A hydraulic cylinder has a tube with a first end and a section end. An algorithmic implementation of this can take the form of creation of a look-up table that stores all the scattering information of all two-dimensional objects needed for the synthesis of the electromagnetic scattered field from the original three-dimensional object. When the magnetic discs are directly rotated by the rotating unit and the winding discs are indirectly rotated by the rotating unit via the transmission unit, magnetic bodies on the magnetic discs and windings on the winding discs are quickly moved in a relative motion to produce relatively large flux change, enabling the wind power generating device to have increased power generation capacity. Compared with the synthetic routes of ligands to be used in the activation of carbon-chlorine bonds in the prior arts, the preparation method of the present invention has the advantages of short route and easy operation.