The magnetic stripe card is the most widely used card technology and it’s often used for access control applications.
They are inexpensive, easily manufactured and encoded, and able to carry alphanumeric data. Most people are familiar with the technology because of its widespread use by bank and credit card operations.
The card can be made of plastic (polyester, pvc or some other material), paper or even some amalgamation of materials.
The domains where magnetic stripe cards are used includes: ATM cards, bank cards (credit and debit cards including VISA and MasterCard), gift cards, loyalty cards, driver's licenses, telephone calling cards, membership cards, electronic benefit transfer cards (e.g. food stamps), and nearly any application in which value or secure information is not stored on the card itself.
Figure 1. Wasp WaspTime Employee Time Cards Seq 1-50 - Magnetic stripe card
The magnetic stripe on the card is composed by very small magnetic particles mixed into a resin to facilitate the orientation of the substrate. The material which is used for magnetization is characterized by the coercivity. The coercivity is the term to designate how strong a magnetic field must be to affect data encoded on the stripe, and therefore, how immune the data is to damage.
It’s measured in Oersteds (Oe). Cards with low coercivity (ex. a common credit card with 300 Oe) generally are made using iron oxide, and the material to obtain high coercivity with values ranging from 2500 to 4000 Oe is generally barium ferrite. The encoding technique is the same for both technologies, except in high coercivity which requires a stronger electrical current in the write head.
Although, the high coercivity cards are virtually immune to domestic-type magnets (such as magnetic money clips, refrigerator magnets, etc.) and decreases the chance of accidental data erasures, they are only used in applications where the need for performance, for example in critical test equipment, outweighs price.
Low coercivity cards continue popular due to the widely established base of low coercivity encoders and the increased cost of high coercivity encoders. Standard magnetic stripe readers, however, can read either high coercivity or low coercivity stripes.
The card is encoded by means of bars of magnetized and non-magnetized material on the strip. The magnetized and non-magnetized areas represent the numbers 1 and 0, forming the binary code that is deciphered by the reader on presentation.
The information data on a typical magnetic card is saved on 3 tracks, according with a set of International Standards Organisation (ISO) standards:
- Track 1 can contain 79 alphanumeric characters. The data on this track is codified by 6 data bit plus one parity bit.
- Track 2 can contain 40 only number characters, each of them composed by 4 data bit plus one parity bit.
- Track 3 can contain 107 only number characters codified as data on track 2.
Track 1 and track 2 are only readable, while track 3 is read-write.
Most common readers read the information on track 2. The card must be swiped or inserted in the reader so that the read head can pick up the card’s encoded data.
Figure 2. MagTek Mini Swipe Magnetic Strip Reader
This contact operation creates wear on both the card and the head. However, with the high-density magnetic stripes, loss of data is now uncommon. However the encoded data can be affected by proximity to magnetic fields.
This technology provides a medium level of security because the card duplication is possible using the right equipment and proper knowledge. However the low cost for both readers and cards makes it an attractive choice.
Usually they are used for low to medium security level installations, as applications with a great number of cards such as club member entrances and parking lots or applications with high turnover, card loss or expiration of memberships or applications where the user wishes to uses existing magnetic cards (such as time and attendance cards) for access control.
The cards are economical and have an average life of 18 to 30 months and the readers can allow over 1 million swipes before maintenance of the reader head is required. However the magnetic stripe is not the best choice for harsh environment.