Bending deformation characterization of a holographic sensor based on a flexible substrate

Abstract Bending deformation characterization of holographic sensor based on an acrylamide polymer with flexible substrate has been studied. Unilateral and bilateral bending deformations, as two significant deformation types, are analyzed using the diffraction spectrum of volume grating. In sensing the unilateral bending deformation, the comparative sensing experimental results are presented using expanding and non-expanding broadband light sources to read the grating. There is little difference between two detecting methods. The linear dependence of the peak wavelength shifts on the unilateral bending angle and its lateral displacement provides an important basis for practical application. The maximum of position sensitivity reaches up to 54.09 nm/mm and the average angle sensitivity is 22.42 nm/deg. In sensing the bilateral bending deformation, a non-expanding broadband light source as the reading light can provide more accurate measurement results and higher sensitivity. The similar linear dependence of the peak wavelength shift on the curvature radius also demonstrated the applicability. The maximum of sensitivity reaches up to 43.95 nm/mm (peak wavelength/ curvature radius). In characterizing the initial bilateral bending before straightening the material, a rainbow diffraction spectrum can efficiently reflect the bending deformation. On one hand, the color spatial distribution of diffraction spectrum provides a qualitative method, on the other hand, the spectrum coverage also brings about a quantitative result for the sensing response. Finally, the Ewald sphere theory was used for analyzing the diffraction spot movement and corresponding peak wavelength shift.