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Browse Prior Art Database

Switchable Permanent Magnet Bias Coil

IP.com Disclosure Number: IPCOM000037845D
Original Publication Date: 1989-Jul-01
Included in the Prior Art Database: 2005-Jan-30
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Andersen, R: AUTHOR [+2]

Abstract

Magnetooptic recording requires a switchable magnetic field for write/erase operations. This function is typically performed by a fast switching electromagnet with soft iron center cores or by a permanent magnet that can be rotated by a slowly responding stepping motor or a solenoid. The disadvantage of the electromagnet is its high power dissipation and inductive losses of the assembly that will slow down the switching time as well as heating up the media and machine. Power needs to be on all the time during write/erase operation. The disadvantage of using the permanent magnet to be rotated mechanically is its slow response, thereby reducing its accessibility.

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Switchable Permanent Magnet Bias Coil

Magnetooptic recording requires a switchable magnetic field for write/erase operations. This function is typically performed by a fast switching electromagnet with soft iron center cores or by a permanent magnet that can be rotated by a slowly responding stepping motor or a solenoid. The disadvantage of the electromagnet is its high power dissipation and inductive losses of the assembly that will slow down the switching time as well as heating up the media and machine. Power needs to be on all the time during write/erase operation. The disadvantage of using the permanent magnet to be rotated mechanically is its slow response, thereby reducing its accessibility.

This invention, as shown in the figure, is to replace the center core with a permanent magnet with its direction of magnetization perpendicular to the magnetooptic media. The core is similarly surrounded by magnet wires, whose turns will be determined by the amount of ampere-turns required to magnetize to the respective north/south polarity determined by the condition of erase vs. write condition. A pulse current will be applied to the winding surrounding the permanent magnet core, so that it will transverse the BH curve to reach its residue magnetization. With the airgap, a magnetic field of 200-250 Oersted is reached. The peak pulse current used in the winding is about 3 amp. With this configuration, it is possible to switch the magnet at a much faster rate than eith...