Showing papers on "Shields published in 2021"

Limits of Low Magnetic Field Environments in Magnetic Shields

Abstract: During the last decades, the development of increasingly sensitive magnetic sensors led to numerous applications of magnetic field measurements in neuro-science, medical diagnostics, brain-computer interfaces, metrology or for experiments testing the fundamental laws of nature. Especially the development of small, lightweight, rather mobile and easy to handle optically pumped magnetometers allows for more advanced and dynamic studies of, for e.g., the brain. The limitation for the quality of such magnetic signals are gradients and drifts in the measuring environment. This article combines the result of many years of work, resulting in calculations to quantitatively predict the areas with ultra-low magnetic fields inside passive magnetic shields, as well as the experimental confirmation. The calculation shows that a conventional three-layer chamber with an improved degaussing system will already provide environmental conditions never reached before. In the most recent implementation an unprecedented residual field of $ 130 pT was repeatedly achieved over 0.5 x 0.5 x 0.5 m inside an easily accessible space, consistent with the numerical modeling.

Analysis of coil constant of triaxial uniform coils in Mn–Zn ferrite magnetic shields

Abstract: Triaxial uniform coils housed in magnetic shields are extensively used in atomic sensors. The coil constant can be affected by the magnetic shield that imposes a ferromagnetic boundary. This study numerically and experimentally analyzes the coil constant dependence on the Mn–Zn ferrite magnetic shield thickness, aspect ratio, air gaps between the magnetic annuli, and the distance from the coils. Results show that the radial coil constant (saddle-shaped coil) only depends upon the distance between the coil and the magnetic shield. The axial coil constant (Lee–Whiting coil) depends on the aspect ratio, distance between the coil and the magnetic shield, and air gap width between the magnetic annuli. The axial coil constant is linearly related to the air gap. When the thickness of the magnetic shield is greater than 2 mm, the radial and axial coil constants are independent of the shield thickness. The difference between the simulated and measured values is only 3.9%. The numerical calculation accuracy was verified by experimental measurements. This study can aid in the design and research of coils in the ferrite magnetic shield in atomic sensors.

Assessment of Critical Shear Stress and Threshold Velocity in Shallow Flow with Sand Particles

Abstract: In this study, the incipient motion of four groups of sand, ranging from medium to very coarse particles, was experimentally examined using an acoustic Doppler velocimeter (ADV) in different water depths under the hydraulically transitional flow condition The transport criterion of the Kramer visual observation method was used to determine threshold conditions Some equations for calculating threshold average and near-bed velocities were derived Results showed that the threshold velocity was directly proportional to both sediment particle size and water depth The vertical distributions of the Reynolds shear stress showed an increase from the bed to about 01 of the water’s depth, after performing a damping area, then a decrease toward the water surface By extending the linear portion of the Reynolds shear stress in the upper zone of the damping area to the bed, the critical shear stress, particle shear Reynolds number, and critical Shields parameter were calculated Results showed that the critical Shields parameter was located under the Shields curve, showing no sediment motion This indicates that the incipient motion of sediment particles occurred with smaller bed shear stress than that estimated using the Shields diagram in the hydraulically transitional flow region The reason could be related to differences between the features of the present experiment and those of the experiments used in the development of the Shields diagram, including the approaches to determine and define threshold conditions, the accuracy of experimental tools to estimate critical shear stress, and sediment particle characteristics Therefore, the change in the specifications of experiments from those on which the Shields diagram has been based led to the deviation between the estimation using the Shields diagram and that of real threshold conditions, at least in the hydraulically transitional flow region with sand particles

Benzoxazine resin as an interesting building block for advanced neutrons shields

Abstract: The design of lightweight neutrons shields has been restricted for quite some time to the use of the epoxy thermosets as the main building blocks. Meanwhile, the recent developments in the field of...

Force and torque model sensitivity and coarse graining for bedload-dominated sediment transport

Abstract: We present results from Euler–Lagrange simulations of turbulent flow over an erodible monodisperse bed of particles at a shear Reynolds number of R e τ = 180 . The Galileo number G a and the ratio of Shields to the critical Shields number Θ / θ c r were varied in the range 11.4 to 29.8 and 1.32 to 5.98, respectively. Two drag force models were investigated along with the influence of lift, particle rotation, and tangential collision forces for each model. Both models give similar results as far as mean particle flux and Shields stress are concerned, however we find that excluding particle rotation, without ignoring the associated tangential collisional force, significantly reduces the particle flux with little influence on Shields stress. On the other hand, when both particle rotation and tangential collision forces are not taken into account, the particle flux is practically unchanged, but the excess Shields stress slightly increases compared to the case where both effects are considered. We also find the lift force to substantially influence particle flux. Additionally, we show the importance of spatial coarse graining and time averaging for Euler–Euler simulations and quantify the reduction in scatter for space and time dependent variables such as sediment flux, Shields stress, and bed surface fluid velocities.

Lightning-Induced Magnetic Fields Inside Grid-Like Shields: An Improved Formula Complemented by a Polynomial Chaos Expansion

Abstract: In industrial facilities, evaluating the magnetic fields induced inside reinforced concrete buildings struck by lightning is fundamental to define protection measures. Since carrying out full-wave simulations is not always feasible nor practical daily, we propose a variant of the formula given in the standard IEC 62305-4 to calculate the peak values of the magnetic field strength inside grid-like shields formed by the reinforcing steel bars of the buildings. The formula is complemented by a sparse polynomial chaos expansion (PCE) to take into account various geometrical configurations of the grid-like shields. The PCE can be used independently to extrapolate the peak values from the results of either the formula or another computational method. The error of the formula and the PCE are estimated based on the simulation of the reinforcement of ten full-scale buildings for the first, and using alternative PCEs and Monte Carlo sampling for the second.

A conceptual study to characterize properties of space debris from hypervelocity impacts through Thin Film Heat Flux Gauges

Abstract: The ever-increasing number of earth-orbiting spacecraft and related space junk is resulting in a dramatic rise in the risk of space debris impacting and damaging satellites and thereby negatively affecting the regular execution of several services provided by space-borne infrastructures. In the past years, the satellite market experienced a paradigm shift with the rise of small satellites and constellations formed by hundreds of satellites. It is anticipated that by the end of this decade, more than a thousand satellites per year will be launched, representing a potential market of more than $300 billion. With continued miniaturization of devices and the evolution of new mission requirements that rely on advanced sensor technology, future spacecraft will have an increasing density of devices and sensors. Moreover, a great research effort is required to improve the efficiency and reduce the weight of spacecraft shields. One route to achieve these goals is developing smart shields able to estimate the level of damage following the impact. In this context, the paper investigates a proof of concept based on the design, manufacture and testing of a measurement system, based on Thin Film Heat Flux Gauges (TFHFG), to assess the damage posed by orbital debris to the satellite shields upon Hyper Velocity Impacts (HVI). The system aims to measure the local increase in shield temperature, which is correlated to the kinetic energy of the debris. Following design and manufacturing, the proposed sensors were calibrated and mounted on a ductile aluminum alloy target, representative of the spacecraft shields, and subjected to a campaign of HVI tests. The results highlight that the signal is composed by the mechanical and thermal contribution, with a dominant mechanical factor.

Sensitivity Analysis of the Transfer Impedance of Shielded Cables With Braided Shields Using a Parameterized FEM Model

Abstract: A parameterized finite-element model of braided cable shields is developed to investigate the analytical model and study the influence of parameter and material dependencies of the transfer impedance of braided cable shields. The parameter influences and their interrelations are analyzed by the use of global sensitivity analysis. Measurements are only needed for the validation of the finite-element model but not for parameter variations. This reduces time and costs and eliminates measurement uncertainties occurring at different measurement procedures.

Quality Assurance of Personal Radiation Shield for Kilovoltage Photon: A Multicentre Experience.

Abstract: Purpose To optimize the maintenance of radiation shields, this study aims to analyze annual inspection files to assess the integrity of radiation shields and their associated factors with regard to defects in radiation shields in clinical settings. Methods A multicenter cross-sectional study was conducted at hospitals in Saudi Arabia. The data from annual inspection files of 1019 clinical lead radiation shields were analyzed. The factors of shield shape, unit where a shield is used, shield thickness, short-term use and number of users were examined. In addition to the inspection file analysis, radiation attenuation measurements were obtained for a subset of shields to compare newly purchased shields with older shields. Statistical analyses were performed using Fisher's exact test and a t-test. Results The results show that the highest percentage of failing shields were found in the emergency unit, fluoroscopy unit and operation room with a failure of approximately 7.14%, 5.61%, and 3.98%, respectively, of these shields. Fluoroscopy and operation room units were statistically significantly associated with shield defects. There was no association between shield damage and shape of shield, shield thickness, short-term use or number of users. Radiation attenuation measurements were similar for new and older shields. Conclusion As fluoroscopy units and operating rooms have a higher percentage of damaged shields, it is recommended that the shields employed in these units should be regularly inspected more frequently than once a year. The study highlights that the shields' age, transmission measurements that confirm that the correct shields are purchased according to the required kVp, physical appearance, and cleanliness should be recorded in annual inspection files. This study highlights the need for uniform inspection files of radiation shields across hospitals. National and international organizations may apply these findings to develop appropriate recommendations.

Development and study of multilayer electromagnetic radiation shields based on powdered oxide-containing materials

Abstract: The electromagnetic shields in the form of two-layer structures, the surface layer of which was the composite material with filler based on powdered titanium dioxide, and the inner one was the composite material with filler based on iron oxide, have been developed. The electromagnetic radiation reflection and transmission characteristics of the developed shields have been studied in the frequency range 0.7-142.8 GHz depending on the content of their inner layers. It has been found that electromagnetic radiation reflection and transmission coefficient values in the frequency range 0.7-142.8 GHz of the developed shields are –4.0...–27.0 dB and –10.0...–40.0 dB respectively. It has been experimentally proved that by impregnating by the calcium chloride aqueous solution of the powdered material that is part of the inner layer of such shields, it is possible to reduce by 5.0...45.0 dB of their electromagnetic radiation transmission coefficient values in the frequency range 2.0...26.0 GHz.

Protective properties of pleated wire mesh shields for spacecraft protection against meteoroids and space debris

Abstract: The use of spacecraft shield protection against orbital debris and micrometeoroids in the design of a spacecraft involves optimizing its mass. Study of the metal mesh protective shields confirmed their higher efficiency compared to the solid shields. Increasing the resistance of protective shields can be achieved, in particular, by using various geometric features of their component parts (mutual arrangement of layers, angle of inclination). In this paper, using high-velocity impact tests, the sturdiness of the authors ’ patented pleated wire mesh shield is investigated. The protective properties of the proposed construction have been confirmed to be increased in comparison with conventional mesh shields of equal specific gravity.

Life Cycle Assessment of Flexible Electromagnetic Shields

Abstract: Nowadays, fiber based flexible electromagnetic shields have widespread applications in ensuring Electromagnetic Compatibility (EMC). Shielding is a solution of EMC, and the main methods to estimate shielding effectiveness are represented by the circuit method and the impedance method. Magnetron sputtering of metallic layers represents a novel technique to impart electric conductive properties to fabrics. Coating of fabrics represents a second main option to manufacture textile shields beside the insertion of conductive yarns in the fabric structure. Life Cycle Assessment (LCA) is often used to assess a comparatively modern with a classical manufacturing process in order to prove its eco-friendly character. This chapter comparatively assesses flexible EM shields manufactured of fabrics with inserted conductive yarns with and without magnetron plasma coating. The copper plasma coating of cotton fabrics with inserted silver yarns increases shielding effectiveness (EMSE) by 8–10 dB. In order to keep for the LCA study the same functional unit of 50 dB at 100 MHz for one sqm of fabric, the fabric structure is modeled with a reduced distance between the inserted conductive yarns. Results of the LCA study show a substantial impact on the environment for the plasma coated fabric upon using a laboratory scale deposition set-up.

Tungsten boride shields in a spherical tokamak

Abstract: The favourable properties of tungsten borides for shielding the central High Temperature Superconductor (HTS) core of a spherical tokamak fusion power plant are modelled using the MCNP code. The objectives are to minimize the power deposition into the cooled HTS core, and to keep HTS radiation damage to acceptable levels by limiting the neutron and gamma fluxes. The shield materials compared are W2B, WB, W2B5 and WB4 along with a reactively sintered boride B0.329C0.074Cr0.024Fe0.274W0.299, monolithic W and WC. Of all these W2B5 gave the most favourable results with a factor of ~10 or greater reduction in neutron flux and gamma energy deposition as compared to monolithic W. These results are compared with layered water-cooled shields, giving the result that the monolithic shields, with moderating boron, gave comparable neutron flux and power deposition, and (in the case of W2B5) even better performance. Good performance without water-coolant has advantages from a reactor safety perspective due to the risks associated with radio-activation of oxygen. 10B isotope concentrations between 0 and 100% are considered for the boride shields. The naturally occurring 20% fraction gave much lower energy depositions than the 0% fraction, but the improvement largely saturated beyond 40%. Thermophysical properties of the candidate materials are discussed, in particular the thermal strain. To our knowledge, the performance of W2B5 is unrivalled by other monolithic shielding materials. This is partly as its trigonal crystal structure gives it higher atomic density compared with other borides. It is also suggested that its high performance depends on it having just high enough 10B content to maintain a constant neutron energy spectrum across the shield.

A Novel and High-Precision Method for Calculating the γ-Ray Build-Up Factor for Multilayer Shields

Abstract: In the field of radiation protection, the point-kernel code method is a practical tool widely used in the calculation of 3-D radiation field, and the accuracy of the point-kernel integration method strongly depends on the accuracy of the build-up factor. It is well known that calculation of the build-up factor for single-layer shields is composed of single material, but it is very complicated to calculate the build-up factor for multilayer shields (MLBUF). Recently, a novel and high-precision method based on the deep neural network (DNN) for calculating MLBUF has been proposed. In this paper, the novel method is described completely by slab models. Through the study of photon transport in multilayer shields, the parameters that mainly affect the calculation of build-up factor are analyzed. These parameters are trained by DNN as the input vectors, and the build-up factor for multilayer shields is predicted based on the trained DNN. The results predicted by DNN confirm that the method can calculate the build-up factor for multilayer shields quickly and accurately. The method has been preliminarily applicated into a 3-D radiation field calculation software, and it has proved that the method for calculating MLBUF has a broad application prospects in 3-D radiation field calculation.

Program BUF: A computer toolkit for primary investigations of buildup factors in single and multilayer shields

Abstract: The buildup factors play a central role in radiation shielding studies for designing of a shield to reduce the intensity of radiations reaching out to any object or at point of observation. In order to meet out the most of practical shielding requirements of buildup factors, it becomes crucial to find a generalized toolkit applicable for multi-layer shields. The Taylor’s approximation has been widely studied for radiation shielding calculations and it is observed that this approximation is accurate enough to evaluate buildup factor data for elements and compounds composing single-layered shields. In this study, the Taylor’s formula is attempted for estimation of buildup factors for multi-layered shields. Numerical calculations have been performed by developing a program source code employing this fitting approximation and the computation is able to reproduce buildup factors data for single-layer shields. Moreover, results for two-layered, three-layered, four-layered and five-layered are also seen to be produced numerically. The program calculates buildup factors in the energy range of 0.5 MeV−10 MeV for shields having effective atomic number lying between 10 and 92. Wherever possible, the validity of the developed source code is tested by comparing outputs with available results in literature.

The Influence of Slit Lamp Shield Size and Design in Reducing Aerosol Transmission.

Abstract: Purpose Previous studies have highlighted the effectiveness of slit lamp shields in reducing aerosol spread. Our study investigated the optimal size and design for such shields. Methods Two sets of shields were made; each set included five cardboards of the following dimensions: 1 (44 × 52 cm), 2 (44 × 44 cm), 3 (22 × 52 cm), 4 (22 × 33.5 cm), and 5 (44 × 22.5 cm). Cardboards in set 1 were kept flat whereas those in set 2 were curved using plastic frames. Aerosol was generated at the patient's position using a water spray bottle, and aerosol levels were measured at the face position of the examiner and on the slit lamp table using two GP2Y1014AU0F sensors. The measurements were recorded in particles/0.01f3 and analyzed using a Mann Whitney U test. Results Mean background indoor aerosol was 559. After aerosol generation, the level increased to a mean of 571 in the absence of any kind of shield but to a mean of 567 when shields were in place (P < 0.05). Flat shield 1 provided the best protection against inhaled aerosol. Flat shield 2, despite its shorter height compared to shield 1, provided the best protection against precipitated aerosol on the table. Curving shield 5 significantly improved its protective properties against both inhaled and precipitated aerosol while keeping the short height that allowed better access during examinations. Conclusions Shields reduced aerosol spread with curved shields being more effective while creating fewer physical restrictions. GP2Y1014AU0F particle sensors are effective tools for quantifying aerosol spread. Translational Relevance An understanding of optimal slit lamp shield design will provide protection for examiners while facilitating effective examination.

Analysis of Hybrid Meander Structures with Additional Shields

Abstract: Models of hybrid meander structures with additional shields are presented in this paper. The influence of additional shields and their grounding positions on the electromagnetic characteristics of the hybrid meander structures was investigated. Three-dimensional models were created and analyzed using the method of moments (MoM) in the Sonnet® and finite-difference time-domain (FDTD) method in CST Microwave Studio® commercial software packages. The computer-based modeling was verified by physical experiment. The analysis showed that it is possible to control the delay time characteristic using different values of lumped inductive elements without the need to change the overall size of the hybrid meander structure. The delay time varied by 1.2 ns in the range of 1.3 ns to 2.5 ns when the inductivity changed from 1 nH to 10 nH in our investigation. On the other hand, the passband decreased from 2.384 GHz to 0.508 GHz. The additional shields and their grounding positions allowed for increasing the passband by up to 1.6%.