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Bubble Memory Bias Magnet Structure with Ferrite Face Plates

IP.com Disclosure Number: IPCOM000089463D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Braun, RJ: AUTHOR [+2]

Abstract

Fig. 1 shows a typical open, bias field structure in a representative bubble memory package application. This includes end permanent magnets 11 which are closed by soft magnetic plates 13. This is sometimes referred to as a Watson structure. The basic problem with this structure is that the soft magnetic plates 13 cause relatively high power dissipation losses of the rotational field energy at frequencies of 200 KHz or higher. While negligible at lower frequencies, the effective losses increase very fast with increasing frequency because of the induced eddy currents. These eddy currents produce a "skin effect" which reduces the available cross-section for high frequency, low-loss flux conduction to a value equivalent to the skin depth. Therefore, conventional soft-iron magnet plates are very inefficient.

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Bubble Memory Bias Magnet Structure with Ferrite Face Plates

Fig. 1 shows a typical open, bias field structure in a representative bubble memory package application. This includes end permanent magnets 11 which are closed by soft magnetic plates 13. This is sometimes referred to as a Watson structure. The basic problem with this structure is that the soft magnetic plates 13 cause relatively high power dissipation losses of the rotational field energy at frequencies of 200 KHz or higher. While negligible at lower frequencies, the effective losses increase very fast with increasing frequency because of the induced eddy currents. These eddy currents produce a "skin effect" which reduces the available cross-section for high frequency, low-loss flux conduction to a value equivalent to the skin depth. Therefore, conventional soft-iron magnet plates are very inefficient.

A considerable improvement in efficiency can be achieved by using high frequency ferrite magnet plates. Because thin ferrite plates are brittle and their thermal conductivity is low, placing a thin ferrite layer 15 on the soft iron magnetic plate 13, as illustrated in Fig. 2, is recommended. Since a very thin ferrite layer represents only a minor heat-conduction barrier between the field coils and the solid magnet plates, the magnet plates would continue to carry most of the bias field flux, and provide the structural support and heat dissipation surface of the assembled bubble memory package. Preferabl...