High-performance Magnetic Shield Research Articles

A High-Performance Magnetic Shield with MnZn Ferrite and Mu-Metal Film Combination for Atomic Sensors.

This study proposes a high-performance magnetic shielding structure composed of MnZn ferrite and mu-metal film. The use of the mu-metal film with a high magnetic permeability restrains the decrease in the magnetic shielding coefficient caused by the magnetic leakage between the gap of magnetic annuli. The 0.1–0.5 mm thickness of mu-metal film prevents the increase of magnetic noise of composite structure. The finite element simulation results show that the magnetic shielding coefficient and magnetic noise are almost unchanged with the increase in the gap width. Compared with conventional ferrite magnetic shields with multiple annuli structures under the gap width of 0.5 mm, the radial shielding coefficient increases by 13.2%, and the magnetic noise decreases by 21%. The axial shielding coefficient increases by 22.3 times. Experiments verify the simulation results of the shielding coefficient of the combined magnetic shield. The shielding coefficient of the combined magnetic shield is 16.5%. It is 91.3% higher than the conventional ferrite magnetic shield. The main difference is observed between the actual and simulated relative permeability of mu-metal films. The combined magnetic shielding proposed in this study is of great significance to further promote the performance of atomic sensors sensitive to magnetic field.

A scalable high-performance magnetic shield for very long baseline atom interferometry.

We report on the design, construction, and characterization of a 10 m-long high-performance magnetic shield for very long baseline atom interferometry. We achieve residual fields below 4 nT and longitudinal inhomogeneities below 2.5 nT/m over 8 m along the longitudinal direction. Our modular design can be extended to longer baselines without compromising the shielding performance. Such a setup constrains biases associated with magnetic field gradients to the sub-pm/s2 level in atomic matterwave accelerometry with rubidium atoms and paves the way toward tests of the universality of free fall with atomic test masses beyond the 10-13 level.

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

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.

High Tc SQUID System for Detection of Small Metallic Contaminant in Industrial Products

A three channel High-Tc SQUID system for detection of magnetic contaminants in industrial products was developed. Finding ultra-small metallic contaminants is a big issue for manufacturers producing commercial products such as lithium ion batteries. When the contamination does occur, the manufacturer of the product suffers a great loss to recall the tainted products. The outer dimension of metallic particles less than 100 micron can not be detected by X-ray imaging, which is commonly used as the inspection method. Therefore, a highly sensitive detection system for small contaminants is required. We developed a detection system based on a three channel high-Tc SQUID microscope with a high performance magnetic shield. Three SQUIDs were installed in one microscope-type cryostat with a 3" sapphire vacuum window which separates the SQUID and atmosphere. This design enables the SQUID to approach an object to be measured as close as 1 mm. The minimal detectable size of the particle is also highly dependent on the magnetic field noise of the SQUID. Therefore, we employed double transformer coupling, which lowers the noise. One transformer was placed at 77 K and the other was at room temperature (RT). As a result, the magnetic field noise of the SQUID was reduced by 36%. Finally we could successfully measure small iron particles as small as 30 micron. This detection level was difficult to achieve when using a conventional X-ray detection method.

SQUID sensor application for small metallic particle detection

High-Tc superconducting quantum interference device (SQUID) is an ultra-sensitive magnetic sensor. Since the performance of the SQUID is improved and stabilized, now it is ready for application. One strong candidate for application is a detection system of magnetic foreign matters in industrial products or beverages. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products such as lithium ion batteries. If this happens, the manufacturer of the product suffers a great loss recalling products. The outer dimension of metallic particles less than 100 μm cannot be detected by an X-ray imaging, which is commonly used for the inspection. Ionization of the material is also a big issue for beverages in the case of the X-ray imaging. Therefore a highly sensitive and safety detection system for small foreign matters is required. We developed detection systems based on high-Tc SQUID with a high-performance magnetic shield. We could successfully measure small iron particles of 100 μm on a belt conveyer and stainless steel balls of 300 μm in water. These detection levels were hard to be achieved by a conventional X-ray detection or other methods.

METALLIC CONTAMINANT DETECTION SYSTEM FOR INDUSTRIAL PRODUCTS BY HIGH TC SQUID MAGNETIC SENSOR

High-Tc superconducting quantum interference device (SQUID) system for detection of magnetic foreign matter in industrial products was developed. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products, such as lithium ion batteries. The outer dimension of metallic particles less than 100 microns cannot be detected by conventional X-ray imaging. Therefore, we developed a detection system based on high-Tc SQUID microscopes with a high-performance magnetic shield. Using SQUID microscopes with a 0.5 mm-thick vacuum window was proposed. This design enables the SQUID to approach an object to be measured as close as 1 mm and enhances the sensitivity. A new magnetic shield with sleeves was carefully designed and built. As a result, we could successfully measure a small iron particle with 100 μm. This detection level was hard to achieve by conventional X-ray detection methods.

A high-Tc SQUID micro-detector with a high performance magnetic shield for contaminant detectionin industrial products

A high-Tc superconducting quantum interference device (SQUID) system for the detection ofmagnetic foreign matter in industrial products was developed. There is a possibility thatultra-small metallic foreign matter has been accidentally mixed with industrial productssuch as lithium ion batteries. Metallic particles with outer dimensions less than100 µm cannot be detected by conventional x-ray imaging. Therefore we developed a detection system based ona high-Tc SQUID microscope with a high performance magnetic shield. The use of SQUIDmicroscopes with a 0.5 mm thick vacuum window was proposed. This design enables theSQUID to approach the object to be measured as close as 1 mm and enhancesthe sensitivity. A new magnetic shield with sleeves was carefully designedand built. As a result, we could successfully measure small particles sized100 µm. This detection level was hard to achieve using a conventional x-ray detection method.

Magnetic Field Leakage From a 45$^circ$-Angle Magnetic Shell and a Reduction Method for a High-Performance Magnetic Shield

A 45deg-angle shell is a key component of a cylindrical magnetic shield by which large shielding effects can be obtained for axially applied magnetic field and for the transversely applied magnetic field under magnetic shaking. A known problem with this shell is that a leakage magnetic field from edges of the shell is large. We have investigated a method to alleviate this problem through the use of passive magnetic layers, made of flexible magnetic sheets, which are padded inside the shell. We also utilized the layer in order to enhance the axial shielding factor (ASF). In this paper, we present our approach and the results of tests we carried out on several structures of thin passive layers with a small experimental model of a 45deg-angle shell. We were able to reduce the shaking leakage down to 1/14 and enhanced the ASF by six times

A proposal of fast self-acting and recovering magnetic shield type superconducting fault current limiter and the analyses of their characteristics

A high-performance magnetic shield type superconducting fault current limiter (MSFCL) has been proposed. It will be fast activated automatically when a short circuit failure occurs. And it will be recovered to superconducting state in a short period of time after the fault is cleared. The designed magnetic shielding body consists of a large number of the flat Bi2223 rings. They are stacked with a small gap between each ring and hence the cooling surface is increased by about 10 times that of an usual tubular shielding body. The toroidal coils (TCs) will be wound around the rings so that a magnetic field may be applied to the rings in a circumference direction. The thin heaters similar in form to the flat ring will also be stuck on both sides of each ring. It is shown that the rings will be automatically heated quickly up to T c or more and accordingly a faster current limiting action will be realized by these two additional effects. A fairly fast recovery to a superconducting state after a fault is also clarified.

Ultralow magnetic fields and Gravity Probe B gyroscope readout

We describe the generation of an ultralow magnetic field of < 10 −11 Tesla in the flight dewar of the Gravity Probe B Relativity Mission. The field was achieved using expanded-superconducting-shield techniques and is maintained with the aid of a magnetic materials control program. A high performance magnetic shield system is required for the proper function of gyroscope readout. The readout system employs a dc SQUID to measure the London moment generated by the superconducting gyro rotor in order to resolve sub-milliarcsecond changes in the gyro spin direction. In addition to a low residual dc magnetic field, attenuation of external field variation is required to be 10 12 at the gyro positions. We discuss the measurement of the dc magnetic field and ac attenuation factor and the performance of the readout system.