微型高精度光纤布拉格光栅土压力传感器研究

Research on the Micro and High-Precision Fiber Bragg Grating Soil Pressure Sensor

结合不锈钢膜片的特性,研制出一种微型高精度光纤布拉格光栅(FBG)土压力传感器。该传感器通过不锈钢膜片与力学传递元件将土压力转化为光纤光栅的轴向拉力,大大提高了传感器的灵敏度,有效避免了光栅受力不均引起的啁啾效应,同时减小了传感器的体积。通过理论计算,得到该传感器的压力敏感系数为29.6557nm/MPa,是裸光栅的9885倍。传感器性能测试实验证实该传感器线性度良好,实测压力敏感系数为27.5nm/MPa,略小于理论值,其主要原因是应变传递效率低于1。为进一步提高实验测量精度,采用Haar小波变换来减小因光纤光栅解调设备模数(A/D)采样速率及转换精度有限带来波长抖动所产生的仪器误差,实验数据表明经Haar小波处理后光栅中心波长的抖动幅值降为原数据的50%左右。

A micro and high-precision fiber Bragg grating soil pressure sensor based on the characteristics of stainless steel patch is developed. Through stainless steel patch and mechanical transfer element, this sensor transfers soil pressure into axial direction tension of the fiber grating and improves its sensitivity greatly. Because of such design, this sensor reduces its volume largely and avoids the chirp effect caused by grating axial stress effectively. The theoretical calculation pressure sensitive coefficient value of this sensor is 29. 6557 nm/MPa, which is 9885 times of the bare grating. The performance test proves that the linearity of this sensor is very well and measured pressure sensitive coefficient is 27.5 nm/MPa and slightly less than the theoretical calculation value, which is mainly caused by strain transfer efficiency lower than 1. In order to improve the experimental measurement precision, Haar wavelet transform is used to reduce the instrument error caused by wavelength dithering brought by the limitation of the sample rate and conversion precision of the demodulating equipment. The experiment data show that the dithering amplitudes of grating central wavelength reduce to 50 % of the origin data after Haar wavelet transformation.