Design of a multi-layered optical bend loss sensor for pressure and shear sensing

A multi-layered optical bend loss sensor for pressure and shear sensing is presented. This design is based on the characteristic of optical bend loss. When external forces applied to the sensor, the optical fibers will bend and cause the light to escape from the fiber. The amount of light attenuation depends on the amount of bending occurred on the fiber. In our previous study, the sensor is composed of two layers of fiber optic mesh sensors that are molded into a thin polydimethyl siloxane (PDMS) substrate. Measuring changes of light intensity transmitted through the fiber provides information about the changes of the fiber's radius of curvature. The new design induces an elastomeric layer to separate the two optical fiber meshes. Pressure is measured based on the force induced light loss from the two affected crossing fibers. Shear was measured based on the relative position changes on these pressure points between the two fiber mesh layers. The additional elastomeric layer provides mobility in the lateral direction to improve the shear sensing. Preliminary testing on the new multi-layered sensor under normal and shear loading is encouraging. By adding the gel layer, when the applied force is 5N, the maximum attenuation is 30% at the top layer and 3% at the bottom layer. For the shear force detection, shifting of loading point at bottom layer was also observed from the experiment.