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Mechanical energy harvesting converts supplied motion or deformation into recoverable energy in an electrical load. A vibrating support can drive a moving magnet, a variable capacitor or a device using piezoelectricity. These are different transducers coupling a mechanical input to an electrical load.

A small generator attached to a vibrating beam provides a useful experiment: measure both the electrical output and the change in the beam's motion as the load is varied. Extracting energy introduces a resisting force or effective damping, so the transducer can change the vibration that drives it. Available average power, response frequency and losses all matter. A large open-circuit voltage alone does not establish useful output power; the device must deliver energy to a specified load while an external source sustains the mechanical motion.