Showing papers on "Shields published in 2017"

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...

A three-axis atomic magnetometer for temperature-dependence measurements of fields in a magnetically shielded environment

Abstract: High performance spin-exchange-relaxation-free (SERF) gyroscopes require stable and homogeneous magnetic fields. These fields are usually sensitive to temperature. In this paper, a three-axis atomic magnetometer to measure the temperature dependence of fields inside the magnetic shields for a SERF gyroscope prototype is constructed and tested. Based on a three-beam configuration, three-axis vector capability is obtained by a cross-modulation scheme of the magnetic field components along orthogonal axes and subsequent demodulation of the relevant probe signals. The relative temperature dependence of magnetic fields inside the prototype shields is measured to be –. The results are useful for estimating the necessary precision of temperature control in both a SERF gyroscope and its fundamental physics applications.

A Novel Configuration for Superconducting Space Radiation Shields

Abstract: Long-time exposure to galactic cosmic rays is one of the most problematic threats for a manned mission in the deep space. In the last decades, several studies of active superconducting magnetic shields were performed leading to the proposals of apparently promising magnetic configurations. However, as the interaction of energetic particles with the materials composing the magnets was not taken into account, the contribution of secondary particles to the astronauts’ radiation dose was neglected, and, consequently, the actual effectiveness of the shields was overestimated. In the frame of the EU-FP7-SR2S project, a study of superconducting space radiation shield was performed associating the optimization of the magnetic configuration with Monte–Carlo simulation of the dose reduction. It was found that most of the magnetic shields proposed in previous works are not adequate, and a novel configuration, transparent to radiation, was proposed based on toroids arranged with their axes perpendicular to the spacecraft axis. Compared to other shields with the same shielding power, such a configuration results in lower magnetic field at the superconductor and very light design.

Comparison of passive shields for coils in inductive power transfer

Abstract: Efficiency and stray magnetic field are two important factors for coils design in inductive power transfer. By adding passive shields to the coils, stray magnetic field is significantly attenuated. However, coils' efficiency is reduced due to losses of the shields. Both efficiency and stray magnetic field should be considered for fair comparison of shields' performances. Four kinds of passive shields for coils in inductive power transfer are analyzed, including plate shield, ring shield, litz shield, and reverse loops. Their performances are compared using Pareto fronts of efficiency versus stray magnetic. The fronts show that coils with litz shield generate smallest stray magnetic field when the four shields are designed for the same efficiency. The stray magnetic field was attenuated by 75% in an experimental 100 W inductive power transfer system using litz shield.

Magnetic Shielding Characteristics of Hybrid High-Temperature Superconductor/Ferromagnetic Material Multilayer Shields

Abstract: Magnetic shielding characteristics of hybrid shields consisting of second generation high-temperature superconducting tapes and ferromagnetic materials are presented. Shields with multiple layers with several combinations of superconducting and ferromagnetic materials showed interesting patterns. Shielding factors as high as 95% are observed for three-layer hybrid shielding structures. The data presented offers new ways to achieve the required shielding factors in a given application with minimal use of expensive superconductors.

The Faraday room of the CUORE experiment

Abstract: The paper describes the Faraday room that shields the CUORE experiment against electromagnetic fields, from 50 Hz up to high frequency. Practical contraints led to choose panels made of light shielding materials. The seams between panels were optimized with simulations to minimize leakage. Measurements of shielding performance show attenuation of a factor 15 at 50 Hz, and a factor 1000 above 1 KHz up to about 100 MHz.

Air-conditioner indoor unit and method for achieving wind-feeling air supply of air-conditioner indoor unit

Abstract: The invention relates to the technical field of air-conditioner equipment, in particular to an air-conditioner indoor unit and a method for achieving wind-feeling air supply of the air-conditioner indoor unit. The air-conditioner indoor unit comprises a unit body, wherein an air outlet is formed in the unit body, at least two wind shields which can slide and/or rotate separately and can be matched to guide air flow are arranged at the air outlet, ventilation holes are formed in the matched wind shields in the thickness directions of the wind shields correspondingly, and the porosity after the two wind shields overlap is smaller than the porosity of any of the two wind shields. The invention further provides the method for achieving wind-feeling air supply of the air-conditioner indoor unit. Through the structures of the wind shields which can slide and/or rotate separately and can be matched to guide the air flow and the ventilation holes, with different sizes, formed in the different wind shields, air flow guided out by cross-flow fan blades is guided at different stages, so that different degrees of wind feeling is formed, and requirements of customers are met.

Magnetically shielded electron–optical system of a continuous gyrotron with an operating frequency of 24 GHz

Abstract: It is shown that it is possible to use warm solenoids with copper winding screened with ferromagnetic shields in order to reduce the solenoid supply power by a factor of 1.8–2 while retaining the strength of the magnetic field in the working space for continuous gyrotrons operating in a frequency range of 24–30 GHz. The configuration of the shields as well as the shape and location of the correcting solenoids providing an extended (up to 10 wavelengths long) section of a uniform field in the region of the gyrotron cavity have been determined. It has been shown that introduction of an additional cathode coil into the magnetic system reduces the degree of nonadiabaticity of the magnetic field approximately by an order of magnitude and thereby makes it possible to use the magnetron injection gun for formation of a helical electron beam. Optimization of the configuration of the gun electrodes based on the trajectory analysis makes it possible to obtain an electron beam whose parameters are as good as parameters of the electron beams formed in classical adiabatic electron–optical systems of gyrotrons.

Experimental and theoretical study of AC losses in variable asymmetrical magnetic environments

Abstract: Measurements of AC losses in a HTS-tape placed in between of two bulk magnetic shields of high permeability were performed by applying calorimetric techniques for various asymmetrical shielding arrangements The experiment was supported by analytical calculations and finite-element simulations of the field and current distributions, based on the Bean model of the critical state The simulated current and field profiles perfectly reproduce the analytic solutions known for certain shielding geometries The evaluation of the consequent AC losses exhibits good agreement with measurements for the central position of the tape between the magnets but increasing discrepancy when the tape is approaching the shields This can be explained by the increasing contribution of the eddy currents and magnetic hysteresis losses in the conducting shields

Open-Type Magnetic Shields for Optical Fiber Coil Protection With Coaxial Foil Tubes

Abstract: To decrease the considerable nonreciprocal phase drift caused by environmental magnetic fields in fiber-optic gyroscope (FOG), magnetic shields on optical fiber coil (OFC) are necessarily used in medium- and high-accuracy FOG protection. Cubic boxes and spherical shells without any gaps have been widely adopted for decades in shields, posing challenge for tradeoff between weight limitation of shields and its shielding demand yet. Here, an open-type magnetic shields (OMSs) with several coaxial permalloy foil tubes in few hundred micrometers thickness is proposed, overlaying on the winding process of fiber coil and finally combining with OFC as an integration module (OFC-OMS). The shielding effectiveness (SE) and longitudinal availability were adjustable by changing permalloy tubes’ thickness, intervals between coaxial foil tubes, and extended length in endcaps. The optimized result showed that an OMS set with six coaxial permalloy foil tubes achieved a longitudinal availability of 82.6% for SE above 20dB in both axial and radial magnetic field and further revealed anisotropic shielding effect in axial magnetic field remarkably resulting in a 40-dB longitudinal availability of 70.1%. Total mass of OMS reduced by around 75% comparing with the conventional magnetic shields for OFC, which showed immense potentials on reduction of FOG size and processing cost.

Eddy-Currents and Force Analysis for the Thermal Shields of the Warm Iron Superconducting Quadrupoles for the FRIB Fragment Separator

Abstract: The fragment separator of the Facility for Rare Isotope Beams uses six warm iron large acceptance high field superconducting quadrupole magnets (see Fig. 1). These magnets are located underground in the target facility hot cell. This location does not allow liquid nitrogen to be used for the cooling of the thermal shield so 35-K helium gas is used instead. In the event of a quench, the decaying field in the magnet induces eddy currents that give rise to a large force on the thermal shields. Because of the multifaceted geometry of the shield, understanding this force is an important aspect of the design. Detailed eddy current simulations were performed and the forces on the different parts of the shield were studied by finite-element analysis. This paper presents the results obtained for the stress distribution, the deformation in the thermal shield, and also mechanical design details.

The Faraday room of the CUORE Experiment

Abstract: The paper describes the Faraday room that shields the CUORE experiment against electromagnetic fields, from 50 Hz up to high frequency. Practical contraints led to choose panels made of light shielding materials. The seams between panels were optimized with simulations to minimize leakage. Measurements of shielding performance show attenuation of a factor 15 at 50 Hz, and a factor 1000 above 1 KHz up to about 100 MHz.

Improving calculation accuracy of currents in cable shields at double-sided grounding of three-phase cable line

Abstract: This paper deals with the calculation of currents in shields of single-core cables at double-sided grounding of three-phase cable lines. We consider flat and trefoil cable lines and receive the analytical expressions for RMS currents in the shields of cables. These expressions allow reducing the shield current calculation error to value of 5 %. We analyze the known approximate expressions for RMS currents in the shields of cables and represent dependencies of corresponding calculation errors on cable line dimensionless parameters. These dimensionless parameters are determined by the distance between the axes of the cables, the radius and the resistance of shields.

Shielding evaluation of on-package conformal shields by numerical modelling and experimental measurement

Abstract: A reliable numerical modelling for shielding evaluation of on-package conformal shields based on the integrated circuit (IC)-stripline method is presented. As a pilot test, the effects of the number of grounding pads and the thickness of a conformal shield on the shielding performance are investigated. For validation, the conformal shield is fabricated and measured by both the IC-stripline method and TEM cell method.

Restricted area automated security system and method

Abstract: A security system includes a plurality of laser scanners to establish light shields in an area to be monitored, with each of the light shields including at least one detection zone, and a controller to detect unauthorized entry to the area to be monitored based on a position and timing of breaks in the detection zones of the light shields.

Time domain magnetic shielding performance of thin shields

Abstract: The shielding effectiveness of thin planar shields against magnetic field is investigated in the time domain. The analysis is performed considering a vertical magnetic dipole as the source and a classical twelve inches diameter loop as receiving antenna. The computations are performed through a recently proposed analytical solution. The relevant features of classical configurations are extracted and the effects of shield constitutive parameters on the relevant time-domain shielding parameters are presented.

Calculation of magnetic field of three-phase cable lines with two-point bonded cable shields covered by ferromagnetic cores

Abstract: In this paper we obtain compact expressions for the magnetic field shielding factor of a high-voltage three-phase cable line consisting of single-core cables with two-point bonded cable shields and ferromagnetic cores installed. To obtain these expressions we develop the analytical model of the cable line. Following assumptions are made to develop the model: the current distribution in each cable shield is uniform, cylindrical ferromagnetic cores covering the cables are not magnetized to saturation and their magnetic permeability is constant, each of the ferromagnetic cores is magnetized only by the core current and the shield current of the cable that it covers, the magnetic field inside ferromagnetic cores is axisymmetric, the magnetic field is planeparallel over the entire cable line. We consider common cases of flat and trefoil cable lines. The proposed expressions for the magnetic field shielding factor are verified experimentally. The physical model is made of three cables of the type NA2XSF(L)2Y110 1240/70. It is shown that the difference between numerical simulation results and experimental data lays within 15 %. References 11, figures 3.

Geometrical aspects of cylindric magnetic shields in strong static fields

Abstract: Motivated by ITER (the International Thermonuclear Experimental Reactor), research on a magnetic shield against a strong field has been carried out. In this paper, a cylindric magnetic shield is studied by using the finite element method with a nonlinear magnetization curve. The geometrical aspects of shielding performance are identified and corresponding suggestions for application are provided. Among them, the effects of the edge and cover thickness have not been mentioned elsewhere to our knowledge.

Design of gas trailing shields for TIG-welding of stainless steels

Abstract: In this paper, the suitability of different constructional concepts of gas trailing shields concerning the reduction of heat-tints is discussed. The evaluation of these concepts as well as the description of the main contamination mechanisms of gas trailing shields with atmospheric gases are performed for tungsten inert gas welding of stainless steel by a purposeful coupling of experimental as well as numerical methods. Furthermore, advantages and disadvantages of these design concepts are investigated regarding their constructional complexity, robustness against varying process parameters, and its feasible working distances. Finally, a modular concept is presented which allows the usage of the same constructional concept for a variety of different welding tasks.

Novel protection method for ground faults detection in cables used in combined overhead-cable lines in power systems

Abstract: This paper presents a new protection method for single phase ground faults detection in cables used in overhead-cable lines in power transmission systems where the shields of the cables are connected according to the cross-bonding method The main contribution of this new protection method is that it can distinguish ground faults in the cable line side from ground faults at the overhead-line side. The new protection method is based on the measurements and analysis of the currents in the shields of the cable at the substation side, not at the cable end in the transition overhead-cable. The new method considers that the shields of the cables at the transition overhead-cable are not grounded sharing the same ground than the ending tower. Shields of the cables are connected according to the cross-bonding method. This new protection method has been validated through computer simulations and experimental laboratory tests.

Magnetic field calculation of cable line with two-point bonded shields

Abstract: This paper discusses the mitigation of the cable line magnetic field by the two-point bonding of shields of cables. We produce a two-dimensional mathematical model of the cable line with two-point bonded cable shields based on the Maxwell-Ampere equation. The calculation of induced shield currents and magnetic field is carried out by the computer simulation using the finite element method. This allows to take into account a nonuniform shield current distribution and therefore to obtain the most accurate solution, as evidenced by the coincidence with the experimental research. We consider the most common case of the flat cable line and tabulate the dependence of the magnetic shielding factor from the cross-sectional area, the diameter of shields, and the distance between cables.

Tunnel magnetoresistive sensor having leads supporting three-dimensional current flow

Abstract: An apparatus, according to one embodiment, includes: a transducer structure having: a lower shield, an upper shield above the lower shield, a current-perpendicular-to-plane sensor between the upper and lower shields, an electrical lead layer between the sensor and one of the shields, and a spacer layer between the electrical lead layer and the one of the shields. The upper and lower shields provide magnetic shielding. The electrical lead layer is in electrical communication with the sensor. A conductivity of the electrical lead layer is higher than a conductivity of the spacer layer. A width of the electrical lead layer in a cross-track direction is greater than the width of a free layer of the sensor.

Hybrid dielectric gap liner and magnetic shield liner

Abstract: In one embodiment, an apparatus includes a transducer structure. The transducer structure has a lower shield and an upper shield above the lower shield, the upper and lower shields providing magnetic shielding. A current-perpendicular-to-plane sensor is positioned between the upper and lower shields. An electrical lead layer is positioned between the sensor and one of the shields. The electrical lead layer is in electrical communication with the sensor. A spacer layer is positioned between the electrical lead layer and the one of the shields. A conductivity of the electrical lead layer is higher than a conductivity of the spacer layer. One or both of the shields has at least one laminate pair comprising a magnetically permeable layer and a harder layer, where the harder layer has a mechanical hardness that is higher than a mechanical hardness of the magnetically permeable layer.

Dose Measurements through the Concrete and Iron Shields under the 100 to 400 MeV Quasi-Monoenergetic Neutron Field (at RCNP, Osaka Univ.)

Abstract: Shielding benchmark experiments are useful to verify the accuracy of calculation methods for the radiation shielding designs of high-energy accelerator facilities. In the present work, the benchmark experiments were carried out for 244- and 387-MeV quasi-monoenergetic neutron field at RCNP of Osaka University. Neutron dose rates through the test shields, 100-300 cm thick concrete and 40-100 cm thick iron, were measured by four kinds of neutron dose equivalent monitors, three kinds of wide-energy range monitors applied to high-energy neutron fields above 20 MeV and a conventional type rem monitor for neutrons up to 20 MeV, placed behind the test shields. Measured dose rates were compared one another. Measured results with the wide-energy range monitors were in agreement one another for both the concrete and the iron shields. For the conventional type rem monitor, measured results are smaller than those with the wide-energy range monitors for the concrete shields, while that are in agreements for the iron shields. The attenuation lengths were obtained from the measurements. The lengths from all the monitors are in agreement on the whole, though some differences are shown. These results are almost same as those from others measured at several hundred MeV neutron fields.

Parametric study for use of stainless steel as a material for thermal shield in PIP2IT transferline at Fermilab

Abstract: Transferline thermal shields are cooled by dedicated cooling lines welded/brazed to the shield at a single point along the circumference. Copper/Aluminium is widely used to fabricate thermal shields because of their higher thermal diffusivity. This causes uniformity of temperature along the surface of the shield thus reducing thermal stresses within allowable values. However, factors such as raw material price, the cost of fabrication depending on standard sizes of pipes/tubes, often drives up the final price of thermal shields. To reduce the cost by making use of easily available stock of standard pipe/tube, it is decided to use stainless steel as a material for thermal shields in the PIP2IT transferline. The present paper discusses the design approach, various factors affecting the conservative selection of thermal shield design.