Showing papers on "Shields published in 2023"
TL;DR: In this article , the roles of wood biomass-derived carbon in various EMW absorbing and shielding materials were emphasized, along with an analysis of related studies, and the main obstacles and the prospects of wood-biomedical derived carbon were proposed.
4 citations
TL;DR: In this paper , the authors report the study and the analyses behind this modification, which impacts on the original already complex magnetic configuration, made particularly difficult by the limited space available and the high voltages.
3 citations
TL;DR: In this article , a technique for manufacturing flexible electromagnetic shields based on resistive materials ( powdered charcoals and sheet foil), as well as the results of experimental justification of the use prospects of this technique in the development of new functional materials are presented.
Abstract: The article introduces the technique for manufacturing flexible electromagnetic shields based on resistive materials ( powdered charcoals and sheet foil ), as well as the results of experimental justification of the use prospects of this technique in the development of new functional materials . This justification consisted of : 1) manufacturing of the experimental samples in accordance with the presented technique ; 2) carrying out the measurements of the electromagnetic radiation reflection and transmission coefficient values in the frequency range of 0.7–17.0 GHz of the manufactured experimental samples . It was discovered that flexible electromagnetic shields based on the powdered charcoals manufactured in accordance with the presented technique are characterized by the electromagnetic radiation reflection coefficient values in the frequency range of 0.7–17.0 GHz , reaching –10.0 dB , when electromagnetic radiation reflection coefficient values reach –20.0 dB . Due to this fact it is possible to r ecommend to use them in order to ensure electromagnetic compatibility of radioelectronic equipment and to protect people from exposure to radiation , emitted by such equipment , as well as to hide ground objects from detection in the radar wavelength range .
2 citations
TL;DR: In this article , the authors present the effectiveness of a combined radiation shield containing an active toroidal shield with a layer of passive shield made of different polymers or low-density hydrides.
Abstract: Exposure to Galactic cosmic rays (GCR) and solar particle events (SPE) has been identified as one of the critical barriers for long term space missions that impose both immediate and delayed health hazards on the astronauts. There are two types of protective shields available namely active and passive shields, and combining these two shields can be a useful strategy. The study aims to present the effectiveness of a combined radiation shield containing an active toroidal shield with a layer of passive shield made of different polymers or low-density hydrides. The active shield is capable of deflecting protons (Z < 1) with energies below 700 MeV/n and for Alpha, and Fe ions (Z > 1) it can deflect up to 200 MeV/n and 175MeV/n respectively. The shielding effectiveness of polymers and hydrides with different thicknesses was investigated with Monte Carlo simulations performed by means of Geant4/MULASSIS. The shielding properties were studied using proton, alpha, and Fe ions with energies of 1 GeV/n. Nuclear stopping power and Fast Neutron Removal Cross Section (FNRCS) were calculated using SRIM and PHY-X/PSD. For the 20 gm/cm2 thick layer made of polymers, the reduction of dose equivalent for proton, alpha, and Fe ion of 1GeV/n are 5.44%, 54.34%, and 63.76% respectively and in the case of Low-density Hydrides with the same dimension, the rates are 4.12%, 55.3%, and 76.88%. Low-density hydrides demonstrated better radiation shielding capability than the polymers. The results are compared with OLTARIS for GCR spectra of 2010 solar minimum. The downsides of this type of shield are also briefly covered.
2 citations
TL;DR: In this paper , the authors summarized the latest advances in additive manufacturing of EMI shielding materials, aiming to provide a deep understanding of the connection between raw materials, manufacturing methods, design considerations, and performances of the fabricated EMI shields.
1 citations
TL;DR: In this paper , the contribution of positrons to the skin irradiation was investigated using the Varskin+ code, and the skin doses were calculated for syringes of various sizes, filled with 18F, 11C or 68Ga solution.
1 citations
01 Jan 2023
TL;DR: In this paper , a linearly decreasing inertia weight particle swarm optimization (LDW-PSO) algorithm was proposed to improve the uniformity of the Lee-Whiting coil.
Abstract: The magnetic field performance of the uniform coils will be affected by magnetic shields and produce errors in the atomic magnetometer. It is necessary to analyze the influencing factors and guide the coil design. Aiming at the above shortcomings, this paper analyzes the coupling effect of magnetic shield and coil and proposed a Lee-Whiting coil design method based on the linearly decreasing inertia weight particle swarm optimization (LDW-PSO) algorithm. Firstly, the magnetic field model under the ferromagnetic boundary is established, and the effects of the size, thickness and permeability of the magnetic shield on the magnitude and uniformity of the Lee-Whiting coil magnetic field are analyzed. The results show that the coupling coefficient of the coil changes monotonically with the change of the size of the magnetic shield, while the uniformity error has a minimum value with the change of the size of the shield. In addition, an improved Lee-Whiting coil is designed by combining the LDW-PSO algorithm, which improves the uniformity of the coil. Compared with the original coil, the measured uniformity error of the improved coil is reduced from 8.39×10−4 to 2.81×10−4. The accuracy of the theoretical analysis is verified by experiments. This paper is of great significance to study the coupling and optimization design of the coil based on the magnetic shields in atomic magnetometers.
1 citations
TL;DR: In this paper , the time to failure in space due to screen grid erosion and electron backstreaming caused by accelerator grid aperture erosion was found to be important only at the lowest throttle levels, and was conservatively estimated to lead to failure after processing over 900 kg of xenon.
Abstract: Abstract NASA’s Evolutionary Xenon Thruster (NEXT) is a candidate for future deep space missions that offers high efficiency and specific impulse over a large power throttling range. One of the key life-limiting components is the ion accelerator system, which is subject to sputter erosion by low energy discharge plasma ions incident on the upstream screen grid and higher energy charge exchange ions that impact the downstream accelerator grid. The grid erosion codes CEX2D and CEX3D were validated with data from tests of NEXT as well as the NSTAR ion thruster and then used to assess the time to failure in space due to screen grid erosion and electron backstreaming caused by accelerator grid aperture erosion. Screen grid erosion was found to be important only at the lowest throttle levels, and was conservatively estimated to lead to failure after processing over 900 kg of xenon. The first failure mode at high power levels was found to be electron backstreaming due to accelerator grid hole wall erosion, which would occur after processing over 700 kg of propellant.
1 citations
TL;DR: In this article , a numerical model for fiber-reinforced composite shields under hypervelocity impact was established by combining the finite element and smoothed-particle hydrodynamics adaptive method and existent mesoscale models.
1 citations
TL;DR: In this article , the authors designed an appropriate neutron and gamma radiation shield for the HPGe detector to be used in the PGNAA facility in the Isfahan MNSR reactor.
Abstract: The purpose of this study was to design an appropriate neutron and gamma radiation shield for the HPGe detector to be used in the PGNAA facility in the Isfahan MNSR reactor. In order to improve the parameters related to shield design, including the thickness of the material used in the design, the different type of materials considered and the relative reduction of neutron and gamma dose, shields were simulated by MCNPX code and the results of calculations were compared. It was concluded that the optimal thickness of lead as gamma absorber is 4 cm and the optimal thickness of borated polyethylene as neutron absorber is 10 cm. In this case, the neutron and gamma dose rate at the location of the detector inside the shield was equal to 5.11 μSv.h−1 and 7.5 μSv.h−1, respectively. Also, according to the investigations conducted for different materials as neutron absorbers, it was found that the best absorber for neutrons is borated polyethylene, which absorbs more neutrons and produces less secondary gamma than other materials and the best absorber for gamma is bismuth. The shielding has brought the relative percentage of neutron and gamma dose reduction about 90%.
1 citations
TL;DR: Wang et al. as discussed by the authors proposed an innovative structural retrofit by adding wind shields with simple structure for both single and double air inlet cooling towers, which can eliminate transverse vortices to improve the distribution homogeneity of airflow velocity and water temperature.
TL;DR: In this article , the principles of EMI shields along with their design and state-of-the-art basis and material architecture along with the drawbacks in research on EMI shield are discussed.
Abstract: Electromagnetic interference (EMI) shielding effectiveness (SE) systems have received immense attention from researchers owing to the rapid development in electronics and telecommunications, which is an alarming matter in our modern society. This radiation can damage the performance of EM devices and may harmfully affect animal/human health. The harmonious utilization of magnetic alloys and conducting but nonmagnetic materials (such as carbon/graphene) is a practical approach toward EMI SE. This review is not exhaustive, although it is comprehensive and aimed at all materials for EMI SE especially graphene-based polymeric composites. It encompasses multifunctional and functional structural EMI shields. These materials comprise polymers, carbons, ceramics, metals, cement composites/nanocomposites, and hybrids. The accessibility of abundant categories of carbon-based materials in their microscale, nanoscale, and quantum forms as EMI shields as polymer–carbon, cement–carbon, ceramic–carbon, metal–carbon, and their hybrids, makes them receive much attention, as a result of their unique amalgamation of electrical, magnetic, dielectric, thermal, and/or mechanical properties. Herewith, we have discussed the principles of EMI shields along with their design and state of the art basis and material architecture along with the drawbacks in research on EMI shields.
19 Jan 2023
TL;DR: In this article , the authors describe a prototype shield system that can be additively manufactured and installed while the vehicle is in orbit, which would allow an operator to add shielding to a vehicle once in orbit and protect it against MMOD traveling at hyper velocities.
Abstract: As time progresses, space becomes more congested with micrometeoroids and orbital debris (MMOD). This increase in debris flux poses a critical threat to satellites already in orbit, manned missions, and future orbiting spacecraft. To reduce the operational impact of MMOD collisions, current protection schemes use Whipple Shields, an aluminum plate with a prescribed standoff distance, as the basis for protection. These aluminum shields are manufactured and installed on the space vehicle while on Earth, which constrains their size and shape, and ultimately, their effectiveness. These fixed shields also cannot be repaired if they are damaged during service. This work describes a prototype shield system that can be additively manufactured and installed while the vehicle is in orbit. This system, designed for manufacture via three-dimensional printing in space, would allow an operator to add shielding to a vehicle once in orbit, protecting it against MMOD traveling at hyper velocities. These on-orbit manufactured shields allow specific tailoring to more-efficiently and effectively meet mission requirements. CTH finite element code was used to simulate hypervelocity impacts (HVI) on computer-aided design (CAD) models of the prototypes. These simulations used structures made of analogous materials such as polycarbonate to make and evaluate new design parameters. The performance of different design parameters in simulations drove a redesign of the original prototype. These new designs were additively manufactured with ULTEM 9085 and underwent testing at a hypervelocity impact laboratory. Six prototypes were tested and successfully survived a hypervelocity projectile impact, indicating their potential effectiveness as spacecraft MMOD shielding.
01 Apr 2023
TL;DR: In this article , the external bus and conductive rod of a vacuum circuit breaker form a U-shaped circuit, which generates an external transverse magnetic field in the arc area of the arc extinguishing chamber.
Abstract: The external bus and conductive rod of a vacuum circuit breaker form a “U” shaped circuit, which generates an external transverse magnetic field in the arc area of the arc extinguishing chamber, resulting in severe asymmetry of the transverse magnetic field in the arc area, reducing the breaking capacity and service life of the circuit breaker. In the paper, we use Maxwell to establish a transverse magnetic field model for single-phase short circuit arc region. The analysis revealed that transverse magnetic field in the arc region is severely asymmetric under the effect of the transverse magnetic field generated by the external bus. So as to eliminate the effect of external transverse magnetic field, this paper has constructed stainless steel and iron shield shields to shield the external transverse magnetic field. The results show that both stainless steel and iron shields can shield against transverse magnetic fields, but the effect of iron shields with high magnetic permeability is more obvious. The research results of this paper provide important basis and reference for eliminating the external transverse magnetic field in the arc region, improving the breaking capacity and service life of circuit breakers.
TL;DR: In this article , the use of aluminum alloy parts for combined mine protection of armored combat vehicles was considered, and the effect of explosion load parameters on the model acceleration was studied using an EinScan Pro 2X Plus 3D scanner.
Abstract: This paper considers the use of aluminum alloy parts for combined mine protection of armored combat vehicles. The study was concerned with anti-mine shields mounted on an armored combat vehicle body model. The model was made of 16 mm armor steel. The total mass of the model (without an anti-mine shield) was 31.1 kg. An anti-mine shield was gripped between two frames and secured with bolts. To eliminate the effect of the soil on the test results, the explosive charges were installed on a 70 mm metal plate. The charges were initiated with an ED-8Zh electrodetonator. TG-50/50 explosive was used. A DYTRAN 3200B acceleration sensor was mounted at the center of the model, and the sensor signal was measured using an experimental system. To assess the model acceleration without any energy loss by elastic or plastic deformations, the acceleration of the model with a rigid anti-mine shield (a rigid armor steel plate of thickness 10 mm and mass 10.7 kg) was assessed. A finite-element simulation of the model was conducted. The effect of explosion load parameters on the model acceleration was studied. The simulated and the actual deflections were compared using an EinScan Pro 2X Plus 3D scanner. The speed and the acceleration of the model with a rigid and a plastic anti-mine shield were simulated and measured. The results showed that annealed parts made of Al-Mg alloys, in particular AMg6 alloy, absorb the explosion energy better. Any of the anti-mine shields made of AMg6 alloy reduces the acceleration at the center of the plate and thus the load on the armored vehicle body by a factor of 20…25 in comparison with the anti-mine shields made of armor steel. It was shown that annealing best provides the required physical and mechanical characteristics of the load-bearing parts of anti-mine shields, it is advisable to shape and structurize their porous energy-absorbing elements by pressing up to 33 MPa, it is most advisable to paste the porous energy-absorbing elements to the load-bearing parts, and after separate tests of load-bearing part and porous energy-absorbing element material specimens it is advisable to try out combined constructions of anti-mine shields for armored combat vehicles of different purposes.
TL;DR: In this paper , five polymer composite shields reinforced with tungsten were selected and their effects as gamma shields on fetal dose reduction were investigated and it was observed that polymers named PHEMA-WO3 and RS-U-30 had an excellent shielding ability among the other studied composites.
TL;DR: In this article , the authors proposed a novel method for designing and improving the shielding factor by optimizing the spacing of every pair of adjacent layers within a limited volume, and the final design result of the multilayer cylindrical magnetic shielding features optimally designed varying layer spacings, which are associated with a specific length and diameter.
Abstract: A stable inner working environment is essential for nuclear magnetic resonance sensors, which requires the absence of remnant magnetic fields and fluctuations caused by the surrounding magnetic fields. In this study, we utilized analytical formulations to derive transverse and longitudinal magnetic shielding factors for multilayer cylindrical magnetic shielding. Subsequently, we proposed a novel method for designing and improving the shielding factor by optimizing the spacing of every pair of adjacent layers within a limited volume. The final design result of the multilayer cylindrical magnetic shielding features optimally designed varying layer spacings, which are associated with a specific length and diameter. After optimization, the transverse shielding factor increased by 5.53%, 8.99%, and 13.51% for the three-, four-, and five-layer shields, respectively, compared to traditional magnetic shielding. The opening in the axial center of the magnetic shielding barrel may cause leakage of the magnetic flux and inhomogeneous remnant magnetic induction. We introduced a stovepipe to the end cap of the axial shield based on the finite element method, resulting in an improvement in the homogeneity of remnant magnetic induction. This modification widened the axial uniform region of the innermost shielding layer by approximately 9 cm within 52.5 cm in our simulation. To implement our proposed optimization method, we established and manufactured a four-layer cylindrical magnetic shielding with stovepipes and varying layer spacings. Moreover, the results indicate that this optimal method works for other applications in which multilayer magnetic shielding is required.
01 Jan 2023
12 Jun 2023
01 Jan 2023
TL;DR: In this article , a nuclear power spacecraft model with a width of 6 m and a length of 25 m is built, and the authors study the coverage of the shadow area formed by the shield and distribution of neutron fluence and photon dose in shadow area.
Abstract: The layout of nuclear-powered spacecraft is very different from the layout of nuclear reactors used on Earth, so the design principle is also different. Taking nuclear-powered spacecraft as the object, this paper studies the coverage of the shadow area formed by the shield and distribution of neutron fluence and photon dose in the shadow area. In this paper, a nuclear power spacecraft model with a width of 6 m and a length of 25 m is built. The Monte Carlo method is used to calculate the transport of neutrons and photons, and the distribution of neutrons and photons in space is obtained. The coverage of the shadow area formed by shields with different widths is obtained, and the main factors affecting the width and angle of the shadow area are summarized. When the diameter of the shield decreases, the width of the shadow area also decreases, and the angle of the shadow area decreases, which greatly reduces the area of the shadow area. The distribution of neutron fluence and photon dose in the shadow area is obtained. At the end of the truss, the maximum value of the photon dose is 1.03 × 10-4 Gy∙s-1, and the average value is 6.42 × 10-5 Gy∙s-1. The maximum value of the neutron fluence rate is 1.01 × 104 n∙cm-2∙s-1, and the average value is 6.18 × 103 n∙cm-2∙s-1. And the influence of spacecraft structure on radiation is analyzed. The truss and droplet emitters have a greater impact on photons, and the heat sink and droplet emitters have a greater impact on neutrons. Based on the above work, a local shield scheme is proposed to reduce the mass. After being blocked by local shield, the photon dose is reduced to 1/10 and the neutron fluence rate is reduced to 1/6.
TL;DR: In this article , a soft spall liner material is used in composite body armor to support defense-related ballistics, which can be used as a model for lightweight, affordable and safe designs for military troops in times of conflict.
Abstract: It is essential to have materials that can support armor systems for the application of body armor composed of anti-ballistic material from coated fibers in trials in order to defend military personnel with better ballistic performance who are lighter against growing threats and conflicts. to support defense-related ballistics. New materials used in personnel protection systems are the subject of this discussion. As ballistic shields, fiber composite materials are currently used due to their light weight and high flexibility. This essay also discusses a thorough analysis of mechanism performance and failure. This study's goal is to advance knowledge about composite material body armor that is covered with a soft spall liner material, which can be used as a model for lightweight, affordable, and safe designs for military troops in times of conflict.
TL;DR: In this paper , the authors presented the design process of a structure that shields the electromagnetic field from the fifth-generation transmitter operating in the 3.5 GHz band, and the results of the computer simulations show that the power density in the eye region can be reduced by almost seven times compared with the unshielded case.
Abstract: This article presents the design process of a structure that shields the electromagnetic field from the fifth-generation transmitter operating in the 3.5 GHz band. The purpose of this project is the limitation of power density in the eye region. For this reason, the structure is made of conducting wires forming a grid that is semitransparent to the light. The design was performed using computer simulations with a finite-difference time-domain method and an evolutionary-based optimization methodology. A simplified model of the face and eyes was developed to reduce the amount of time needed for the simulation. The construction of the shielding structure presented here can be easily fabricated in the form of protective goggles. The results of the computer simulations show that the power density in the eye region can be reduced by almost seven times compared with the unshielded case.
06 Feb 2023
TL;DR: In this paper , the authors present a scheme to enhance the atom number in magneto-optical traps of strontium atoms operating on the 461 nm transition by resonantly driving the $1$S$_0\to^3$P$_1$ intercombination line at 689 nm, which continuously populates a short-lived reservoir state and, as expected from a theoretical model, partially shields the atomic cloud from losses arising in the cooling cycle.
Abstract: We present a scheme to enhance the atom number in magneto-optical traps of strontium atoms operating on the 461 nm transition. This scheme consists of resonantly driving the $^1$S$_0\to^3$P$_1$ intercombination line at 689 nm, which continuously populates a short-lived reservoir state and, as expected from a theoretical model, partially shields the atomic cloud from losses arising in the 461 nm cooling cycle. We show a factor of two enhancement in the atom number for the bosonic isotopes $^{88}$Sr and $^{84}$Sr, and the fermionic isotope $^{87}$Sr, in good agreement with our model. Our scheme can be applied in the majority of strontium experiments without increasing the experimental complexity of the apparatus, since the employed 689 nm transition is commonly used for further cooling. Our method should thus be beneficial to a broad range of quantum science and technology applications exploiting cold strontium atoms, and could be extended to other atomic species.
TL;DR: In this article , a carbon-fiber-reinforced polymer (CFRP) laminate with additional Cu mesh layers was investigated for use as an electromagnetic interference (EMI) shield in aerospace applications.
14 Mar 2023
TL;DR: In this article , the magnetic shielding performance of the same device can be affected by different degaussing and test conditions, which remains to be systematically studied, and the results show the influence of these different conditions on the shielding performances of the cubic device, consistent with the numerical calculation.
Abstract: In recent decades, magnetic shields have provided basic experimental environments for the measurements of extremely weak magnetic fields represented by the biological magnetic signal. Excellent shielding performances, including the low residual field and high shielding factor (SF), are necessary to ensure the quality of these weak magnetic signals and avoid the interference of external magnetic fields. The magnetic shielding performance of the same device can be affected by different degaussing and test conditions, which remains to be systematically studied. In this paper, experiments with variable magnetization conditions, including different degaussing orders, test fields and environmental fields, are established in a nearly zero-field space to simulate the different situations during measurement. The residual field and SF of the cubic shielding device are tested in these cases. Meanwhile, these shielding performances are analyzed from the perspective of the magnetization state and calculated based on the magnetic properties which are tested and fitted by the Jiles–Atherton model. The results show the influence of these different conditions on the shielding performances of the cubic device, consistent with the numerical calculation. Under the same environmental field, the different degaussing order and test field lead to completely different residual field and shielding performance, respectively. The influence of the Earth’s magnetic field on the SF can be ignored due to its tiny equivalent bias field determined by the anhysteretic magnetization curve.
TL;DR: The early discovery of the 64 Viking Age round shields from the Gokstad ship burial has almost singularly shaped our understanding of the construction and role of shields from this period as mentioned in this paper .
Abstract: The early find of the 64 Viking Age round shields from the Gokstad ship burial has almost singularly shaped our understanding of the construction and role of shields from this period. Despite their significance, however, the shield material has never been published in full nor been subjected to any substantial examination since their discovery in 1880. The current understanding of the shields is thus highly limited, tainted also in part by the preconception that they potentially represent ceremonial shields for the burial rite as well as assumptions of homogeneity. This preliminary study critically assesses these preconceptions and presents the results from a re-examination of the shield boards from the Gokstad ship burial. Despite their fragmented state, these artefacts significantly contribute to a more nuanced understanding of shield constructions of the Viking Age, especially when coupled with other well-preserved archaeological shield finds and the scholarly corpus available on such shields. As such, the preliminary findings of this paper offer new insights into the complexities of Viking Age shield technologies and their use in funerary rites, underlining the need for more comprehensive treatment of this material in the future.