Showing papers on "Shields published in 2001"

Shielding method and apparatus using transverse slots

Abstract: A shielding method and apparatus for providing predetermined attenuation of one or more electromagnetic energy field components as the field components interact with the shield. The shield composed of a flexible strip or cylindrical body and respectively comprising a transverse conductive element or a transverse slot therein. The shields being adapted to cover an antenna mounted on a support. The shields being compatible for use in conjunction with saddle, tilted coils or multi-layered tri-axial coils to produce a pure transverse magnetic dipole electromagnetic field.

The Effectiveness of the ASOS, MMTS, Gill, and CRS Air Temperature Radiation Shields

Abstract: Periodic upgrades of air temperature measurement systems in surface weather station networks cause data discontinuities. From a climatological viewpoint, it is necessary to evaluate the air temperature data discontinuities when air temperature radiation shields are upgraded. This study was undertaken to investigate the effectiveness of four common air temperature radiation shields including the Automated Surface Observing System (ASOS), the Maximum–Minimum Temperature System (MMTS), the Gill, and the Cotton Region Shelter (CRS) shields. The solar radiation shielding effectiveness for each shield under typical grass ground surface and different artificial surfaces (black, white, and aluminum) were investigated. The shield effectiveness was evaluated by measuring the interior solar irradiance and the inner surface temperatures of radiation shields. Parabolic curves describe the fraction of solar radiation entering shields, which increased as the solar reflectivity of the underlying surface increase...

Airflow Characteristics of Commonly Used Temperature Radiation Shields

Abstract: The air temperature radiation shield is a key component in air temperature measurement in weather station networks; however, it is widely recognized that significant errors in the measured air temperature exist due to insufficient airflow past the air temperature sensor housed inside the shield. During the last several decades, the U.S. National Weather Service has employed a number of different shields in air temperature measurements. This paper focuses on the airflow characteristics inside air temperature shields including the Maximum–Minimum Temperature System (MMTS), the Gill shields, and the Cotton Region Shelter (CRS). Average airspeed profiles and airflow efficiency inside the shields are investigated in this study under both windtable and field conditions using an omnidirectional hot-wire sensor. Results from the windtable measurements indicate that the average airspeeds inside the shields oscillated along the center line of the Gill and MMTS shields as the “windtable air” speed was chang...

Design of multilayered cylindrical shields using a genetic algorithm

Abstract: The design of infinitely long multilayered cylindrical shields with circular cross-section are considered and a method based on the genetic approach is proposed. An analytical method for the calculation of the shielding effectiveness of a cylindrical shield, consisting of homogeneous layers is presented for the case of an obliquely incident plane wave. By making use of this method, a genetic algorithm is implemented for the design of multilayered cylindrical shields in order to achieve a prespecified shielding effectiveness for a given band of frequencies or a range of angles of incidence.

Capacitive shield for containing radiofrequency magnetic fields

Abstract: RF magnetic shields which support tangential electric fields. The RF shields are particularly suited for use in magnetic resonance imaging (MRI) systems, but may also be used in other radio frequency applications. The RF magnetic shields may include a dielectric layer having conductive regions separated by non-conductive regions on each side thereof to form a plurality of capacitive elements. The capacitive elements are partially non-conductive at radio frequencies such that the electrical component tangent to the shield is supported and the magnetic component perpendicular to the shield is blocked. The size and shape of the non-conductive and conductive regions are selected to develop a capacitive voltage across the capacitive elements at radio frequencies, and be substantially non-conductive at frequencies other than RF. The RF magnetic shields provide an electrical field that is uniform around the entire sample volume.

Magnetic read head wherein the shields are used as electrical leads and have a minimized anisotropic magneto-resistance effect

Abstract: A ferromagnetic shield material having a minimized anisotropic magneto-resistance effect permits the use of a combined shield/electrical lead for magneto-resistive read elements. The shields/electrical leads may therefore be placed closer together, maximizing the recording density that may be read by a magnetic recording head using a read element having such shields/leads.

A 2-D Numerical Simulation of ITER-FEAT Disruptive Hot Plasma-Wall Interaction and Model Validation Against Disruption Simulation Experiments

Abstract: The two-dimensional (2-D) radiation-magnetohydrodynamic (R-MHD) code FOREV-2 was developed for modeling of disruptive hot plasma-wall interaction, for calculation of erosion by evaporation of the ITER-FEAT vertical divertor target, and for calculation of the impurity transport in the divertor. FOREV-2 uses a 2 1/2-D MHD model, a 2-D scheme for anisotropic radiation transport, and a solution of the magnetic field equations in the plasma shield for all three components of the magnetic field. Details of FOREV-2 with emphasis on the MHD equations, the equations for the magnetic field, the vaporization model, the angular dependent multigroup radiation transport, and the optical properties of plasmas, and validation of FOREV-2 against analytical results are discussed.Moreover, disruption simulation experiments, performed at the plasma gun facilities at TRINITI Troitsk were used for validation of FOREV-2 and for investigations of the MHD of typical plasma shields. From the results of the numerical analysis of the simulation experiments, it is concluded that turbulence in the experimental plasma shields is absent and that the stability of the cold and dense part of the plasma shields, which determines the target erosion, can be adequately modeled by FOREV-2 by use of the classical magnetic field diffusion coefficient. The experimentally observed downstreammore » drift of plasma shields along the surface of the vertical targets is due to the lateral motion of a cold and dense plasma layer close to the target. The observed upstream shift of the erosion profiles of vertical targets is due to reradiation from the expanding plasma shield. Line radiation and an appropriate model for anisotropic radiation transport are necessary for a realistic calculation of the reradiation from carbon plasma shields. Moreover, inclusion of the line radiation allows one to get a realistic radiation cooling after switching off the heating. Target erosion in the simulation experiments is caused by radiation. The agreement between calculated and measured erosion for graphite and quartz demonstrates the adequacy of the calculated 2-D radiative target heat loads.The 2-D numerical analysis of the disruption simulation experiments allows one to conclude that such experiments adequately simulate the tokamak plasma shield properties and its dynamics. The extensive validation exercise of FOREV-2 against disruption simulation experiments gives confidence that the numerical analysis of erosion for the ITER-FEAT vertical targets during the thermal quench phase of a disruption and the impurity production during ELMs and its transport toward the x-point to be performed with FOREV-2 is based on sound principles and covers all important aspects of plasma shield behavior and plasma shield stability.« less

Magnetic field concentration: comparison between several shapes of superconducting shields

Abstract: This paper deals with a system of flux density concentration using superconducting shields. The development of single grain high, temperature superconductors allows the conception of large sized magnetic shields. These shields force the flux density to be concentrated by modifying its spatial distribution. The authors' system consists of two low field solenoids, which have the same arrangement as Helmoltz coils. Between these two coils, two superconducting plates are arranged on both sides of the axis. For this study, the superconductor is considered as perfect. They propose to discuss the efficiency of several concentrating devices. To make their study, they performed a 3D-field calculation tool using a Monte-Carlo method. The main advantage of this method is a very simple algorithm to compute, even if the geometry is complicated. The authors have shown that if the distance between the two plates is small enough in respect to the coils diameter, the flux density is much higher than the one inside the coils. They also show the influence of the shape of the shields in the guidance of the flux lines. They have validated their simulations with an experiment.

Homogeneous and Multilayered Shields for Neutrons and Gamma-Rays

Abstract: Measurements were carried-out to compare the attenuation properties of homogeneous shields and shields of two layers and three layers for fast neutrons and total gamma rays. These were performed by measuring the fast neutron and total gamma-ray spectra behind homogeneous shields of magnetite–limonite, ilmenite–ilmenite and magnetite–magnetite concretes. The two layers assembly consists of iron and one of the above mentioned concretes, while the three layers shield consists of water, iron and one of the previously mentioned concretes. All measurements were carried-out using a neutron-gamma spectrometer with stilbene scintillator coupled to a fast photomultiplier tube. Separation between pulses of recoil protons and recoil electrons was achieved by a pulse shape discrimination technique. The obtained data are presented in the form of neutron and gamma spectra measured behind homogeneous shields and shields of two layers and three layers. The spectra measured behind homogeneous shields were used to derive the total macroscopic cross-sections for neutrons and the total attenuation coefficients for total gamma rays.

Magnetic head that detects leakage fluxes from a medium at a high resolution and leads the fluxes into a magneto-resistive element

Abstract: Magnetic heads capable of recording and reading with high sensitivity and resolution are provided by minimizing the outflow of magnetic fluxes from a flux guide to magnetic shields while using a flux guide structure for an MR element. In the magnetic head, magnetic shields exposed on a surface opposite a magnetic recording medium (air bearing surface) and a flux guide exposed between the magnetic heads via a non-magnetic layer are provided, and magnetic fluxes are guided by the flux guide to a magnetoresistive (MR) element formed in a position not exposed on the air bearing surface. The height of the magnetic shields in a direction perpendicular to the air bearing surface is less than the distance from the air bearing surface to the MR element, and the lengthwise direction of the magnetic shields is in parallel to the air bearing surface in the vicinity of the position in which the flux guide is formed.

Development of a split-toroid high-temperature superconducting cryogenic current comparator

Abstract: Cryogenic current comparators (CCCs) based on split toroidal shields show promise for the construction of high-accuracy ratio devices using high-temperature superconductors. To test this approach we have carried out measurements on a low-temperature superconducting prototype built of three layers of toroidal shields. We find that ratio accuracies of about 1 in 10/sup 7/ are achievable for this prototype. After several attempts, we were also able to construct a toroidal two-layer CCC fabricated of YBCO (YBa/sub 2/Cu/sub 3/O/sub 7/) components using split shields. The results from measurements on this device at low temperatures (4 K) indicate that the shielding provided by these layers does not provide sufficient attenuation of the leakage flux. The challenge remains to find a processing technique to produce YBCO in a machinable form with satisfactory magnetic shielding properties.

Method for manufacturing radiation detector of two- dimensional array type and x-ray shield wall

Abstract: PROBLEM TO BE SOLVED: To provide a radiation detector which is equipped with a collimator that can be easily worked, functions with high accuracy and can be manufac tured at much lower costs. SOLUTION: Vertical groove shields 11a and lateral groove shields 11b are formed by irradiating a photosensitive glass 1 with ultraviolet rays with a mask by an ultraviolet-ray mask exposure method, processing the glass, etching it with an acid, making grooves shaped like a lattice in the direction of the incidence of X rays and filling and encapsulating the powder of heavy metal like tungsten into the grooves. The shields 11a and the shields 11b are used as a collimator for an X-ray shield wall arrayed two-dimensionally, and a radiation detector is constituted by combining with the collimator an X-ray detector component (a scintillator array 4, a photoelectric conversion element 5, a scanning circuit 7 and a glass substrate 6) that is compatible with the collimator.

Comparison between analytical and numerical simulations of LF shielding efficiency

Abstract: In industrial applications, efficient shields are often required to prevent electromagnetic interference. In the past, several formulae for the evaluation of the shielding efficiency were proposed. This paper is aimed at the comparison of their results with the Finite Element Method, in order to assess their range of applicability. Evidence is given that expressions determined for planar and cylindrical shields of infinite structure can be suitably used to estimate the shielding efficiency of more realistic shaped shields.

Effects of conducting shields on the performance of pulsed rotating machines

Abstract: Conducting shields are often used in pulsed rotating machines to protect the surrounding electronic devices and humans from exposure to high oscillating magnetic fields. These conducting shields are subjected to rotating magnetic fields due to excitation currents in rotor windings. This induces eddy currents, which reduce the magnitude of the operating component of magnetic fields (radial component in drum machine and axial component in disk machine), and thus reduce the mutual inductance between rotor and stator windings. The eddy currents also induce drag torques on the rotor windings, which results in a degradation of machine performance. In this paper, both disk and drum pulsed alternators are investigated by the finite element code EMAP3D. The effects of conducting shields on drag torques and the operating components of the magnetic field are studied, and the results are presented as functions of the gap between the rotor and the shield.

Shielded magnetic tunnel junction magneto-resistive read head and assembly

Abstract: PROBLEM TO BE SOLVED: To provide an MR read head having an MTJ device formed to be sufficiently thin for attaining the high surface density by reducing the space between magnetic shields. SOLUTION: As to the magnetic tunnel junction MTJ device 100, the magneto-resistive(MR) read head has the MTJ device 100 located between two spaced-apart magnetic shields S1, S2. The magnetic shields function also as electrical leads for connecting the head to a detection circuit. Conductive spacer layers 102, 104 are located at the top and bottom of the MTJ device 100 to connect the MTJ device 100 to the shields. The thickness of the spacer layer is selected to optimize the spacing between the shields. Each of the shields has the pedestal region for reducing the electric short-circuit between the shields in the case the space between the shields is too small, and the MTJ device 100 is located between these two pedestals.

Optimization of magnetic multilayered shields

Abstract: In this paper a procedure for the optimization of multilayered shields for low-frequency magnetic fields is presented. The shield is optimized with respect to the total volume of the composing materials, being the magnetic flux density magnitude at test points in the shielded region smaller than a given threshold value. For simplicity, shields composed of two different materials only are considered. The number and thickness of the shield layers belong to the set of the control variables. Only one layer thickness at a time is allowed to vary. The procedure is repeated for the different multilayered shield configurations, starting from the single-layer ones for each material, until the optimum shield volume is reached.

Material for electromagnetic wave shields

Abstract: PROBLEM TO BE SOLVED: To provide a material for electromagnetic wave shield, which can be freely processed in shape and fixed in shape after shape processing. SOLUTION: The material for electromagnetic wave shields contains a liquid resin and magnetic powder.

Charts for estimating the axial shielding factors for triple-shell open-ended cylindrical shields

Abstract: Describing the shields with the number of shells greater than two differs from the previously done work in having a significant increase in the number of charts needed. To limit the number of charts, only the shields were examined that have the most-used exterior aspect ratio, namely, equal to 5. It was also assumed that all the shielding shells are made of the same material with an equal and relatively small thickness, which is a practical case as well. Since the three-shell structure does not allow much freedom for variations in the air gaps between the shells, only the shields having air gaps of 5% and 10% of the diameter of the outermost shell were considered. Finally, a set of charts was computed with the help of a standard ANSYS(R) software employing an FEM method. The charts are represented as logarithmic contour plots where the ratio of the inner to outer shells' lengths and permeability normalized to the thickness-to-diameter ratio of the outermost shell are independent variables; and the air gaps and ratio of the middle to outer shells' lengths are fixed parameters. The charts calculated allow one to quickly estimate the axial shielding factor and to clearly observe the effect of the shield's parameters on the axial shielding.

Device for introducing hot air for drying ceramic molds comprises fixed supported covering shields arranged on an air distribution pipe having outlet nozzles

Abstract: Device for introducing hot air to dry materials comprises fixed supported covering shields (21) arranged on an air distribution pipe (14). The shields are arranged at a short distance from the outer casing surface. Outlet nozzles (15) inserted into the distribution pipe and the size and number of shields are coordinated with each other in such a way that at least one row of nozzles brushes over a free space provided between the shields during rotation of the distribution pipe. Preferred Features: The shields are arranged at an angle of 45-90, preferably 60 deg . The air distribution pipe is composed of four uniform segments with right angled flanges.

Short communication Effect of radiation shield on pressure losses and power output of AMTEC cell

Abstract: Pressure loss in a PX-3A alkali metal thermo-electric converter (AMTEC) cell was investigated by varying the heat radiation between the beta alumina solid electrolyte (BASE) and the condenser. Chevron radiation shields were used to change the heat radiation between the BASE and the condenser in different numbers and at different angles. Results show that the pressure losses and also the pressure on the cathode side increase using chevron shields. The cell electrical power output and the cell efficiency decrease as the pressure on the cathode side increases when chevron shields are placed. The power output and efficiency increase as the chevron angle increases up to a certain limit. # 2001 Elsevier Science B.V. All rights reserved.

Shielded magnetic tunnel junction magnetoresistive read head

Abstract: A magnetic tunnel junction (MTJ) magnetoresistive read head for a magnetic recording system has the MTJ device (110,120,130) located between two spaced-apart magnetic shields (S1,S2). The magnetic shields, which allow the head to detect individual magnetic transitions from the magnetic recording medium without interference from neighboring transitions. also function as electrical leads for connection of the head to sense circuitry. Electrically conductive spacer layers (102,104) are located at the top and bottom of the MTJ device and connect the MTJ device to the shields. The thickness of the spacer layers is selected to optimize the spacing between the shields, which is a parameter that controls the linear resolution of the data that can be read from the magnetic recording medium. To reduce the likelihood of electrical shorting between the shields if the shield-to-shield spacing is too small, each of the shields can have a pedestal region (161,163) with the MTJ device located between the two pedestals, so that the shield-to-shield spacing outside the pedestal regions is greater than in the pedestal regions.

Neutronics and Shielding Analysis of an Ignitor

Abstract: This paper presents the Monte Carlo calculations made to test the effectiveness of the shields required to allow hands-on maintenance in the Ignitor tokamak.

Prediction of impact damage on double bumper shields for the protection of orbiting manned modules

Abstract: Hypervelocity impacts of space debris, represented by aluminium spheres, against typical shielding systems for the International Space Station (ISS) manned modules are simulated using the AUTODYN-2D hydrocode. The considered shield type is the double bumper shield, i.e., two separate bumpers placed in front of the structure to be protected. Numerical tools are first tested and calibrated through the simulation of available tests, at the maximum impact velocity currently attainable (around 6.5 km/s). As the estimated debris average impact velocity along the ISS orbit is around 10 km/s, the model giving the best agreement with the experiments is then used for the ballistic limit extrapolation in the velocity range not experimentally achievable. The results of numerical extrapolation are compared with the semi-empirical curves actually used for the ballistic limit estimation in the high velocity regime, based on the assumption of damage proportional to projectile momentum.