Any element which exhibits the direct piezoelectric effect (converts mechanical energy to electrical energy)
can be considered an energy harvesting device.
These are often refered to as "sensors", "generators", "scavangers" or "harvesters".
Single sheets, benders, extenders, and stacks may all be employed to collect energy.
PIEZOELECTRIC ENERGY HARVESTING KIT
The Energy Harvesting Kit consists of one Double Quick-Mount
Harvesting Bender and one Energy Harvesting Circuit.