Experimental Study of Effect of Temperature Variations on the Impedance Signature of PZT Sensors for Fatigue Crack Detection

Structural health monitoring (SHM) is recognized as an efficient tool to interpret the reliability of a wide variety of infrastructures. To identify the structural abnormality by utilizing the electromechanical coupling property of piezoelectric transducers, the electromechanical impedance (EMI) approach is preferred. However, in real-time SHM applications, the monitored structure is exposed to several varying environmental and operating conditions (EOCs). The previous study has recognized the temperature variations as one of the serious EOCs that affect the optimal performance of the damage inspection process. In this framework, an experimental setup is developed in current research to identify the presence of fatigue crack in stainless steel (304) beam using EMI approach and estimate the effect of temperature variations on the electrical impedance of the piezoelectric sensors. A regular series of experiments are executed in a controlled temperature environment (25°C–160°C) using 202 V1 Constant Temperature Drying Oven Chamber (Q/TBXR20-2005). It has been observed that the dielectric constant ε₃₃^T which is recognized as the temperature-dependent constant of PZT sensor has sufficiently influenced the electrical impedance signature. Moreover, the effective frequency shift (EFS) approach is optimized in term of significant temperature compensation for the current impedance signature of PZT sensor relative to the reference signature at the extended frequency bandwidth of the developed measurement system with better outcomes as compared to the previous literature work. Hence, the current study also deals efficiently with the critical issue of the width of the frequency band for temperature compensation based on the frequency shift in SHM. The results of the experimental study demonstrate that the proposed methodology is qualified for the damage inspection in real-time monitoring applications under the temperature variations. It is capable to exclude one of the major reasons of false fault diagnosis by compensating the consequence of elevated temperature at extended frequency bandwidth in SHM.     

基于TDLAS技术的CH4气体检测与温度补偿方法

CH₄气体的精准检测对防止矿井瓦斯爆炸,确保安全生产至关重要。目前基于可调谐半导体激光吸收光谱技术（TDLAS）存在因温度变化导致气体浓度测量误差较大。探究了基于TDLAS的CH₄气体检测系统与温度补偿方法,分析温度对CH₄气体吸收谱线的影响,通过算法补偿模型消除环境温度对CH₄气体检测的影响。依据TDLAS技术原理及相关理论,对系统发射单元、吸收池、信号接收单元、数据处理单元进行设计,搭建了基于TDLAS技术的CH₄气体浓度检测系统,实验检测了不同环境温度（10~50 ℃）时0.04%CH₄气体浓度,分析温度变化对CH₄气体在波长为1.653 μm处吸收谱线强度和半宽度的影响。为消除温度对CH₄气体检测的影响并提高补偿效果,采用粒子群优化算法（PSO）优化BP神经网络（BPNN）的最佳权值和阈值,建立CH₄气体的PSO-BP温度补偿模型,克服了BP神经网络收敛速度慢、易陷入局部最优的缺点。结果表明：（1）基于TDLAS的CH₄气体检测浓度随环境温度升高而下降,整个实验温度内相对误差范围为4.25%~12.13%,不同环境温度下CH₄气体检测浓度与温度之间的关系可用一元三次多项式表示;（2）CH₄气体的吸收强度和半宽度随着温度的升高而下降,与温度变化之间的关系为单调递减函数,温度对CH₄气体吸收谱线强度的相对变化率大于吸收谱线半宽度的相对变化率,CH₄气体吸收谱线的强度更容易受温度变化的影响;（3）BP神经网络和PSO-BP模型测试样本的绝对平均误差（MAE）分别为12.88%和1.81%,平均绝对百分比误差（MAPE）分别为2.3%和0.3%,均方根误差（RMSE）分别为15.96%和2.69%,相关系数R2分别为0.980 6和0.999 6。通过建立PSO-BP温度补偿模型,补偿效果大部分分布在±1.0%的误差范围内,MAE,MAPE,RMSE和R2等评价指标均大幅度提升,对提高TDLAS技术在矿井CH₄的精准检测具有一定的参考意义。     

复合场中的滚轮线

带电质点在正交的匀强电场(重力场)和匀强磁场中运动,轨迹为滚轮线.处理滚轮线问题的关键是构造匀速直线运动以平衡电场力(重力),从而将带电质点的运动分解为匀速直线运动和匀速圆周运动,简化问题的处理过程.     

动力调谐陀螺动态误差的两种补偿方案

本文针对动力调谐陀螺的动态误差模型，提出了动力调谐陀螺的动态误差补偿的计算机算法。算法中的输出值是角增量，它是二次拟和函数。该算法具有精度高，实时性好的特点。     

压力场中光纤应变测量方法研究

本文对压力场环境下的光纤应变测量方法进行了研究，在理论上分析了由于测试环境的压力变化产生虚假应变的原因，提出了采用补偿的方法消除虚假应变。通过具有补偿功能的马赫－泽得干涉系统对应变场进行了测量，证明了补偿法的可靠性，为光纤应变测量方法向实用化转变进行了有益的探讨。     

船用pH计检定装置的研究

研制了船用pH计检定装置。以基准电压集成电路作为电压标准,以单片机为控制中心,组成船用pH计检定核心部分,控制船用pH计检定装置输出标准电位。检定装置的pH值输出范围:0～14.0000 pH;pH示值误差:0.0003 pH;电压输出范围:-1999.99～+1999.99 mV;电压分辨率:0.01 mV;温度补偿范围:0～99.9℃。     

基于FA-RBF神经网络的压力传感器的温度漂移补偿法

针对温度对硅压阻式压力传感器输出的影响问题,提出基于因子分析和RBF神经网络相结合的补偿方法.利用因子分析实现对原始信息的筛选和降维;结合RBF神经网络的非线性映射、自适应能力和强容错性对补偿过程进行建模,减少网络的输入,利于简化网络结构,进而加快收敛,节省运行时间,提高网络的学习速率与泛化能力.研究结果表明,该方法有效地抑制了温度对压力传感器的影响,提高传感器的稳定性和准确性.     

Improved luminescent properties of red-emitting Ca0.54Sr0.16Eu0.08Gd0.12(MoO4)0.2(WO4)0.8 phosphor for LED application by charge compensation

The red-emitting Ca_0.54Sr_0.16Eu_0.08Gd_0.12(MoO₄)_0.2(WO₄)_0.8 phosphor is improved in the emission charateristics by charge compensation, of which chromaticity coordinates (CIE) are x=0.66 and y=0.33. Three approaches to charge compensation are investigated, namely (a) 3Ca²⁺/Sr²⁺→2Eu³⁺/Gd³⁺+vacancy, (b) 2Ca²⁺/Sr²⁺→Eu³⁺/Gd³⁺+M⁺(M⁺ is a monovalent cation like Li⁺, Na⁺ and K⁺ employed as a charge compensator) and (c) Ca²⁺/Sr²⁺→Eu³⁺/Gd³⁺+N⁻ (N⁻ is a monovalent anion like F⁻, Cl⁻, Br⁻ and I⁻ employed as charge compensation ions). Through photoluminescent spectra analyzing the radiative and non-radiative relaxation mechanisms of luminescent system are obtained. Under 20 mA forward-bias current, one red-emitting LED is made by combining 390-405 nm-emitting LED chip and the phosphor. The red-emitting phosphor has broad prospects in LED application field.     

Examination of the upper measurement limit in displacement measurement using fringe compensation in digital holography

Digital holography is a widely used method for displacement measurement in coherent optical metrology. An obvious limit of the method is that too large displacements result in dense fringes, so the fringes are practically invisible. The maximum number of contour fringes in displacement measurement is limited, because the cameras are discrete devices and sampling theory plays an important role. Because of the limited measurement range, compensation methods are promising tools for practical measurements. It can be shown that the practical measurement range can be extended above the Nyquist sampling limit. Compensation methods can be digital, because digital holographic interferometry operates with images recorded with a digital camera. In our research work the upper measurement range of fringe compensation method was examined. Our goal was to perform automatic compensation even if the displacement is higher than the measurement range of the basic method. The operation of the automatic fringe compensation method was based on the combination of two types of out-of-plane displacement measurements with different sensitivities.     

40Gbps NRZ在基于宽带CFBG色散补偿的G.652光纤中无电中继传输500km

在基于宽带CFBG色散补偿的G.652光纤中,40Gbps NRZ码无电中继传输500km,在误码率BER=10(-10)下的功率代价约为2.2dB,积累1h的误码率为7.3×10(-12).传输系统中采用的CFBG的3dB带宽约为1.2nm,中心波长处时延纹波小于25ps,反射谱纹波小于2dB,差分群时延小于1ps....