A Multi-Sensor Wearable Belt Based on Fiber Bragg Grating Sensors for Cardiorespiratory Monitoring

The continuous rise in global population and the increasing demand for food resources require the development of advanced monitoring systems for sustainable agriculture. Plant wearable sensors enable real-Time, high-resolution data acquisition while minimizing interference with natural physiological processes. Among these, fiber Bragg grating (FBG) sensors stand out due to their inherent high sensitivity to strain and temperature variations, transparency, lightweight and immunity to electromagnetic fields and chemical corrosion. Encapsulating FBGs in flexible matrices enhances their suitability for plant monitoring, and recent efforts have focused on developing adhesive matrices to maximize reliability and minimize invasiveness, by avoiding any tapes or supports. This study aims to optimize a previously developed selfadhesive plant wearable sensor by improving the matrix interaction with the embedded FBG, the adhesion of the sensor to plant surfaces, and its overall handling. Following matrix optimization by tuning polymer composition, the sensor was fabricated, metrologically characterized, and tested in situ for 5 consecutive days on leaves of two different plant species (i.e. Fragaria and Coffea arabica). The developed sensor (\mathrm{S}_{\varepsilon}=0.122 \left.\mathrm{nm} / \mathrm{m} \varepsilon, \mathrm{R}^{2}\gt0.99; \mathrm{S}_{\mathrm{T}}=0.008 \mathrm{~nm} /{ }^{\circ} \mathrm{C}, \mathrm{R}^{2}\gt0.99\right) demonstrated the capability to effectively detect the small deformations associated with plant growth and leaf physiological movements, while maintaining stable adhesion. Furthermore, the enhanced robustness of the matrix improved sensor handling, facilitating easier application.