Assessment of the mechanical and optical properties of buckling periodic elastic materials as optical force sensors

In this work, we report on the fabrication and characterization of a buckling system constituted by square array holes able to modify its structural configuration and its optical response as a function of the applied force. Herein, polydimethylsiloxane (PDMS) auxetic structures are fabricated by means of 3D printing mold and casting/peeling off steps. From a mechanical point of view, it has been demonstrated that the structure presents a transformation to a strikingly different pattern of alternating mutually orthogonal ellipses above a nominal force of 23 N, a clear signature of the auxetic structures behavior. This feature has been exploited to create a reversible and sensitive optical force sensor, that makes use of the variation on the light intensity or its optical rotation (?) upon application of a force. In fact, it has been demonstrated that the application of the force induces a variation of the refractive index of the auxetic system, associated to the presence of stress. For the structure realized a sensitivity of about ?(??) ?F = 0.033 rad/N in the range between 23 N and 28 N has been determined. Finally, the presented study suggests that it is possible to realize a sensitive and reversible optical force sensor taking advantages of the peculiar features of buckling periodic elastic materials.