Investigations of the corrosion of rebars in concrete structures are widely studied because of the serious damage to concrete caused by rebar corrosion. The rebar corrosion products in reinforced concrete take up 2~6 times the volume of the rebar. Based on this principle, a new type of fiber Bragg grating (FBG) corrosion sensor is proposed in this paper, which consists of two sensors, an FBG corrosion measurement sensor to measure the expansion strain caused by rebar corrosion, and a temperature compensation sensor to eliminate the cross-sensitivity of FBG corrosion sensor. The corrosion rate is derived by the wavelength shift of FBG corrosion sensor, so rebar corrosion can be monitored and assessed by the FBG wavelength shift. A customized rebar with epoxy fixing groove is designed to install a corrosion sensor on its surface and an embedded temperature compensation sensor. The corrosion sensor is embedded in cement mortar and subsequently casted in concrete. The performance of the corrosion sensor is studied in an accelerated electrochemical corrosion test. Experimental results show that the new type of corrosion sensor has advantage of relatively large measurement range of corrosion rate. The corrosion sensor is suitable to monitor slightly and moderately corroded rebars.
The widely investigated signals are mainly nonstationary and nonlinear signals, thus it is difficult to get the precise information from the nonstationary and nonlinear signals. Here we introduce a new method to process the nonstationary and nonlinear signals. And this new algorithm makes a good performance on processing the nonstationary and nonlinear signals. This paper mainly describe the basic theory of the new algorithm——Hilbert-Huang Transform. The Hilbert-Huang Transform is composed of Empirical Mode Decomposition and Hilbert transform. The problems of this arithmetic are summarized, such as the end effects, stop criterion and so on, and the solutions of these problems are put forward. This paper also provides some improved methods based on the Empirical Mode Decomposition in the end, such as Adaptive Time Varying Filter Decomposition, Extremum filed Mean Mode Decomposition and Improved Extremum field Mean Mode Decomposition.
This paper introduces a new kind of electronic product — Package Security Recorder of
Vibration. It utilizes STC89C54RD+ LQFP-44 MCU as its main controller. At the same time, it also utilizes
Freescale MMA845A 3-Axis 8-bit/12-bit Digital Accelerometer and Maxim DS1302 Trickle Charge
Timekeeping Chip. It utilizes the MCU to read the value of the accelerometer and the value of the
timekeeping chip, and records the data into the inner E2PROM of MCU. The whole device achieves
measuring, reading and recording the time of the vibration and the intensity of the vibration. When we need
the data, we can read them out. The data can be used in analyzing the condition of the cargo when it
transported. The device can be applied to monitor the security of package. It solves the problem of
responsibility affirming, when the valuable cargo are damaged while it transported. It offers powerful
safeguard for the package. It’s very value for application.
In this paper, we propose and demonstrate a novel torsion sensor based on a long-period fiber grating (LPFG) induced symmetrically by three beams of focused high-frequency CO2 laser pulses (20~24 kHz). Experimental results show, when the LPFG is twisted clockwise, the resonant wavelength shifts toward shorter wavelengths, and the peak loss decreases. When the LPFG is twisted anticlockwise, the resonant wavelength shifts toward longer wavelengths, and the peak loss increases. The resonant wavelength and the peak loss are all similarly proportional to the twist angle applied. Based on this LPFG, a new kind of fiber-optic torsion sensors can be made, which can not only directly measure the torsion angle, but also determine the torsion direction simultaneously by means of measuring the shift of the resonant wavelength and/or the peak loss of the LPFG.
We report a new fiber-optical solution concentration sensor based on an etched long-period fiber grating with one opening head coated with a silver film, which is written symmetrically by three beams of focused high-frequency CO2 laser pulses in a standard single-mode fiber (Corning SMF-28). This sensor is tested with two kinds of solution, i.e. sugar and CaCl2, and the experimental results show that this etched fiber-optical sensor with one opening head is flexible to operate and has very high resolution. The resolution of this sensor increases with approximate linearity, as the concentration of solution increases, and the resolutions for sugar solution at low and high concentrations are 1.65 (g/l) and 1.36 (g/l), respectively. Its average resolution has been improved above 28% after the cladding radius of this sensor is reduced to 61μm by etching with HF acid. The method of etching with HF acid can also be used to tune the resonant wavelengths of a long-period fiber grating.
In this paper, we studied temperature characters of LPFG fabricated with a new designed system, which focuses the CO2 laser pulse beam on standard single mode fiber with azimuthally symmetric irradiation. A high temperature optical fiber sensor based on such a LPFG has average high temperature sensitivity of 0.16nm/°C, large dynamic range of 0°C to 600°C, good temperature repeatability and simple configuration. Meanwhile, the sensor with different temperature measurement range can be easily obtained by adjusting the fabricating parameter of LPFG. The temperature sensor with those advantages has a potential of measuring temperature as high as 900°C.