Fig. 1. Model of PTP grating sensor device structure

Fig. 2. Schematic of PTP waveguide equivalent medium

Fig. 3. Schematic of the principle of inertial vibration sensing

Fig. 4. Principle of vibration sensing for flexible grating PTP structure devices

Fig. 5. Transmissivity and reflectance of PTP structure with various grating periods simulated by finite element method under broad spectral conditions. (a) Transmissivity under different grating periods; (b) reflectance under different grating periods; (c) transmissivity curve and normalized electric field distribution for grating period T=425 nm

Fig. 6. Fabrication process of flexible grating PTP structure devices and microstructure of sample. (a) Fabrication process; (b) SEM image of microscopic top views of TiO₂-PDMS; (c) SEM image of cross-section views of PTP

Fig. 7. Design diagram of vibration sensor and two arrangements. (a) Horizontal placement on the surface of detection object; (b) vertical placement on the surface of detection object

Fig. 8. Static test of sensor performance. (a) Schematic of testing system; (b) experimental setup of testing system

Fig. 9. Static testing results of the performance of flexible PTP structure devices. (a) Variation in reflectance spectra with the increasing of strain tensions; (b) variation in reflectance spectra with the decreasing of strain tensions; (c) relationship between center wavelength of the reflected spectra and the applied strain; (d) temperature and humidity resistance test results of the flexible PTP structure devices; (e) variation in reflected center wavelength under 5% increasing strain in ten times repeatability tests; (f) variation in reflected center wavelength under -1.5% decreasing strain in ten times repeatability tests

Fig. 10. Vibration sensing testing. (a) Testing equipment and testing points; (b) schematic of sensor testing front view

Fig. 11. Results of vibration-sensing testing. (a) Spectrum change of reflected intensity in the process of vibration; (b) vibration perception change of center wavelength of reflection spectra; (c) spectrum analysis of center wavelength of reflection spectra; (d) calculated time-domain distribution of vibration acceleration