Acoustic metasurface carpet cloak has suffered from narrowband limitation due to highly frequency-dependent phase response. Here, we adopt two entirely different ways to broaden the working frequency range of the carpet cloak with dynamic or static metasurface structure. Numerical simulations and experimental measurements demonstrate that the designed dynamic or static metasurface carpet cloak can both exhibit a broadband stealth performance. The proposed design strategy is expected to break the narrowband limitation of metasurfaces, making a significant difference to the practical applications of the broadband acoustic devices.
For the benefit of electrical isolation, corrosion resistance and quasi-distributed detecting, Fiber Bragg Grating Sensor has been studied for high-speed railway application progressively. Existing Axle counter system based on fiber Bragg grating sensor isn’t appropriate for high-speed railway for the shortcoming of emplacement of fiber Bragg grating sensor, low Sampling rate and un-optimized algorithm for peak searching. We propose a new design for the Axle counter of high-speed railway based on high-speed fiber Bragg grating demodulating system. We also optimized algorithm for peak searching by synthesizing the three sensor data, bringing forward the time axle, Gaussian fitting and Finite Element Analysis. The feasibility was verified by field experiment.
Fiber Bragg gratings (FBGs) sensor has been widely used in all kinds of detection spaces. Nonlinear effects of the fiber Bragg gratings have been observed in high-temperature conditions, however, it occurred in low-temperature as well. In this paper, we take the low-temperature experiments in the low-temperature thermostat bath, temperature range from 10°C to -80°C, the Bragg wavelength shift with the temperature decreasing linearly at the very beginning and it shows linear characteristic range from room temperature to -45°C. However with the temperature goes down continuously, the nonlinear effects emerged, the turning point temperature of the nonlinear effect is at -45.3°C. Besides, the sensitivity of the FBGs decreased as well from 8.96pm/°C to 6.72pm/°C. Considering the physical characteristic of the silica fiber, which the thermo-optic coefficient and the thermal expansion coefficient of the fused silica is not constant if temperature goes down and it shows nonlinear features, therefore we conclude the nonlinear effect at low-temperature is attributed to the thermal expansion and the thermo-optic effect of the silica fiber. Thus, we predict that appropriate doping improvements in the silica fiber can modify the linear range of FBGs which can enhance the measure precision. In addition, we find that high sensitivity FBGs has a lower temperature turning point of the nonlinear effect. The invar packaged FBGs has a sensitivity of 24.3pm/°C at room temperature. It is higher than bare FBGs’ sensitivity which is about 8.96pm/°C at room temperature. The invar packaged FBGs’ temperature turning point is at about -54.5°C, which is lower than the bare FBGs’, -45.3°C, temperature turning point. This indicates that high sensitivity FBGs can also increase the linear temperature range. The experiment results and analysis show that we can either by increasing the sensitivity of FBGs or doping in the silica fiber to modify the linear range.
In recent years, Fiber Bragg Grating (FBG) sensors have been attracted a lot of interest, and widely and
increasingly researched in many important areas. In this work, we present the field of railway dynamic monitor
concerning the application of FBG sensors. We have built the principle and established the sensing system based on FBG
to monitor the situation of train and railway through the analysis of track strain during the train passage. We have
illustrated that FBG sensors set on the lateral and underside of the rail can detect the strain of rail and sensors on
different positions show distinct results. We have presented that the underside of the rail structure is the most suitable
position to monitor the strain in railway.
In the present paper, closed analytical expressions and universal relations for the effective coefficients are given. Matrix
and inclusions materials belong to symmetry class 6mm. It is remarkable that the analytical formulae derived for all
effective properties have a simple form. The computational implementation is easy. Besides its theoretical importance,
they can be used for checking the implementation of experimental, numerical and analytical models.
Conference Committee Involvement (5)
Health Monitoring of Structural and Biological Systems XVII
13 March 2023 | Long Beach, California, United States
Health Monitoring of Structural and Biological Systems XVI
7 March 2022 | Long Beach, California, United States
Health Monitoring of Structural and Biological Systems XV
8 March 2021 | Online Only, California, United States
Health Monitoring of Structural and Biological Systems XIV
27 April 2020 | Online Only, California, United States
Health Monitoring of Structural and Biological Systems XIII
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