Field strength: The intensity of a magnetic field

The field strength is a physical quantity that indicates how intense a magnetic field is at a certain point. It describes the strength of the magnetic field regardless of the type of source that generates the field. The magnetic field strength is usually denoted by the symbol H and is measured in units of amperes per metre (A/m).

How is the field strength defined?

The field strength is defined as the vector that describes the direction and intensity of a magnetic field. It is directly related to the strength of the electric current or the magnetisation that generates the magnetic field. The relationship can be described by the following equation:

H = B / μ

Where:

• H: Magnetic field strength (in A/m)
• B: Magnetic flux density (in Tesla)
• μ: Magnetic permeability of the material

Properties of the field strength

• Vector magnitude: The field strength has both a direction and a magnitude.
• Distance from the source: The strength decreases with increasing distance from the source of the magnetic field.
• Material dependence: The field strength is influenced by the material through which the magnetic field passes.

How is the field strength measured?

Different devices are used to measure the field strength, depending on the area of application:

• Magnetometer: Measures the field strength directly and is often used in geophysical applications.
• Coils: The induction voltage in a coil provides indirect information about the field strength.
• Hall sensors: These electronic sensors measure the field strength precisely in technical applications.

Applications of field strength

• Electric motors: The field strength is used to control the power and efficiency of a motor.
• Medical technology: In MRI systems (magnetic resonance imaging), the field strength is controlled in order to generate high-precision images.
• Sensor technology: Field strength measurements are crucial in sensors for position or speed detection.
• Research: Geophysicists use field strength measurements to investigate variations in the Earth's magnetic field.

Interesting facts about field strength

Did you know that the field strength of typical magnets in the home is around 10-100 A/m, while the field strength in an MRI machine can reach up to 100,000 A/m? This enormous range shows the versatility of magnetism in various applications.