magnetic strip

A magnetic strip is a band of magnetized material, typically 0.375 inches (9.5 mm) wide and between 0.005 and 0.009 inches (0.13 to 0.23 mm) thick, laminated onto the back or edge of a card or label. It stores digital information as patterns of magnetic charge along its length. An electronic reader head passes over the strip and detects these charge patterns, converting them into electrical signals that a device can interpret. The most common magnetic strips contain three tracks, each capable of storing around 75 to 210 alphanumeric characters depending on coercivity and track density.

Magnetic strips appear on credit cards, debit cards, hotel key cards, employee badges, and library cards. The technology encodes data at 75 bits per inch (bpi), 210 bpi, or 4,064 bpi depending on the application and ISO standard. Track 1 typically holds cardholder name and card number; Track 2 holds card number and expiration date; Track 3 is less commonly used and may contain PIN or account information. The strip's magnetic material is usually an oxide coating, commonly ferric oxide or barium ferrite, applied to a polyester or PVC backing.

Reliability and degradation

Magnetic strips degrade when exposed to strong external magnetic fields, physical abrasion, or delamination. Repeated swiping wears the head contact surface. Heat above 50 degrees Celsius can partially erase data. The strip's coercivity, measured in oersteds (Oe), determines its resistance to erasure; high-coercivity strips (around 2,750 to 4,000 Oe) hold data longer than low-coercivity versions. Creasing, folding, or scratching the strip renders it unreadable.

The magnetic strip became standard in banking and retail during the 1960s and 1970s following ISO 7810 and ISO 7811 specifications. It remains in widespread use despite the emergence of chip and contactless payment methods, largely because of the cost of replacing existing reader infrastructure and the simplicity of the technology. However, its vulnerability to copying and cloning makes it less secure than EMV chip technology, which is now mandatory in most developed payment systems.

When selecting magnetic strip cards or applying magnetic material to labels, specify coercivity, track count, and encoding density to match your reader equipment. Store cards away from magnets, motors, and heat sources. Expect a card with moderate use to retain readable data for five to seven years before degradation becomes significant.