Showing papers on "Shields published in 2012"

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.

Investigation and Optimization of Protective Properties of Metal Multi-Layered Shields: A Review

Abstract: Effort to enhance protective properties of shields against high speed impact triggered investigations of the ballistic performance of multilayer barriers having different structure, their comparison with each other and with the monolithic barriers. In spite of a large number of publications on these topics there are no comprehensive surveys of this field. The goal of the present review is to close this gap. This review includes analytical, numerical and experimental investigations which can be useful for elucidating general properties of multi-layered metallic shields, e.g. effect of layering, spacing and change of the order of the plates on the protective performance of shields, and also studies which suggested analytical methods for optimization of multi-layered shields.

Investigation of Models of Grid-Like Shields Subjected to Lightning Electromagnetic Field: Experiments in the Frequency Domain

Abstract: In this paper, frequency-domain measurements of magnetic and electric field shielding effectiveness of grid-like spatial shield models exposed to lightning action are presented. Scaled experimental models of nearby and direct lightning strikes are proposed. Models of single-layer and double-layer wire shields of two different mesh widths are examined. Differences between the shielding effectiveness of magnetic and electric fields are discussed. The measurement results are compared to the results of numerical simulations.

Limited-use radiation attenuating shields, liners for radiation attenuating shields and methods

Abstract: Wearable radio-opaque shields may be formed from relatively low-cost materials, which may include a non-toxic radio-opaque material. The use of such materials may render the wearable radio-opaque shields suitable for limited use or even for single use. The useful life of a wearable radio-opaque shield may be extended, and hygiene improved, by way of a liner configured for assembly with the wearable radio-opaque shield. Methods for using and disposing of wearable radio-opaque shields and liners are also disclosed.

Application of hemisphere radiation shields with temperature-dependent emissivity for reducing heat transfer between two concentric hemispheres

Abstract: The radiation network method has been applied to calculate the net radiation heat transfer between two concentric hemispheres separated by two hemispherical radiation shields with temperature-dependent surface emissivities. Three different materials are chosen for radiation shields: aluminum oxide, silicon carbide, and tungsten. The reduction in heat transfer with shields depends not only on the surface characteristics of the two shields, but also on the locations of the shields. Three illustrative examples are presented to illustrate the effects of temperature dependent emissivities and shield locations on the percentage heat transfer reduction. The analysis can be used to study other cases as warranted.

Effects of Fan-Aspirated Radiation Shield for Temperature Measurement in Greenhouse Environment

Abstract: Purpose: Provision of accurate temperature measurement is an essential element to ensure a precise control in greenhouse environment. This study was organized to compare the effects of six solar radiation shields with different shapes for temperature measurement and find the most appropriate shield for greenhouse environment. Methods: A fan-aspirated radiation shield was designed and manufactured. Using the fan-aspirated radiation shield and five other shapes i.e., the cup shape, horizontal pipe, vertical pipe, parallel boards and commercial shields, temperature measurement was conducted over the lawn surface as well as greenhouse indoor environment. The measurement height varied at 0.5, 1.0 and 1.5 m from the floor. Results: The measured temperatures by the fan-aspirated radiation shield were 1.30-1.49℃ lower than the values recorded by other different-shaped shields at 1.5 m of measurement height. As the measurement height decreases, observed differences between measured temperatures of the fan-aspirated radiation shield and other shields demonstrate a declining trend. However, at low measurement heights, the radiation emitted from the bottom surface would be the source of error in temperature measurement. Conclusions: The fan-aspirated radiation shield is a required tool for exact measurement of air temperature in greenhouse temperature control.

Analysing the Effectiveness of the 1750 Tonne Shields At Moranbah North Mine

Abstract: Moranbah North Mine has a challenging geotechnical environment that historically resulted in cavity formation on the longwall face with its an associated reduction in productivity. Due to the complex geology at the mine, the increased depths of cover in future panels and the aging of the previous 980 t shields, longwall face stability became a concern. In order to ensure effective strata control in future panels, a new set of 1750 t powered supports were installed into the longwall 108 panel in 2009. These shields were, and still remain, the highest rated capacity shields in the world. This paper presents the results of an investigation into the effectiveness and necessity of the new powered supports. The investigation was undertaken in the form of a comparative analysis to determine the relative effectiveness of the two sets of different capacity shields by analysing the performance of the shields in panels that were directly adjacent and, subsequently, subject to similar conditions. Anglo American has plans to commence two additional longwall mining operations in the same region and the outcome of the investigation will allow the suitability of the larger capacity shields to be determined for the future operations.

Electric machine e.g. internal-rotor electric motor, has bearing shields provided with bearings at front ends of stator and separated from stator, where radial position of bearing shields is adjusted with respect to stator

Abstract: The machine i.e. electric motor (1), has a stator (2), and a rotor (4) rotatably mounted in the stator. Bearing shields (7, 9) are provided with bearings (8, 10) at front ends of the stator. The bearing shields are separated from the stator, where a radial position of the bearing shields is adjusted with respect to the stator. The bearing shields are welded with the stator, and a power electronics (11) is held in the bearing shields. The stator is connected to a stator housing (3), and the bearing shields are connected with the stator housing. An independent claim is also included for a method for manufacturing an electric machine.

Experimental and simulation optimization analysis of the Whipple shields against shaped charge

Abstract: Occasionally, the Whipple shields are used for the protection of a space station and a satellite against the meteoroids and orbital debris In the Whipple shields each layer of the shield depletes part of high speed projectile energy either by breaking the projectile or absorbing its energy Similarly, this investigation uses the Whipple shields against the shaped charge to protect the light armour such as infantry fighting vehicles with a little modification in their design The unsteady multiple interactions of shaped charge jet with the Whipple shield package against the steady homogeneous target is scrutinized to optimize the shield thickness Simulations indicate that the shield thickness of 075 mm offers an optimum configuration against the shaped charge Experiments also support this evidence

Substrate shielding of transformers in millimeter-wave integrated circuits

Abstract: Shielding structures intended to improve the performance of millimeter-wave transformers are presented. The loss mechanisms of the components are discussed and the losses related to the silicon substrate are shown to be the most relevant. A patterned ground shield and a floating shield are detailed and their influences in terms of inductance, quality-factors, coupling coefficients and minimum insertion loss are evaluated through measurement and electromagnetic simulations. Results indicate that quality-factors are deteriorated by the use of patterned ground shields, whereas the use of floating shields allows a slight improvement without degrading other characteristics of the transformer.

Device provided with sensor laminate, shield, and first shield stabilization structure, device provided with sensor laminate, shield, and magnetic layer, device provided with data storge medium, recording head, and arm, and method with step for providing sensor structure and annealing the same

Abstract: PROBLEM TO BE SOLVED: To provide a device including a sensor laminate, a shield, and a first shield stabilization structure.SOLUTION: The device includes sensor laminates (92, 122, 162, 202, 262), first and second shields (94, 96; 124, 126; 164, 166; 204, 206; 264, 266) positioned at a side confronting the sensor laminates, a first shield stabilization structures (102, 132, 172, 212, 268) adjacent to the first shields (94, 124, 164, 204, 264) to apply a bias magnetic field to the first shields. The second shield stabilization structures (186, 234) can be positioned adjacently to the second shields (164, 204).

Efficiency evaluation via finite element method of 3D magnetostatic shields using different types of magnetic potentials

Abstract: The efficiency of spherical and cylindrical magnetic shields placed in a magnetostatic field are modeled numerically, with FEM, taking into account: a) type of magnetic potential: scalar or vector; b) for certain types of shields comparisons with the measured values will be performed; c) comparison between analytical values and numerical values. It is a beginning of a study which will continue with the study shielding efficiency at low and high frequencies respectively.

Dynamic magnetic shield for the CLAS12 central TOF detector photomultiplier tubes

Abstract: The Central Time-of-Flight detector for the Jefferson Laboratory 12-GeV upgrade is being designed with linear-focused photomultiplier tubes that require a robust magnetic shield against the CLAS12 main 5-T solenoid fringe fields of 100 mT (1 kG). Theoretical consideration of a ferromagnetic cylinder in an axial field has demonstrated that its shielding capability decreases with increasing length. This observation has been confirmed with finite element analysis using POISSON model software. Several shields composed of coaxial ferromagnetic cylinders have been studied. All difficulties caused by saturation effects were overcome with a novel dynamical shield, which utilizes a demagnetizing solenoid between the shielding cylinders. Basic dynamical shields for ordinary linear-focused 2-in. photomultiplier tubes were designed and tested both with models and experimental prototypes at different external field and demagnetizing current values. Our shield design reduces the 1 kG external axial field by a factor of 5000.

Characteristics of shields composite coatings based on nanodisperse particles

Abstract: The dependences of shielding effectiveness of electromagnetic field on the structure of inhomogeneous nano-composite material are studied.

Numerical simulation of high-speed penetration-perforation dynamics in layered armor shields

Abstract: Penetration models and calculating algorithms are presented, describing the dynamics and fracture of composite armor shields penetrated by high-speed small arms A shield considered consists of hard (metal or ceramic) facing and multilayered fabric backing A simple formula is proved for the projectile residual velocity after perforation of a thin facing A new plastic-flow jet model is proposed for calculating penetration dynamics in the case of a thick facing of ceramic or metal-ceramic FGM materials By bringing together the developed models into a calculating algorithm, a computer tool is designed enabling simulations of penetration processes in the above-mentioned shields and analysis of optimization problems Some results of computer simulation are presented It is revealed in particular that strength proof of pliable backing can be better as compared with more rigid backing Comparison of calculations and test data shows sufficient applicability of the models and the tool

Asphalt stirring equipment

Abstract: The utility model discloses asphalt stirring equipment which comprises dust leakage points and a dust waste gas processing system. The dust waste gas processing system comprises shields (1) and air sucking devices (2) sucking air from the interiors of the shields (1), and the shields (1) are arranged on the outer sides of the dust leakage points. Since the shields and the air sucking devices are arranged at all the dust leakage points in the asphalt stirring equipment, the dust waste gas at each dust leakage point of the asphalt stirring equipment per se can be processed, so as to achieve overall environment friendliness and prevent environment pollution.

The dosimetry of eye shields for kilovoltage X-ray beams.

Abstract: The objective of this work was to evaluate the dosimetry of tungsten eye shields for use with kilovoltage X-ray beam treatments. The eye shields, originally designed for megavoltage electron beams, were made of 2 mm tungsten thickness and inside diameters of 11.6 and 15.0 mm with optional aluminium caps of 0.5 and 1 mm thickness. The relative dosimetry of the eye shields were examined by measurement of transmission doses with full scatter conditions, central axis depth doses and beam profiles underneath the eye shield. The X-ray beams used in this study ranged in energy from 50 to 280 kVp. Transmission measurements were performed using an Advanced Markus ionisation chamber located at the surface of an RMI457 Solid Water phantom with a 3 cm diameter applicator flush against the phantom surface. Depth doses and profiles measurements were performed in a PTW MP3 scanning water tank with a PTW diamond detector. Results for transmission doses for the medium size eye shield increased from 1 to 22 % for 50–280 kVp while for the smaller eye shield the percentage dose increased from 3.5 to 30 % for the same energy range. There were minimal differences between using the 0.5 and 1 mm aluminium caps. Central axis depth doses measured with and without the eye shields demonstrated the 125 and 180 kVp beams had higher peak doses behind the eye shields. These results show that these tungsten eye shields are suitable for use with kilovoltage X-ray beams. However, the clinical impact needs to be considered for the higher X-ray beam energies.

X-ray source having cooling and shielding functions

Abstract: Disclosed herein is an X-ray source having cooling and shielding functions The X-ray source includes an X-ray generation unit (100) which has one or more insulation columns (160) and emits X-rays in a vacuum; a cooling unit (180) which is provided around a periphery of the X-ray generation unit and removes heat generated from the X-ray generation unit; and a shielding unit (190) which is provided around a periphery of the cooling unit and shields an area exposed to X-rays other than the areas related to the emission of the X-rays

Device for fast neutrons radiation cancer therapy

Abstract: FIELD: medical equipment. ^ SUBSTANCE: invention relates to medical equipment, in particular to the devices for cancer fast neutrons radiation therapy; the device comprises the neutrons generator surrounded from above by the shield protecting from the broad beams of boronized polyethylene; the generator located against the biological shield on the same axle with the built in it neutron channel; the device is also equipped with the functional shield; the biological and functional shields are performed in the shape of adjacently placed stunned cones with a big footing from the side of the outlet aperture of the neutron channel and a smaller one - from the side of the neutrons generator; the shields are executed fungible from the same material or composite consisting of the parts in the shape of blunted cones put one inside the other, at that the parts of the biological shield and/or functional shield are made fungible or have interstratified layers; the biological and functional shields or their parts are made of metal or metal hydrides or metal alike substances or porous materials containing light nucleuses or hydric compositions; herewith the radius of the inlet aperture of the neutron channel and of the thickness of the biological and functional shields is selected on the basis of the conditions of provision of the therapeutic efficiency determined by the formula F=D/L, wherein D is the distance from the back edge of the outlet channel of the neutron channel on the surface of the shield to the point whereat the kerma counts to 20% of the kerma in the beam center, and L is the distance passed by the fast neutron without interacting with the shields materials up to the point whereat the kerma amounts to 20% of the kerma in the beam center. ^ EFFECT: application of the invention allows to enhance the operation characteristics of the device due to the creation of the optimal shaper of the radioactive fields and the requisite radiation protection of the patient. ^ 9 cl, 4 dwg.

Magnetic shielding device for transformer

Abstract: PROBLEM TO BE SOLVED: To provide a magnetic shielding device for a transformer capable of reducing a stray loss due to a leakage magnetic flux.SOLUTION: A device comprises an iron core 110; a plurality of first magnetic shields 140 provided on each of a pair of opposed inner walls of a tank 130 housing the iron core 110, extending in a lamination direction of plural first magnetic steel plates 111, and constituted by plural second magnetic steel plates 141 laminated in a direction orthogonal to the lamination direction; and a plurality of second magnetic shields 150 provided on each of another pair of opposed inner walls of the tank 130, extending in a direction orthogonal to the lamination direction, and constituted by plural third magnetic steel plates 151. In the plural first magnetic shields 140, one end faced to the iron core 110 is adjacent to the iron core 110. The iron core 110 serves as a magnetic path for flowing a leakage magnetic flux generated from a coil 120 and passing through the plural first magnetic shields 140.

Integrated Leak testing of 80 K Thermal Shields of SST-1 in Room Temperature and Cold condition

Abstract: SST-1 has implemented bubble type 80 K thermal shields cooled with single-phase liquid Nitrogen around the superconducting magnet system. These panels have been designed to maintain temperature uniformity within ┴ 5 K with pressure drops below 1.5 bar for nominal flow conditions. Another extremely critical criterion towards the functionality of these thermal shields is the leak tightness of these panels under any normal and off-normal scenarios. Integrated helium leak testing on each of these panels as well as group of assembled panels both at room temperature (RT) as well as at cold temperature of 80 K have been carried out to ensure leak-tightness. All the panels have been tested in component levels before and after thermal shocks between RT and 80 K three times. As per defined groups, these assembled panels around SST-1 vacuum vessel modules and sectors have been tested inside a dedicated high vacuum (HV) chamber having vacuum < 5.0 x 105 mbar. The panel temperature was obtained to be 80 K with inlet pressure of 1.83 bar (a). Before cool down and after achieving 80 K, these panels were leak tested by pressurizing helium gas at 8.0 bar (g). RGA spectra does not show traces of helium gas indicating the leak tightness of integrated system.

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.

Vapor transport deposition system and method employing removable shields

Abstract: A method and system includes removable shields arranged inside a deposition chamber to prevent vaporized material from accumulating on the walls of the chamber. The removable shields can be removed for cleaning.

Removal of stray radiation from warm shields in cooled infrared optical systems

Abstract: Stray radiation may be introduced after warm shields are mounted in cooled infrared systems.The stray radiation consists of radiation and reflection from the warm shields.Since it degrades the SNR,dynamic range and image quality of the system,it shall be avoided by design.The stray radiation was analyzed based on the theory of radiation and heat transfer,and NETD was calculated.The scheme to avoid stray light effects was proposed and verified by ray tracing.The stray radiation of flat shields and spherical reflective shields was analyzed and compared in LIGHT TOOLS.Stray radiation effects were avoided if spherical reflective warm shields with proper radius are properly positioned.A spherical reflective warm shield with radius 30.3mm was used to replace the original flat one,and the stray radiation dropped by more than 99%.

Performances of single and two-stage pulse tube cryocoolers under different vacuum levels with and without thermal radiation shields

Abstract: Single and two-stage Pulse Tube Cryocoolers (PTC) have been designed, fabricated and experimentally studied. The single stage PTC reaches a no-load temperature of similar to 29 K at its cold end, the two-stage PTC reaches similar to 2.9 K in its second stage cold end and similar to 60 K in its first stage cold end. The two-stage Pulse Tube Cryocooler provides a cooling power of similar to 250 mW at 4.2 K. The single stage system uses stainless steel meshes along with Pb granules as its regenerator materials, while the two-stage PTC uses combinations of Pb along with Er3Ni/HoCu2 as the second stage regenerator materials. Normally, the above systems are insulated by thermal radiation shields and mounted inside a vacuum chamber which is maintained at high vacuum. To evaluate the performance of these systems in the possible conditions of loss of vacuum with and without radiation shields, experimental studies have been performed. The heat-in-leak under such severe conditions has been estimated from the heat load characteristics of the respective stages. The experimental results are analyzed to obtain surface emissivities and effective thermal conductivities as a function of interspace pressure.

Eddy-currrents and the Force Analysis for the Thermal Shields of the MICE Spectrometer Solenoids

Abstract: MICE Note-420 Eddy-currents and the Force Analysis for the Thermal Shields of the MICE Spectrometer Solenoids H. Pan 1 , S. O. Prestemon 1 , S. Virostek 1 , R. Preece 2 and M. A. Green 1 Abstract—The MICE spectrometer solenoids contain five superconducting solenoids with different structural parameters. Two coils are each separately powered. The other three coils are connected in series. The five coils are wound on a single 6061- aluminum mandrel. If one of the coils quenches, the quench will propagate by quench-back and cause other coils quench sequentially. The decaying field will induce a significant eddy current and Lorentz force on the surrounding shields. Shield eddy current heating is non-issue for the spectrometer solenoids, but the Lorentz force becomes an important aspect for designing because the five coils are not symmetric. In this paper, the detailed eddy current simulations were performed. The net lateral forces on each part of shields and the stress distribution were analyzed. Based on the Finite-element analysis, adding cuts on shields is an effective way to avoid the collapse of the shield due to changing current path direction. The shield cuts layout is presented in detail. the radiation heat from the room temperature. The main structure of shields consist of two 9.5 mm thick neck copper shields and a 6.35 mm thick main aluminum shields including main cylinder, endplates and inner bore. Based on the previous test results, the main shields are expected to use 1100 aluminum to enhance the thermal uniformity [5]. Index Terms—Eddy current, force, quench, superconducting magnets, shields, transient stress. I. I NTRODUCTION T HE objective off the Muon Ionization Cooling Experiment (MICE) is to demonstrate the designing and engineering on a section of cooling channel capable of giving the desired performance for a Neutrino Factory [1]. Two spectrometer solenoids in the MICE cooling channel will provide a uniform magnetic field for five plane scintillating fiber trackers to analyze the changing of the muon beam emittance in the cooling channel [2]. Each of the spectrometer magnet consists of five coils wound on a 2543-mm long 6061-Al mandrel as represented in Fig.1 (not drawn to scale). The center and end coils are the tracker section of the spectrometer solenoids, providing a uniform magnetic field (0.3 percent) over a length of 1000 mm and in a diameter of 300 mm; The two match coils are to match the muon beam from the Absorber Focus Coil module (AFC) into the tracker section [3,4]. All the coils are bath-cooled in liquid helium and use cryocoolers to re-condense helium vapor. In order to reduce the heat load to the cold mass, a set of shields cooled by the first-stages of thee coolers were adopted to intercept most of Manuscript received October 9, 2012. This work was supported in part by the U.S. Department of Energy under contract DE-AC02-05CH11231. H. Pan, S. O. Prestemon, S. Virostek and M. A. Green are with Lawrence Berkeley National Laboratory, Berkeley, CA, 94720 USA (phone: 510-612- 7137; e-mail: hengpan@lbl.gov). R. Preece is with Rutherford Appleton Laboratory, Didcot, OX11 0QX UK. (e-mail: Roy.Preece@stfc.ac.uk). Fig. 1. The cold mass and shields cross section of the spectrometer solenoids Because the cold mass is asymmetric, the interaction of its local magnetic field with the eddy current induced on the conductive parts of the cryostat during a quench could introduce significant lateral forces on the mandrel and the shields. Eddy currents don’t affect the mandrel mechanical stability due to a high electrical resistivity of 6061-Al. The big concern is with the shields where their low electrical resistivity causes a large-forces during a quench. One must reduce the eddy current impact by redesigning the shields. II. MICE S PECTROMETER S OLENOIDS P ARAMETERS The Spectrometer solenoid consists of five coils wound on the slotted aluminum 6061 bobbin, and covered by Al bandage wound on top of each coil to avoid separation between coil and mandrel. Table I represents the parameters of coils for this study. TABLE I D ESIGN P ARAMETERS FOR C OILS Parameter No. turns/layer No. layers Inner radius (mm) Outer radius (mm) Axial coil build (mm) Initial current (A) M1 M2 E1 C E2

The Application of Radiation Shields for Thermal Control of Superheater Tubes in Boiler

Abstract: Superheater tubes temperature control is a necessity for long lifetime, high efficiency and high load following capability in boiler. This study reports a new approach for the control strategy design of boilers with special shields. The presented control strategy is developed based on radiation thermal shields with low emissivity coefficient and high reflectivity or scattering coefficient. In order to simulate the combustion event in boiler and heat transfer to superheater tubes, an effective set of computational fluid dynamic (CFD) codes is used. Results indicate a successful identification of over- heated zones on platen superheater tubes and effect of radiation shields for solving this problem.

Anti-dazzle flood light

Abstract: The invention relates to an anti-dazzle flood light, which comprises a light source (1), a transmitting lamp shade (2) and a lamp body (3), wherein the periphery of the light source (1) is provided with a plurality of glare shields (4) the sides of which are antidazzle; the glare shields (4) comprise fixed glare shields (41) and adjustable glare shields (42), wherein the adjustable glare shields (42) are fixed on substrates (6) of the glare shields; and the fixed glare shields (41) are fixed on a pressing plate (5). The periphery of the light source is provided with a plurality of glare shields the sides of which are antidazzle, so that the irradiation light of certain sides can be shielded by the glare shields arranged at the preset position, the antidazzle function of lateral surface can be achieved, and the optimum antidazzle effect can be realized through adjusting the position of the glare shields to ensure the adjustability of lateral surface antidazzle. Furthermore, the light of the invention is simple in operation and is convenient to prompt and use.

A research on the optimum parameters for multishell cylindrical magnetic shields

Abstract: This paper gives a general theory of shielding efficiencies for magnetic shields including single-layer and multishell cylindrical ones. The differences of shielding efficiencies between multishell cylindrical shields with and without end-caps are also discussed. The optimum parameters (the innermost radius and length and radial and axial air gap) for five-shell cylindrical magnetic shields are expressed here after a detail theoretical analysis. While three of the four parameters are fixed, the optimum value of the last one is found. The residual magnetic field inside a set of three nested magnetic shields is measured experimentally, which is found to agree well with the theory.