Dynamic magnetic information storage or retrieval – Head – Core
Patent
1989-07-17
1991-10-15
Heinz, A. J.
Dynamic magnetic information storage or retrieval
Head
Core
360123, G11B 5127
Patent
active
050579584
DESCRIPTION:
BRIEF SUMMARY
The invention concerns writing and/or reading magnetic heads for magnetic tracks with strong coercive fields, i.e. with values ranging from 24,000 to 40,000 A/m.
In order to improve the protection of digital magnetic recordings, especially in the field of computerized money systems, magnetic layers with strong coercive fields have been developed. These have gradually attained very high values, generally greater than 20,000 A/m. This type of magnetic medium is particularly difficult to saturate and, therefore, necessitates a magnetic recording head of a special type. In effect, the geometry usually employed for the making of these heads cannot be entirely called into question since the principle of magnetic recording consists in the use of a magnetic circuit enabling the concentration of a magnetic field in a restricted section of said circuit. This zone, called a gap, which is very short and has a permeability of the order of 1, has great reluctance which contributes to and promotes the spread of the magnetic field outside the circuit. This zone is therefore a source of "leaks" which ensure the magnetic polarization of the layer forming the recording track, which is in contact, in varying degrees, with this zone of the recording head.
Generally, the magnetic circuit contributing to this field concentration (created by the passage of a current in a coil placed on said circuit) is made of a magnetic material having characteristics that are suited to this application. The magnetic permeability is chosen to be as high as possible so as to ensure that the magnetic flux, created by the passage of the current in the excitation coil, is properly channelled. Furthermore, there is a demand for a suitable induction at saturation in order to minimize the excitation current. Owing to the application in frequency, there is a demand for materials showing low losses (eddy current losses and hysteresis losses) as a function of frequency. The most adapted materials, having intrinsic characteristics that are precisely suited to these three variables, are generally sintered materials of the ferrite type which, owing to their structure, ensure a worthwhile compromise between these variables. However, for the application in question, these materials do not have a sufficiently high induction at saturation to ensure proper saturation of the recording layer. Generally, the small sections used in the leakage zone (the gap zone) lead to a premature saturation of the concentration material and, consequently, do not make it possible to work in very strong fields such as those needed to ensure the saturation of a recording track with a coercive field of up to 40,000 A/m or more.
To overcome these disadvantages, the invention proposes a magnetic head which enables the saturation of magnetic layers with coercive fields of more than 20,000 A/m. This magnetic head is compatible with the reading and writing devices already in use. The invention uses a solid metal magnetic material with magnetic characteristics that are well suited to obtaining the saturation of a highly coercive field track (of more than 20,000 A/m for example). It enables the making of heads that can be used for recording on tracks with strong coercive fields and are, at the same time, highly resistant to wear and tear. This latter point, which is of a strictly mechanical order, is very important in use, inter alia , for the maintenance and reliability of electromagnetic writing performance characteristics. It provides for the mechanical (plane, cylindrical trueing, etc.) of a material which, by its composition, is reputed to be very sensitive to stresses without being obliged to be subjected to a final heat treatment capable of restoring its original characteristics to this material.
The invention therefore has an object, a single track or multiple-track reading and/or writing magnetic head characterized in that it comprises, for a magnetic track:
two pole pieces made of a solid metallic material and separated by a gap, each being housed in cavity machined in a mounting m
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Patent Abstracts of Japan, vol. 7, No: 188, Aug. 17, 1983, & JP, A, 5888814 (Matsushita Denki Sangyo K.K.) May 27, 1983.
Patent Abstracts of Japan, vol. 6, No: 192 Sep. 30, 1982, & JP, A, 57103116 Jun. 26, 1982, (Sony K.K.).
Patent Abstracts of Japan, vol. 4, No: 78, Jun. 6, 1980, & JP, A, 5542351 (Matsushita Denki Sangyo K.K.) Mar. 25, 1980.
Compagnie Europeenne de Composants Electroniques - LCC
Heinz A. J.
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