Two simple modifications to improve the magnetic field profile in radial magnetic systems

Li, Shisong; Schlamminger, Stephan

doi:10.1088/1361-6501/aa5f9c

Cited by 6 publications

(9 citation statements)

References 19 publications

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“…In a BIPM-type magnet, the yoke-air boundary at the end of the air gap, however, is not symmetric even when the heights of inner and outer yokes are equal (h i = h o ) [62]. The difference is noticeable: the inner boundary contains the permanent ring and the yoke, while the outer yoke has only yoke material.…”

Section: Reducing the Fringe Fieldmentioning

confidence: 99%

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The irony of the magnet system for Kibble balances -- a review

Li,

Schlamminger

2021

Preprint

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The magnet system is an essential component of the Kibble balance, a device that is used to realize the unit of mass. It is the source of the magnetic flux, and its importance is captured in the geometric factor Bl. Ironically, the Bl factor cancels out and does not appear in the final Kibble equation. Nevertheless, care must be taken to design and build the magnet system because the cancellation is perfect only if the Bl is the same in both modes: the weighing and velocity mode. This review provides the knowledge necessary to build a magnetic circuit for the Kibble balance. In addition, this article discusses the design considerations, parameter optimizations, practical adjustments to the finished product, and an assessment of systematic uncertainties associated with the magnet system.

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Section: Reducing the Fringe Fieldmentioning

confidence: 99%

“…First, the symmetry can be restored by adding additional magnetic material on the outside yoke [62]. Second, the magnetic symmetry can be restored by lowering the outer yoke such that magnetically the two sides of the air gap have identical heights.…”

Section: Reducing the Fringe Fieldmentioning

confidence: 99%

The irony of the magnet system for Kibble balances -- a review

Li,

Schlamminger

2021

Preprint

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“…In reality, however, fringe fields and asymmetries of the boundaries between the inner and outer and the air gap can produce significant vertical components of the magnetic field component, especially when the inner and outer yokes have the same height. In [21], two possible modifications to the magnetic circuit are proposed: (1) add permanent magnets and (2) reduce the height of the outer yoke. Each measure significantly reduces the vertical component of the magnetic field, and, hence, improves the radial dependence of the field.…”

Section: B Field Uniformity Along the Radial Directionmentioning

confidence: 99%

“…Each measure significantly reduces the vertical component of the magnetic field, and, hence, improves the radial dependence of the field. The effect on the utilization factor that these two measures might have is not discussed in [21]. Here, we investigate the 1/r uniformity of B r with the proposed profile compensation.…”

Section: B Field Uniformity Along the Radial Directionmentioning

confidence: 99%

“…The 2-dimensional flatness of the radial magnetic field is calculated for four configurations: (a) The inner and outer yokes have the same height without compensating rings; (b) The height of outer yoke is 8 mm shorter as suggested in [21] to reduce B z at the air gap center; No inner yoke compensation is applied; (c) The inner and outer yokes have the same total height with compensation rings (h 0 = 2 mm, w 0 = 1.5 mm) according to section III; (d) Combination of conditions (b) and (c); A compensation ring with h 0 = 2 mm and w 0 = 1.5 mm) plus the outer yoke is 2 mm shorter. The desired qualities of the profile in r and z can be visualized by plotting rB r (r, z).…”

Section: B Field Uniformity Along the Radial Directionmentioning

confidence: 99%

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A Simple Improvement for Permanent Magnet Systems for Kibble Balances: More Flat Field at Almost No Cost

Schlamminger

Wang

2020

IEEE Trans. Instrum. Meas.

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Permanent magnets together with yokes to concentrate the magnetic flux into a cylindrical airgap are widely employed in Kibble balances. These experiments require a uniform magnetic flux density along a vertical path, typically a substantial fraction of the length of the air-gap. Fringe fields that are present at both ends of the air-gap limit the region where the flux density does not change more than a certain relative fraction (here: 5 × 10 −4 ) of the flux density in the center of the magnet system. By simply adding an iron ring with a rectangular cross-section to the inner yoke at each end of the air gap, the effects of the fringe fields can be counteracted, and, hence, the length of the region, where the flux density remains within a given tolerance band is increased. Compared to the alternative, employing a taller magnet, the proposed method yields a magnet system with an extended region of a uniform field without significantly increasing the mass of the magnet system. Potential applications include compact and table-top Kibble balances. We investigate possible adverse effects on the performance of the magnet system caused by the additional rings: magnetic field strength, coil-current effect, and a dependence of the radial field on the radial position in the field. No substantial disadvantage was found. Instead, the method presented here outperformed previously suggested methods to improve the radial dependence of the radial field, e.g., shorter outer yoke. In summary, adding rings to the inner yoke improves the uniformity of the field without a detrimental effect to function, cost, and form factor of the magnet system.

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A new magnet design for future Kibble balances

Stöck

Schlamminger

2018

Metrologia

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We propose a new permanent magnet system for Kibble balance experiments, which combines advantages of the magnet designs invented by the National Physical Laboratory (NPL) and by the Bureau International des Poids et Mesures (BIPM). The goal of the proposed magnet system is to minimize the coilcurrent effect and to optimize the shielding at the same time. In the proposed design, a permanent magnet system with two gaps, each housing a coil, is employed to minimize the coil current effect, by reducing the linear coilcurrent dependence reported for the single air gap design by at least one order of magnitude. Both air gaps of the magnet are completely surrounded by highpermeability material, and hence the coils are shielded from outside magnetic fields and no magnetic field leaks outside of the magnet system. An example of the new magnet system is given and the analysis shows that the magnetic field in the air gap can be optimized to meet the requirement to be used in Kibble balances.

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Two simple modifications to improve the magnetic field profile in radial magnetic systems

Cited by 6 publications

References 19 publications

The irony of the magnet system for Kibble balances -- a review

The irony of the magnet system for Kibble balances -- a review

A Simple Improvement for Permanent Magnet Systems for Kibble Balances: More Flat Field at Almost No Cost

A new magnet design for future Kibble balances

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