SiO2 nano-dopant enhanced ZnS: Cu@Al2O3/PDMS mechanoluminescent for efficient fluorescence-coupled tapered optical fiber passive bending sensor

• A novel flexible and wearable passive bending sensor based on a tapered optical fiber is proposed. The sensor features a unique sandwich structure, in which a tapered optical fiber is embedded within a PDMS matrix doped with ZnS:Cu@Al 2 O 3 powders and 10 nm silica nanoparticles, forming a mechanoluminescent thin-film cladding. • The inclusion of silica nanoparticles enhances the elastic modulus of the PDMS matrix, thereby increasing the mechanoluminescent intensity of the sensing film under bending deformation. • The use of a tapered optical fiber expands the fluorescence collection area, thereby improving the efficiency of signal acquisition and enhancing the sensor’s flexibility, which in turn increases its sensitivity over a wide range of bending angles. • By monitoring the change in photon count at the end of the tapered optical fiber, the relationship between the relative variation in light intensity and the bending speed/angle was established, enabling successful differentiation of joint movements under various bending conditions. • Building upon the advantages of existing optical wearable bending sensors, the developed sensor additionally exhibits high stability, flexibility, and structural simplicity, thereby expanding the application landscape of optical methods in bending detection. This paper presents a flexible, wearable, and passive tapered optical fiber sensor for bending detection, based on ZnS:Cu@Al₂O₃/PDMS mechanical luminescence enhanced by SiO₂ nanoparticle doping. The sensor is fabricated by embedding a tapered optical fiber into a PDMS matrix doped with ZnS:Cu@Al₂O₃ luminescent materials and 10 nm SiO₂ nanoparticles. The SiO₂ nanoparticles function as dopants that adjust the elastic modulus of the PDMS matrix, thereby enhancing the mechanical luminescence (ML) intensity of the composite elastomer. The tapered optical fiber increases the effective area for fluorescence collection, improving the signal collection efficiency by approximately 33 %, which in turn enhances the sensor’s sensitivity across a broad angular range. Experimental results indicate that the sensor exhibits a sensitivity of 1.4965 × 10⁻³ (rad⁻¹·min) within a bending speed range of 100 to 500 rad/min, with a resolution of 1.8 rad/min. Within an effective angular range of 10° to 150°, the sensor achieves a sensitivity of 6.6 × 10⁻³ ° ⁻¹ , a resolution of 0.49°, an ascent time of 36.12 ms, and a descent time of 46.1 ms. Furthermore, the repeatability and stability of the sensor have been systematically evaluated. By analyzing relative changes in normalized light intensity in response to variations in bending speed or angle, distinct joint motion states were successfully identified. This study not only expands the application potential of optical bending measurements but also highlights the sensor's promise for human health monitoring, clinical diagnosis of movement disorders, and rehabilitation training.