A simple electronic speckle shearing interferometer

A new speckle shearing interferometer with simple setup is proposed. The interferometer can be converted easily from a speckle referenced speckle pattern interferometer into a speckle shearing interferometer and vice versa. A beamsplitter and a mirror are used to generate the shear. The amount of shear can be adjusted by simply rotating the mirror. The costs involved are low and it is particularly useful for fast inspection in non-destructive testing of structural integrity. Both the theoretical studies of the method of measurement and the experimental results are presented.     

Hybrid numerical—experimental approach for investigation of dynamics of microcantilever relay system

The time average holography measurements of the vibrating microelectromechanical switch (MEMS) were performed in this study. Experimental measurement results exhibit good agreement with computer generated holographic interferogram analysis. The validation of experimental investigations versus numerical analysis provides the necessary background to analyze the dynamical characteristics of micromechanical systems in virtual numerical environments. Direct application of fringe counting techniques for reconstruction of motion from time average holograms cannot be straightforward if the analyzed micromechanical systems contain motion limiters. Modifications of a classical time average holographic technique enable qualitative analysis of MEMS and can be applied for investigation of dynamical properties of much broader classes of MEMS systems.     

起爆药爆轰场和燃烧场的干涉法显示及其图像处理

本文介绍了利用脉冲YAG激光引爆起爆药产生爆轰流场或燃烧温度场,用时间序列干涉法首次获得了爆轰流场和起始燃烧过程的时间序列干涉图的实验结果.在此基础上,采用条纹曲线检测法和双三次多结点插值样条函数从干涉图上提取爆轰场冲击波的波阵面,并通过序列波阵面配准算法,定量地计算了冲击波的传播速度.同时,还定量计算了燃烧场温度随时间变化的分布.     

数字散斑干涉技术在振动分析中的应用

首次将相移技术应用于频闪数字散斑干涉计量中,对物体的振动进行了定量分析.实验证明,这种方法有广泛的实用价值.另外,介绍了一套自动分析系统,讨论了各参数对测量结果的影响.     

Study of a vibrating plate: comparison between experimental (ESPI) and analytical results

Real-time electronic speckle pattern interferometry (ESPI) was used for tuning and visualization of natural frequencies of a trapezoidal plate. The plate was excited to resonant vibration by a sinusoidal acoustical source, which provided a continuous range of audio frequencies. Fringe patterns produced during the time-average recording of the vibrating plate—corresponding to several resonant frequencies—were registered. From these interferograms, calculations of vibrational amplitudes by means of zero-order Bessel functions were performed in some particular cases. The system was also studied analytically. The analytical approach developed is based on the Rayleigh–Ritz method and on the use of non-orthogonal right triangular co-ordinates. The deflection of the plate is approximated by a set of beam characteristic orthogonal polynomials generated by using the Gram–Schmidt procedure. A high degree of correlation between computational analysis and experimental results was observed.     

Quantitative vibration amplitude measurement with time-averaged digital speckle pattern interferometry

A new method of using time-averaged digital speckle pattern interferometry for the quantitative measurement of vibration amplitude was developed. Signal processing techniques especially the Hilbert transformation for quantitative evaluation of the Bessel fringes obtained in time-averaged digital speckle pattern interferometry were explored. The quadrature signal after Hilbert transformation is equivalent to a 90° phase-shifted interferogram for a monotonically increasing or decreasing phase function. An algorithm was developed for Bessel fringe contrast enhancement and phase extraction. The techniques were tested numerically and experimentally. Sub-fringe quantification of the time-averaged vibration fringes is realised with the proposed method. Compared with the commonly used phase shift method which requires a minimum of two images for image processing, this method requires only one fringe pattern for data extraction.     

Quantitative evaluation of two-dimensional dynamic deformations using digital holography

An optical system for the parallel evaluation of in- and out-of-plane dynamical deformations will be described. A double pulse laser with pulse separation in the microsecond range is used for the investigations. Two separate interferograms of an object under test, in its undeformed and deformed state, are recorded in a few microseconds. The object is illuminated from two different directions and imaged onto a CCD sensor. This produces two sensitivity vectors. The reference beams have different directions in order to produce two directional spatial carriers. The Fourier method is used for quantitative evaluation, and the measurements along different sensitivity vectors are separated in the Fourier domain. The phases of the two interferograms are obtained from the complex amplitudes and the two dimensional deformation is calculated from the phases. Experimental results are presented.     

Geometrically qualified ESPI vibration analysis of an engine

This paper presents an application in the automotive industry where a combination of electronic speckle-pattern interferometry and laser doppler velocimetry were used at a critical stage in the design process of an internal combustion engine. Combined deformation and surface relief measurements were used to study the phase and amplitude of deformation of a vibrating engine. The relief data was combined with the interferometer geometry and used to geometrically correct the deformation data, in an effort to improve accuracy. The measurements allowed rapid identification and quantification of design weaknesses, particularly those causing undesirable resonances. This led to a significant reduction in the design time and lowering of costs, when compared with existing design optimisation methods.