micronano-scale-strain-distribution-measurement-from-sampling-moir

Micro/Nano-scale Strain Distribution Measurement from Sampling Moir&#233; Fringes

This work describes the measurement procedure and principles of a sampling moir&#233; technique for full-field micro/nano-scale deformation measurements. ...

National Institute of Advanced Industrial Science and Technology (AIST)

A camera based on the digital micromirror device (DMD) technology has been previously developed. In this optical system, the correspondence of each mirror of the DMD to each pixel of the CCD cannot readily be done since the pixel sizes of the DMD and the CCD are very small. An accurate pixel-to-pixel correspondence adjustment in the DMD camera by means of the phase-shifting moiré method is proposed. To perform high accurate adjustment of the optical system, the phase distribution of a moiré fringe pattern is analyzed when the CCD pixels and the DMD mirrors have a mismatch and/or misalignment with each other. This technique does not need a complicated setting or complex image processing to generate the moiré fringe pattern, and it needs only one captured image. In the adjustment experiment, the proposed method provided very accurate adjustment whose error was less than 1/25 pixel. An experiment of phase analysis to demonstrate the usefulness was performed.

Accurate pixel-to-pixel correspondence adjustment in a digital micromirror device camera by using the phase-shifting moiré method.

Phase-measuring profilometry is an accurate and effective technique for performing three-dimensional (3D) shape and deformation measurements of diffuse objects by fringe projection. However, phase analysis cannot be performed in underexposed or overexposed areas of the detector when an object with wide reflectance is measured. A novel intensity range extension method using a digital micromirror device (DMD) camera is proposed. In the optics of the DMD camera, each pixel of the CCD corresponds exactly to each mirror of the DMD. The phase-shifted fringe patterns with high contrast can be easily captured by programming an inverse intensity pattern that depends on the reflectance of the object. Our method can provide a wider intensity range and higher accuracy for 3D shape measurement than other conventional methods in both underexposed and overexposed areas. The measurements of a replica of a metallic art object and a flat plane are analyzed experimentally to verify the effectiveness of our method. In the experiment, the percentage of invalid points due to underexposure and overexposure can be reduced from 20% to 1%.

Intensity range extension method for three-dimensional shape measurement in phase-measuring profilometry using a digital micromirror device camera.

Recently, a rapid and accurate single-shot phase measurement technique called the sampling moiré method has been developed for small-displacement distribution measurements. In this study, the theoretical phase error of the sampling moiré method caused by linear intensity interpolation in the case of a mismatch between the sampling pitch and the original grating pitch is analyzed. The periodic phase error is proportional to the square of the spatial angular frequency of the moiré fringe. Moreover, an effective phase compensation methodology is developed to reduce the periodic phase error. Single-shot phase analysis can perform accurately even when the sampling pitch is not matched to the original grating pitch exactly. The primary simulation results demonstrate the effectiveness of the proposed phase compensation methodology.

Theoretical error analysis of the sampling moiré method and phase compensation methodology for single-shot phase analysis.

In this study, a novel, fast, and accurate in-plane displacement distribution measurement method is proposed that uses a digital camera and arbitrary repeated patterns based on the moiré methodology. The key aspect of this method is the use of phase information of both the fundamental frequency and the high-order frequency components of the moiré fringe before and after deformations. Compared with conventional displacement methods and sensors, the main advantages of the method developed herein are its high resolution, accuracy, speed, low cost, and easy implementation. The effectiveness is confirmed by a simple in-plane displacement measurement experiment, and the experimental results indicate that an accuracy of 1/1000 of the pitch can be achieved for various repeated patterns. This method is useful for various applications ranging from the study of displacement and strain distributions in materials science, the biomimetics field, and mechanical material testing, to secure the integrity of infrastructures.

Accurate full-field optical displacement measurement technique using a digital camera and repeated patterns.

This study proposed to generate digital sampling Moiré fringes by two-pixel down-sampling as a substitute for microscope scanning Moiré fringes, and further reconstruct multiplication Moiré fringes for micron/nano-scale deformation measurement. The displacement and strain sensitivities of the proposed reconstructed multiplication Moiré method are 2 times higher in a wide field of view. Besides, two-dimensional deformation is easily measurable without rotating the sample stage or the scanning lines, no matter whether the scanning resolution is adjustable or not. As an example, the deformations of a carbon fiber reinforced plastic specimen were measured and analyzed. The proposed method effectively expands the application range of the Moiré technique to deformation measurement.

Digital sampling Moiré as a substitute for microscope scanning Moiré for high-sensitivity and full-field deformation measurement at micron/nano scales.

Article	Year
Accurate pixel-to-pixel correspondence adjustment in a digital micromirror device camera by using the phase-shifting moiré method. Applied optics\| PubMed ID: 16946769	2006
Intensity range extension method for three-dimensional shape measurement in phase-measuring profilometry using a digital micromirror device camera. Applied optics\| PubMed ID: 18846182	2008
Theoretical error analysis of the sampling moiré method and phase compensation methodology for single-shot phase analysis. Applied optics\| PubMed ID: 22695552	2012
Accurate full-field optical displacement measurement technique using a digital camera and repeated patterns. Optics express\| PubMed ID: 24787855	2014
Digital sampling Moiré as a substitute for microscope scanning Moiré for high-sensitivity and full-field deformation measurement at micron/nano scales. Applied optics\| PubMed ID: 27607259	2016

Shien Ri

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