Soft Iron Material

• Eddy current loss occurs in the stator and rotor iron parts
  • The high operating speed of motor will cause higher switching frequency. The stator teeth sees high frequency for flux density, leads to higher losses.
• Thinner lamination reduces eddy current loop, enhancing resistance to eddy current. This lowers the eddy current loss

Sleeve Material

• For magnet with typical mechanical strength, higher speed of rotation of the rotor results in higher centrifugal forces on the rotating magnet
  • Need of sleeve (0.3 to 0.5 mm thick) on magnet prevent magnet breakage
• Presence of sleeve leads to
  • Increased effective airgap lowers magnet operating point. This increase the need for higher magnet volume for desired flux which increase magnet cost.
  • Increased cost due to additional component and assembly complexity.
  • High motor speed causes high frequency of flux direction change in sleeve. Hence, increase the eddy current loss in sleeve
  • Sleeve material with high resistivity lower the eddy current loss
• Use of high strength MQ1^TM magnet can eliminate the need for sleeve