Shields

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

A high-performance magnetic shield with large length-to-diameter ratio.

Abstract: We have demonstrated a 100-fold improvement in the magnetic field uniformity on the axis of a large aspect ratio, cylindrical, mumetal magnetic shield by reducing discontinuities in the material of the shield through the welding and re-annealing of a segmented shield. The three-layer shield reduces Earth's magnetic field along an 8 m region to 420 μG (rms) in the axial direction, and 460 and 730 μG (rms) in the two transverse directions. Each cylindrical shield is a continuous welded tube which has been annealed after manufacture and degaussed in the apparatus. We present both experiments and finite element analysis that show the importance of uniform shield material for large aspect ratio shields, favoring a welded design over a segmented design. In addition, we present finite element results demonstrating the smoothing of spatial variations in the applied magnetic field by cylindrical magnetic shields. Such homogenization is a potentially useful feature for precision atom interferometric measurements.

Stress controlling semiconductive shields in medium voltage power distribution cables

Abstract: The construction of current extruded-dielectric, medium-voltage underground residential distribution (URD) cable is described, and requirements for semiconductive shields are examined. Conductor shields, insulation shields, semiconductive jackets, shields for high-voltage cables, and shields for rubber insulation are included. The composition of carbon black and polymer shields is discussed, and the mechanism of conduction in semiconductive shields are described. The historical development of shields is traced, starting with early types and covering developments in the 1970s, 1980s, and 1990s. >

Intercalated graphite fiber composites as EMI shields in aerospace structures

Abstract: The requirements for electromagnetic interference (EMI) shielding in aerospace structures are more complicated than those for ground structures because of their weight limitations. As a result, the best EMI shielding materials must combine low density, high strength, and high elastic modulus with high shielding ability. EMI shielding characteristics were calculated for shields formed from pristine and intercalated graphite fiber/epoxy composites and compared to preliminary experimental results for these materials and to the characteristics of shields made from aluminum. Calculations indicate that effective EMI shields could be fabricated from intercalated graphite composites which would have less than 12% of the mass of conventional aluminum shields, based on mechanical properties and shielding characteristics alone. >

Weight-Efficiency of Conventional Shielding Systems in Protecting Unmanned Spacecraft from Orbital Debris

Abstract: Unmanned spacecraft typically require protection only from much smaller orbital debris as compared to manned missions. This paper presents quantification and comparison of the weight efficiency of conventional shielding concepts, which were originally developed for manned spacecraft, when designed to protect a robotic satellite against small-size (1 mm) orbital debris impacts. The shielding systems under comparison comprise two categories: “single-purpose orbital debris shields,” represented by the Whipple shield and the stuffed Whipple shield; and “multipurpose structural panels,” represented by honeycomb-core and foam-core sandwich panels. First-order estimates of the shields’ parameters are obtained using the well-known ballistic limit equations. These estimates are then used as starting points for further optimization of the shields conducted by means of hydrocode simulations. The simulations employ a combination of the ANSYS Autodyn finite element and smooth particle hydrodynamics solvers. The result...

Numerical Analysis of the Transient Response of Advanced Thermal Protection Systems for Atmospheric Entry

Abstract: Equations for the transfer of heat through thermal protection shields are derived in finite difference form. These equations are applicable to charring ablators, impregnated ceramics, subliming ablators, heat sinks, and insulating materials and have been programed for solution on a high-speed digital computer. In the program, thermal properties can be functions of temperature. Provision is made for analysis of heat shields subjected to simultaneous convective and radiative heat inputs. Some typical results are presented. Limited comparisons with experimental results are made.