Paper tickets is a thing of the past (at least in China). But apparently the French are more nostalgic (However, the Paris Metro has decided to phase out paper tickets after 120 years).

Have you ever thought about why such a small ticket (even including the transfer information) can be recognized by the tickets checking machine? The magic is all about the magnetic strip on it, a black or brown stripe on the back side of your ticket. The information such as when the ticket is issued, the date and time of the purchase, the validation of the stations is encoded, and can be readout and decoded to give the final control if you can pass or not when you swipe it. Each character that is encoded on the stripe is made of a number of bits. The polarity of the magnetic particles in the stripe are changed to define each bit.

Magnetic stripes are actually used in many applications and everywhere: bank cards (credit, debit, and ATM), Airline tickets, Boarding pass, transit (bus or train) ticket and so on.

In a broader sense, magnetic recording is a widely-used and fastly-developed technology. From the outdated audio casette, magnetic tapes, to the up-to-date Hard-Disk-drive for massive data storage, they are changing and revolurevolutionizing the way we interacte with information.

Obviousely, it even calls back on what I did in my research projects: Spintronics, Magnetisim…

For more information about machanisms of magnetic strips and their applications, have a look at the link below: Introduction to Magnetic Stripe, Magnetic Stripe Encoding