831eb72a_es_content_from_Machine_Design__Induction_motor
[0] POWER DENSITY [PMAC] Rare-earth permanent magnets produce more flux (and resultant torque) for their physical size than induction types [Servomotor] Capable of high peak torque for rapid acceleration [Induction motor] 
Induction produced by squirrel cage rotor inherently limits power density
The difference between AC induction, permanent magnet, and servomotor technologies | Motors/Drives content from Machine Design
Induction motor