Zhengfang Wang

Development and application of subminiature multipoint FBG displacement sensor

Traditional electrical displacement sensors usually are big and insensitive, difficult to multiplex, therefore, they are not suitable for model test. In this paper, a novel subminiature multipoint FBG displacement sensor which has overcome the shortages of above displacement sensors is designed especially for the model test based on analysis of displacement detecting principle. It mainly consists of several FBGs, springs, crusts and the bases. FBGs which are sensitive device connect with springs in series. When key point moves, stretching deformation of spring will occur, so that FBG will receive axial force which will make central wavelength of FBG drifts. According to drift of center wavelength of the sensor, displacement of several points can be detected simultaneously. Calibration experiments of several sensors are carried out, in which it could get the conclusions that the sensitivity is about 1.3nm / mm and the linearity is over 0.99. FBG displacement sensors are embedded in the tunnel wall rock symmetrically to monitor precursory information of disaster. In the process of tunnel excavation, displacement increased gradually, and the detecting results had a strong symmetry.

Design and Optimization of FBG Implantable Flexible Morphological Sensor to Realize the Intellisense for Displacement

The measurement accuracy of the intelligent flexible morphological sensor based on fiber Bragg grating (FBG) structure was limited in the application of geotechnical engineering and other fields. In order to improve the precision of intellisense for displacement, an FBG implantable flexible morphological sensor was designed in this study, and the classification morphological correction method based on conjugate gradient method and extreme learning machine (ELM) algorithm was proposed. This study utilized finite element simulations and experiments, in order to analyze the feasibility of the proposed method. Then, following the corrections, the results indicated that the maximum relative error percentages of the displacements at measuring points in different bending shapes were determined to be 6.39% (Type 1), 7.04% (Type 2), and 7.02% (Type 3), respectively. Therefore, it was confirmed that the proposed correction method was feasible, and could effectively improve the abilities of sensors for displacement intellisense. In this paper, the designed intelligent sensor was characterized by temperature self-compensation, bending shape self-classification, and displacement error self-correction, which could be used for real-time monitoring of deformation field in rock, subgrade, bridge, and other geotechnical engineering, presenting the vital significance and application promotion value.

Experimental and technical research on fiber Bragg grating vibration measuring based on two matching gratings demodulation

The analysis of a novel demodulation technique for Fiber Bragg Grating (FBG) vibration sensors based on two parallel matching gratings has been carried out both theoretically and experimentally. The lineally model between transformed formula of optical power and the central reflection wavelength of sensing grating has been obtained. In addition, the FBG vibration sensor based upon cantilever with equalized strength is designed and the natural frequency of sensor has been obtained by calculations. The vibration experiment have been carried out to verify the feasibility of the modulation approach and the performance of the sensor, the results show that frequency measured by the FBG vibration sensor is agreement with the setting value. Moreover, the experiment also indicate that the sensor have a excellent frequency response at the measuring range of 0~30Hz, and the demodulation technique with two parallel matching gratings work well in the vibration sensing system.