Magnetostriction

Magnetostriction

• Ferromagnetic materials possess ordered domains where electrons align their magnetic moments, generating a collective magnetization.

• Applying a magnetic field influences these domains, causing them to realign and optimize their energy state.

• This realignment subtly changes the spacing between atoms, leading to the observed dimensional shift.

The direction and magnitude of the deformation depend on the material and the applied field. In most cases, the change is small, around a few millionths of the original dimension. But don't underestimate its significance!

Applications of Magnetostriction:

• Transducers: Convert electrical signals to sound waves and vice versa, used in sonar, medical imaging, and underwater communication.

• Fuel injectors: Precisely control fuel flow in engines due to the high-frequency vibrations generated.

• Vibration control: Dampen unwanted vibrations in structures and machines.

• Magnetic sensors: Detect minute changes in magnetic fields for various applications.

Demystifying Acousto-magnetic Anti-theft Systems:

Imagine tiny metal strips trigger alarms! That's the basic premise of Acousto-magnetic (AM) anti-theft systems, similar to the familiar magnetic tags but with a twist.

The Components:

• Two strips:

  • Magnetostrictive: This special metal vibrates when exposed to a magnetic field, like a tiny tuning fork.

  • Semi-hard magnetic: This acts as a booster, amplifying the vibration and allowing deactivation.

• Detectors: These emit sound bursts at a specific frequency, "waking up" the vibrating strip.

• Receiver antenna: Picks up the vibrations as electrical signals.

Torsion delay lines used steel wire as the storage medium. Transducers were built by applying the magnetostrictive effect; small pieces of a magnetostrictive material, typically nickel, were attached to either side of the end of the wire, inside an electromagnet. When bits from the computer entered the magnets, the nickel would contract or expand (based on the polarity) and twist the end of the wire. The resulting torsional wave would then move down the wire just as the sound wave did down the mercury column.

Unlike the compressive wave used in earlier devices, torsional waves are considerably more resistant to problems caused by mechanical imperfections, so much that the wires could be wound into a loose coil and pinned to a board. Due to their ability to be coiled, the wire-based systems could be as long as needed, so tended to hold considerably more data per unit;  1 kbit units were typical on a board only 1 square foot (~30 cm × 30 cm). Of course, this also meant that the time needed to find a particular bit was somewhat longer as it traveled through the wire, and access times on the order of 500 microseconds were typical.

• Inverse magnetostriction effect: When pressure is applied to certain materials (called magnetostrictors), their magnetic properties change. This device uses the opposite effect, where changing the magnetism creates pressure.

• Improved device: This year's version is 1,000 times larger and more powerful than last year's, generating 2,000 mW (2 watts) compared to 2 mW.

• Potential for further improvement: Scaling the device up 1,000 times further could theoretically generate several kilowatts, enough for a home.

• Device design: The device uses two long Galfenol rods with weights attached, acting as two magnetostrictors arranged in a "parallel beam structure." Coils wrapped around them convert the generated pressure into electricity.