Selective Shielding Research Articles

Stealth RF energy harvesting in MRI using selective shielding.

To utilize the transmit radiofrequency (RF) field in MRI as a power source, near or within the field of view but without affecting image quality or safety. Power harvesting is performed by RF induction in a resonant coil. Resulting RF field distortion in the subject is canceled by a selective shield that couples to the harvester while being transparent to the RF transmitter. Such shielding is designed with the help of electromagnetic simulation. A shielded harvester of 3 cm diameter is implemented, assessed on the bench, and tested in a 3T MRI system, recording power yield during typical scans. The concept of selective shielding is confirmed by simulation. Bench tests show effective power harvesting in the presence of the shield. In the MRI system, it is confirmed that selective shielding virtually eliminates RF perturbation. In scans with the harvester immediately adjacent to a phantom, up to 100 mW of average power are harvested without affecting image quality. Selective shielding enables stealthy RF harvesting which can be used to supply wireless power to on-body devices during MRI.

A Comprehensive Review of Electromagnetic Interference Shielding Composite Materials.

The interaction between matter and microwaves assumes critical significance due to the ubiquity of wireless communication technology. The selective shielding of microwaves represents the only way to achieve the control on crucial technological sectors. The implementation of microwave shielding ensures the proper functioning of electronic devices. By preventing electromagnetic pollution, shielding safeguards the integrity and optimal performances of devices, contributing to the reliability and efficiency of technological systems in various sectors and allowing the further step forwards in a safe and secure society. Nevertheless, the microwave shielding research is vast and can be quite hard to approach due to the large number and variety of studies regarding both theory and experiments. In this review, we focused our attention on the comprehensive discussion of the current state of the art of materials used for the production of electromagnetic interference shielding composites, with the aim of providing a solid reference point to explore this research field.

Selective Shielding of the (002) Plane Enabling Vertically Oriented Zinc Plating for Dendrite-Free Zinc Anode.

Uncontrolled growth of Zn dendrites hinders the future development of aqueous Zn-ion batteries. Despite that the (100) plane possesses better zincophilic ability and fast kinetics, dendrites are generally suppressed via (002) plane-oriented Zn deposition in previous reports; the ordered (100) plane-dominant Zn deposition, especially under high current density has not yet been realized. Herein, vertically-oriented Zn plating with preferential growth of (100) plane is reported using disodium lauryl phosphate (DLP) as an electrolyte additive. DLP is preferentially anchored on the Zn (002) crystal plane via the polar phosphate group, then the deposition of Zn atoms on the (002) plane is retarded by the long alkyl chain, finally promoting the preferred growth of the (100) plane. This unique growth pattern results in ultrastable Zn plating/stripping at a super-high current density of 50mA cm-2 , with a cumulative capacity of 8500 mAh cm-2 . The Zn//Zn symmetric cell also cycles steadily for 700h with a large areal capacity of 10 mAh cm-2 at a current density of 10mA cm-2 . This study provides new insights into the realization of dendrite-free Zn anodes by crystal plane modulation.

Facile Preparation of a Low-Cost Liquid Interlayer Material with Intelligent UV-NIR-Shielding Function for Smart Windows.

High-performance interlayer materials have garnered considerable interest owing to their low manufacturing costs and applicability in smart windows. In this study, a novel smart-window interlayer material capable of selective shielding against both near-infrared (NIR) and ultraviolet (UV) radiation is developed based on the light transmittance control mechanism. An excellent thermoresponsive liquid, denoted as CDs@TRL (viz., carbon quantum dots at thermal-responsive liquid), is synthesized by compositing biomass-based fluorescent carbon quantum dots (CDs) and poly(N-isopropylacrylamide) (pNIPAM) at natural ambient temperature and in an aqueous phase. Due to the characteristics of CDs and synergistic effect of hydrogen bonds, CDs@TRL exhibits a high specific heat capacity (4.41 kJ kg-1 K-1), large thermal storage capacity (264.6 kJ kg-1), and better UV-NIR-blocking properties, compared to pure pNIPAM, as well as improves the sensitivity of thermal response. When injected into a window as a liquid interlayer, CDs@TRL can intelligently adjust the light transmittance according to ambient light intensity to achieve an intelligent response. The shielding rate of a 10 mm-thick CDs@TRL composite liquid against UV radiation (200-400 nm) was more than 95% in an overcast environment with insufficient light and close to 100% in a well-lighted environment. In addition, CDs@TRL is a cost-effective material that can be prepared from a wide range of raw material sources using a simple preparation process and exhibits excellent mobility and recyclability. Because of these features, it is considered to be a promising candidate for developing energy-saving and climate-adapted smart windows.

Surrogate model assisted design optimization of composite bone plates to achieve selective stress shielding

ABSTRACT Optimal composite bone plate is designed for Periprosthetic Femoral Fracture (PFF) fixation using genetic algorithm (GA) by hybrid and varying fiber orientation. The bone plate should allow higher displacement in axial direction and minimum movement in shear direction. Composite material is considered for the bone plate, the most important constraint in this design problem is that the axial movement and shear movement are limited to 2 and 0.5 mm, respectively. The simulated data from the finite element analysis (FEA) are used for creating the artificial neural network (ANN) surrogate models for the bone displacements in both the directions, which act as the objective functions for the GA-driven optimization in the multi-objective fashion. FEA is used to validate the solutions derived through the design optimization process. The FE simulations have shown only 10% deviation in the simulation output when compared to the achieved optimum solutions.

Electromagnetic shielding behaviors of planar frequency selective surface fabrics, with emphasis on decoupling analysis, lamination direction and tunable selective frequency

Planar frequency selective surface (FSS) fabrics with grids, strips or patches by simple methods of patching, embroidery, clipping and carving were fabricated. The periodic structures, laminated structures, processing method and materials pertaining to the electromagnetic shielding behaviors were investigated. Firstly, equivalent circuit and electromagnetic (EM) shielding behavior of basic frequency selective structure units and complex fretwork structure were provided, involving the decoupling of complex fretwork structure. In addition, various laminating structures of SPs and SGs were determined, one of superposition of SPs and SGs provides a SE peak of 40.2 dB (average SE of 25.1 dB in the whole frequency domain), the other presents a SE peak of 27.1 dB (average SE of 19.1 dB in the whole frequency regime). Furthermore, tunable selective electromagnetic shielding by a simple mechanical way was provided, which can realize a tunable SE peak varying from 730 MHz to 1580 MHz. This work might provide a perspective for the assemble and analytical approximation of FSS fabrics for scientists and engineers in this cross-disciplinary field.

Temperature-controlled fabrication of semiconducting polymeric nanocatalysts for selective carbon dioxide conversion and X-ray shielding capacity

The intrinsic semiconducting poly (1-aminoanthraquinone) (PAAQ) was synthesized by simple oxidative polymerization of 1-aminoanthraquinone at 25, 40, and 50 °C in the biphasic system. Seventy percent of perchloric acid was used to enhance the acidity, and 30% of hydrogen peroxide was acted as an oxidant. The synthesized materials were undergone the studies for crystalline nature, surface morphology, optical behavior, and electrochemical potential using X-ray powder diffraction, scanning electron microscopy (SEM), ultraviolet–visible spectroscopy-, fluorescence spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering, and cyclic voltammetry. The crystalline sizes were found to be 45.47, 45.88, and 45.51 nm, and their band gap energies were 3.89, 3.70, and 3.55 eV at 25, 40, and 50 °C, respectively. The SEM images reveal the formation of well-defined nanocubes with sheets, and the average particles size was 75 nm. Redox peaks in impedance curve proved the efficiency in electrochemical properties of synthesized PAAQ polymers. The PAAQ at 25 °C has showed an optimized catalytic conversion of carbon dioxide to carbon trioxide and the stabilized shielding property against X-ray irradiation during radiation therapy effectively.

Microfluidic Surface Shields: Control of Flow and Diffusion over Sensitive Surfaces

Selective shielding of surfaces from flow and diffusion is essential in many domains of physics and engineering. We propose and characterize experimentally a framework to shield both flow and diffusion simultaneously within a reshapable fluid volume. To do so, we directly use flow singularities to generate conformal transforms of the diffusion profile, taking inspiration from classical cloaking devices. The properties of microfluidic surface shields as open-space diffusion filters (O-filters) are further investigated. An analytical model is provided, which yields an outstanding match with experimental measurements of both flow and tracer diffusion. Via conformal mapping, these measurements reveal a strong topological link with classical H-filters in microfluidics.

A biomechanical study on the laminate stacking sequence in composite bone plates for vancouver femur B1 fracture fixation

Background and objectivesComposite bone plates are proposed for fracture fixation in periprosthetic femoral fracture. Metallic plates, having high stiffness compared to bone lead to stress shielding, reduce the compression force in the fracture site, affectthe healing process. Reduction of stiffness in the axial direction due to above reason without lowering the stiffness in transverse to avoid much of shear strain and thus avoiding instability at the fracture site leads to selective stress shielding. This can only be achieved through meticulously designed fiber reinforced composite. In the present work varied fiber orientations in the stacked laminates with varied fiber types are employed in a post-operative femur fixation for the in-silico analyses of their effectiveness using finite element analysis. MethodsIn this study a Total Hip Arthroplasty (THA) model is constructed with composite bone plates. Three-dimensional narrow type metal plate is modeled with 12 holes and length of 194 mm. Three different types of composite bone plates are modeled with 12 holes of different size for the analysis i.e. Type 1 (5.6 mm thickness and 16 mm width), Type 2 (6 mm thickness and 16 mm width) and Type 3(6 mm thickness and 18 mm width). Anatomical 3D FE models of THA with composite bone plates are constructed to find out the interfacial stresses and strains. The finite element software ANSYS is used to perform the analysis. ResultsA three-dimensional FE model of immediately post-operative femur fixation is developed and studied the maximum stress distribution, strain and movement in axial/shear direction in the metal and composite bone plate near to the fracture site. In the present study, the metal and composite plate (carbon/epoxy, glass/epoxy and flax/epoxy) used for most common Vancouver type B1 fracture to observe the biomechanical behavior of different models in IPO condition using FEA. ConclusionsOptimizing the fiber orientations of composite bone plates of Total Hip Arthroplasty (THA) model by controlling the biomechanical stresses could be a favorable approach. The finite element analysis approach gives a viable solution to design the composite bone plate and for designing future models that preserves the biomechanical function of THA with composite bone plate.

Effect of the Rotation Angle in Multi-Ring Metallic Meshes on Shielding Effectiveness

Metallic mesh is particularly advantageous for electromagnetic interference shielding in optical transparent devices. In this letter, we propose an equivalent period method (EPM) to achieve fast and effective shielding effectiveness (SE) simulation for multi-ring metallic meshes under various rotation angles, and experimental results indicate that a clear SE difference is observed with the rotation of multi-ring to verify the validity of EPM. The equivalent period can be obtained for multi-ring under different rotation angles by EPM, and the SE can be calculated by combining the equivalent period with the known SE evaluation models. The role of rotation angle for SE difference can be attributed to selective shielding under different polarization states, which can be explained by the negative correlation between the shielding performance and the equivalent period. The results have certain guiding significance for design and simulation of various metallic meshes with the rotatable basic unit.

P-lsGOF: A parallel learning-selection-based global optimization framework

When optimizing complicated engineering design problems, the search spaces are usually extremely nonlinear, leading to the great difficulty of finding optima. To deal with this challenge, this paper introduces a parallel learning-selection-based global optimization framework (P-lsGOF), which can divide the global search space to numbers of sub-spaces along the variables learned from the principal component analysis. The core search algorithm, named memory-based adaptive differential evolution algorithm (MADE), is parallel implemented in all sub-spaces. MADE is an adaptive differential evolution algorithm with the selective memory supplement and shielding of successful control parameters. The efficiency of MADE on CEC2017 unconstrained problems and CEC2011 real-world problems is illustrated by comparing with recently published state-of-the-art variants of success-history based adaptative differential evolution algorithm with linear population size reduction (L-SHADE) The performance of P-lsGOF on CEC2011 problems shows that the optimized results by individually conducting MADE can be further improved.

Spectrally Selective Shielding Material Based on Graphene Photonic Crystal

A novel graphene photonic crystal structure is proposed and designed in this paper; each unit period is composed of graphene, metal, and magnesium fluoride. We investigate the optical properties of this structure in the visible to near-infrared range by means of finite-difference time-domain method. We examined the influence of structural parameters (metal material, thickness, period number, etc.) on the optical response of the structure and found that it can be transparent in visible range and can shield most of the near-infrared rays. As a result, the proposed graphene photonic structure enables potential applications in selective near-infrared shielding material.

Layered hybrid composites using multi-walled carbon nanotube film as reflection layer and multi-walled carbon nanotubes/neodymium magnet/ epoxy as absorption layer perform selective electromagnetic interference shielding

This work develops a unique layered structural composite to prevent the device from internal electromagnetic (EM) waves’ self-disturbance and external EM wave interference. The composite is composed of two layers, the inner layer is a hybrid composite, using MWCNTs and NdFeB powders as fillers and epoxy as matrix, which is designed as absorbent layer, and the outer is MWCNT-coated non-woven fabric, which is treated as reflection layer. The inner layer containing MWCNTs and magnetic powder of NdFeB can firstly absorb parts of EM waves generating from inside devices, and when the rest EM waves transmit through the inner layer and impinge to the outer layer, almost all of the waves will be reflected back. The reflected waves will go through the inner layer and be absorbed again. In the meanwhile, as the external EM waves impinge to the outer layer, they will be reflected immediately. The optimal combination of this study is able to achieve over 92% (−23.09 dB) absorption and leave least than 8% (−11 dB) reflection of internal EM waves, and over 99.99% reflection of external EM waves.

Transparent heat insulation coatings with high selective shielding ability designed with novel superstructures of copper sulfide nanoplates

In the present work, novel CuS superstructures composed of intersectional CuS nanoplates (CuS i-nanoplates) and snowflake-like CuS nanoplates (CuS s-nanoplates) were successfully synthesized at a low temperature (80 °C) by a simple chemical precipitation method. It has been found that the as-synthesized CuS superstructures were formed by the growth of CuS i-nanoplates along the direction perpendicular to the basal nanoplate with a thickness of 29.64 ± 3.16 nm and CuS s-nanoplates were prepared with the snowflake-like morphology with a thickness of 16.82 ± 3.62 nm. Subsequently, a new transparent heat insulation coating with CuS superstructures composed of CuS i-nanoplates as NIR shielding agent (coded as H–X coating) was prepared by mixing with acrylic-amino-alkyd baking varnish and coating to ordinary glass substrates. Simultaneously, another transparent heat insulation coating with s-nanoplates (coded as S–X coating) was also synthesized. Optical properties of those coatings were studied as a function of the CuS content by using ultraviolet–visible–near-infrared spectrophotometer. And the H–X coatings were shown to have a higher selective shielding ability for solar light than S–X coatings since the shielding ability of S–X coatings in the region of 1180–2500 nm rapidly weakened with increasing wavelength. The comparative study on the properties of nanomaterials with different morphologies in this paper may provide some new guidance for material design to improve its performance. Moreover, the CuS superstructure-based transparent heat insulation coatings with excellent NIR shielding property have a potential application in energy-saving windows for architectures and vehicles.

Woven metamaterials with an electromagnetic phase-advance for selective shielding

This study deals with the development of a large woven metamaterial surface for applications in the submillimeter frequency band. Before weaving, design of the metamaterial textile is investigated to obtain a phase-advance near 500 GHz. Then, a large sample is produced by semi-industrial machine and characterized in terms of dimensional homogeneity and electromagnetic behaviours in the frequency band [325 – 700 GHz]. Dimensional heterogeneity is measured to be less than 2% and shows that weaving process is well controlled. A phase-advance and high-pass filter behaviors are experimentally evidenced by electromagnetic characterizations with potential applications for selective shielding and phase manipulation of the wave.

Selective Shielding of Bone Marrow: An Approach to Protecting Humans from External Gamma Radiation.

The current feasibility of protecting emergency responders through bone marrow selective shielding is highlighted in the recent OECD/NEA report on severe accident management. Until recently, there was no effective personal protection from externally penetrating gamma radiation. In Chernobyl, first-responders wore makeshift lead sheeting, whereas in Fukushima protective equipment from gamma radiation was not available. Older protective solutions that use thin layers of shielding over large body surfaces are ineffective for energetic gamma radiation. Acute exposures may result in Acute Radiation Syndrome where the survival-limiting factor up to 10 Gy uniform, homogeneous exposure is irreversible bone marrow damage. Protracted, lower exposures may result in malignancies of which bone marrow is especially susceptible, being compounded by leukemia's short latency time. This highlights the importance of shielding bone marrow for preventing both deterministic and stochastic effects. Due to the extraordinary regenerative potential of hematopoietic stem cells, to effectively prevent the deterministic effects of bone marrow exposure, it is sufficient to protect only a small fraction of this tissue. This biological principle allows for a new class of equipment providing unprecedented attenuation of radiation to select marrow-rich regions, deferring the hematopoietic sub-syndrome of Acute Radiation Syndrome to much higher doses. As approximately half of the body's active bone marrow resides within the pelvis region, shielding this area holds great promise for preventing the deterministic effects of bone marrow exposure and concomitantly reducing stochastic effects. The efficacy of a device that selectively shields this region and other radiosensitive organs in the abdominal area is shown here.

Reduction of wireless signals in indoor environments by using an active frequency selective wall based on spectrum sensing

SummaryThis paper presents a wireless local area network (WLAN) spectrum control system that uses active frequency selective shielding walls to selectively reduce or pass WLAN signals in the 5 GHz band indoors. The proposed system utilizes a well‐known active frequency selective structure based on a rectangular loop with PIN diodes and is thus capable of either reducing or passing the WLAN frequency by using the on/off switching of the PIN diode based on the measured electric field strength in indoor. We designed and simulated the proposed active frequency selective shielding wallpaper by using commercial electromagnetic simulation software and confirmed that the proposed structure can reduce the WLAN signal by switching the PIN diode by applying the manufactured prototype on the exterior of an experimental apparatus containing a WLAN receiver antenna that is capable of measuring the received electric field strength. Extension of the results presented herein can be applied to reduce the wireless signal to enhance the spectrum efficiency of an indoor space.

Preparation and transparent heat insulating properties of aqueous acrylic–amino–alkyd coatings with CuS nanoplates

A novel aqueous transparent heat insulation coating (C–X–Y) with CuS nanoplates as solar heat insulating functional nanomaterial and acrylic-amino-alkyd baking varnish (AAA) as coating-forming material was prepared. The C–X–Y coating was applied to the surface of ordinary glass substrates. Those C–X–Y coated glass substrates have good transparency in the visible region (390–780 nm) and strong absorption in the near-infrared region (780–1750 nm). For instance, a 150 μm-thick C–X–Y coating with 1.0 wt% CuS nanoplates (C–1.0–150) can transmit 60% visible light and shield 80% near-infrared light. The stable temperature inside the box covered with the C–X–Y coating C–1.0–150 was 12.0 °C lower than that with the reference coating (without nano-CuS) under the irradiation of a 250 W infrared lamp. Based on their special characteristics, such as selective transparency in the visible region and selective shielding in the near-infrared region of solar light, the CuS nanoplates based transparent heat insulation coatings might have a potential application in architectures and vehicles for energy saving and environmental protection due to the unique optoelectronic properties of the CuS nanoplates.

Electromagnetic properties of carbon nanotube reinforced concrete composites for frequency selective shielding structures

Carbon nanotube reinforced concrete composites (RCC) were characterized in microwave bands currently employed in wireless telecommunication systems. Dielectric permittivity was retrieved by waveguide method and adopted to compute shielding effectiveness of RCC structures having different thickness/filler content. The shielding was also evaluated by reverberation chamber set up; theoretical calculations and measured values are in close agreement, thus testifying to the procedure reliability. Finally, a frequency selective absorber made of RCC layers was designed with the aid of a numerical optimization tool (particle swarm algorithm); the discussion of results is supported by a finite element method analysis of the layered structure.

Synthesis and microwave absorption properties of coiled carbon nanotubes/CoFe2O4 composites

Coiled carbon nanotubes (CCNTs) were coated by CoFe2O4 (CFO) nanoparticles to form the CCNTs/CFO composites. The phase composition, morphology, electrical and magnetic performances of the composites were characterized by means of modern analytical techniques. The results indicated that the conductivity and magnetic performances of the samples were related to their compositions. The CCNTs/CFO composite with ωCCNT/ωCFO of 0.4 exhibited the best microwave absorption property in the prepared samples, whose minimum reflection loss was about −14dB in the frequency range of 2–18GHz for a layer of 2.5–3.0mm thickness, and the available bandwidth corresponding to RL less than −10dB can reach 4.0GHz. Hence, the obtained composite could be used as a new candidate for selective frequency shielding and lightweight microwave absorbing material.