How anti-theft tags work - magnetostriction

TL;DR

Anti-theft tags use magneto-acoustic technology to detect shoplifting, with a metal strip inside that oscillates in response to a magnetic field.

Transcript

today on Applied Science I'd like to talk about these anti-theft tags you've probably seen these little rectangular tags that set the alarm off if you try to exit the store before this is deactivated and they actually work by having a little tuning fork inside here that's controlled by a magnet and so I'll show with the scope what the signals look ... Read More

Key Insights

• 😒 Anti-theft tags use magneto-acoustic technology, with a metal strip inside that oscillates when exposed to a magnetic field.
• 🕵️ The oscillating strip resonates at a frequency of 58 kilohertz, which is detected by the store's security system.
• ⚡ Activation and deactivation of the tag rely on magnetization and demagnetization of a small magnet strip inside the tag.

Questions & Answers

Q: How do anti-theft tags work?

Anti-theft tags work by utilizing magneto-striction, where a metal strip inside the tag oscillates when exposed to a magnetic field. This creates a resonating effect that is detected by the store's security system.

Q: What is the purpose of the metal strip in the tag?

The metal strip in the tag is crucial to the tag's functioning, as it is responsible for the oscillation that allows detection. This strip is designed to resonate at a frequency of 58 kilohertz.

Q: How are anti-theft tags activated and deactivated?

Anti-theft tags are activated by a small magnet strip inside the tag that is magnetized. This magnetization puts the tag in a state where it will respond to the magnetic field of the store's security system. To deactivate a tag, the magnet strip is demagnetized, causing the tag to no longer respond to the magnetic field.

Q: Can the movement of the metal strip in the tag be observed?

The movement of the metal strip in the tag can be observed using a setup that detects the changes in length caused by magneto-striction. However, the movement is extremely small, on the order of hundreds of nanometers.

Summary & Key Takeaways

• Anti-theft tags, specifically hard plastic rectangular ones, use magneto-acoustic technology.

• The metal strip inside the tag is key to its functionality, as it responds to a magnetic field by oscillating.

• These tags work by resonating at 58 kilohertz and are detected by archways equipped with coils that emit and receive signals at this frequency.