Ultrasonic array imaging algorithms have been widely used and developed in non-destructive evaluation in the last 10 years. In this paper, a widely-used imaging algorithms, Total Focusing Method (TFM), was further developed with using the phase statistical information of the scattering field from a scatterer, i.e., Circular Coherence Factor (CCF). TFM and TFM with using CCF are compared through both simulation and experimental measurements. In the simulation, array data sets were generated by using a hybrid forward model containing a single defect amongst a multitude of randomly distributed point scatterers to represent backscatter from material microstructure. The number of point scatterers per unit area and their scattering amplitude were optimized to reduce computation cost. The Signal to Noise Ratio (SNR) of the finial images and their resolution were used to indicate the quality of the different imaging algorithms. The images of different types of defect (point reflectors and planar cracks) were used to investigate the robustness of the imaging algorithms. It is shown that, with using CCF, higher image resolution can be achieved, but that the images of cracks are distorted. It is also shown that the detection limit of the imaging algorithms is almost equal for weakly scattering defects.
There has been a massive increase in the use of ultrasonic arrays for non-destructive evaluation (NDE) in recent years.
However, much of this technology is either based on medical ultrasound imaging or is designed simply to mimic
traditional NDE inspections performed with monolithic transducers. This paper addresses the issue of array system
design and data processing specifically for quantitative NDE. It is shown that arrays offer huge potential for defect
characterization in NDE beyond that currently exploited and possible directions are discussed. In particular, it is shown
that obtaining all the time-domain signals from every transmitter receiver combination combined with post-processing is
the preferable strategy for NDE. Not only can information in the full data-set provide the highest possible resolution
image, but that it can also be exploited to perform sub-wavelength reflector characterization by extracting portions of the
reflector scattering matrix. Experimental results on artificial defects are used to illustrate this point.
As an optical focus detection technique, confocal microscopy has been received much attention in the last few years. It has not only the particular property of depth discrimination, but also the ability of enhancement of contrast by suppression of light scattered from defocused object location. Therefore, the techniques based on confocal microscopy have been developed as a powerful tool for surface profiling. However, in order to maintain the high resolution, it is difficult to make fiber-optic sensor as small as possible, and which restrict the measurement of small internal curve surface. For the purpose of uniting micromation and high-precision in profile, based on a fiber confocal microscopy theory, a new fiber optical scanning microscope made up of splitter and GRIN lens is presented. Compared with other confocal technique, it has smaller size, higher anti-jam, and higher axial resolution. Especially, it has the characteristic of absoluteness zero point, which can be used for 3D and super-glossy inner surface profile. Experiment results show that the axial resolution with 30nm and linearity range 40μm can be achieved. This linearity, high resolution and small cubage permit non-contacting surface profilometry to be readily obtained for specimens of uniform reflectivity and small internal curve surface profile.
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