Magnetic field generator and its manufacturing method

Abstract

There is provided a magnetic field generator ( 10 ) and a method of manufacturing it, capable of reducing decline in the magnetic field intensity and deterioration of magnetic field uniformity during transportation. The magnetic field generator ( 10 ) includes a pair of plate yokes ( 12 a ), ( 12 b ). The plate yokes ( 12 a ), ( 12 b ) are opposed to each other, with their opposing faces provided with permanent magnet assemblies ( 14 a ), ( 14 b ) respectively. The permanent magnet assemblies ( 14 a ), ( 14 b ) have faces opposing to each other, to which pole pieces ( 16 a ), ( 16 b ) are fixed respectively. The permanent magnet assemblies ( 14 a ), ( 14 b ) include permanent magnets ( 18 ). The pole pieces ( 16 a ), ( 16 b ) include annular projection ( 24 ) and permanent magnets ( 28 ) for prevention of magnetic flux leakage provided on an outer side surface of the annular projection ( 24 ). The permanent magnets ( 18 ), ( 28 ) include R—Fe—B magnets magnetized to a magnetization rate not smaller than 80% and not greater than 99.9%. When manufactured, the assembled magnetic field generator ( 10 ) is heated in its entirety at a temperature not lower than 40° C. and not higher than 70° C.

1 . A magnetic field generator comprising: 
 a pair of first magnets including a R—Fe—B magnet which are faced to each other with a space in between; and    a yoke supporting the first magnets,    wherein the R—Fe—B magnet is magnetized to a magnetization rate not smaller than 80% and not greater than 99.9%.    
     
     
         2 . The magnetic field generator according to  claim 1 , further comprising pole pieces provided on the opposed faces of the first magnets respectively, 
 wherein the pole piece includes an annular projection and a second magnet for prevention of magnetic flux leakage provided on an outer side surface of the annular projection.    
     
     
         3 . The magnetic field generator according to  claim 1  or  2 , wherein the R—Fe—B magnet does not essentially contain Co and/or Dy.  
     
     
         4 . The magnetic field generator according to  claim 1  or  2 , wherein required uniformity of magnetic field intensity is within 100 ppm.  
     
     
         5 . The magnetic field generator according to  claim 1  or  2 , to be transported in a container.  
     
     
         6 . The magnetic field generator according to  claim 1  or  2 , wherein a uniform magnetic field space has a magnetic field intensity not smaller than 0.25 T.  
     
     
         7 . A method of manufacturing a magnetic field generator, comprising: 
 a first step of assembling a magnetic field generator including a R—Fe—B magnet, and a second step of heating the entire magnetic field generator which has been assembled, at a temperature not lower than 40° C. and not higher than 70° C.    
     
     
         8 . A method of manufacturing a magnetic field generator, comprising: 
 a first step of assembling a pole-piece unit by fixing a magnet including a R—Fe—B magnet to a plate yoke;    a second step of heating the pole-piece unit which has been assembled, at a temperature not lower than 40° C. and not higher than 70° C.; and    a third step of fixing the heated pole-piece unit to a supporting yoke.    
     
     
         9 . A method of manufacturing a magnetic field generator, comprising: 
 a first step of forming a magnet including a R—Fe—B magnet;    a second step of heating the magnet at a temperature not lower than 40° C. and not higher than 70° C.;    a third step of magnetizing the heated magnet; and    a fourth step of fixing the magnetized magnet to a plate yoke.    
     
     
         10 . A method of manufacturing a magnetic field generator, comprising: 
 a first step of forming a magnet including a R—Fe—B magnet;    a second step of magnetizing the magnet to a magnetization rate exceeding 99.9%;    a third step of demagnetizing the magnetized magnet to a magnetization rate not smaller than 80% and not greater than 99.9%; and    a fourth step of fixing the demagnetized magnet to a plate yoke.