scholarly journals Combined Reduced Phase Dual-Directional Illumination Digital Holography and Speckle Displacements for Shape Measurement

2019 ◽  
Vol 2019 ◽  
pp. 1-6
Author(s):  
Davood Khodadad
Keyword(s):  
Phase Difference ◽  
Digital Holography ◽  
Relative Phase ◽  
Groove Depth ◽  
Phase Unwrapping ◽  
Shape Measurement ◽  
Phase Ambiguity ◽  
Holographic Method ◽  
Height Range ◽  
Phase Differences

We present a digital holographic method to increase height range measurement with a reduced phase ambiguity using a dual-directional illumination. Small changes in the angle of incident illumination introduce phase differences between the recorded complex fields. We decrease relative phase difference between the recorded complex fields 279 and 139 times by changing the angle of incident 0.5° and 1°, respectively. A two cent Euro coin edge groove is used to measure the shape. The groove depth is measured as ≈300  μm. Further, numerical refocusing and analysis of speckle displacements in two different planes are used to measure the depth without a use of phase unwrapping process.

scholarly journals Ambiguity Resolution for Passive 2-D Source Localization with a Uniform Circular Array

Sensors ◽  
2018 ◽  
Vol 18 (8) ◽  
pp. 2650 ◽  
Author(s):  
Jinlong Xin ◽  
Guisheng Liao ◽  
Zhiwei Yang ◽  
Haoming Shen
Keyword(s):  
Ambiguity Resolution ◽  
Relative Phase ◽  
Elevation Angle ◽  
Estimation Accuracy ◽  
Observation Model ◽  
Circular Array ◽  
Phase Ambiguity ◽  
Two Phase ◽  
Phase Observation ◽  
Phase Differences

This paper proposes two novel phase-based algorithms for the passive localization of a single source with a uniform circular array (UCA) under the case of measuring phase ambiguity based on two phase difference observation models, which are defined as the unambiguous-relative phase observation model (UARPOM) and the ambiguous-relative phase observation model (ARPOM). First, by analyzing the varying regularity of the phase differences between the adjacent array elements of a UCA, the corresponding relationship between the phase differences and the azimuth and elevation angle of the signal is derived. Based on the two phase observation models, two corresponding novel algorithms, namely, the phase integral accumulation and the randomized Hough transform (RHT), are addressed to resolve the phase ambiguity. Then, by using the unambiguous phase differences, the closed-form estimates of the azimuth and elevation angles are determined via a least squares (LS) algorithm. Compared with the existing phase-based methods, the proposed algorithms improve the estimation accuracy. Furthermore, our proposed algorithms are more flexible for the selection of an array radius. Such an advantage could be applied more broadly in practice than the previous methods of ambiguity resolution. Simulation results are presented to verify the effectiveness of the proposed algorithm.

Noise Filter Reducing Deformation in Digital Holography

2020 ◽  
Vol 38 ◽  
pp. 71-75
Author(s):  
Yoshitaka Takahashi ◽  
Takaya Okada ◽  
Ryutaro Sekiguchi ◽  
Madoka Fukushima
Keyword(s):  
Phase Difference ◽  
Digital Holography ◽  
Phase Shifting ◽  
Shape Measurement ◽  
Difference Image ◽  
Noise Filter ◽  
Contact Shape

A phase difference image using phase-shifting digital holography, which is applied for non-contact shape measurement, contains speckle noises and filtering to reduce them is inevitable for its application. We have developed a new filter which causes less deformation than commonly used filters.

Friedel'S law breakdown and interpretation of stacking fault images in tetrahedral semiconductors

1987 ◽  
Vol 45 ◽  
pp. 318-319
Author(s):  
Rob. W. Glaisher ◽  
A.E.C. Spargo
Keyword(s):  
Relative Phase ◽  
Point Group ◽  
Binary Compound ◽  
Stacking Fault ◽  
Fold Axis ◽  
Atom Pair ◽  
Tetrahedral Semiconductors ◽  
Group Symmetries ◽  
Thin Crystal ◽  
Phase Differences

Images of <11> oriented crystals with diamond structure (i.e. C,Si,Ge) are dominated by white spot contrast which, depending on thickness and defocus, can correspond to either atom-pair columns or tunnel sites. Olsen and Spence have demonstrated a method for identifying the correspondence which involves the assumed structure of a stacking fault and the preservation of point-group symmetries by correctly aligned and stigmated images. For an intrinsic stacking fault, a two-fold axis lies on a row of atoms (not tunnels) and the contrast (black/white) of the atoms is that of the {111} fringe containing the two-fold axis. The breakdown of Friedel's law renders this technique unsuitable for the related, but non-centrosymmetric binary compound sphalerite materials (e.g. GaAs, InP, CdTe). Under dynamical scattering conditions, Bijvoet related reflections (e.g. (111)/(111)) rapidly acquire relative phase differences deviating markedly from thin-crystal (kinematic) values, which alter the apparent location of the symmetry elements needed to identify the defect.

Phase difference-based multichannel phase unwrapping

2005 ◽  
Vol 14 (7) ◽  
pp. 960-972 ◽  
Author(s):  
G. Fornaro ◽  
A. Pauciullo ◽  
E. Sansosti
Keyword(s):  
Phase Difference ◽  
Phase Unwrapping

3D shape measurement with temporal phase unwrapping and 1-D continuous wavelet transform

2021 ◽  
Author(s):  
Susana L. Burnes-Rudecino ◽  
José de Jesús Villa Hernández ◽  
Gamaliel Moreno ◽  
Ismael de la Rosa ◽  
Efrén González ◽  
...  
Keyword(s):  
Wavelet Transform ◽  
Continuous Wavelet Transform ◽  
Phase Unwrapping ◽  
Shape Measurement ◽  
Continuous Wavelet ◽  
3D Shape ◽  
3D Shape Measurement ◽  
Temporal Phase

Fast 3D Shape Measurement of Complex Objects Combining S-transform Profilometry and Sub-Pixel Refinement

2020 ◽  
Author(s):  
Feng Lu ◽  
Jikun Yang
Keyword(s):  
Fringe Pattern ◽  
Vision System ◽  
Phase Unwrapping ◽  
Shape Measurement ◽  
Complex Objects ◽  
3D Shape ◽  
3D Shape Measurement ◽  
Phase Slope ◽  
S Transform ◽  
Hybrid Function

Abstract In the fast 3D shape measurement of complex objects, the process of phase unwrapping affects the measurement accuracy and measurement speed. To omit phase unwrapping, a fast 3D shape measurement method is proposed based on S-transform profilometry and sub-pixel refinement. In this work, Deformed fringe pattern is analyzed based on S-transform to get wrapped phase. To reduce the effect of phase unwrapping, a stereo vision system is employed. Firstly, a deformed fringe pattern is directly used and a hybrid function is proposed to get an initial parallax. Secondly, a phase slope algorithm is proposed to confirm edge point. At last, sub-pixel parallax is refined fromIcoordinate. Experiments are carried out to verify the feasibility and advantage of the proposed method. Results verify that the proposed method can provide fast and accurate 3D shape measurement of complex objects, especially for discontinuous objects and shiny objects.

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