Respiratory rate (RR) monitoring has received widespread attention in medical field. Complex, expensive, and bulky commercial equipment limits the monitoring cost. To take full advantage of lab-on-fiber technologies, we present a novel, compact size lab-on-fiber breathing monitoring sensor based on a tapered no-core fiber (NCF) structure. The sensor is composed of humidity-sensitive polymer materials, single-mode fiber (SMF)–NCF-SMF structure, and monitors human RR by measuring exhaled humidity. The theoretical results prove that the self-imaging phenomenon can be induced by the changing of NCF diameter. The static relative humidity test results show a maximum relative humidity sensitivity of 0.0438 nm/%RH in the range of 35%RH–58%RH. Through the single-wavelength intensity fluctuation experiment, human respiratory information is collected. In the breathing process, a response time of 0.67 s can be achieved. The RR monitoring under different heart rates, breathing patterns, and human postures displays real-time tracking and high repeatability. Moreover, the compact size, low cost, and high sensitivity make our lab-on-fiber sensor more competitive in the field of medical treatment and our daily life.

Combing macroscopic experimental method and mesoscopic numerical method, this study analyses the strain-softening behaviours of granite and sandstone. From the macroscopic perspective, the stress–strain curves of granite and sandstone under different confining pressures are studied by laboratory triaxial compression test. Variations of post-peak reduction modulus and critical plastic shear strain versus confining stress are obtained. Evolution of strength parameters at peak, residual and strain-softening stage are proposed. Then a method to develop the strain-softening model of hard and soft rocks is presented. From the mesoscopic perspective, based on the laboratory test results, the parameters of discrete element method PFC for the samples of the granite and sandstone are calibrated. Comparing the basically consistent results of laboratory experiment and numerical simulation, the feasibility of discrete element method is verified. Evolutions of mesoscopic crack propagation and mesoscopic particle displacement field in the complete failure process are analysed. Typical stresses of granite sample and sandstone sample in the failure stage are investigated. Above combined macroscopic experimental method and mesoscopic numerical method systematically analyse the characteristics of hard rock and soft rock in the strain-softening stage. Failure process and mechanical property of hard rock and soft rock are revealed at the macroscopic and mesoscopic levels. The initiation and propagation process of micro-cracks in rock are thoroughly investigated. The research results provide a scientific foundation for the analyse of strain-softening behaviour of hard rock and soft rock. The result shows that both the mesoscopic numerical method and macroscopic experimental method indicate that the failure pattern of sandstone is influenced by both confining pressure and axial stress, while granite is mainly affected by axial stress.

Highly sensitive and integrated optical multi-band CO₂ sensors are significant at the shortwave infrared (SWIR) region and still lack research. A compact CO₂ sensor composed of a Au-disk/TiO₂-cylinder/Au-film metasurface coated by polyhexamethylene biguanide (PHMB) film, functioning at multi-band resonances as well as having high sensitivity to gas concentrations, is presented. It can be employed as a dual-band narrowband absorber, producing two strongly resonant modes at the SWIR region under a reflection-type framework of linearly polarized incidence. Moreover, the metasurface sensor possesses high refractive index sensitivity of 109.25 pm/ppm at around 1040 nm and 42.57 pm/ppm at around 1330 nm in the range of 200–600 ppm, which is suitable for detecting atmospheric CO₂. Furthermore, the numerical results show that the sensitivity increases with a thicker PHMB film and optimizes at a thickness above 600 nm. The physical mechanism reveals that the higher order mode exhibits more extended near-field energy than the lower order mode, resulting in more sensitivity towards the surroundings. The design and results of our investigation show high-quality CO₂ sensing performance which functions at dual spectrum bands in the SWIR region and is promising for integrated photonic applications.