光纤温度/应变复合传感器及其在800℃高温下的应用

高温应变是材料和结构在高温环境中物理性能的主要参数之一,对高温应变的准确测量是结构热强度试验的重要组成部分。目前在高温应变测量方面存在安装工艺复杂、耗费时间长、测量分散性大、高温胶造成应变传递误差、热输出标定带来二次误差等不足。本文将光纤温度/应变复合传感器应用到热强度试验中,该传感器结合布拉格光栅光纤传感器和非本征法珀传感器,可以同时测量同一点的温度和应变。该传感器具有不依赖高温胶传递应变,不需要标定热输出等优点。当前已实现了800℃环境下温度和应变的测量。试验结果证明,传感器性能稳定,一致性良好。

Lorentzian型布里渊频谱特征提取时模型的影响（英文）

为了在提取Lorentzian型布里渊频谱特征时选择最佳模型,以线性最小二乘法和非线性最小二乘法构造的目标函数为研究对象,系统地比较目标函数构造对频谱特征提取的影响。数值产生了不同信噪比、扫描频率间隔、g0、vB和ΔvB的布里渊信号,比较了两种模型得到的频谱特征参数的准确性和计算耗时,并用真实布里渊散射信号进行了验证。结果表明:在不含干扰的理想状态下两种模型都能达到非常高的精度,随着噪声含量/扫描频率间隔的增加两种模型的准确性都下降,但线性模型明显大于非线性模型,实际时应采用非线性模型。实验测量的布里渊散射谱信号验证了分析结果的正确性。

采用Voigt模型的布里渊散射谱关键特征高精度提取方法(英文)

布里渊散射谱满足Voigt函数,现有的拟合算法提取得到的特征参数容易存在误差。为了保证布里渊谱特征提取时的准确性,从而提高温度和应变测量的准确性,提出了一种采用Voigt函数的布里渊散射谱特征参数提取算法。采用了高斯-厄米特积分来计算Voigt函数,采用最小二乘拟合方法给出了对应的目标函数,同时给出了初值提取方法,采用Levenberg-Marquardt算法来最小化目标函数,一旦目标函数趋于最小化即可获得特征参数。此外还实现另外一种算法,该算法采用随机值方式求解初值,然后采用Levenberg-Marquardt算法来优化目标函数。基于数值产生大量不同信噪比的布里渊谱和实测布里渊谱,两种算法的计算结果表明,随机值算法的收敛概率为80%~90%,文中算法在所有情况下均能收敛。文中算法的计算误差仅为随机值算法的1/1011~1/7,计算耗时仅为随机值算法的1/8~1/3。

采用Voigt模型的布里渊散射谱关键特征高精度提取方法

布里渊散射谱满足Voigt函数，现有的拟合算法提取得到的特征参数容易存在误差。为了保证布里渊谱特征提取时的准确性，从而提高温度和应变测量的准确性，提出了一种采用Voigt函数的布里渊散射谱特征参数提取算法。采用了高斯一厄米特积分来计算Voigt函数，采用最小二乘拟合方法给出了对应的目标函数，同时给出了初值提取方法，采用Levenberg—Marquardt算法来最小化目标函数，一旦目标函数趋于最小化即可获得特征参数。此外还实现另外一种算法，该算法采用随机值方式求解初值，然后采用Levenberg—Marquardt算法来优化目标函数。基于数值产生大量不同信噪比的布里渊谱和实测布里渊谱，两种算法的计算结果表明，随机值算法的收敛概率为80％～90％，文中算法在所有情况下均能收敛。文中算法的计算误差仅为随机值算法的1／1011～1／7，计算耗时仅为随机值算法的1／8～1／3。

A dual measurement method of strain and temperature

With the rapid development of China's foreign trade, the coastal and inland waterway transport has been increased rapidly. The potential market for marine engines is more and more obvious. The measurement of the engine temperature and strain becomes very important. The fluorescence fiber sensors are broadly used to measure temperature, concentration, and pH value, etc. The fluorescence sensing systems are based on different principles, namely fluorescence intensity, fluorescence intensity ratio, and fluorescence lifetime. The fluorescence lifetime is an effective parameter for sensing purpose, because it is independent of the intensity of the pumping source and does not need expensive narrow-band filters. An experiment system has been established, in which some samples were produced to measure the fluorescence lifetime and temperature characteristics and the relationship of the strain and temperature versus the fluorescence lifetime was achieved at the same time. The experiment result was fitted and analyzed. The test results show that the fluorescence lifetime decreases with the increasing of temperature. The change of fluorescence lifetime with the strain is inconspicuous comparing to that with the temperature.

Implementation of Interrogation Systems for Fiber Bragg Grating Sensors

The development of two simple methods for wavelength-optical intensity modulation techniques for fiber Bragg grating （FBG） sensors is presented. The performance is evaluated by measuring the strain and temperature. The first method consists of a narrow band source, an optical circulator, an FBG; and a power meter. The source and Bragg reflected signal from the FBG need to be matched to get linear results with good power levels. The source spectral power levels are very critical in this study. The power reflected from a matched reference FBG is fed into the measuring FBG in the second method. Since the FBGs are matched, the entire power is reflected back initially. During the measurement, the change in the measurand causes the reflected power from the sensing FBG to vary. A costly high resolution spectrum analyzer is required only during the characterization of the FBG and source. The performances of two interrogators are compared by measuring the strain and temperature. In the second method, the strain measurements can be made insensitive to the temperature variation by selecting a source with a flat spectrum at the measurement range. Highlights of these methods are the portability, cost effectiveness and better resolution.

Mechanocaloric materials for solid-state cooling

This article reviews the up-to-date progress in mechanocaloric effect and materials near ambient temperature. For elastocaloric materials, we focus on directly measured temperature change and its entropy origin in nonmagnetic and magnetic shape memory alloys. In terms of barocaloric materials, change in magnetic state, volume and shift of transition temperature due to hydrostatic pressure are systematically compared. We propose advantages and challenges of elastocaloric materials for solidstate cooling. Strategies to enhance elastocaloric and mechanical stability under long-term mechanical cycles are presented. Finally, we conclude with an outlook on the prospect of elastocaloric cooling application.