A utilization of active materials of an electric motor can be characterized by:

• power density , i.e., output (shaft) power-to-mass or output power-tovolume ratio;

• torque density , i.e., shaft torque-to-mass or shaft torque-to-volume ratio. Torque density is a preferred parameter to power density when comparing low speed motors, e.g., gearless electromechanical drives, hoisting machinery, rotary actuators, etc. The utilization of active materials increases with the intensity of the cooling system, increase of the service temperature of insulation and PMs, increase of the rated power, rated speed and electromagnetic loading, i.e., Pout/(D21inLi) ∝ Selm/(D21inLi) = 0.5π2kw1BmgAmns as expressed by eqns (5.67) and (5.70).