The present invention relates to a rotation-type actuator which includes a fiber having a twisted structure, which is manufactured by rotating the fiber in the opposite directions. Here, the fiber is divided into a top portion and a bottom portion with respect to the center thereof, at least one of the top and bottom portions of the fiber is fixed, and the top and bottom portions of the fiber each independently have a coiled shape as a chiral Z-type or chiral S-type structure. The rotation-type actuator has an excellent rotation speed, and also exhibits no significant decrease in rotation speed due to excellent durability and stability even when used for a long period of time. In addition, the rotation-type actuator uses a polymer fiber manufactured through electro spinning alone or using a polymer sheet obtained by aligning the polymer fiber in a single direction, and can efficiently convert heat energy, which is wasted in the air, into mechanical energy without providing a high temperature fluctuation since the rotation-type actuator has reversible, rapid and efficient actuation using persistent temperature gradient supplied from a temperature difference present in surrounding environments. Accordingly, energy harvesting devices, having improved efficiency and excellent service life characteristics in recovering heat energy as electrical energy using the rotation-type actuator, can be provided.

The present invention relates to a rotation-type actuator which includes a fiber having a twisted structure, which is manufactured by rotating the fiber in the opposite directions. Here, the fiber is divided into a top portion and a bottom portion with respect to the center thereof, at least one of the top and bottom portions of the fiber is fixed, and the top and bottom portions of the fiber each independently have a coiled shape as a chiral Z-type or chiral S-type structure. The rotation-type actuator has an excellent rotation speed, and also exhibits no significant decrease in rotation speed due to excellent durability and stability even when used for a long period of time. In addition, the rotation-type actuator uses a polymer fiber manufactured through electro spinning alone or using a polymer sheet obtained by aligning the polymer fiber in a single direction, and can efficiently convert heat energy, which is wasted in the air, into mechanical energy without providing a high temperature fluctuation since the rotation-type actuator has reversible, rapid and efficient actuation using persistent temperature gradient supplied from a temperature difference present in surrounding environments. Accordingly, energy harvesting devices, having improved efficiency and excellent service life characteristics in recovering heat energy as electrical energy using the rotation-type actuator, can be provided.

A piston apparatus includes a plurality of piston assemblies respectively having a first piston body and a first piston disposed within a first volume defined by the first piston body, a second piston body and a second piston disposed within a second volume defined by the second piston body, and a connection member coupled to the first piston and the second piston. The first and second volume respectively include an expansion chamber and a compression chamber defined by opposite sides of the corresponding piston. The respective expansion chambers fluidly communicate with a corresponding compression chamber of another one of the piston assemblies. The first volume of a first piston assembly fluidly communicates with the first volume and the second volume of a second piston assembly, and the first volume of a third piston assembly fluidly communicate with the first volume and the second volume of the second piston assembly.