Magnetostriction is a physical phenomenon where certain ferromagnetic materials (e.g., iron, nickel, cobalt, and their alloys) undergo slight shape changes (expansion, contraction, or twisting) when exposed to a magnetic field. Conversely, mechanical stress on these materials can alter their magnetic properties. This two-way effect is key to its applications in sensors.

‌Core Mechanism‌

  1. ‌Direct Magnetostriction‌:

    • When a magnetic field is applied, the material’s internal magnetic domains (tiny magnetic regions) realign, causing a measurable physical deformation.
    • ‌Example‌: A nickel rod slightly elongates in a magnetic field and returns to its original length when the field is removed.

  2. ‌Inverse Magnetostriction (Villari Effect)‌:

    • Applying mechanical stress (e.g., pressure or strain) to the material changes its magnetic state, which can be detected as a magnetic signal.
    • ‌Example‌: Squeezing a magnetostrictive rod generates a detectable change in its surrounding magnetic field.

‌Application in Sensors‌

Magnetostrictive level sensors use the ‌inverse magnetostriction effect‌ to measure liquid levels:

  1. A ‌magnetostrictive waveguide wire‌ (e.g., iron-cobalt alloy) runs through the sensor.
  2. A float (with a permanent magnet) moves along the wire as the liquid level changes.
  3. A current pulse sent through the wire creates a magnetic field that interacts with the float’s magnet, generating a ‌torsional stress wave‌ in the wire.
  4. The sensor calculates the liquid level by measuring the time it takes for the stress wave to travel from the float to the detector.

‌Advantages & Limitations‌

  • ‌Pros‌: High accuracy (±0.5 mm), non-contact measurement, resistance to extreme temperatures/pressures, and strong immunity to interference.
  • ‌Cons‌: Higher material costs (e.g., Terfenol-D alloy), sensitivity to strong external magnetic fields.

‌Common Materials‌: Terfenol-D (terbium-dysprosium-iron alloy), nickel-iron ferrites.