Real-time surface profile measurement using a feedback type of sinusoidal phase modulating interferometer

In this paper, we propose a sinusoidal phase modulating (SPM) interferometer that is insensitive to external disturbances, and its measuring principle is analyzed theoretically. In the SPM interferometer, the interference signal is detected by a high-speed image sensor based on a low-speed CCD and a signal processing circuit is used to obtain the phase of each point on the surface. Therefore, the surface profile can be measured real-time. The experiments measuring the surface profile of a wedge-shaped optical flat show that the measurement time of the SPM interferometer is less than 10 ms, the repetitive measurement accuracy is 4.2 nm. The results show that the impacts of nonlinear distortion of the piezoelectric transducer (PZT) and part external disturbance are removed.     

System for controllable magnetic measurement with direct field determination

This work describes a specially designed setup for magnetic hysteresis and Barkhausen noise measurements. The setup combines two main elements: an improved fast algorithm to control the waveform of magnetic induction and simultaneous direct determination of the magnetic field. The digital feedback algorithm uses only the previous measurement cycle to correct the magnetization voltage without any additional correlation parameter; it usually converges after several tens of cycles. The magnetic field is measured at the sample surface using a vertically mounted array of sensitive Hall sensors. Linear extrapolation of the tangential field profile to the sample surface determines the true waveform of the magnetic field. This unique combination of physically based control for both parameters of the magnetization process provides stable and reliable results, which are independent of a specified experimental configuration. This is illustrated for the industrially attractive measurements of non-oriented electrical steels with a 50 Hz sinusoidal induction waveform.     

Phase measurement accuracy of feedback interferometers

Feedback interferometers are described with specific reference to potential applications in micro-machines. A theoretical analysis is developed to determine the linearity, stability, and noise performance of this type of interferometer. The theoretical analysis was tested using a prototype high-precision feedback interferometer which showed that, at a feedback loop gain which enabled the system to track 6 fringes, the linearity of the interferometer was better than λ/100 and single phase measurements could be made with an accuracy of λ/80.     

两种波形调控方法获得单次谐波光源的研究

本文利用啁啾波形调控和双色场波形调控对单次谐波光源的产生进行了研究.结果发现：在啁啾波形调控下,单次谐波光源的调节范围在170次到370次谐波区间,能量调节范围较宽.并且,单次谐波的产生对激光脉宽和光强的要求不高.在双色场波形调控下,单次谐波光源的调节范围仅在80次到110次谐波区间,能量调节范围较窄.并且,单次谐波的产生对激光脉宽和光强的要求较高.     

Improving the signal amplitude of meandering coil EMATs by using ribbon soft magnetic flux concentrators (MFC)

This paper presents a new method of improving the ultrasonic signal amplitude from a meander line EMAT by using soft magnetic alloy ribbon (Fe₆₀Ni₁₀V₁₀B₂₀) as a magnetic flux concentrator (MFC). The flux concentrator is a thin soft amorphous magnetic material (Fe₆₀Ni₁₀V₁₀B₂₀) which is very sensitive to a small flux change. The MFC is used with the EMAT to improve the signal amplitude and it was observed that the peak signal amplitude increases by a factor of two compared to the signal without MFC. Two dimensional numerical models have been developed for the EMAT with MFC to quantify the improvement of the received signal amplitudes. Model calculations and experiments have been carried out for a wide range of ultrasonic frequencies (500 kHz-1 MHz) in different materials.     

Precise interferometric length measurement using real-time fringe fitting

We created a simple device for the measurement of nanoscale displacements consisting in a Twyman-Green interferometer with one mirror having a slight offset in the horizontal plane with respect to the direction perpendicular to the incoming beam and one mobile mirror, a CCD array camera that captures frames of fringes (interferograms) generated by the interferometer and a software that acquires the interferograms captured by the camera and fits the fringes in order to determine the initial spatial phase of the series of fringes and, consequently, to monitor the movement of the mobile arm of the interferometer. Because the interferograms were acquired and analyzed sequentially, the algorithm could be parallelized easily on a multiprocessor/multicore platform. The device can work in real-time in which case the maximum speed of the mobile arm of the interferometer for which we can obtain unambiguous results is 30 λ/8/s, which is, assuming a He-Ne laser as the light source, almost 2.5 μm/s. In real-time conditions, the precision and accuracy of the measurement are low. In stationary conditions, however, the precision was determined to be below 1 nm.     

太阳能聚焦光斑能流密度测量方法评估

为了确定一种新型间接测量太阳能热发电系统聚焦光斑能流密度分布方法的测量误差范围,对其进行了进一步研究。从理论公式出发,分析了该测量方法的误差源;使用球面小定日镜、CCD相机、漫反射板、中性密度滤光片等设备进行了能流密度测量的实验,使用MATLAB软件对实验数据进行处理,得到了漫反射板上聚焦光斑的能流密度分布和总能量;实验时借助全站仪测量并计算了定日镜中心的光线入射角,根据定日镜的面积和反射率、太阳直射辐射值、余弦效率等计算了光斑能量的理论值,并与测量得到的聚焦光斑总能量比较,得出了实验条件下该方法测量光斑总能量以及能流密度的相对误差为3.5%。该测量误差在允许范围内,进一步证实了该能流密度测量方法的正确性和可行性。     

Superconducting film flux transformer for a sensor of a weak magnetic field

The object of study is a superconducting film flux transformer in the form of a square shaped loop with the tapering operative strip used in a sensor of a weak magnetic field. The magnetosensitive film element based on the giant magnetoresistance effect is overlapped with the tapering operative strip of the flux transformer and is separated from the latter by an insulator film. It is shown that the topological nanostructuring of the operative strip of the flux transformer increases its gain factor by one or more orders of magnitude, i.e. increases its efficiency, which leads to a significant growth of important parameters of a magnetic field sensor.     

基于磁通压缩技术的爆炸磁频率发生器的参数选择

 爆炸磁频率发生器是一种结构简单、小型化的电磁脉冲产生和辐射装置。为了优化其性能,从数学模型入手进行研究,得出输出信号所满足的Bessel函数,分析了在不同电参数下输出信号的模式及电路中的能量分配。研究结果表明,当电感变化到初始值的1/e所需时间与初始载波频率的乘积较大时,发生器的输出信号为振荡模式,且二者乘积越大,载波频率越高,对其辐射越有利。     

螺旋形爆磁压缩发生器跳匝现象分析

 分析了螺旋形爆磁压缩发生器的跳匝现象,考虑了膨胀电枢与定子线圈的交线,采用更加精确的计算模型,得出了更为精确的发生器装配公差表达式,通过计算验证了简化模型的结论可以满足设计要求,并对电枢表面和电枢壁厚等的不规则因素,以及圆管爆轰的边缘效应导致跳匝作了深入的分析计算。结果表明：如果电枢的装配公差合适,则可消除由于电枢和定子之间的轴线偏差导致的跳匝现象;圆管爆轰的边缘效应会导致起爆端部分线匝的磁通损失,因而发生器设计时电枢要比定子线圈长一部分;电枢厚度的径向不均匀分布会引起电枢的不对称膨胀,从而导致跳匝发生。     

基于表面磁感应强度的铁磁构件应力恒磁表征方法

便捷获取铁磁承载构件应力对维护基础设施安全具有重要意义.其关键在于准确快速地确定随应力变化灵敏度高、线性度好的表征参数.现有电磁检测法一般在时变磁场线圈激励下,逐点分析实验结果来确定合适的表征参数,会带来线圈发热、涡流影响结果的问题,表征磁参数的确立繁琐.为此,本文提出基于表面磁感应强度的铁磁构件应力恒磁表征方法,采用永磁恒定磁化器产生全局衰减局部均匀的空间变化磁场作激励,用正交磁场测量单元拾取构件表面轴向和法向磁感应强度以表征应力.着重阐述基于表面磁感应强度的应力表征原理：根据退磁场理论、磁场强度切向连续性和磁场高斯定理,建立表面轴向和法向磁感应强度关于应力导函数之间的关系方程.最后开展实验验证.结果表明：根据该关系方程可快速准确地确定随应力灵敏度最高的表面磁感应强度,且其随应力变化线性度较好,拟合优度R²大于0.98,可作为应力表征磁参数.本文所提方法可为在线检测铁磁构件应力提供新途径.     

利用啁啾激光调制分子谐波信号

数值研究了啁啾激光驱动H_2~+辐射谐波的特点.结果表明,(1)在低强度和高强度激光驱动下,谐波光谱分别呈现红移和蓝移现象.引入正负向啁啾参数后,谐波频移和谐波辐射强度都可以得到调控.(2)谐波光谱在高强度激光驱动下呈现非奇次谐波.理论分析表明,非奇次谐波产生的原因是双H核频移不一致所导致的不对称相消干涉引起的.     

数字图像消卷积在显微测量中的应用

研究了数字图像消卷积在显微测量中的应用。在测量系统点扩展函数的基础上,利用频谱空间变换消卷积图像处理方法,消除了传统光学显微成像中的几何不清晰度。通过对显微图像进行复原,实现了反射式一维线宽的显微精确测量。在医用接骨钢板表面质量的评价中,对10μm量级的划痕宽度实现了精确和方便的测量。该技术对相关计量技术的发展具有重要意义。     

螺旋型爆磁压缩脉冲发生器2维磁流体力学数值模拟

 基于任意拉氏- 欧拉方法的2维磁流体力学程序APMFCG被用于简单绕制的螺旋型爆磁压缩脉冲发生器动力学过程的模拟,给出了德克萨斯技术大学简单绕制的爆磁压缩发生器数值计算结果,输出电流和线圈电感的模拟结果与实验测量基本吻合。该程序也用于研究由于种子电流的不同所导致的欧姆电阻非线性效应对爆磁压缩过程的影响,实验结果证明了该程序计算的可靠性。     

Enhancement of measurement accuracy in fiber Bragg grating sensors by using digital signal processing

Wavelength detection accuracy in fiber Bragg grating (FBG) sensors can be increased by use of digital signal processing after photo-detection. Finite impulse response and infinite impulse response algorithms were implemented and used to improve the wavelength detection accuracy of peak detection and time-zero-crossing techniques. The wavelength detection resolution can be improved by an order of magnitude compared with that obtained directly from an optical spectrum analyzer/tunable laser.     

Simple phase method for measurement of magnetic field gradient waveforms

Magnetic field gradients play a fundamental role in MR imaging and localized spectroscopy. The MRI experiment, in particular fast MRI, relies on precise gradient switching, which has become more demanding with the constantly growing number of fast imaging techniques. Here we present a simple MR method to measure the behavior of a magnetic field gradient waveform in an MR scanner. The method employs excitation of a thin slice, followed by application of the studied gradient and simultaneous FID acquisition. Measurements of different gradient waveforms were performed with a spherical phantom filled with doped water and positioned at the isocenter of the gradient set. The presented experiments demonstrate the capability of the technique to measure different gradient waveforms with an estimated error of less than 200 microT/m.     

内爆圆柱套筒磁通量压缩的磁流体力学计算

在一维反应流体动力学程序SSS的基础上扩充编制一维磁流体力学计算编码SSS/MHD,并对炸药内爆驱动的圆柱形套筒磁通量聚积发生器(MC-1装置)进行了一维磁流体力学模拟计算。分析了空腔磁场向压缩套筒和样品套筒壁中的磁扩散现象,结果表明,在压缩套筒壁中距离空腔0.2mm处的磁感应强度最大值只有十几T;而在样品套筒壁中距离空腔0.2mm处的磁感应强度最大值达到几百T,这主要是内外套筒运动速度不同,电磁力与内爆作用力平衡引起的。计算了空腔中磁感应强度的变化曲线和样品套筒内壁的速度历程曲线,得到与实验测试符合的结果。