Standard Magnetics Card Technology

The standard magnetic stripe is composed of a polyester film backing with an applied slurry of ferric oxide particles. These particles are aligned by a forming magnet during the manufacturing process. The tape is then oven set to fix the physical orientation of the particles.

The classic particle orientation is parallel to the length of the tape.

The magnetic properties of ferric oxide particles are such that when a magnetic field of 300 Oe is applied, the particles will retain the applied magnetisation.

By alternating the polarity of the applied magnetic field, a pattern of North/South and South/North regions of magnetisation may be applied across the length of the tape. When this pattern complies with the ISO Standards for encoding magnetic tape, that pattern may be interpreted by any ISO compliant reading device as a series of 0's and 1's which can then be built up into numerals and/or alpha numeric characters.

In this way, account numbers and names may be stored on the magnetic tape to be read by the reading devices installed in ATM's, EFTPOS machines etc.

The ISO standards allow for encoding along three tracks. The combined memory capacity of those three tracks is 1000 bits (0's or 1's).

The information on a magnetic stripe is not permanent. It will decay over time. It may also be erased by any magnetic field in the vicinity of 300 Oe in strength. Unfortunately such magnets are common place eg fridge magnets.

A solution to this accidental erasure problem is what is termed Hi Coercivity magnetic tape. Unlike standard magnetic tape, Hi-Co tape is not made of ferric oxide particles but rather uses a rare earth metal oxide such as Barium rather than Iron to increase the magnetic field strength necessary to encode and/or erase the tape.

Hi-Co tape requires special encoding equipment which can generate the magnetic field strengths necessary. It can, however, be read by most normal magnetic tape readers as they are essentially detecting remanent field strength in a passive way. Even though the field strength is higher, they can usually still detect the transitions ie North/South South/North and so detect the encoded bit pattern.

Whilst Hi-Co tape more or less solves the inconvenience factor of accidental erasure by fridge magnets or purse clips, it does not mitigate against the inherent security flaws of magnetic tape which are that with relatively cheap equipment the information encoded onto the tape may be copied to another piece of tape. The counterfeit copy is indiscernible from the original and so poses a serious problem for the use of classic magnetic tape encoding for secure applications.

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