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What is the meaning of power/energy density of an actuator?

Context: As a novel kind of actuator, the dielectric elastomer ( DE ) demonstrates high-strain response [ 1 ] , high energy densities ( seventy times higher than conventional electromagnetic actuators ) [ 2 ] , and high energy conversion ef fi ciencies ( 60% – 90% [ 3 ]) .

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Power density is defined and understood as the average power over the weight and/or volume of the actuator (depending on the unit). Here, it is understood as the effective power output divided by weight (or volume)

For example, if your actuator is made from $2kg$ of DE and delivers $5W$ worth of power, then the power density is $5/2=2.5W/kg$

Thanks @Phil Sweet for this comment. I'd add an example for power density per unit volume.

Again, the DE actuator is $5W$ in output, and it has a volume of $0.02m^3$, the its power density will be $5/0.02=250W/m^3$

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  • $\begingroup$ With any luck, it is only used for volume. Specific energy and specific power should be used for per-unit-mass terms. I don't get too worked up if this isn't the case, but please change the example to reflect the preferred usage. $\endgroup$ – Phil Sweet Aug 21 '19 at 3:11

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