Microwave Shielding Research Articles

Selective capture of lanthanum and lead cations over biomass-derived ion-imprinted biomacromolecule adsorbents

Selective and ultrasorption materials are of practical significance in the fields of rare earth element (REE) capturing and heavy metal (HM) remediation. Here, we exploited ion-imprinted engineering, which was based on a watermelon-inspired strategy. This type of engineering was first coupled with renewable alginate biomacromolecules. The imprinted target metal ions could be optionally changed and recovered for different purposes. La and Pb cations were selected as the representatives for REE and HM to demonstrate the tunable adaption. Sodium alginate is cost-effective and environment-friendly biomass and is thus frequently used as a carbon source or matrix in materials science. Some other high-performance metal-incorporated functional materials for catalysis and microwave shielding might also be synthesized facilely under our engineering. Metal sources for the abovementioned composites might be selectively extracted from natural metal-bearing solution or industrial wastewater by selecting specific target metals.

Ultralight and high-elastic carbon foam with hollow framework for dynamically tunable electromagnetic interference shielding at gigahertz frequency

Electromagnetic interference (EMI) shielding materials with lightweight and tunability are highly desirable for practical applications in complex environments. Carbon-based materials as EMI materials are lightweight and highly environment-friendly, but generally rigid. Herein, we demonstrate novel nitrogenous carbon foams (NCFs) with the hollow framework, possessing multiple merits of ultralight, ultraelasticity and proper electrical conductivity. Such a significant architecture thus results in an excellent EMI shielding performance. Experimental characterizations combining with the first principle calculations indicate that the origins of microwave absorption and shielding characteristics are ascribed to the atomic-scale nitrogen substitutions in carbon matrix, which induce the structural symmetry breaking and the re-distribution of localized charge, forming a high density of electric dipoles. By compressing/releasing the NCFs, the electromagnetic (EM) performance can be arbitrarily tuned due to the phase cancellation within the three-dimensional foam structure and the tunable conductivity. The present work has important implications in understanding the intrinsic origin of strengthening EM radiation, and meanwhile provides a strategy for the design of “dynamic” EM functional materials.

Conducting La0.5Sr0.5CoO3−δ foams for harsh condition microwave shielding

La0.5Sr0.5CoO3−δ (abbreviated as LSCO) foams with broad range of porosities (76.9 to 90.3%) having near spherical cells were prepared through emulsion freeze gelcasting route. The LSCO foam bodies had compressive strength and Young’s modulus in ranges of 1–7MPa and 57 to 428MPa, respectively. The increase in resistance of the foams with temperature shows their metallic conducting nature. Out of the three studied samples, the trend in the room temperature conductance follows the order in which their EMI shielding values vary. Compared to the dense LSCO, the electrical conductivity values are inferior in foams, by an order. Impressive electromagnetic interference shielding effectiveness as high as 33dB has been achieved for LSCO foams prepared at a porosity level of 80% with 10vol.% LSCO in the composition. The developed LSCO foams are lightweight and capable of withstanding harsh environmental conditions, since they are free from oxidation and survivable at high temperature.

STRUCTURAL AND DIELECTRIC EVOLUTION OF COBALT FERRITE NANOPARTICLES FOR MICROWAVE APPLICATIONS

In this paper, coprecipitation method was used in the synthesis of cobalt ferrite nano particles, while investigations were carried out to determine the effect of sintering temperature on the structural and dielectric properties of the prepared samples. The structural/morphological and dielectric properties of the products were determined by X-raydiffraction (XRD), transmission electron microscopy (TEM), and open ended coaxial probe (OECP). Results from analysis confirms that heat treatment influences the magnitude of dielectric constant and the structural evolution of the samples. TEM mages reveal that the samples surfaces exhibit well-defined crystalline nanoparticles of spherical shapes with small agglomeration at higher sintering temperature while the sizes of the particles increases with annealing temperature due to grain boundary growth. The magnitude of dielectric constant was influenced by interfacial polarization as well as iron hopping of Fe2+ to Fe3+ and Co2+ to Co3+ at B-sites. Sintering temperature also influenced the dielectric characteristics, and this is confirmed from the dielectric measurements at room temperature. Based on the result obtained for dielectric constant, these samples are suitable for small microwave shielding.

Development of Quality Tungsten Coating on Ceramics as a Microwave Shield for ITER High-Frequency Magnetic Sensor

High-quality tungsten coating deposition on sintered aluminum nitride ceramic substrates (both of thin flat chips and structural boxes) was realized using an adapted plasma-aided coating deposition rig. The tungsten coating produced using this technique and the accompanying apparatus setup are of high-purity, strong adhesion, and controlled three-dimensional uniformity (<20% thickness variations). The coating also exhibits well-structured and smooth (Ra < 1.0 µm) microscopic surface landscape with densely clustered tungsten granulations. The coated samples were tested under load conditions expected during ITER operation, including thermal cycling and superheated (up to 500°C) steam. Exposure to thermal cycles and hot steam made no apparent changes to the coating’s microscopic structure with no sign of cracks, blistering, or exfoliation seen under electron microscopy. These successes validated the microwave shield design for the ITER high-frequency magnetic sensor, which is based on this concept, and laid a solid foundation for the production of this component in the forthcoming procurement phase. Besides, a failure test was conducted for the tungsten coating in the temperature range of 500°C to 1500°C. Surface smoothing, pores, delamination, and mass loss in substrate were observed when temperature exceeded 1000°C, possibly due to the evaporation of aluminum atoms. These findings unveiled the changes of tungsten coating properties under extreme conditions that are of both academic and practical values.

An Ingenious Strategy to Construct Helical Structure with Excellent Electromagnetic Shielding Performance

AbstractHerein, a unique, 3D helical composite with excellent electromagnetic interference (EMI) shielding capability is fabricated. The alkali treated natural cotton fiber (NaCF) is adopted as the helical templet. The compacted polyaniline (PANI) clusters are grafted over NaCF surface via in situ polymerization technology. The correlation between structure and electromagnetic characteristics is investigated in details. The high doping degree and high crystalline phase of PANI coating layer results in the enhanced electrical conductivity. The improved polarization combined with high electrical conductivity boosts the dielectric loss and microwave attenuation properties. The analysis of skin depth, attenuation constant, and the comparisons of theoretical predictions and experimental results are conducted to investigate the effects of helical structure on the fundamental EMI shielding mechanisms. Absorption is the dominating microwave shielding mechanism due to the efficient multiple reflection. The EMI shielding effectiveness (SE) up to 48.83 dB (i.e., &gt;99.998% attenuation) indicates excellent shielding capability. This SE value is fairly superior among PANI‐based shielding composites. All the above results demonstrate a significant fundamental basis for designing a novel high‐performance EMI shielding material. The results and techniques also promise an ingenious and efficient strategy to achieve light‐weight and thin PANI‐based composite for shielding application potentials.

Ultraviolet- and Microwave-Protecting, Self-Cleaning e-Skin for Efficient Energy Harvesting and Tactile Mechanosensing.

Smart, self-powered, and wearable e-skin that mimics the pressure sensing property of the human skin is indispensable to boost up cutting edge robotics, artificial intelligence, prosthesis, and health-care monitoring technologies. Here, fabrication of a facile and flexible hybrid piezoelectric e-skin (HPES) with multifunctions of tactile mechanosensing, energy harvesting, self-cleaning, ultraviolet (UV)-protecting, and microwave shielding properties is reported. The principal block of the HPES is an SnO2 nanosheets@SiO2 (silica-encapsulated tin oxide nanosheets)/poly(vinylidene fluoride) (PVDF) nanocomposite (SS)-based PES acting as a single unit for simultaneous energy harvesting and tactile mechanosensing. Gentle human finger imparting onto the PES showed outstanding energy conversion efficiency (16.7%) with high power density (550 W·m-3) and current density (0.40 μA·cm-2). This device can generate high enough electrical power to directly drive portable electronics like a light-emitting diode (LED) panel (consisting of 85 commercial LEDs) and to charge up capacitors very rapidly. Thin PES mechanosensors demonstrated promising performance for quantitatively detecting static and dynamic pressure stimuli with a high sensitivity of 0.99 V·kPa-1 and a short response time of 1 ms. PES was also integrated to a health-data glove for precisely monitoring and discriminating fine motions of proximal interphalangeal, metacarpophalangeal, and distal interphalangeal joints of a human finger and bending motion of different human fingers. A (4 × 4) sensing matrix of PES was successfully employed to detect the spatial distribution of static pressure stimuli. The sensing matrix can precisely record the shape and size of an object placed onto it. PES was encapsulated with a nanocomposite film for providing self-cleaning and UV and microwave protection capability to the HPES. The hydrophobic SS film wrapping (water drop contact angle ∼85.6°) of the HPES enables the self-cleaning feature and makes HPES resistive against water and dirt. The HPES was integrated with in-house-made robotic hands, and the responses of the sensors due to grabbing of an object were evaluated. This work explores new prospects for UV- and microwave-protective, self-cleaning e-skin for energy harvesting and mechanosensation, which can eventually boost up the self-powered electronics, robotics, real-time health-care monitoring, and artificial intelligence technologies.

Role of silanized magnetic Fe2O3 particle in heat dissipation and microwave shielding behavior of E-glass fibre-reinforced epoxy resin composite

In this present work importance of adding silanized fine Fe2O3 particle into E-glass fibre-reinforced epoxy composites in microwave shielding and heat dissipation behavior was studied. The principal aim of this work is explicating the need of Fe2O3 particles in microwave shielding effectiveness of epoxy composite. Particle of dimensions 800, 200 and <100 nm were used for this study with silanized condition. Composites were prepared with 0.5 and 1.0 vol% of Fe2O3 particles along with 30 vol% of E-glass fibre. The dielectric constant of 6.7 was observed for composite designation RFI1 at 100 Hz (polarization frequency). Heat dissipation factor was increased with increase of frequency and particle content. Maximum wave attenuation percentage of 36.2 was observed for composite designations RFI1 and RFI22 in ‘J’ band region with highest magnetic permeability of 0.3. These mechanically and electromagnetically strengthened shielding materials could be used as microwave shielding helmet to prevent brain related hazards for peoples who are working in high electromagnetic radiation. Similarly more heat dissipation with high mechanical strength material could be used to fabricate storage containers where constant warm up is required.

Design and optimization of a flexible water-based microwave absorbing metamaterial

Water is one of the most promising dielectric materials for microwave absorption due to its superior broadband dielectric loss. Inspired by the mechanism of traditional metamaterials, we have designed a water-based dielectric loss microwave absorber based on 3D-printing technology. Through stepwise structural optimization, the fabricated flexible water-based metamaterial experimentally demonstrated an ultra-broadband absorption in the frequency range 5.9–25.6 GHz with a thickness of 4 mm. Meanwhile, its angular tolerance also demonstrated wide-angle absorption capability. All these properties make it suitable for practical electromagnetic applications such as microwave radiation protection technology and microwave shielding boxes.

Carbon nanotubes vs graphene nanoplatelets for 3D-printable composites

Polymer-based composites with nanocarbon fillers are of great interest for the wide application range including the needs of wireless communication and the development of precise measuring means and medical devices. However, the composite properties such as excellent electromagnetic energy dissipation or tailorable conductivity are not enough to solve practical problems in engineering. To be fully applicable, the composite material must be low-cost and suitable for conventional methods of fabrication, for example 3D-printing. In current research the electromagnetic properties of PLA-based composites with graphene nanoplatelets and multiwall carbon nanotubes were investigated in microwave frequency range. The synergistic effect of two fillers was observed, the investigated materials proved to be prospective for 3D-printable composite production for electromagnetic applications such as fabrication of complex geometry microwave shields and antennas.

Highly aligned nonwoven vapor grown carbon fibre based polyurethane fibrous membrane for direction-dependent microwave shielding

Highly aligned nonwoven vapor grown carbon fibre (VGCF) based polyurethane (PU) fibrous membrane (VGCF@PUFM) was fabricated by rotation spinning based on DMF-H2O exchange for directional microwave shielding. This VGCF@PUFM showed obviously different electrical conductivity and mechanical strength in parallel and perpendicular directions. Variational microwave shielding effectiveness (SE) could be observed by changing the rotation angles of VGCF@PUFM with vibrational direction of electromagnetic (EM) wave. There was the shielding difference more than 10 dB (above 20 dB in 0°, below 8 dB in 90°). Greater shielding effectiveness could be expected by enhancing the anisotropy of electrical conductivity of the VGCF@PUFM. In addition, oriented alignment of VGCF in fibre is promising for further improvement of the electrical conductivity in fibre direction.

A Flexible Microwave Shield with Tunable Frequency‐Transmission and Electromagnetic Compatibility

AbstractWireless techniques have improved life quality for many. However, the drawbacks like instable signal and high loss in air of electromagnetic interference hinder its further development. One solution is to develop a smart material or device, which can selectively receive a specific frequency (fs) of electromagnetic wave with less loss, and simultaneously show effective shielding against unwanted waves (frequency is denoted as fp). A bottleneck has been reached, such that using materials alone is unable to achieve the above due to the limitation of the intrinsic physical properties of materials. Here, a strategy combining the material structure design with a voltage control is proposed to overcome the limitation of materials toward the aforementioned task. The efforts are focused on exploring a suitable electrically tunable material with a sensitive response to an external voltage and the flexibility to be engineered to the needed macrostructure. As a result, the fs region can be fine‐tuned to 8–8.4, 8–9.3, and 8–10.3 GHz.

Enhancing absorption dominated microwave shielding in Co@C-PVDF nanocomposites through improved magnetization and graphitization of the Co@C-nanoparticles.

Using composites of polyvinylidene fluoride (PVDF) and carbon nanostructures embedded with Co-nanoparticles we demonstrate that electromagnetic shielding effectiveness depends strongly on the graphitic carbon concentration and the magnetic properties of Co-particles. Cobalt nanoparticles encapsulated by graphitic carbon embedded in an amorphous carbon-matrix were synthesized by a one-pot pyrolysis method at two different synthesis temperatures, TS = 800 °C (Co-800) and 1000 °C (Co-1000). We demonstrate that TS plays an important role in determining the structure, morphology and magnetic properties of the carbonaceous matrix, the graphite layer and the Co nanoparticles. Higher amounts of graphitic carbon and high saturation magnetization were observed for the Co-1000 sample than that for the Co-800 sample. We observed that the electromagnetic interference (EMI) shielding behavior of the PVDF-Co-1000 nanocomposite shows higher shielding effectiveness than that of the PVDF-Co-800 specimen. A more inhomogeneous dielectric medium in the PVDF-Co-1000 composite results in higher dielectric loss and impedance mismatch. A direct correlation between the shielding effectiveness with dielectric permittivity and magnetic permeability is demonstrated. The synergy between the multiple reflections at the interfaces and absorption of the microwave radiation in the conducting species confirms that a higher degree of graphitization and highly magnetic particles in nanocomposites are effectively superior for EMI shielding of microwave radiation.

Fabrication of gradient vapor grown carbon fiber based polyurethane foam for shape memory driven microwave shielding.

Gradient vapor grown carbon fiber (VGCF) based shape memory polyurethane foam (VGCF@SMPUF) was fabricated by alternate dipping in a gradually diluted VGCF@SMPU/DMF solution and distilled water for shape memory driven microwave shielding. Shape memory performance for this VGCF@SMPUF was achieved by heat transfer of thermally conductive VGCF. Shielding effectiveness (SE) was adjusted through different degrees of angle recovery. A consistent shielding effect from either side indicated that electromagnetic reflection may take place at both the surface and inside of the non-homogeneous composite shield. For shape memory effect, hot compression made this VGCF@SMPUF achieve a faster recovery time and higher recovery ratio owing to improved thermal conductivity. Moreover, VGCF@SMPUF, which was bent to the positive side (PS) with a higher VGCF content, showed shorter recovery time and higher recovery ratio than that bent to the negative side (NS) with a lower VGCF content. We attribute this result to the relatively small mechanical compression strength of the negative side with the lower VGCF content at the bending point when expanding from the positive side. Furthermore, hot compression obviously improved the shielding effectiveness of the VGCF@SMPUF, mainly through a considerable increase of the electrical conductivity. The VGCF@SMPUF hot compressed to a thickness of 0.11 mm achieved a SE value of ∼30 dB, corresponding to a shielding efficiency of ∼99.9%.

Self-assembled nanostructures of 3D hierarchical faceted-iron oxide containing vertical carbon nanotubes on reduced graphene oxide hybrids for enhanced electromagnetic interface shielding

The self-assembled three dimensional (3D) hybrids nanostructure containing uniform growth of vertical carbon nanotubes (VCNTs) with faceted iron oxide nanoparticles (f-Fe3O4 NPs) on the surfaces of reduced graphene oxide nanosheets (rGO NSs) is achieved using microwave assisted approach. The formation of hierarchical 3D f-Fe3O4-VCNTs@rGO hybrids, using microwave method is a rapid, simple, and inexpensive synthetic route. First, the VCNTs grow with help of Fe NPs, and after oxidizing of Fe NPs in form of f-Fe3O4 NPs, the growth has terminated resulting in formation of small size (<500 nm) VCNTs containing f-Fe3O4 NPs on its tip. The defect- and oxygen-rich sites of rGO NSs favor the heterogeneous nucleation and growth of f-Fe3O4 NPs on the tip of VCNTs. The synthesized 3D f-Fe3O4-VCNTs@rGO hybrid shows the improved electromagnetic interference (EMI) for microwave shielding effectiveness (SE) as compared to both rGO NSs and Fe3O4 NPs@rGO NSs materials. This 3D f-Fe3O4-VCNTs@rGO hybrid demonstrates the shielding effectiveness value more than ∼25 dB as compared to Fe3O4 NPs@rGO NSs for 1.0 mm thin film of 3D f-Fe3O4-VCNTs@rGO hybrids in microwave X-band (8.2–12.4 GHz). This applied microwave synthesis approach for 3D f-Fe3O4-VCNTs@rGO hybrids is simple, fast, reproducible and scalable for advanced EMI shielding materials. It can be concluded that the faceted Fe3O4 NPs on the tip of VCNTs which are grown in-situ on rGO NSs shows synergetic performance for EMI shielding elements in advanced application areas like spacecraft and aircraft.

Highly efficient low cost EMI shielding by barium ferrite encapsulated polythiophene nanocomposite

Barium ferrite encapsulated polythiophene (BaFe12O19/PTh) nanocomposite has been synthesized to analyse electromagnetic interference (EMI) shielding. The morphological analysis of the synthesized composites has been investigated by scanning electron microscopy (SEM), which confirmed the encapsulation of BaFe12O19 nanoparticles by PTh forming a core-shell structure. Highest loading of BaFe12O19 in composite (NC-100 i.e. BaFe12O19:PTh = 1:1) exhibits excellent magnetic properties with a magnetic moment and coercivity of 25.78 emu/gm and 2.5 kOe, respectively. Microwave shielding behaviour of the nanocomposite samples has been tested in X-band region by vector network analyser. Highest −43.27 dB shielding effectiveness at 11.65 GHz has been obtained in NC-100 composite. The excellent shielding effectiveness is due to the synergistic effect of dielectric and magnetic loss of the nanocomposite. These results suggest that the BaFe12O19/PTh nanocomposite (NC-100) exhibited superior EMI shielding properties and find wider application as low cost, high performance, lightweight microwave absorbing material.

Ultrathin and anisotropic polyvinyl butyral/Ni-graphite/short-cut carbon fibre film with high electromagnetic shielding performance

Ultrathin, flexible and anisotropic polyvinyl butyral (PVB)/graphite coated with nickel (Ni-Gr)/short-cut carbon fibre (SCF) cast films were fabricated using a convenient solution casting method. The effects of the filler components, contents, and their distribution structures on the electromagnetic shielding effectiveness (SE) of the composites are investigated. The results indicate that the hybridisation and distribution of fillers with different shapes could significantly improve the electromagnetic shielding performance. The anisotropic SE of the composites is due to the orientation of the SCFs in the casting direction, which was induced by the traction from the carrier tape of the casting machine. Moreover, the measured electromagnetic SE in the perpendicular direction was higher than that in the casting direction. The experimental results showed that the prepared composite films had excellent anisotropic SE in the measured frequency range of X band. The SE and specific SE of the PVB/Ni-Gr/SCF cast film with a mass ratio of 69/26/5 are 32 dB and 159 dB/mm, and 20 dB and 101 dB/mm, across and along the casting direction, respectively. The SE difference between the two directions of the microwave shielding material provides the potential to prepare a direction selective composite with an ultrahigh electromagnetic shielding performance. Moreover, the prepared composites showed great potential as microwave shielding materials in military and civilian applications.

Electromagnetic shielding, magnetic and microwave absorbing properties of Polypyrrole/Ba0.6Sr0.4Fe12O19 composite synthesized via in-situ polymerization technique

In this article, we have synthesized the Polypyrrole/Ba0.6Sr0.4Fe12O19 (PBSF) composite via in-situ polymerization technique. The synthesized samples were further characterized for structural, electrical, magnetic and microwave absorbing characterizations. The X-ray diffraction patterns reveal the formation of pure hexagonal ferrite phase whereas the Fourier transform infrared spectrums and X-ray photoelectron spectroscopy confirms the formation of polypyrrole/BSF composite structure. The microwave absorbing and shielding properties were studied in the frequency range 8–18 GHz. Using X and Ku band. The magnetic properties were studied using VSM and the PBSF37 composite shows the highest magnetic moment 59.58 emu/gm rather than the other PBSF composites and pure BSF ferrite. The PBSF37 shows the maximum microwave absorption of 89% over the broadband frequency range 8–18 GHz. The maximum shielding effectiveness 37.49 dB at 15.2 GHz corresponding maximum microwave properties were also observed for the same sample.

Layered structural design of flexible waterborne polyurethane conductive film for excellent electromagnetic interference shielding and low microwave reflectivity

A highly efficient electromagnetic interference (EMI) shielding waterborne polyurethane (WPU) composite film with low microwave reflectivity is designed by constructing an FeCo alloy decoration reduced graphene oxide (FeCo@rGO) /nano silver (Ag) layered structure. The FeCo@rGO layer formed by natural sedimentation at the bottom of the WPU film acts as a microwave absorption layer, and the ultra-thin Ag layer covered on the top surface serves as a highly efficient shielding layer. This unique layered structure combines the microwave-reflecting characteristic of nano Ag and the microwave-absorbing characteristic of rGO@FeCo to achieve strong microwave shielding effectiveness (SE) with low microwave reflection. The obtained Ag/rGO@FeCo/WPU composite film (10 wt% rGO@FeCo and Ag layer of 500 nm in thickness), which is only 300 μm in thickness, possesses an outstanding EMI SE of 50.5 dB and the microwave reflection coefficient is as low as 0.49 (average SER of 3.2 dB). This flexible and highly efficient shielding film with extremely low reflectivity is suitable for application in portable and wearable smart electronics, and this strategy offers a new method for designing the flexible electromagnetic interference shielding materials with low reflection characteristic.

Printable Hierarchical Nickel Nanowires for Soft Magnetic Applications.

Hierarchical nickel nanowires (h-NiNWs) were synthesized by a simple reduction method and their electrical, magnetic, and electromagnetic characteristics were investigated. These nanowires possess a high magnetic saturation (Ms) of 51 emu/g and also a coercivity (Hc) of 34.5 Oe, which makes them suitable for soft magnetic sensor applications. Hall transport is being reported for the first time for h-NiNWs, and electrical conductivity at room temperature was studied to assess their applicability as a Hall sensor wherein the Hall coefficient RH was found to be −1.39 × 10–12 Ω cm/Oe. Electromagnetic characterization of synthesized h-NiNWs shows excellent microwave shielding effectiveness of above 24 dB for the Ku band (12.4–18 GHz) and a maximum value of 32 dB at 14 GHz for a sample with a thickness of about 1 mm. A room-temperature-curable screen-printable ink was formulated using the synthesized magnetic nanostructures and printed on different flexible substrates. Printed patterns show promising ferromagnetic properties, and they could be potential candidates for soft magnetic sensor applications.