Showing papers on "Shields published in 2008"

Calculation of magnetic field noise from high-permeability magnetic shields and conducting objects with simple geometry

Abstract: High-permeability magnetic shields generate magnetic field noise that can limit the sensitivity of modern precision measurements. We show that calculations based on the fluctuation-dissipation theorem allow quantitative evaluation of magnetic field noise, either from current or magnetization fluctuations, inside enclosures made of high-permeability materials. Explicit analytical formulas for the noise are derived for a few axially symmetric geometries, which are compared with results of numerical finite element analysis. Comparison is made between noises caused by current and magnetization fluctuations inside a high-permeability shield and also between current-fluctuation-induced noises inside magnetic and nonmagnetic conducting shells. A simple model is suggested to predict power-law decay of noise spectra beyond a quasi-static regime. Our results can be used to assess noise from existing shields and to guide design of new shields for precision measurements.

Reduction of Lightning-Induced Magnetic Fields and Voltages Inside Struck Double-Layer Grid-Like Shields

Abstract: This paper presents a numerical analysis of the reduction of lightning-induced magnetic fields and voltages inside double-layer grid-like spatial shields typically used in reinforced concrete buildings, e.g., nuclear power plants. The calculations are performed with the CONCEPT computer code, which solves Maxwell's equations using the method of moments in the frequency domain. The computer code is extended with the well-known transmission line model (TL-model) in order to simulate direct lightning strikes. The structure under study comprises a cubic cage of 2 m side length having single- or double-layer grid-like spatial shields with square meshes of 0.25 m width. Three lightning-channel attachment points are considered at the cage roof, namely, the center, the midedge, and the corner. The simulated lightning currents are the positive, the negative first, and the negative subsequent strokes at lightning protection level I (LPL I) according to the international standard series IEC 62305. The computed quantities comprise the currents through some selected wires of the grid-like spatial shields, the magnetic fields, the magnetic-field derivatives, and the induced voltage across a typical installation loop inside the shield. The results of the single-layer shield are compared to those of the double-layer one to evaluate the additional reduction of the latter shield.

Magnetic sensing device with reduced shield-to-shield spacing

Abstract: A magnetic sensor assembly includes first and second shields each comprised of a magnetic material. The first and second shields define a physical shield-to-shield spacing. A sensor stack is disposed between the first and second shields and includes a seed layer adjacent the first shield, a cap layer adjacent the second shield, and a magnetic sensor between the seed layer and the cap layer. At least a portion of the seed layer and/or the cap layer comprises a magnetic material to provide an effective shield-to-shield spacing of the magnetic sensor assembly that is less than the physical shield-to-shield spacing.

Shielding data for 100–250 MeV proton accelerators: Attenuation of secondary radiation in thick iron and concrete/iron shields

Abstract: Double differential distributions of neutrons produced by 100, 150, 200 and 250 MeV protons stopped in a thick iron target were calculated with the FLUKA Monte Carlo code at four emission angles: forward, 45°, transverse and 135° backwards. The attenuation in thick iron shields of the dose equivalent due to neutrons, protons, photons and electrons was also calculated. The contribution to the total ambient dose equivalent from photons and protons is limited to a few percent at maximum. Source terms and attenuation lengths are given as a function of energy and emission angle, along with fits to the Monte Carlo data, for shallow depth and deep penetration in the shield. A brief discussion of simulations performed with composite iron/concrete shields is also given, showing the need for further investigations.

Shielding of High Magnetic Fields

Abstract: This paper revisits the problem of shielding low- frequency high magnetic fields. Such fields are encountered in the domain of electromechanical energy conversion in particular during railgun operation. Using finite-element (FEM) analysis, we investigate, separately, the mechanism of redirection of the magnetic flux due to induced eddy-currents and the magnetic flux shunting due to highly permeable materials. In a first phase, various shapes of highly conductive shields are analyzed in the frequency domain. In a second phase, we study the shunt effect of different shields being made of magnetic materials. In a magnetostatic model afterwards, for a shield that combines both highly conductive and magnetically highly permeable materials, the case of a double-exponential shaped magnetic field is treated in the time domain. Finally, we make some remarks on the concept of shielding effectiveness.

Shielding of High Magnetic Fields

Abstract: This paper revisits the problem of shielding low- frequency high magnetic fields. Such fields are encountered in the domain of electromechanical energy conversion in particular during railgun operation. Using finite-element (FEM) analysis, we investigate, separately, the mechanism of redirection of the magnetic flux due to induced eddy-currents and the magnetic flux shunting due to highly permeable materials. In a first phase, various shapes of highly conductive shields are analyzed in the frequency domain. In a second phase, we study the shunt effect of different shields being made of magnetic materials. In a magnetostatic model afterwards, for a shield that combines both highly conductive and magnetically highly permeable materials, the case of a double-exponential shaped magnetic field is treated in the time domain. Finally, we make some remarks on the concept of shielding effectiveness.

Thermal Properties of Double-Aluminized Kapton at Low Temperatures

Abstract: Double-aluminized kapton (DAK) is commonly used in multi-layer insulation blankets in cryogenic systems. NASA plans to use individual DAK sheets in lightweight deployable shields for satellites carrying instruments. A set of these shields will reflect away thermal radiation from the sun, the earth, and the instrument's warm side and allow the instrument's cold side to radiate its own heat to deep space. In order to optimally design such a shield system, it is important to understand the thermal characteristics of DAK down to low temperatures. We describe experiments which measured the thermal conductivity and electrical resistivity down to 4 Kelvin and the emissivity down to 10 Kelvin.

Genetic Algorithm and Bezier Curves-Based Shape Optimization of Conducting Shields for Low-Frequency Magnetic Fields

Abstract: Electromagnetic shields play a very significant role in the modern power and electrical industry. Efficient shields are also used in medicine, physics, and when making high-sensitivity electric and magnetic measurements to shield them from electromagnetic interference. Unfortunately, complete, unperforated shells cannot be used in real applications. In this paper, we show a new optimization technique which, by coupling the finite-element method with a genetic algorithm and Bezier curves, supports the design of efficient and esthetic shields.

Composite shield structure and perpendicular magnetic recording head

Abstract: PROBLEM TO BE SOLVED: To provide a perpendicular magnetic recording head capable of improving a magnetic field gradient while maintaining sufficient magnetic field intensity in use of a high recording density and a narrow track width. SOLUTION: A main recording magnetic pole 20 having a magnetic pole tip 20t in ABS, and a shield structure 100 formed around the same, are included. This shield structure 100 includes a leading shield 22, a trailing shield 21, two side shields 23 and 24 which are partial side shields, magnetic couplers 25 and 28 for magnetically coupling together the leading shield 22 and the two side shields 23 and 24, and magnetic couplers 26 and 27 for magnetically coupling together the trailing shield 21 and the two side shields 23 and 24. Magnetic potential of the leading shield 22, the trailing shield 21, and the two side shields 23 and 24 is optimized. COPYRIGHT: (C)2009,JPO&INPIT

A low-drift, open-loop controlled, single crystalline silicon micromirror with floating field-limiting shields

Abstract: This paper describes the design, fabrication and testing of a one-axis micromirror in order to suppress the electric charging problem related to its actuation. The electrostatically-actuated torsional micromirror is of the parallel-plate type. Since the dielectric around the electrodes below the mirror plates is highly exposed, we installed gold shields in the floating state around the electrodes, so as to cover the exposed dielectric surface. The gold shields played a leading role in limiting the electric field between the electrodes. This effect was characterized and the tilting angle stability was measured by observing the micromirror performance with and without the floating field-limiting shields. Drift measurements of these two types of micromirrors were made using a position-sensing detector (PSD). The micromirror with the field-limiting shields, namely micromirror type A, showed a tilting angle drift of 0.005° at 83% of the pull-in voltage, while a tilting angle drift of 0.5° was measured at the same percentage of the pull-in voltage for the micromirror without the field-limiting shields, namely micromirror type B. At 97.7% of the pull-in voltage, the pull-in phenomenon occurred after 220 s for micromirror type B due to the charging effect. On the other hand, micromirror type A showed no pull-in phenomena with elapsed time at a bias of 97.7% of the pull-in voltage due to the resolution of the charging effect.

Systems and methods for shielding an electric machine

Abstract: A method for reducing leakage currents in an electric machine is described. The method includes positioning a plurality of leakage current shields between windings and teeth of a stator, and coupling at least one of the plurality of leakage current shields to a reference point, wherein an electric potential at the reference point is not earth ground.

An inert gas shield for welding or heat treatment

Abstract: Provisions of shields for protecting welds as well as providing heat treatments are advantageous. Previously such shields were bespoke constructions produced iteratively and empirically for particular applications and uses. By utilisation of accurately cut sheets of material within which labyrinths are created it is possible to produce an output flow which is even and incorporates no vortexes. In such circumstances problems with regard to edge entrainment of oxygen causing possible oxidation problems in output flows as well as variations in heat treatments can be avoided. The shield also avoids use of welds which may become distorted during welding or heat treating processes. For reproducibility the shield is formed from accurately produced reproducibility components such that shields can be made at a number of sites to provide the same shield function.

Degradation of Hubble Space Telescope Aluminized-Teflon Bi-Stem Thermal Shields

Abstract: A section of retrieved Hubble Space Telescope (HST) bi-stem thermal shields (BSTS), which experienced 8.25 years of space exposure, was analyzed for space environmental durability. The shields were comprised of 2 mil (0.051 mm) aluminized-Teflon® fluorinated ethylene propylene (Al-FEP) rings fused together into a circular bellows shape. As the circular thermal shields had solar, anti-solar and solar-grazing surfaces and were exposed to the space environment for a long duration, it provided a unique opportunity to study solar effects on the environmental degradation of Al-FEP, a commonly used spacecraft thermal control material. Therefore, the objective of this research was to characterize the degradation of retrieved HST BSTS Al-FEP with particular emphasis on solar effects. Data obtained included tensile properties, density (as-retrieved and after 200 3C heating), solar absorptance, and surface morphology and chemistry. The solar-facing surfaces of the thermal shields were found to be extremely embrittle...

Reduction in SAR Using RF Shields Made of Nickel–Zinc Spinel Ferrite at 2.4 GHz

Abstract: This paper presents the experimental evaluation of the ‘Specific Absorption Rate’ (SAR) reduction in a human head due to radio frequency (RF) shields attached to a mobile handset. Shields of various shapes and sizes were made from a nickel–zinc spinel ferrite. The human head was simulated by a fibre glass container filled with NaCl solution to represent the muscle tissues. An E-field probe was used to measure the electric field strength at various points in the head model with and without the RF shields. The E-field variations in the head model show that the developed ferrite RF shields reduce the ‘SAR’ effectively.

Effect of shields in perpendicular recording

Abstract: Micromagnetic simulations have been used to investigate magnetization dynamics in a perpendicular recording head with a trailing shield. The numerical experiment was carried out on a set of head models with shields. Trailing shields used in modelling had a thickness of 20 nm and spacing of 50, 100 and 150 nm from the trailing edge of the tip. Results of our investigations show that shields not only increase the gradient of the recording field but also help to generate more surface charges on the tip and on the SUL below it. For specific configurations and head to shield spacing (>50 nm) this leads to higher field magnitudes, leading to the 4–6% increase in the perpendicular field at 10 nm below ABS.

A Method for Decreasing Magnetic Shaking Leakage from Separated Magnetic Shields by Combining an Additional Shaking Coil in Reverse Direction(Biomagnetism and Medical Application)

Abstract: In actual magnetic shielding applications, having easy access to the internal space volume of the shield is essential. We propose a new model of the shield composed of two separate cylindrical halves with a flat extention. The leakage magnetic field is calculated by using the finite element method on several models of magnetic shields in which two configurations of the conductor location of shaking coils and the ratio of two shaking coil currents are used as design parameters. We found that using the combination of two shaking currents, one positive and the other negative, and adjusting their ratios was effective in reducing the magnetic leakage.

Cryostat Optimization Through Multiple Stage Thermal Shields

Abstract: Thermal radiation and conduction through structural elements represent a large heat input to the cryogenic environment, especially for cryostats with a large surface area such as those for superconducting transmission lines. In this paper, we discuss methods of decreasing the refrigerator power when the inner cryostat is near liquid nitrogen temperature and the outer cryostat is at room temperature. The use of multiple shield temperature stages is described.

Experimental performance investigation of double-layer shields at power frequency magnetic shielding

Abstract: Double-layer shields have received attention in magnetic shielding at extremely low frequency. Also, cylindrical shape is one of shielding structures widely used in industry. In this study, cylindrical shaped shields with commonly available and inexpensive materials used for power frequency magnetic field shielding. The magnetic shielding performances are investigated experimentally for single and double-layer shields at power frequencies. The aim of this work is to extend the discussion in the area of shielding performance of the double-layer shields.

Electric connection method of shield

Abstract: PROBLEM TO BE SOLVED: To provide a method of properly connecting respective shields of a plurality of extra fine coaxial wires via a common conductive member. SOLUTION: The coaxial wires 1 having the shields 13 that are partially exposed are arranged in parallel. A metal piece 4 is mounted on the respective shields 13 of the coaxial wires 1 and the metal piece 4 is melted by being irradiated with laser light L. Then, the respective shields 13 are connected electrically via the common conductive member 3 by mounting a common conductive member 3 on the melted metal piece 4. COPYRIGHT: (C)2009,JPO&INPIT

Dual-purpose topee

Abstract: The utility model relates to a dual-purpose sun hat, comprising a hat body and a hat brim. Two sun shields are symmetrically and moveably connected with two sides of the hat brim on the hat body, the tops of the two sun shields are connected through stayguy. Limiting baffles are processed on the hat body corresponding to the lower parts of the sun shields. The sun shields are made of an elastic material. When using the sun hat, users can stretch the two sun shields upwardly, the sun shields deform and abut on the hat body because the sun shields are made of the elastic material, using the stayguy to connect for fixing; when sunlight is strong, opening the stayguy and putting down the sun shields at two sides, limiting the position through the limiting baffles, and the sun shields are flatly positioned, which effectively enlarges the sheltering area of the hat. The utility model has the characteristics of simple structure, convenient use, beautiful appearance, economy, etc.

Shield Penetrating Water Cooled Bus Ducts for Radiation Resistant Magnets at J-PARC

Abstract: The high intensity proton accelerator facility J-PARC is now in its final stage of construction. Soon intense primary proton beams will be slowly extracted to an experimental hall (HD-hall) and transported to a production target. Since the radiation level around the target will be very high, the beam line tunnel needs to be surrounded by 2.5 m-5 m thick concrete shields in the HD-hall. Radiation resistant magnets for handling high intensity beams are buried inside these thick concrete shields. This structure, however, brought us a problem of leading electric power lines to the magnets. For a solution to this problem, we have developed water cooled bus ducts penetrating radiation shield. These bus ducts enable us to connect the power supplies placed outside the shields to the magnets in the shortest power line length without any deterioration of protection ability of radiation shielding. The maximum power capacity of the bus duct is over 5000 A. The bus ducts plays an important part in our radiation resistant magnet system.

Frontal electric machine of enclosed design with external air cooling

Abstract: FIELD: electricity. ^ SUBSTANCE: invention is attributed to electric engineering, specifically to enclosed electric machines of frontal design with one stator and one rotor. Frontal electric machine of enclosed design with external air cooling includes housing consisting of two shields, toroidal stator and rotor cores with windings, shaft, bearing assemblies and blower. The machine contains ribbed from outside shields; on the outer surface of shield opposite to protruding shaft end, bracket is installed on which electric motor with blower is mounted which blower is placed into chamber bounded at electric motor side by protective blower plate with holes to pass through ambient cooling air, external part of the shield and shield ribs enveloping the blower with some clearance. To arrange flow of ambient cooling air in the direction of machine shields, cylindrical air distributor enveloping the shields is mounted. ^ EFFECT: improvement of cooling conditions for heat-producing elements and its operation reliability enhancement. ^ 1 dwg

Modeling and analysis of the planar spiral inductor including the effect of magnetic-conductive electromagnetic shields

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Diffraction of the electromagnetic wave on the tape lattice located above shielded anizotropic environment

Abstract: Interaction of an electromagnetic wave with an anisotropic substrate in presence of periodic shields has been investigated. The fields reflected from the structure have been obtained in analytic form. The electrodynamic approach for finding a scattered field from plane periodic shields above a full anisotropy medium placed on the conducting plane, is suggested. The analytical expressions for the components of a scattered electromagnetic field are obtained.