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For over 60 years, the MuShield Company of Londonderry, New Hampshire has been designing and producing mumetal magnetic shielding components for multiple industries worldwide.
Such industries include:
- Aerospace
- High tech / Electronic
- Defense
- Medical / Healthcare
- Industrial / Manufacturing
- Education
- Trade
If it concerns building a high permeability magnetic shield for low frequencies and static magnetic shielding applications , we are your trusted source. We will work in conjunction with you and your colleagues to provide feasible, efficient, and cost effective shielding solutions for your unique application need – from development through production.
Contact us today at info@mushield.com or 603-666-4433
with any mumetal or magnetic shielding questions.
A few short examples of applications
There is a story behind every shielding application. Contracted by NASA to design and build atomic clocks for space exploration, the people at SAO had the opportunity to test Einstein’s Theory of Relativity. Our role was to provide them with some carefully constructed mumetal magnetic shields that are used to maintain the precision of the atomic clocks. Working with minds like this is an honor; as is every opportunity to create a shield design that works.
Our expertise lies in understanding the science of magnetic shielding and providing design and fabrication solutions for a wide range of applications. Typical sources of magnetic interference include:
- Permanent magnets
- Transformers
- Motors
- Solenoids
- Cables
- Earth’s magnetic field
In operation, a mumetal magnetic shield both absorbs and diverts magnetic flux by providing a path around the sensitive area. In addition, shielding is used to contain the magnetic field generated by a device.
MuShield is fortunate to have several design engineers on staff who bring extensive experience in the field of magnetic shielding to the table. In many cases two design minds are better than one, and we work as a team to develop an end product that works. We’re a small company that tackles big problems for our clients. Our flexibility enables us to build, test, and ship prototypes within reasonable time frames to ensure that you get what you need when you need it.
MuShield works closely with customer design engineers to create a viable shield and then build them according to agreed upon specifications, and test for performance. Simple. Effective. Efficient.
Should you have an existing shield design we’ll will provide cost effective production parts. Along with traditional machining capabilities such as metal forming, hydroforming, spinning, and welding, MuShield has talented machine operators specializing in CAM, precision laser work, and tool making. We are fully equipped for production runs; big and small.
MuShield is an industry leader in the fabrication of high permeability mumetal magnetic shields. Our capabilities include:.
- Convention Sheet Metal Fabrication
- CNC Machining and Turning
- Laser Cutting, Machining and Welding
- Hydroforming
- Heat Treating
Video highlights how MuShield
works with mumetal
What Is mumetal?
Mumetal is a “soft” ferromagnetic material that does not retain a macroscopic internal field after the removal of an external magnetizing field. Most alloys are permalloys meeting spec ASTM A753 Alloy Type 4 and containing approximately 80% Nickel (Ni), 20% Iron (Fe) and small amounts of Molybdenum (Mo). Mumetal high permeability magnetic shielding material is a non-oriented 80% nickel-iron-molybdenum alloy which offers extremely high initial permeability and maximum permeability with minimum hysteresis loss.
Ferromagnetism originates at the quantum level. Ferromagnetic elements have a lowest energy e- orbital state that aligns the e- spins parallel, thus giving an intrinsic magnetic moment to the atom. The lowest microscopic energy state of an ensemble of atoms is with these magnetic moments aligned to produce a net magnetic field. Since maintaining an external magnetic field would require energy, the lowest macroscopic energy state requires that the atoms divide into domains about 1,000 atoms across and that the magnetic orientation of these domains be randomized.
In the presence of an externally applied magnetic field, the domains magnetically realign to some degree and thus generate their own external field. The primary field continues to exist, but now the net field is the sum (or superposition) of the primary and induced field. The induced field must have an alignment of opposite polarity to the primary field (just like two bar magnets must align North to South and South to North), and the superposition of the two fields results in a lower observed field, and there you have magnetic shielding.
MuShield works closely with customer design engineers to create a viable magnetic shield and then build them according to agreed upon specifications, and test for performance. Simple. Effective. Efficient. We’re a small company that tackles big problems. Our flexibility and talented mix of engineers enables us to build, test, and ship prototypes on time, every time.
The Process
Planning and collaboration
We work in conjunction with you and your colleagues to provide feasible, efficient, and cost effective shielding solutions. We’ve had countless opportunities to provide initial design assistance for new products which has enabled our customers to significantly shorten their design cycle. In some cases, a formal contract for this service is appropriate as it is the most cost effective and least time-consuming alternative to magnetic shield design. In other cases, a quick study of the shield design you have created will enable us to guide you as you develop your product for production.
You may find it helpful for us to give you our perspective on a complicated magnetic shield you have designed for production. Our manufacturing experience enables us to look at a part from a production standpoint, and to offer suggestions for improving cost efficiencies.
On occasion, MuShield is asked to visit a customer site for formal consulting on an electromagnetic interference problem. In cases such as these, we are contracted to provide a suggested solution, complete engineering drawings, and create prototypes as necessary.
Hydrogen Heat Treating
Hydrogen Heat Treating
MuShield heat treats mumetal magnetic shields and materials onsite.
With every magnetic shield MuShield manufactures, the goal is to attain the maximum shielding capacity or permeability for that part while maintaining its dimensional and structural integrity. MuShield meets these objectives by heat treating magnetic shields and materials onsite.
Why is heat treatment necessary?
Typical manufacturing methods for magnetic shielding involve:
- Bending
- Forming
- Welding
- Cold working
- Mechanical finishing.
Bending and forming are mechanical operations which can work-harden and/or stress high permeability materials. Welding introduces oxygen to the material, and mechanical finishing and cold working can introduce carbon. Each of these factors contribute to the degradation of a magnetic shield’s ability to perform effectively.
What is permeability?
Imagine a sponge. Some sponges have big holes, some are more tightly structured; each of them absorbs liquid to the point of saturation. Mumetal reacts in much the same way. Depending upon its structure, the material absorbs magnetic interference to a point of saturation. As magnetic interference increases, so too should the permeability of the material.
How does heat treatment increase the permeability of mumetal?
When the magnetic shielding materials that MuShield uses are exposed to extremely high levels of heat (2100ºF for 1-2 hours), the grains of the material grows, increasing the materials ability to absorb magnetic flux. In addition, the hydrogen atmosphere in the heat chamber produces a chemical reaction with the shielding material, removing impurities such as carbon and oxygen, thereby enhancing permeability.
Finally, rapid and controlled cooling of the magnetic shield “freezes” the desired grain of the shield, yielding maximum permeability. MuShield engineers regulate the temperature and the time the parts are in the heat chamber with care as it is critical that the parts maintain their structural and dimensional integrity.
In the case where a hydrogen furnace cannot be used for heat treating mumetal, a vacuum furnace is a suitable replacement.
Does MuShield provide heat treatment services for parts other than their own?
Absolutely. MuShield has a large heat treating capacity and is committed to investing in additional equipment to keep up with the demand for these services. Fast turnaround of heat treated magnetic shields is critical to MuShield customers.
Mumetal is a non-oriented 80% nickel-iron-molybdenum alloy which offers extremely high initial permeability and maximum permeability with minimum hysteresis loss.
Alloys meet military specification MIL-N-14411 and ASTM A753.
Unprotected Assets
Protected Assets
mumetal News & Press
Mu-metal is a nickel–iron soft ferromagnetic alloy with very high permeability, which is used for shielding sensitive electronic equipment against static or low-frequency magnetic fields. It has several compositions. One such composition is approximately 77% nickel, 16% iron, 5% copper, and 2% chromium or molybdenum.[1][2] More recently, mu-metal is considered to be ASTM A753 Alloy 4 and is composed of approximately 80% nickel, 5% molybdenum, small amounts of various other elements such as silicon, and the remaining 12 to 15% iron.[3] The name came from the Greek letter mu (μ) which represents permeability in physics and engineering formulae. A number of different proprietary formulations of the alloy are sold under trade names such as MuMETAL, Mumetall, and Mumetal2.
Mu-metal typically has relative permeability values of 80,000–100,000 compared to several thousand for ordinary steel. It is a 'soft' ferromagnetic material; it has low magnetic anisotropy and magnetostriction,[1] giving it a low coercivity so that it saturates at low magnetic fields. This gives it low hysteresis losses when used in AC magnetic circuits. Other high-permeability nickel–iron alloys such as permalloy have similar magnetic properties; mu-metal's advantage is that it is more ductile, malleable and workable, allowing it to be easily formed into the thin sheets needed for magnetic shields.[1]
Mu-metal objects require heat treatment after they are in final form—annealing in a magnetic field in hydrogen atmosphere, which increases the magnetic permeability about 40 times.[4] The annealing alters the material's crystal structure, aligning the grains and removing some impurities, especially carbon, which obstruct the free motion of the magnetic domain boundaries. Bending or mechanical shock after annealing may disrupt the material's grain alignment, leading to a drop in the permeability of the affected areas, which can be restored by repeating the hydrogen annealing step.
Magnetic shielding[edit]
Mu-metal is a soft magnetic alloy with exceptionally high magnetic permeability. The high permeability of mu-metal provides a low reluctance path for magnetic flux, leading to its use in magnetic shields against static or slowly varying magnetic fields. Magnetic shielding made with high-permeability alloys like mu-metal works not by blocking magnetic fields but by providing a path for the magnetic field lines around the shielded area. Thus, the best shape for shields is a closed container surrounding the shielded space. The effectiveness of mu-metal shielding decreases with the alloy's permeability, which drops off at both low field strengths and, due to saturation, at high field strengths. Thus, mu-metal shields are often made of several enclosures one inside the other, each of which successively reduces the field inside it. Because mu-metal saturates at such low fields, sometimes the outer layer in such multilayer shields is made of ordinary steel. Its higher saturation value allows it to handle stronger magnetic fields, reducing them to a lower level that can be shielded effectively by the inner mu-metal layers.
Mu Metal Sheet
RF magnetic fields above about 100 kHz can be shielded by Faraday shields: ordinary conductive metal sheets or screens which are used to shield against electric fields.[5]Superconducting materials can also expel magnetic fields by the Meissner effect, but require cryogenic temperatures.
The alloy has a low coercivity, near zero magnetostriction, and significant anisotropic magnetoresistance. The low magnetostriction is critical for industrial applications, where variable stresses in thin films would otherwise cause a ruinously large variation in magnetic properties.
History[edit]
Mu-metal was developed by British scientists Willoughby S. Smith and Henry J. Garnett[6][7][8] and patented in 1923 for inductive loading of submarine telegraph cables by The Telegraph Construction and Maintenance Co. Ltd. (now Telcon Metals Ltd.), a British firm that built the Atlantic undersea telegraph cables.[9] The conductive seawater surrounding an undersea cable added a significant capacitance to the cable, causing distortion of the signal, which limited the bandwidth and slowed signaling speed to 10–12 words per minute. The bandwidth could be increased by adding inductance to compensate. This was first done by wrapping the conductors with a helical wrapping of metal tape or wire of high magnetic permeability, which confined the magnetic field. Telcon invented mu-metal to compete with permalloy, the first high-permeability alloy used for cable compensation, whose patent rights were held by competitor Western Electric. Mu-metal was developed by adding copper to permalloy to improve ductility. 80 kilometres (50 mi) of fine mu-metal wire were needed for each 1.6 km of cable, creating a great demand for the alloy. The first year of production Telcon was making 30 tons per week. In the 1930s this use for mu-metal declined, but by World War II many other uses were found in the electronics industry (particularly shielding for transformers and cathode ray tubes), as well as the fuzes inside magnetic mines. Telcon Metals Ltd. abandoned the trademark 'MUMETAL' in 1985.[10] The last listed owner of the mark 'MUMETAL' is Magnetic Shield Corporation, Illinois.[11]
Uses and properties[edit]
Mu-metal is used to shield equipment from magnetic fields. For example:
- Electric powertransformers, which are built with mu-metal shells to prevent them from affecting nearby circuitry.
- Hard disks, which have mu-metal backings to the magnets found in the drive to keep the magnetic field away from the disk.[citation needed]
- Cathode-ray tubes used in analogue oscilloscopes, which have mu-metal shields to prevent stray magnetic fields from deflecting the electron beam.
- Magnetic phonograph cartridges, which have a mu-metal case to reduce interference when LPs are played back.
- Magnetic resonance imaging (MRI) equipment.
- The magnetometers used in magnetoencephalography and magnetocardiography.
- Photomultiplier tubes.
- Vacuum chambers for experiments with low-energy electrons, for example, photoelectron spectroscopy.
- Superconducting circuits and especially Josephson junction circuits.
- Fluxgate magnetometers and compasses as part of the sensor.
- Proximity sensors (inductive type)
Similar materials[edit]
Mu Metal Tape
Other materials with similar magnetic properties include Co-Netic, supermalloy, supermumetal, nilomag, sanbold, molybdenum permalloy, Sendust, M-1040, Hipernom, HyMu-80 and Amumetal.In recent times pyrolytic graphite (also incidentally used in some OLED panels as a heat sink) has been used as it also shows useful magnetic field exclusion properties.[citation needed]
References[edit]
- ^ abcJiles, David (1998). Introduction to Magnetism and Magnetic Materials. CRC Press. p. 354. ISBN978-0-412-79860-3.
- ^Weast, Robert (1983). Handbook of Chemistry and Physics (64th ed.). CRC Press. p. E-108. ISBN978-0-8493-0464-4.
- ^'MuMetal Home'. mu-metal.com. Josh Wickler. Retrieved 2015-07-06.
- ^'Mu Metal specifications'. Shielding Specifications. Nick Murby. 2009-03-25. Retrieved 2013-01-21.
- ^'Magnetic Fields and Shields'. FAQ. Magnetic Shield Corp. Archived from the original on 2008-12-18. Retrieved 2008-12-14.
- ^Patent 279549[permanent dead link] Willoughby Statham Smith, Henry Joseph Garnett, New and improved magnetic alloys and their application in the manufacture of telegraphic and telephonic cables, granted July 27, 1926
- ^US Patent 1582353 Willoughby Statham Smith, Henry Joseph Garnett, Magnetic Alloy, filed January 10, 1924, granted April 27, 1926
- ^US Patent 1552769 Willoughby Statham Smith, Henry Joseph Garnett, Magnetic Alloy, filed January 10, 1924, granted September 8, 1925
- ^Green, Allen (2004). '150 Years Of Industry & Enterprise At Enderby's Wharf'. History of the Atlantic Cable and Undersea Communications. FTL Design. Retrieved 2008-12-14.
- ^'Trademark Status & Document Retrieval'. tsdr.uspto.gov. Retrieved 2017-07-28.
- ^'Trademark Status & Document Retrieval'. tsdr.uspto.gov. Retrieved 2017-07-28.
External links[edit]
Mu Metal Machinability
- Zero gauss chambersArchived 2013-02-17 at the Wayback Machine
Mu Metal Suisse