The invention relates to a micromotor apparatus and method for extracting energy from a fluid. The inventive method consists in passing a fluid under suitable conditions through a conduit containing a prism which is connected to the walls of the conduit by means of elastic elements. The elastic elements enable the prism to oscillate in a plane containing the axis thereof. The movement of the fluid around the prism excites the Karman vortex street in a resonant manner and generates periodic forces around the prism, which produce an oscillatory movement having a frequency and amplitude that depend on the design parameters of the micromotor apparatus and the fluid dynamic variables. The oscillatory movement of the prism is used to extract energy from the fluid. The micromotor can be used for the propulsion and generation of energy for microsystems.