An absolute method for determination of misalignment of an immersion ultrasonic transducer

An absolute methodology has been developed for quantification of misalignment of an ultrasonic transducer using a corner-cube retroreflector. The amplitude based and the time of flight (TOF) based C-scans of the reflector are obtained for various misalignments of the transducer. At zero degree orientation of the transducer, the vertical positions of the maximum amplitude and the minimum TOF in the C-scan coincide. At any other orientation of the transducer with the horizontal plane, there is a vertical shift in the position of the maximum amplitude with respect to the minimum TOF. The position of the minimum (TOF) remains the same irrespective of the orientation of the transducer and hence is used as a reference for any misalignment of the transducer. With the measurement of the vertical shift and the horizontal distance between the transducer and the vertex of the reflector, the misalignment of the transducer is quantified. Based on the methodology developed in the present study, retroreflectors are placed in the Indian 500 MWe Prototype Fast Breeder Reactor for assessment of the orientation of the ultrasonic transducer prior to the under-sodium ultrasonic scanning for detection of any protrusion of the subassemblies.     

扩散硅压力变送器的曲面拟合补偿

为解决扩散硅压力传感器因非线性特性及易受温度影响从而导致其测量精度降低这一问题,提出了基于最小二乘曲面拟合的补偿方案。建立了传感器的被测压力、工作温度和输出电压间的曲面拟合数学模型,在获得传感器的输出电压和工作温度后能简便地计算出被测点的压力值。实验表明,该     

基于激光超声场检测的材料常数测量方法

由于采用干涉仪的激光超声技术造价较高,对环境噪声极为敏感,很难在工业中得到广泛应用,为此开发了基于压电传感器的激光超声场检测仪(LUFT)。该系统采用激光激发、压电传感接收的方式,既保留了激光高分辨率的优势,又兼具了系统造价低、使用方便的特点。本文中,利用该检测仪对标准钢试样及不同厚度的铝试样进行了测量,获得其表面波和纵波波速,并根据固体力学理论得到铝的泊松比和杨氏模量。计算结果与文献参考值误差较小,说明该方法的可行性,也说明了该激光超声场检测仪的可靠性。     

Selective generation of ultrasonic Lamb waves by electromagnetic acoustic transducers

In this paper, we describe a modal expansion approach for the analysis of the selective generation of ultrasonic Lamb waves by electromagnetic acoustic transducers(EMATs). With the modal expansion approach for waveguide excitation, an analytical expression of the Lamb wave's mode expansion coefficient is deduced, which is related to the driving frequency and the geometrical parameters of the EMAT's meander coil, and lays a theoretical foundation for exactly analyzing the selective generation of Lamb waves with EMATs. The influences of the driving frequency on the mode expansion coefficient of ultrasonic Lamb waves are analyzed when the EMAT's geometrical parameters are given. The numerical simulations and experimental examinations show that the ultrasonic Lamb wave modes can be effectively regulated(strengthened or restrained) by choosing an appropriate driving frequency of EMAT, with the geometrical parameters given. This result provides a theoretical and experimental basis for selectively generating a single and pure Lamb wave mode with EMATs.     

基于三路舵机驱动的扑翼飞行模型气动特性研究

扑动而形成非定常气动现象是扑翼飞行过程中产生高升力的主要原因。本文以Ellington实验的鹰蛾翅膀为原形,设计扑翼实验及数值计算模型。通过压差传感器对翅膀模型上翼面固定位置进行测压,分析前缘涡的产生及脱落情况(考虑动压效应)。测量上下翼面固定位置处的压差,揭示扑翼飞行中产生高升力的主要原因。利用烟风洞观察扑翼模型周围流场结构及特殊涡产生变化情况。另外,根据Ellington提供的升力关系式估算了扑翼模型在一个周期内的平均升力。最后,基于三维欧拉方程对扑翼飞行气动特性进行数值模拟,计算结果与实验吻合良好。     

Determination of displacement with a piezoelectric transducer using phase-shift algorithms

This investigation accurately measures the relationship between applied voltage and the displacement of a piezoelectric transducer device both by analyzing phase shifting interferometry algorithms and using a Twyman-Green interferometer. Simulations are performed to calculate unknown phase shifts, especially around π/2 and 3π/2. It is indicated that the Hariharan algorithm is indeed an effective phase shifting interferometry algorithm.     

Self-calibration of a phase-shifting adapter for Fizeau interferometers

Phase-shifting interferometers with three piezoelectric transducers (PZTs) on their phase-shifting adapter (PSA) are widely used in precision measurement. The guarantee of the PSA to stretch as a flat is very important to the accuracy of the measurement. In this paper, we propose a systematic self-calibration method to calibrate the different displacements of the PZTs so that the PSA can be moved evenly as a flat. The proposed method uses only the interference patterns to calibrate the three PZTs and information about the exact position of the PZTs and the instrument parameters of the interferometer are not required. Experimental results show that, after calibration by the proposed method, the deviation of the measured phase shift error could be reduced about 43.1 times from 3.492 to 0.081°.     

Development of an optical ammonia sensor based on polyaniline/epoxy resin (SU-8) composite

Polyaniline (PANI)/glycidyl ether of bisphenol A (SU-8) composite film is elaborated in order to detect ammonia gas. These composite films are characterized by ultraviolet-visible (UV-vis) spectroscopy, Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The sensitivity to ammonia is measured by optical absorption changes. The ammonia sensing properties of PANI/SU-8 composite films are studied, and then are compared to pure PANI films elaborated by chemical way. Experimental results show that the PANI/SU-8 optical sensor has simultaneously a rapid response to ammonia gas and regenerates easily, that is advantageous compared to pure PANI films.     

超声换能器带宽对光声成像的影响

研究了不同尺寸吸收体产生的光声压的频谱特性：对于厘米量级、毫米量级和几百个微米量级的吸收体,产生光声压频谱的主要范围分别约为20～300kHz、70kHz～2．5MHz和400kHz～20MHz;讨论了不同频率范围的光声信号对重建图像的影响,低频段的光声信号能反映物体的非边界区域,而高频段的光声信号能突出物体的细微结构,尤其是物体的边界特征。提出了不同尺寸的吸收体要选用或设计不同带宽范围的探测器进行检测的方法．当探测器的带宽范围与光声压频谱范围基本吻合时,损失的频率成份较少,重建的光声图像效果较好,这一结论在仿真和实验结果中都得到了证明。实验用的光源为YAG激光器,波长为532nm,重复频率为30Hz,脉宽为7ns,探测器为针状的PVDF膜水听器,接收面积的直径为1mm。