No abstract

A new optical fiber humidity sensor with high sensitivity is reported. We effectively control the light-intensity changes in a smaller sensing area and achieve a significant increase in sensitivity by adjusting the depth of the evanescent field of the tapered fiber. The sensor is designed with an 8 µm diameter single-mode tapered fiber structure coated with a thickness of a 10 mm length carbomer layer in the tapered area. The average and maximum relative humidity (RH) sensitivities are 2.59 dB/%RH and 5.43 dB/%RH in the range of 68%–90%. To our best knowledge, the sensitivity of the sensor is highest compared with that of the previously reported. Moreover, the fast response time and recovery time of the sensor are ideal. In addition, the proposed humidity sensor has good repeatability and lower-temperature cross talk. Due to the excellent indicators, the proposed sensor has promising potential for highly sensitive RH sensing applications, especially early warning of special environments.

No abstract

Both of Buckling and post-buckling are fundamental problems of geometric nonlinearity in solid mechanics. With the rapid development of nanotechnology in recent years, buckling behaviors in nanobeams receive more attention due to its applications in sensors, actuators, transistors, probes, and resonators in nanoelectromechanical systems (NEMS) and biotechnology. In this work, buckling and post-buckling of copper nanobeam under uniaxial compression are investigated with theoretical analysis and atomistic simulations. Different cross sections are explored for the consideration of surface effects. To avoid complicated high order buckling modes, a stressbased simplified model is proposed to analyze the critical strain for buckling, maximum deflection, and nominal failure strain for post-buckling. Surface effects should be considered regarding critical buckling strain and the maximum post-buckling deflection. The critical strain increases with increasing nanobeam cross section, while the maximum deflection increases with increasing loading strain but stays nearly the same for different cross sections, and the underlying mechanisms are revealed by our model. The maximum deflection is also influenced by surface effects. The nominal failure strains are captured by our simulations, and they are in good agreement with the simplified model. Our results can be used for helping design strain gauge sensors and nanodevices with self-detecting ability.

A new coupled fiber optic humidity sensor based on a double-tapered fiber twisted weakly coupled structure coated with a graphene oxide/polyvinyl alcohol (GO/PVA) film has been reported for the first time, to the best of our knowledge. The sensor adopts a 2 × 2 coupler structure with a waist diameter of 20 µm. The GO/PVA composite film is coated in the weakly coupled area to increase the sensitivity of the sensor. The thickness of the coating layer is about 3 µm. The sensor can realize linear sensing in the relative humidity (RH) range of 45%–85%RH with a dynamic response time of 1.9 s and a recovery time of 5.7 s. The sensitivity of the sensor is up to 0.002/%RH, and the linearity of the sensor is as high as 98.65%. Moreover, the sensor has good stability, reversibility, and low-temperature crosstalk.