Dynamic visual cryptography scheme on the surface of a vibrating structure

Dynamic visual cryptography scheme based on time-averaged fringes generated by Ronchi-type geometric moire gratings on finite element grids is proposed in this paper. A single cover image is used to encode the secret image and is formed on the surface of a deformable structure. Time-averaged moire fringes leak the secret when the structure is oscillated according to a predefined Eigen-shape. The envelope functions determining the motion induced blur of the Ronchi-type moire grating depend on the characteristic features of the motion. And though harmonic oscillations do not result into a completely uniform time-averaged image of the Ronchi-moire grating, initial phase scrambling and phase normalization algorithms are used to encode the secret in the cover image. Theoretical relationships between the amplitude of the Eigen-shape, the order of the not completely developed time-averaged fringe and the pitch of the deformable one-dimensional Ronchi-type moire grating are derived.