Power density is simply the ratio of output power or horsepower to physical size or volume of the motor. There are many factors such as material characteristics and temperature constraints that limit how much power a machine can deliver of a certain size. Different topologies and machine configurations address these limitations in various ways. For example, rare earth permanent magnets produce more flux for their physical size than the magnetic energy (and resultant torque) produced by an induction motor’s “squirrel cage rotor”. As such, a DEC Star® motor can have higher power density than an equivalent rated IM.