magnetic tape (MT)
Magnetic tapes (MT) are used to record, play back and eraseinformation. They are used in tape drives as a storage medium for digital data and for storing analog signals, audio and video signals.
The carrier material of magnetic tapes consists of a tensile polyester film, such as Terylene or Mylar, that is only a few micrometers (4 µm to 10 µm) thick. A magnetically effective layer of iron oxide or chromium dioxide is applied to this flexible carrier film. The layer thickness is only a few micrometers (about 2 µm). For this purpose, the oxide crystals, which used to be less than 1 µm in size but have since been reduced to less than 10 nm, are provided with a binder and applied to the carrier film. The oxide crystals used are needle-shaped with an aspect ratio of about 1:10.
During the magnetization process, the oxide crystals are aligned by the magnetic field of a magnetic head and persist in their remanence. The hysteresis of the oxide particles has a high remanence and coercivity. During readout, only the remanence comes into play, since the magnetic fields of the read head do not magnetize via the coercive force. Only during the erasing process are very strong magnetic fields applied so that the oxide crystals change from remanence to another state.
In tape drives, digital data is stored on the magnetic tape by means of encoding processes. Return to Bias( RB), Return to Zero( RZ) and the various NRZ processes, such as NRZ-L, NRZ-M and NRZ-S, are used to encode the data.
Magnetic tapes are available as video cassettes or in cartridges. They vary in width according to the applications. For example, magnetic tapes are available in 2", 1", 3/4", 1/2", 3/16", 1/8" and 8 mm versions.
The quality of a magnetic tape recording is determined by the magnetic tape, its surface roughness, the size of the magnetic particles, the magnetic track width and the magnetizability. In addition, there are the characteristics of the magnetic head, such as its gap width and the tape speed. For audio recordings, high tape speeds of 38 cm/s or 76 cm/s degrade the frequency range for bass reproduction. At slower tape speeds, the low frequencies are reproduced better.