Single-step Manufacturing of Flux-Directed Permanent Magnet Assemblies

Abstract

A flux directed magnet and a method of manufacturing a flux-directed magnet in a reduced number of process steps is described and claimed. The present invention is, in an embodiment, a single-step manufacturing of flux directed magnet assemblies such as, but not limited to, Halbach arrays of arbitrary multipole order. Even tube-shaped flux directed magnet assemblies such as Halbach arrays with large aspect ratio, i.e. length to diameter, can be produced in single steps using the method of the invention. Alternatively, the present invention may be one step of a plurality of steps in a process for manufacturing of flux directed magnet assemblies.

What is claimed is: 
     
         1 . A method for producing a flux-directed magnet assembly, comprising the steps of:
 a. Providing an assembly having a first region, second region and a third region in cross section, wherein said second region is disposed between said first and said third regions, and wherein said second region comprises permanent magnet material; and   b. Wherein, in said cross section of said flux directed magnet assembly, said first region, said second region, and said third region form concentric circles, said second region being defined as having a radius; and   c. Wherein, for inside-directed flux, said first region contains an enhanced magnetic flux and said third region is quasi flux-free, and wherein for outside-directed flux said first region is quasi flux-free said third region contains an enhanced magnetic flux;   d. Wherein the magnetization of any point in said second region is defined as being continuously variable, substantially independent for the point along the radius due to the operation of the magnetization field as being above the saturation magnetization of the permanent magnetic material, and is given by the equations:
     M _ r (φ)= B _ rem *cos( n φ)
 
     M _φ(φ)= B _ rem *sin( n φ)
 
    where φ is the azimuthal direction, Brem is the remanent flux density of the magnetic material and n is the multipole order; and   e. wherein the absolute value of the magnetization is substantially constant throughout said second region.   f. using amplitudes B rem  of different size in front of the cosine and sine functions above enables flux-directed assemblies with elliptical cross section.   
     
     
         2 . The method for producing a flux directed magnet assembly of  claim 1 , wherein said magnetic flux directed magnet assembly is defined as a Halbach array. 
     
     
         3 . The method of  claim 1 , wherein the equations for the magnetic flux density in said first region and said second region for inside-directed flux, multipole order greater than 1 in cylindrical coordinates are:
 for said first region, (n>1):
     B _ r ̂|=( B _ rem*n )/( n− 1)*(1−( R _ i/R _ o )̂( n− 1))*( r/R _ i )( n− 1)*cos( n φ)
 
     B _φ̂|=−( B _ rem*n )/( n− 1)*(1−( R _ i/R _ o )̂( n− 1))*( r/R _ i )( n− 1)*sin( n φ)
 
   For said second region, (n>1):
     B _ r ̂∥=( B _ rem*n )/( n− 1)*(1−( r/R _ o )̂( n− 1))*cos( n φ)
 
     B _ φ̂∥=−B _ rem /( n− 1)*(1− n ( r/R _ o )̂( n− 1))*sin( n φ)
 
   
     
     
         4 . The method of  claim 1 , wherein the equations for the magnetic flux density in said second region and said third region for outside-directed flux, multipole order greater than 1 in cylindrical coordinates are:
 For said third region, (n<−1):
     B _ r ̂|∥=( B _ rem*n )/( n− 1)*(1−( R _ i/R _ o )̂(1− n ))*( R _ o/r )̂(1− n )*cos( n φ)
 
     B _φ̂|∥=−( B _ rem*n )/( n− 1)*(1−( R _ i/R _ o )̂(1− n ))*( R _ o/r )̂( 1 − n )*sin( m φ)
 
   For said second region, (n<−1):
     B _ r ̂∥=( B _ rem*n )/( n− 1)*(1−( R _ i/r )(1− n ))*cos ( n φ)
 
     B _ φ∥=−B _ rem /( n− 1)*(1− n ( R _ i/r )̂(1− n ))*sin( n φ)
 
   
     
     
         5 . The method of any of  claims 1 - 4 , wherein said magnetic flux is produced by at least one double-helix magnet configurations. 
     
     
         6 . The method of  claims 1 - 4 , wherein said magnetic flux is produced by at least one direct double-helix magnet configurations. 
     
     
         7 . The method of any of  claims 1 - 6 , wherein the magnetic material is further defined as being manufactured from a powdered metal, produced by the steps of:
 a. Preparing the powdered metal by providing the appropriate amounts of neodymium, iron, and boron;   b. Heating the powdered to a melting point under vacuum.   c. Cooling said powdered metal;   d. Crushing and then grinding said powdered metal into a fine powder.   e. Placing said powdered metal into a die that has the approximate shape of the finished magnet;   f. Applying a magnetic field to the powdered material to line up the powder particles;   g. While the magnetic force is being applied, pressing the powder from the top and bottom with hydraulic or mechanical rams to compress it to within about 0.125 inches (0.32 cm) of its final intended dimensions;   h. Sintering the compressed powdered metal, which fuses the powder into a solid piece;   i. Annealing the compressed powdered metal the sintered material in a second controlled heating and cooling process to remove residual stresses within the material and strengthen it;   j. Machining the annealed material to produce a smooth surface; and   k. Applying a protective coating to the annealed material.