Magnetic Tape

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On recording tape, particles are magnetized in a pattern that follows the input waveform. Graph A shows an example of an audio input waveform. Graph B shows relative polarity and intensity of magnetization for selected particles on the tape surface.

Magnetic tape, also called recording tape, consists of millions of ferromagnetic particles attached to a flexible, thin plastic strip. In the tape recorder, a fluctuating magnetic field, produced by the recording head, polarizes these particles. As the field changes in strength next to the recording head, the tape passes by at a constant speed. This produces regions in which the ferromagnetic particles are polarized in either direction (Above Figure).

When the tape is run at the same speed through the recorder in the playback mode, the magnetic fields around the individual particles cause a fluctuating field that is detected by the pickup head. This field has the same pattern of variations as the original field from the recording head. Magnetic tape is available in various widths and thicknesses. Thicker tapes result in cassettes that don’t play as long, but the tape is more resistant to stretching. The speed of the tape determines the fidelity of the recording. Higher speeds are preferred for music and video, and lower speeds for voice and data.

The impulses on a magnetic tape can be distorted or erased by external magnetic fields. Therefore, tapes should be protected from such fields. Keep the tape away from magnets. Extreme heat can also result in loss of data, and can cause permanent physical damage to the tape.