r<6 r> 丌a2J→ 121 e.×一 H2 e x 2丌r H=h+h e.× B=H=0e2×r 2 < r<a 丌F J 兀rJ→r H e x e x 2丌r 2丌r B=Ho H=H ce. x[r-r=Ho re XC' 2 2 ' 1 2 ' ' ' 2 1 2 2' ' 2 0 0 2' ' 2 1 r H H 2 2 H H H 2 B H 2 r H 2 z z z z z r b a r J r a J r e e r r r r J r e r a r J r e r a r r b a r J e r           =  = −    = + =  −       = =  −       = ( ) 2' ' 2 ' ' ' 0 0 0 H 2 B H 2 2 z z z r r J r e r r r J J e r r e C       = −  = =  − = 