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Method for Producing Large Area Thin Magnets

IP.com Disclosure Number: IPCOM000118263D
Original Publication Date: 1996-Nov-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 99K

Publishing Venue

IBM

Related People

Beeteson, J: AUTHOR [+2]

Abstract

Disclosed is a method for overcoming the problems associated with producing large area permanent magnets and methods of controlling the field intensity in the vicinity of the magnet. In a permanent magnet, the strength of the magnet is determined by the flux density in the region outside the magnetic material. Within the material, flux lines tend to be oriented to connect the South and North poles. Any flux lines which close through the material have to overcome this internal field. In the case of bar magnets, the energy required to do this is much greater than taking the alternative route through air outside the material, i.e., flux lines prefer the path of least resistance.

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Method for Producing Large Area Thin Magnets

      Disclosed is a method for overcoming the problems associated
with producing large area permanent magnets and methods of
controlling the field intensity in the vicinity of the magnet.  In a
permanent magnet, the strength of the magnet is determined by the
flux density in the region outside the magnetic material.  Within the
material, flux  lines tend to be oriented to connect the South and
North poles.  Any flux  lines which close through the material have
to overcome this internal field.  In the case of bar magnets, the
energy required to do this is much greater than taking the
alternative route through air outside the  material, i.e., flux lines
prefer the path of least resistance.

      For magnets which are thin compared to their surface area (the
opposite case to a bar magnet), the path of least resistance is
through the material.  Thus, the net flux density outside the magnet
is very low,  i.e., a very poor magnetic performance.

      This problem is recognized by magnet manufacturers both in
terms of the properties of the magnet produced and also that
magnetizing such a magnet in the first instance is impossible.  The
magnetizing problem can be understood by considering that during the
magnetizing process, as the field intensity in the material
increases, so flux lines from this field flow through the material,
opposing the flux lines from the external field trying to establish
the field. The  net result of this effect is that the area of a
useful magnet is limited  by it's thickness.  Permanent magnets are
commonly used for two purposes:

      Bar magnets produce an essentially linear field similar to
that produced by a solenoid.  The field is characterized by being of
essentially uniform intensity at the poles.  An example application
is a monitor/TV lin coil.

      Plate magnets are often formed by a series of alternating
N-S-N poles fabricated as strips within the overall structure.  This
arrangement gives rise to a large number of flux lines closing
external to the magnet surface and thus, is useful as an "adhesive".
The attractive force is determined by the flux density flowing the
object being attracted to the magnet's surface.)  An example
application is a  magnetic chuck for milling and grinding machines.

      In a bar magnet, the length of the bar must be long to ensure
sufficient flux density outside the material.  Large area thin
magnets can be formed but, due to the need for the different
magnetization directions (N-S-N-S, etc.) across the surface,
processing of the material to induce the field is complicated.

      By forming a number of holes through a large area thin magnet,
flux lines may locally close through these holes.  The holes have the
effect of increasing the apparent aspect r...