A Practical Guide toLow Frequency Magnetic Shielding

STUART KOCHVice President of Technical Products

Amuneal Manufacturing Corp.Philadelphia, PA

A Practical Guide toLow Frequency Magnetic Shielding

• Introduction to Amuneal

• Typical Magnetic Shielding Projects

• Common Terms in Magnetic Shielding

• The Major Magnetic Shielding Mechanisms

• Shield Design Considerations

• Fabrication and Handling

• Questions, Comments, and Discussion

Introduction to Amuneal

Industries and Technologies Supported

• Particle and Nuclear Physics

• Atomic Magnetometry

• Medical Systems

• Metrology

• Wafer Processing Equipment

• Microscopy

• Aerospace and Defense

• Astrophysics

• Biomagnetics

Magnetic Shields of All Sizes

Common Magnetic Shielding Terms

“The Beginning Of Wisdom Is ToCall Things By Their Right Names”

. . . . Ancient Chinese Proverb

Common Magnetic Shielding Terms

• Field Strength (H)

• Flux Density (B)

• Frequency (F)

• Permeability (µ)

• Saturation (Bs)

• Attenuation (A)

Field Strength (H)(Oe, mOe, A/M)

Field strength depends on the intensity level of the source and its distance from the shield.

Flux Density (B)(G, mG, T)

Flux density measures lines of flux per square centimeter.

Permeability (µ=B/H)

Permeability measures the capacity of a material to provide a flux path.

Permeability Factors

• Manufacturers’ µ data on rings, not shields

• Flux density evenly distributed and measurable

• Known factors: diameter, length, spacing, material thickness, frequency, etc.

• Unknown factors: end caps, holes, stress, seams, joints, doors, furnace loading variation, material lot variation, etc.

B H Curves

Permeability vs. Thickness

Saturation (Bs)

Saturation is the maximum level of magnetic flux that a given material can conduct.

Saturation

• Assumes high permeability (µ) material

• Flux lines which are within 2 radii from the center of the

shield will be pulled into the shield material

• The shield will not saturate as long as 𝑩𝒔𝒂𝒕 >𝑩𝒂𝒑𝒑𝒍𝒊𝒆𝒅 ∗ 𝟐𝒓

𝑻

𝑩𝒎𝒂𝒕′𝒍 =𝑩𝒂𝒑𝒑𝒍𝒊𝒆𝒅 ∗ 𝟐 𝑺𝒉𝒊𝒆𝒍𝒅 𝑹𝒂𝒅𝒊𝒊

𝑴𝒂𝒕𝒆𝒓𝒊𝒂𝒍 𝑻𝒉𝒊𝒄𝒌𝒏𝒆𝒔𝒔

Frequency (f)Permeability @ B40 vs. Frequency and Material Thickness

Permeabilityaffects the overall shielding factor as a function of frequency and material thickness.

Major Magnetic Shielding Mechanisms

• Flux Shunting– Ferromagnetic Materials

– Function of Permeability

• Eddy Currents– Conductive Materials

– Function of Frequency

Magnetic Shield Design Considerations

• Magnetic Field Intensity and Frequency

• Material Selection

• Shield Configuration and Geometry

Common Magnetic Shielding Materials

Material Saturation Permeability (µ ) Resistivity

(Gauss) Mill Cert / Effective (µohm-cm)

Amumetal 8,000 60,000 15,000 72

Amumetal 4K* 9,000 70,000 17,500 72

ULCS/LCS 22,000 1,000 500 12

Aluminum N/A 1 1 5

Copper N/A 1 1 2

* Cryogenic application

University of MarylandFour Layer Magnetic Shield Components for the Study of

Intrinsic Magnetic Characteristics of Superconductors

Permeability vs. Operating Temperature

Shield Configuration / Geometry

• Shape

• Dimensions

• Number of Layers

• Seams and Connections

• End Effects

100

1000

10000

100000

1000000

0 1 2 3 4 5

Att

enuation

Number of Shield Layers

Attenuation as a Function of Layers

Seams

Joiner Bands

Stanford University Atomic Equivalence Experiment

“End Effects”

End Caps

Three Layer Magnetometer Shield with Access Door and Flanged Lid

LAWRENCE BERKELEY

NATIONAL LABORATORY

Advanced Light Source

MAGNETIC SHIELD FOR THE

THIRD GENERATION PHOTON

EMISSION ELECTRON

MICROSCOPE (PEEM3)

Magnetic Shield Fabrication and Handling

• Sheet Metal....Not Machining!

• Hydrogen Annealing

• Handle Like Glass

SEM Photos of Grain Boundary Grooves in Amumetal

Figure 1: 1,000x Magnification Figure 2: 2,100x Magnification

Attenuation Testing

Effects of MishandlingDrop Test Data

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

1.800

Drops from 30.5 cm

Drops from 61.0 cm

Drops from 93.0 cm

µ/1

05

Demagnetization

Procedure for Cylinder Demagnetization

𝐻 =𝑁𝐼

𝐿𝑓𝑒

Method: This method allows varying the current in order to minimize the number of coil windings.Using a VARIAC, ramp up slowly to the selected current over 15 seconds, hold for 15 seconds, and then ramp down to zero amps over 15 seconds.Repeating the cycle three times will optimize demagnetization. Additional cycles beyond that tend to have little, if any, benefit.

H = Magnetization field in A/cm (1.0 A/cm for Amumetal)N = Number of coil windingsI = Current AmperesLfe = Outer circumference of cylinder in cm

Major Cost Factors

• Material Cost

• Shield Dimensions and

Complexity

• Engineering

• Fabrication

• Hydrogen Annealing

• Ease of Assembly and

Installation

One final note…

• The terms

• How magnetic shielding works

• The right material for your application

• Important design considerations

• Does the shield meet my attenuation needs?

• Why hydrogen annealing is so important

• And please remember to get us involved early in your project.

SOME REFERENCES FOR LOW FREQUENCY MAGNETIC SHIELDING (1)

• “A New Estimation of the Axial Shielding Factors for Multishell Cylindrical Shields”, E. Paperno, H. Koide, I. Sasada, Journal of Applied Physics, Vol. 87, Nbr 9, 1 may 2000

• “Amuneal’s Cryoperm Magnetic Shielding”, 4 pages. COLD FACTS Buyer Guide December 2004 Volume 20, Number 5

• “Application of Atomic Magnetometry in Magnetic Particle Detection”, S. Xu, M. H. Donaldson, • A. Piners, S.M. Rochester, D. Budker, V. V. Yashchuk. Applied Physics Letters 89, 224105 (2006)

• ASTM A753-02 “Standard Specification for Wrought Nickel-Iron Soft Magnetic Alloys”, 6 pages. American Society for Testing and Materials. 2002

• “Conventional Magnetic Shielding”, T. J. Sumner, J. M. Pendlebury, K. M. Smith, J. Phys. D: Applied Physics 20 (1987) 1095-1101

* Cryomodule Design for a Superconducting LINAC with Quart-Wave, Half-Wave and Focusing Elements”, M. Johnson et. al, National Superconducting Cyclotron Laboratory, Michigan State University

• Cryoperm 10 Data Set HT-EM, 11 pages. Vacuumschmelze GmbH

• “Custom Magnetic Shielding for Low Temperature Applications”, 4 pages. Amuneal Manufacturing Corporation

• “Definitive Guide to Magnetic Shielding”, 27 pages. Amuneal Manufacturing Corporation

MORE REFERENCES FOR LOW FREQUENCY MAGNETIC SHIELDING (2)

• “Design of the Magnetic Shield for TRASCO Low Beta Elliptical Cavities”, P. Pierini, S. Barbanotti, L. Monaco, N. Panzeri, INFN Milano - LASA

• “Experience With Magnetic Shielding of a Large Scale Accelerator”, S. Nagaitsev, C. Gattuso, S. Pruss, J. Volk, FNAL

• “Ferromagnetism”, Richard M. Bozorth, IEEE Press, 1951, Rev 1978, (968 pages)

• “Magnetic Shielding”, Vacuumschmelze GmbH Publication FS-M9, 1989 (46 pages)

• “Magnetic Shielding Theory and Practice”, L. Maltin and A. Kamens, in ITEM EMC Directory & Design Guide, 2001 (3 pages)

• “Magnetic Shields”, Albrecht Mager, IEEE Transactions on Magnetics, March 1970

• “Material Efficiency in Magnetic Shielding at Low and Intermediate Frequency”, U. Adriano, O. Bottauscio, M. Zucca, IEEE Transactions on magnetics, Vol. 39, No. 5, September 2003

• “Optimal Shell Separation for Closed Axial Cylindrical Magnetic Shields”, Eugene Paperno, SaeePeliwal, Michael V. Romalis, Anton Plotkin, Journal of Applied Physics 97, 10Q104 (2005)

• “Optimal Three-Layer Cylindrical Magnetic Shield Sets for Scientific Applications”, E. A. Burt and C. R. Ekstrom, Review of Scientific Instruments Vol 73, Number 7,July 2002, 2699-2704

MORE REFERENCES FOR LOW FREQUENCY MAGNETIC SHIELDING (3)

• “Principles of Quasistatic Magnetic Shielding with Cylindrical and Spherical Shields”,J. F. Hoburg, IEEE Transactions on Electromagnetic Compatibility, Vol 37, No. 4, November 1995

• “Review of Magnetic Properties of Fe-Ni Alloys”, Gilbert Y. Chin, IEEE Transactions on Magnetics, Vol MAG-7, No. 1, March 1971

• “Simple Formula for Multiple Mu-metal Shields”, D. Dubbers, Nuclear Instruments and Methods in Physics Research A243 511-517 (1986)

• “SNS Cavity Intrinsic Quality Factor Requirements Based on a Cryomodule Magnetic Shielding Calculation”

• Sun An, SNS-NOTE-CRYO-120, March 2004

• “Soft Magnetic Materials Handbook: Fundamentals, Alloys, Properties, Products, Applications”, Richard Boll (ed.) Vacuumschmelze GmbH, 1979 (353 pages)

• “Systematic Design of Magnetic Shields”, E. Baum and J. Bork, Journal of Magnetism and Magnetic Materials 101 (1991) 69-74

• “The Drop Test: Deterioration of Magnetic Shielding Due to Mishandling or Abuse”, S. M. Kamens and R. M. Koren, in EMC Technology 1987

• Westinghouse Designers Handbook: The When, Why and How of Magnetic Shielding, C. H. Arendt, Jr., Westinghouse Electric Corporation publication, (1966) 35 pages

For a complimentary copy of today’s presentation and the list of reference

documents, please visit:

www.amuneal.com/workshop