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Diamagnetic Shielding of Nuclei: Local Diamagnetic Current01:14

Diamagnetic Shielding of Nuclei: Local Diamagnetic Current

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An applied magnetic field causes the electrons present in the molecule to circulate, setting up a local diamagnetic current within the molecule. The local diamagnetic current arising from circulating sigma-bonding electrons induces a magnetic field, Blocal that opposes the applied magnetic field, B0. The effective magnetic field experienced by these nuclei is given by the difference between the applied and local magnetic fields in a phenomenon called local diamagnetic shielding. Essentially,...
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Magnetic Damping01:17

Magnetic Damping

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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...
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Magnetostatic Boundary Conditions01:28

Magnetostatic Boundary Conditions

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An electric field suffers a discontinuity at a surface charge. Similarly, a magnetic field is discontinuous at a surface current. The perpendicular component of a magnetic field is continuous across the interface of two magnetic mediums. In contrast, its parallel component, perpendicular to the current, is discontinuous by the amount equal to the product of the vacuum permeability and the surface current. Like the scalar potential in electrostatics, the vector potential is also continuous...
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Potential Due to a Magnetized Object01:24

Potential Due to a Magnetized Object

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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...
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Magnetic Susceptibility and Permeability01:31

Magnetic Susceptibility and Permeability

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In linear magnetic materials, like paramagnets and diamagnets, magnetization is proportional to the magnetic field intensity. The constant of proportionality, a dimensionless number, is called magnetic susceptibility. The value of the susceptibility depends on the type of material.
When diamagnetic materials are placed under an external magnetic field, the moments opposite to the field are induced. Hence, the susceptibility for diamagnets has a minimal negative value of 10-5–10-6. Since...
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Galvanometer01:25

Galvanometer

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Common devices, including car instrument panels, battery chargers, and inexpensive electrical instruments, measure potential difference (voltage), current, or resistance using a d'Arsonval galvanometer. This electromechanical instrument is also known as a moving coil galvanometer.
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Related Experiment Video

Updated: Dec 11, 2025

Optimized Setup and Protocol for Magnetic Domain Imaging with In Situ Hysteresis Measurement
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Compensation System for Biomagnetic Measurements with Optically Pumped Magnetometers inside a Magnetically Shielded

Anna Jodko-Władzińska1, Krzysztof Wildner1, Tadeusz Pałko1

  • 1Warsaw University of Technology, Faculty of Mechatronics, Institute of Metrology and Biomedical Engineering, Boboli 8 St, 02-525 Warsaw, Poland.

Sensors (Basel, Switzerland)
|August 23, 2020
PubMed
Summary

A new, cost-effective Helmholtz coil system compensates ambient magnetic fields, improving room-temperature optically pumped magnetometers (OPMs) for medical magnetography. This setup enhances OPM usability in magnetically shielded rooms.

Keywords:
Helmholtz coilsbiomagnetismmagnetically shielded roomoptically pumped magnetometer

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Area of Science:

  • Biophysics
  • Medical instrumentation
  • Magnetometry

Background:

  • Superconducting quantum interference device (SQUID) magnetography faces limitations due to liquid helium cooling requirements.
  • Optically pumped magnetometers (OPMs) offer room-temperature alternatives but demand ultra-low magnetic fields.
  • Standard two-layer magnetically shielded rooms (MSRs) often have residual magnetic fields (around 50 nT) insufficient for zero-field OPM operation.

Discussion:

  • A novel, cost-efficient compensation system utilizing square Helmholtz coils was developed to mitigate ambient magnetic fields.
  • This system successfully reduced static magnetic fields within a magnetically shielded room (MSR).
  • Preliminary measurements demonstrated the system's effectiveness with commercially available zero-field OPMs.

Key Insights:

  • The Helmholtz coil system provides a practical solution for creating a suitable operating environment for OPMs.
  • It enhances the usability of OPMs by reducing reliance on the initial magnetic conditions of the MSR.
  • This advancement supports the broader adoption of OPMs in biomedical magnetic field measurements.

Outlook:

  • Further optimization of the compensation system could enable more sensitive biomagnetic measurements.
  • Integration with advanced OPMs may lead to new diagnostic tools.
  • This approach could reduce the cost and complexity of advanced magnetography systems.