We propose an air gap fiber Bragg grating (g-FBG) sensor that can measure strain and temperature simultaneously. The sensor is made by aligning two fiber Bragg gratings (FBGs), and an air gap exists between these two sub-gratings. This sensor’s architecture allows it to form a spectrum with phase-shifted fiber Bragg grating (PSFBG) spectroscopy and Fabry–Perot interference (FPI) spectroscopy. Since the sensitivity of PSFBG and FPI spectra is different for strain and temperature, it is possible to measure both strain and temperature by measuring one of the reflected dips of PSFBG and the interference dip of FPI. The experimental results show that the strain sensitivity is about 11.95 pm/με via the dip wavelength detection of FPI, and the temperature sensitivity is about 9.64 pm/°C via the dip wavelength detection of PSFBG. The g-FBG sensor demonstrates a resolution of approximately ±3.7 με within the strain range of 0 to 1000 με and about ±0.6 °C within the temperature range of 25 °C to 120 °C. The proposed g-FBG sensor, characterized by its simple structure, compact size, and cost-effectiveness, exhibits significant potential in the field of multi-parameter measurements.

The crack-based ultrasensitive sensor inspired by spider has an efficient electro-mechanical conversion mechanism and shows superiority in extremely small movements monitoring. However, a complete explanation of the sensing mechanism and the theoretical study of the optimization of the crack structure is still a challenge. Here, we simplify the bionic sensing layer into a parallel equal-length crack structure and implement the mechanical analysis using the method of complex variable function, from which, three typical stages of the crack structure under different force levels are summarized, which are overlap, transition and tunneling, respectively. The sensing characteristics at each stage is studied and a pressure-resistance model is established, also the influence law of the crack parameters on the sensitivity and measuring range is investigated, all to support the design of a bionic crack pressure sensor aiming for ultrahigh sensitivity. To fabricate the pressure sensor, the elastic substrate for the cracks is successfully prepared by gold ion sputtering, and the morphology of the metal cracks is precisely controlled using a photolithography-assisted method. According to experiments, the fabricated pressure sensor shows an ultrahigh sensitivity of 2.39×10 ⁷ kPa ^-1 in the range of 0.28-0.35 kPa, as well as pleasing repeatability within at least 1000 testing cycles. The sensitivity of the bionic crack pressure sensor is desirable comparing with a group of recently reported pressure sensors. Combining with other benefits of stability and reliable fabrication, our bionic crack pressure sensor is attractive for ultra-precision applications, such as human-machine interfaces and biological health monitoring.

This paper aims to develop a resonant accelerometer for high-sensitivity detection and to investigate the nonlinear vibration of the MEMS resonant accelerometer driven by electrostatic comb fingers. First, a nonlinear vibration model of the resonator with comb fingers in a MEMS resonant accelerometer is established. Then, the nonlinear and nonlinear stiffness coefficients are calculated and analyzed with the Galérkin principle. The linear natural frequency, tracking error, and nonlinear frequency offset are obtained by multi-scale method. Finally, to further analyze the nonlinear vibration, a sample-based stochastic model is established, and the uncertainty analysis method is applied. It is concluded from the results that nonlinear vibration can be reduced by reducing the resonant beam length and increasing the resonant beam width and thickness. In addition, the resonant beam length and thickness have more significant effects, while the resonant beam width and the single concentrated mass of comb fingers have little effect, which are verified by experiments. The results of this research have proved that uncertainty analysis is an effective approach in nonlinear vibration analysis and instructional in practical resonant accelerometer design.

A compensation method for nonlinear vibration of a silicon micro resonant sensor is proposed and evaluated to be effective through simulation and experimental analysis. Firstly, the parameter characterization model of the silicon micro resonant sensor is established, which presents significant nonlinearity because of the nonlinear vibration of the resonant beam. A verification circuit is devised to imitate the nonlinear behavior of the model by matching the simulation measurement error of the frequency offset produced by the circuit block with the theoretical counterparts obtained from the model. Secondly, the principle of measurement error compensation is studied, and the compensation method dealing with nonlinear characteristics of the resonant beam is proposed by introducing a compensation beam and corresponding differential operations. The measurement error, compensation rate, and measurement residual between the two scenarios that use single beam and double beams, respectively, are derived and are compared with their simulation and experimental counterparts. The results coincide with the predicted trend, which verifies the effectiveness of the compensation method.

A high-sensitivity optic fiber pressure sensor based on balloon-like single-mode fiber (SMF) is proposed and thoroughly investigated. Under pressure, the balloon-like SMF and the substrate collaborate, resulting in changes in the stress state of the core and cladding of the fiber in the sensor, which leads to changes in the difference between the effective refractive index of the core and cladding of the fiber, and shifts the spectra, so as to achieve pressure measurements. Firstly, the mechanical model of the proposed sensor is established, explaining the relationship between the varying of refractive index of the sensing unit involving fiber and substrate, and the pressure. Then, the effects of the substrate stiffness and fiber bending diameter on the sensor sensitivity are analyzed, so as to optimize the sensor’s structural and relevant parameters. It reveals that, under pressure, the substrate stiffness has a significant effect on the sensor sensitivity. A series of experimental tests were carried out based on the fabricated substrate using iron, caoutchouc, and PDMS, respectively, as substrates and applying different bending diameters for the SMF, it shows that when the substrate is caoutchouc and the bending diameter of the fiber is 3.8 mm, the sensitivity of the optimized balloon-like SMF optic pressure sensors can reach up to 90.3 nm/N in the range of 0-1 N. The experimental results effectively verify the feasibility of the optimized design method of the balloon-like SMF optic pressure sensors as well as the achievability of the high-sensitivity pressure detection.

A multimode interference methane sensor based on a ZIF-8/PDMS composite film is proposed. The sensing principle is that the refractive index of the ZIF-8/PDMS composite film changes when it adsorbs methane, leading to a measurable optical path difference during the coupling of the cladding higher-order modes and the fundamental mode in the multimode interference fiber (MMI). The environmental methane concentration is then detectable by detecting the wavelength shifts of the interference peaks in the resulted spectrum. Through simulations and experiments aimed at enhancing sensor sensitivity, we optimized three parameters within the sensor structure: the length of the Tapered Single-Mode Fiber (TSMF), the composite film thickness, and the TSMF taper diameter. The experimental results indicate that the sensor’s sensitivity reaches a maximum of 0.231 nm%⁻¹. Additionally, the sensor exhibits excellent structural stability and measurement repeatability. The response time is as short as 40 s, and the recovery time ranges between 3 and 5 min. The proposed multimode interferometric methane sensor based on the ZIF-8/PDMS composite film has great potential to support highly sensitive methane concentration detection in many applications.