EMC Question of the Week: September 19, 2022

Illustration of low-frequency magnetic field lines being redirected around a circuit board by a magnetic material

Which device can be useful for determining whether a material is suitable for low-frequency (0-100 Hz) magnetic field shielding? 

  1. ohm meter
  2. E-field meter
  3. magnetron
  4. permanent magnet


The best answer is “d.” Low-frequency magnetic field shielding requires a magnetic material (high permeability) to reroute lines of magnetic flux around the objects being shielded. Generally, if a material has a high permeability at low frequencies, a permanent magnet will stick to it.

Ohm meters measure resistance, which is an indicator of a material's conductivity. E-field meters measure electric fields, which may be affected by a material's conductivity or permittivity. However, at low frequencies, the electric and magnetic fields are relatively independent and it is very difficult to learn anything about a material's magnetic properties from an electric field measurement.

Magnetrons are microwave frequency sources and would be of little value for determining the behavior of 0-100 Hz magnetic fields.

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