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Magnetic Damping

Magnetic Damping

Eddy currents can produce significant drag on motion, called magnetic damping. For instance, when a metallic pendulum bob swings between the poles of a strong magnet, significant drag acts on the bob as it enters and leaves the field, quickly damping the motion.
If, however, the bob is a slotted metal plate, the magnet produces a much smaller effect. When a slotted metal plate enters the field, an emf is induced by the change in flux; however, it is less effective because the slots limit the...

Potential Due to a Magnetized Object

Potential Due to a Magnetized Object

Magnetic dipoles in magnetic materials are aligned when placed under an external magnetic field. For paramagnets and ferromagnets, dipole alignment occurs in the direction of the magnetic field. However, the dipoles align opposite to the field in the case of diamagnets. This state of magnetic polarization due to the external field is called magnetization. Magnetization is defined as the dipole moment per unit volume. It plays a similar role to polarization in electrostatics.
The vector...

Other Unique Bacteria

Other Unique Bacteria

Magnetic bacteria exhibit a directed movement called magnetotaxis, driven by structures called magnetosomes. These magnetosomes consist of chains of magnetic particles made of either magnetite (Fe₃O₄) or greigite (Fe₃S₄) and are organized in a linear conformation by a protein scaffold within invaginations of the cell membrane. The bacteria align along the north–south magnetic field lines, much like a compass needle. They are typically microaerophilic or anaerobic...

Magnetism

Magnetism

Magnets are commonly found in everyday objects, such as toys, hangers, elevators, doorbells, and computer devices. Experimentation on these magnets shows that all magnets have two poles: one is labeled north (N) and the other south (S). Magnetic poles repel if they are alike and attract if unlike. Moreover, both poles of a magnet attract unmagnetized pieces of iron.
An individual magnetic pole cannot be isolated. No matter how small, every piece of a magnet contains a north pole and a south...

Diamagnetism

Diamagnetism

Materials consisting of paired electrons have zero net magnetic moments. However, when these materials are placed under an external magnetic field, the moments opposite to the field are induced. Such materials are called diamagnets. Diamagnetism is the response of the diamagnets when placed in an external magnetic field.
Diamagnetism was discovered by Anton Brugmans in 1778 when he observed that bismuth gets repelled by magnetic fields, thus theorizing that diamagnets get repelled by magnets....

Eddy Currents

Eddy Currents

Since eddy currents occur only in conductors, magnets can separate metals from other materials. For example, in a recycling center, trash is dumped in batches down a ramp, beneath which lies a powerful magnet. Conductors in the trash are slowed by eddy currents, while nonmetals in the trash move on, separating from the metals. This works for all metals, not just ferromagnetic ones.
Other major applications of eddy currents appear in metal detectors and the braking systems of trains and roller...

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Related Experiment Video

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A Paired Bead and Magnet Array for Molding Microwells with Variable Concave Geometries

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A new magnet design for future Kibble balances.

Shisong Li¹, Michael Stock¹, Stephan Schlamminger^2,3

¹Bureau international des poids et mesures (BIPM), F-92312 Sèvres, France.

Metrologia

|July 12, 2021

Summary

A novel permanent magnet system for Kibble balances minimizes coil-current effects and optimizes magnetic shielding. This new design, integrating NPL and BIPM advantages, significantly reduces coil-current dependence for enhanced measurement accuracy.

Keywords:

Kibble balance Planck constant magnetic field mass measurement watt balance

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Area of Science:

Metrology
Electromagnetism
Instrumentation

Background:

Kibble balances are crucial for realizing the definition of the kilogram.
Existing magnet designs present challenges with coil-current effects and magnetic shielding.
Optimizing permanent magnet systems is key to improving balance performance.

Purpose of the Study:

To propose a new permanent magnet system for Kibble balances.
To minimize coil-current effects and enhance magnetic shielding.
To combine the strengths of NPL and BIPM magnet designs.

Main Methods:

A dual-air-gap permanent magnet system design is proposed.
High-permeability material is used to fully enclose the air gaps.
Analysis of magnetic field distribution and coil-current dependence is performed.

Main Results:

The proposed system reduces linear coil-current dependence by at least an order of magnitude compared to single air gap designs.
Effective shielding of coils from external magnetic fields is achieved.
No magnetic field leakage outside the system is observed.

Conclusions:

The new permanent magnet system offers significant improvements for Kibble balance applications.
Optimized magnetic field in the air gap meets Kibble balance requirements.
This design enhances measurement precision and reliability in metrology.