Shields

About: Shields is a research topic. Over the lifetime, 1456 publications have been published within this topic receiving 10896 citations.

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.

Shielding effectiveness of different polymers and low-density hydrides in a combined radiation shield for crewed interplanetary space missions

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.

High frequency sending device for plasma heating

Abstract: PURPOSE:To facilitate the replacement of a protection member and to improve the operation rate by covering Faraday shields with a Faraday shield protection plate which has slits matching their gaps. CONSTITUTION:An antenna 10 stored in a jacket 9 radiates a high-frequency wave for heating to plasma 3 through its opening part. Then the Faraday shields 17 fitted to the opening part in a hurdle shape short-circuit electric field parts which are not necessary to heat the plasma 3. The device is provided with the shield protection plate 31 which has the slits 32 matching the gaps between the shields 17, is made of a high-fusion-point material, and passes high frequency waves while protecting the shields 17 from a thermal load from the plasma 3 and wear due to particles. One or a small number of protection plates 31 are used and not joined with the shields 17, and the four corners are clamped to a jacket 9 with bolts. Therefore, its replacement is easily performed in a short time through remote operation even in a vacuum container 2.

Significance of shields in high voltage performance of vacuum interrupters

Abstract: Vacuum Interrupters use a metallic cylinder to shield the ceramic from the metal vapor during arcing. Rightly so, this metallic cylinder is termed as “shield” or “arcing shield” or “vapor condensing shield”. This shield plays an equally important role in the high voltage performance of the vacuum interrupter. The number, position, dimensions and profiles of these shields govern the electrostatic field distribution and hence the high voltage performance of the vacuum interrupter. The high voltage performance of the vacuum interrupter is evaluated through analytical means like FEM simulations and high voltage tests. This paper presents the significance of the shield through results of electrostatic simulations and experimental results of commercial vacuum interrupters with various combinations of shields. The paper also presents the role of multiple shields, especially for higher voltage interrupters. A case study, highlighting the importance of the annular gap between contacts and shield for the impulse voltage performance of the contacts is also presented in this paper.

Fabrication and performance of cylindrical iron shields for mri systems.

Abstract: Using analytic and experimental methods, we have investigated the design, fabrication,and performance of axially symmetric shields which minimize the field perturbation withinthe central bore of an MR magnet. Magnetic resonance shields have been built for 1.9tesla /60 cm bore and 1.5 tesla /100 cm bore superconducting magnets. The 1.9 T system isenclosed by a simple cylindrical shield having a weight of 49,000 pounds. The 1.5 T systemshield is a 100,000 pound tapered thickness cylinder with conic ends. The shields areconstructed from cold rolled steel sections which are welded in place at the magnet site.A low carbon, specially annealed steel with particularly desireable properties of inducedmagnetism has been employed. The 5 gauss line is constrained to a point 4.0 meters to theside of the 1.9 T magnet, 3.0 meters to the side of the 1.5 T magnet and 7.0 meters off theend of both magnets.IntroductionHigh field, large bore magnets used for magnetic resonance imaging and spectroscopy pro-duce magnetic fields which can influence the environment at distances far from the magnet.Within this sphere of influence, which may have a radius greater than 15 meters, ferrousobjects will become intensely magnetized and perturb the normally homogeneous field withinthe magnet. Consequently, many high field MR systems have been installed within large,free -standing buildings of a ferrous -free design which are remote from direct patient carefacilitiesl.Discontinuous asymmetrical iron shields enclosing high field MR magnets have been usedto constrain the magnet sphere of influence2. The return magnetic fields resulting frominduced shield magnetism perturb the uniform field within the magnet and can compromisesystem performance, particularly for spectroscopy applications. Using analytic and experi-mental methods, we have investigated the design, fabrication, and performance of axiallysymmetric shields which minimize the field perturbation within the central bore of the MRmagnet.MethodsWe have designed magnetic resonance shields for two magnetic resonance systems: