种波束赋形可调的导航天线设计

提供一种新的调节半功率波束宽度的思路,并设计了一款可实现波束宽度变换以应用于不同波束赋形场景的北斗二号B3频段的导航天线。基于四阵元双馈源的微带贴片天线阵列,在HFSS有限元仿真软件中根据理论进行建模仿真并优化。在保持右旋圆极化的基础上,不用改变阵列的结构,只需适当调节各个阵元激励的幅度与相位,就能实时缩小或者扩大半功率波束宽度,分别实现主瓣方向可调的定向波束赋形与宽波束赋形以应对不同的工作环境,并且具有定向抗干扰能力。仿真结果表明:定向波束赋形与宽波束赋形在B3中心频点的最大增益分别约为7.13,3.56 dBi,半功率波束宽度分别为52°,119°,3 dB轴比宽度分别为90°,166°;在整个B3频段内各个馈电端口反射系数低于?11 dB,相邻端口隔离度低于?28 dB。设计的波束赋形方式可调的导航天线适用于在无遮挡的开阔空间与特定的遮挡环境之间经常切换的工作场景,改善传统的机动式导航终端在“城市峡谷”等高遮蔽角环境下增益较低的缺点。     

Excellent electromagnetic interference shielding effectiveness of chemically reduced graphitic oxide paper at 101 GHz*

Graphitic oxide (GO) was synthesized by oxidation of graphite powder using Hummer’s method and the formed GO is solution processed into paper-like macroscopic form. Subsequently, chemically reduced graphitic oxide paper (CRGOP) is prepared by hydrazine vapours induced reduction of formed GO precursor based paper. The formation of GO and its successful reduction to RGO phase is confirmed by FTIR, Raman Spectroscopy and X-ray diffraction. It has been observed that due to high electrical conductivity ~200 micron thick CRGOP display excellent EMI shielding performance at very high frequency of 101 GHz frequency with total shielding effectiveness (SE) value of ?35.49 dB (i.e. >99.97% blocking of incident EM radiation) which is much higher compared to pristine GO paper (?1.55 dB) or comparable to expanded graphite (EG) sheet (?35.61 dB). Due to their lightweight nature, these freestanding CRGOPs display average specific SE value of ?221.8 dB cm³/g. Besides, their excellent flexibility and makes them potential candidate for lightweight EMI gasketing material compared to other forms of flexible carbons like EG.     

Experimental studies of using wireless energy transmission for powering embedded sensor nodes

A major challenge impeding the deployment of wireless sensor networks for structural health monitoring (SHM) is developing a means to supply power to the sensor nodes in an efficient manner. In this paper, we explore possible solutions to this challenge by using a mobile-host based wireless energy transmission system to provide both power and data interrogation commands to sensor nodes. The mobile host features the capability of wirelessly transmitting energy to sensor nodes on an as-needed basis. In addition, it serves as a central data repository and processing center for the data collected from the sensing network. The wirelessly transmitted microwave energy is captured by a receiving antenna, transformed into DC power by a rectifying circuit, and stored in a storage medium to provide the required energy to the sensor node. The application of wireless energy transmission is targeted toward SHM sensor nodes that have been recently developed by the authors, which can be used to collect peak mechanical displacements or piezoelectric impedance measurements. This paper will describe considerations needed to design such energy transmission systems, experimental procedure and results, method of increasing the efficiency, energy conditioning circuits and storage medium, and target applications. Experimental results from a field test on the Alamosa Canyon Bridge in southern New Mexico will also be presented.     

In situ SEM studies on strain sensing mechanisms of PPy-coated electrically conducting fabrics

This paper studies a flexible fabric strain sensor from PPy-coated fabrics prepared by a chemical vapor deposition method under low temperature, placing an emphasis on mechanisms of its strain sensing behavior. In situ tensile tests in a scanning electron microscope (SEM) were conducted for PPy-coated electrically conducting yarns, which were prepared by the same procedure as that for the PPy-coated fabrics, enabling it possible to observe in situ the phenomena that occurred on the fiber surface during fabric deformation. The investigation revealed that the PPy-coated nylon/polyurethane fabrics exhibited a high strain sensitivity of over 400 and very large workable strain range greater than 50%, which mainly attributes to the high conductivity and crack-opening and crack-closing mechanisms of PPy-coated polyurethane yarn, as well as the excellent properties of knitted fabric structure.     

蓝牙技术在大型镜面能动磨盘加工中的应用研究

利用蓝牙无线通信方式解决大型光学镜面加工中对能动磨盘的控制。该方法利用单片机控制蓝牙模块，采用基于HCI层的单片机对蓝牙模块控制的方法及PC机端通过RS232接口连接蓝牙模块互相配合，实现PC机与能动磨盘之间的通信。单片机根据蓝牙HCI层协议对蓝牙接收和发送数据进行处理。在蓝牙传输协议的基础上给出了应用于镜面能动磨盘加工中的软硬件实现方案。该技术克服了现在使用导电环带来的易磨损、成本高的缺点，对降低加工成本，减少复杂的工业布线有很大的意义。可以替代其他镜面加工中的导电环来进行控制数据传输，也可应用在其他无线串行通信领域。     

Electronic structure and optical properties of CuAlO2 under biaxial strain

An ab initio calculation has been carried out to investigate the biaxial strain ( - 10.71% < ε < 9.13%) effect on elastic, electronic and optical properties of CuAlO(2). All the elastic constants (c(11), c(12), c(13), c(33)) except c(44) decrease (increase) during tensile (compressive) strain. The band gap is found to decrease in the presence of tensile as well as compressive strain. The relative decrease of the band gap is asymmetric with respect to the sign of the strain. Significant differences between the parallel and perpendicular components of the dielectric constant and the optical properties have been observed due to anisotropic crystal structure. It is further noticed that these properties are easily tunable by strain. Importantly, the collective oscillation of the valence electrons has been identified for light polarized perpendicular to the c-axis. From calculations, it is clear that the tensile strain can enhance the hole mobility as well as the transparency of CuAlO(2).     

Synthesis of atomically thin GaSe wrinkles for strain sensors

A wrinkle-based thin-film device can be used to develop optoelectronic devices, photovoltaics, and strain sensors. Here, we propose a stable and ultrasensitive strain sensor based on two-dimensional (2D) semiconducting gallium selenide (GaSe) for the first time. The response of the electrical resistance to strain was demonstrated to be very sensitive for the GaSe-based strain sensor, and it reached a gauge factor of –4.3, which is better than that of graphene-based strain sensors. The results show us that strain engineering on a nanoscale can be used not only in strain sensors but also for a wide range of applications, such as flexible field-effect transistors, stretchable electrodes, and flexible solar cells.