Online sequential analysis of cardiac activity as observed on the chest wall by digital speckle pattern interferometry
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A technique based on digital speckle pattern interferometry is described to obtain cardiac displacement pattern during entire cardiac cycle. The sequential analysis of the displacement pattern may provide useful information on cardiac function in health and diseases.Keywords:
Cardiac cycle
Speckle imaging
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The speckle interferometry is an effective technique in the displacement measurement of a structure with a rough surface. However, when the fringe scanning technique is introduced to speckle interferometry for improving the measurement resolution, generally two speckle patterns before and after the deformation of the measurement object and another speckle pattern obtained under different conditions from these two speckle patterns are required at least. So, three speckle patterns are generally required for precise fringe analysis as a minimum condition. In this paper, a method for introducing the fringe scanning method is proposed by controlling the phase of the specklegram as a fringe image using filtering techniques. Then, the temporal fringe analysis method that uses only two speckle patterns are proposed for speckle interferometry. As the result of experiments, it is shown that high precise fringe analysis can be realized by the fringe scanning methods using only two speckle patterns for the displacement measurement with a large deformation.
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Digital speckle-pattern interferometry systems for automatic measurement of in-plane deformation of a diffuse object are presented, based on phase shifting of a speckle interferogram. Before deformation, three digital speckle patterns are recorded as changing the phase of reference light such as 0,pi/4, pi/2. After deformation, three digital speckle patterns are recorded with phase shifts - pi/2, 3pi/4, pi, respectively. A calculation of the arctangent with phase-shifted speckle pattern gives the optical path difference which is proportional to the deformation.
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It is shown that the speckle nature of electronic speckle pattern interferometry images can be reduced in quasireal time with the use of only three consecutive video images. By use of additive-subtractive phase modulation processing the technique is essentially insensitive to environmental noise, and distortion of fringes does not occur. By further removing the random speckle phase we show, using speckle statistics, that the number of dark speckles in the resulting fringe pattern is close to zero.
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Measurement of Dynamic Characteristics of Structures by the Speckle Interferometry on Single Speckle
- In this article the results associated with the use of speckle interferometry on a single speckle to determine the dynamic characteristics of mechanical constructions are presented. The optical scheme of the speckle interferometer on a single speckle is proposed, which makes it possible to simultaneously record the form and amplitude of the resonant vibrations of mechanical constructions. Theoretical and experimental results demonstrating the behavior of the output signals from the speckle interferometer on a single speckle in the study of the resonant vibrations are presented. The resonance method for measuring the logarithmic decrement of vibrations and other dynamic characteristics of a mechanical constructions using speckle interferometry on a single speckle is proposed.
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Speckle imaging
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Intensity
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The speckle interferometry is an effective technique in the displacement measurement of a structure with a rough surface. However, when the fringe scanning technology is introduced to speckle interferometry for improving the measurement resolution, two speckle patterns before and after the deformation of the measurement object and another speckle pattern under different situation from two speckle patterns shown before generally are required. In this paper, the methods for introducing the fringe scanning method are proposed by controlling the phase of specklegram as a fringe image using filtering technologies. Then, the spatial and the temporal fringe analysis methods that use only two speckle patterns are proposed for speckle interferometry. As results, the high precise fringe analysis can be realized by the fringe scanning methods using only two speckle patterns in the displacement measurement with a large deformation. The results show that the possibility of the method based on spatial fringe analysis methods in practical uses would be higher than that of temporal methods.
Speckle imaging
Speckle noise
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With regard to the three-dimensional (3D) shape measurement, based on speckle interferometry, of an object with a fine structure beyond the diffraction limit of the objective lens, phase distribution of each speckle region in a speckle pattern and a specklegram is discussed. The experimental results confirmed that the phase distribution with respect to the shape of an object exists spatially even in the speckle region of the speckle pattern. However, the measurement results of a superfine structure by speckle interferometry indicated that the spatial continuity of the phase distribution does not exist in each speckle but in the specklegram. This feature was used to confirm that a wide range of 3D shape measurements of an object with a fine structure can be realized by analyzing specklegrams calculated from speckle patterns before and after a lateral shift in speckle interferometry. Furthermore, it is confirmed that the shape measurement of a nonperiodical structure can be performed.
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In the experimental set-up for measuring temperature fields in fluid flows by using speckle interferometry ( e.g. electronic speckle pattern interferometry or phase shift speckle interferometry ), the part of the; arrangement for the object light beam is just like a subjective speckle photographic system. Therefore, in general, speckle displacements are generated. The speckle displacements can change the intensity distribution of spatial speckle fields. As a result, the intensity distribution of a speckle interferogram is also changed. In this paper the effect of speckle displacements on the speckle interferometry is analyzed and discussed in detail. A physical model and mathematical treatment for the effect are proposed. Experimental results are shown. A method for elimination of the effect is provided. Using the provided method, the temperature measurement error of speckle interferometry can be reduced and the measurement accuracy can also be increased.
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