Degaussing Magnetic Media

The Process Of Erasing Magnet Media

     Degaussing is used for security purposes, to conform to privacy laws and to reuse the media. Some media, for example 1/4" Mini Cartridges, are in most cases pre-formatted or servo-written. Degaussing may require new formatting, which can become difficult. So care has to be taken to determine which media to degauss.
     Degaussing takes its meaning from the Gauss; the unit measure for the magnetic flux density. It is used today to describe the process of erasing magnetic media, removing from the media remnants of previously recorded signals.

About Magnet Media
     The term magnetic media covers a vast range of material from audio and videotapes and cassettes to computer diskettes and reels, supplied in a wide choice of sizes and complexities. All of them however, perform in the same basic way.
     The media consists of material that is coated with minute magnet particles that react to magnetic influences applied to them. Such influences fall into two types: The first is the intended influence during recording of a signal that creates the desired orientation of the magnet particles in response to the recording signal. This magnetic pattern is used to produce the desired "play-back" after recording. Ideally the replay should replicate the original recording, whether this is from an audio, video or computer data source. The second influence is the unwanted signal, which can take the form of distortion, bias, corruption or interference and can produce undesirable effects such as poor quality in audio or video media or software glitches in data material. Clearly any process, which enhances the first and eliminates the second is desirable, degaussing magnet media can help to achieve this.

About Degaussers
     The process of degaussing is achieved by passing the magnet media through a powerful alternating magnet field to rearrange the magnetization of the magnetic particles, completely removing any resemblance of the previously recorded signal. Degaussers are constructed in such a way as to enable the generated magnetic field cover the entire magnet media when it is transported through it, either by physically holding the media by hand and moving it through the field or automatically conveyed by a belt transporter.
     Magnetic media is characterized by its coercivity, which is a measure for the media's resistance to erasure. The higher the coercivity the higher the degaussing field has to be. So-called High Energy Media has very high coercivities. Generally speaking the field produced by a degausser should exceed the media coercivity by a factor of 3-4. Further degaussing effectiveness can be achieved by using more than one coil in multi-axial orientation. Additional improvements can be obtained by rotating the coils during the degaussing process.

GLOSSARY OF TERMS

Coercivity or coercive force - The field strength required to bring the flux density to zero in a magnets material.
Degauss - To return the magnetization in a media coating or in a head to a zero state by applying a decaying and alternating magnetic field.
Gauss - A unit of magnetic flux density.
High energy tape - Magnetic tape having coercivity higher than 600 Oersted.
Magnetic flux - The magnetic lines of force produced by a magnet for electric current.
Magnets field strength - The magnitude of a magnetic field vector, usually expressed in Oersted or ampere-turns per meter.
MMF magnetomotive force - The magnetic analogue of electromotive force, which, when due to a current in a coil, is proportional to the product of current in amperes and the number of turns.
Maxwell - A unit of magnetic flux.
Oersted - A unit of magnetic field strength.

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