Showing papers on "Moiré pattern published in 2016"

A universal moire effect and application in X-ray phase-contrast imaging

Abstract: A moire pattern is created by superimposing two black-and-white or gray-scale patterns of regular geometry, such as two sets of evenly spaced lines. We observed an analogous effect between two transparent phase masks in a light beam which occurs at a distance. This phase moire effect and the classic moire effect are shown to be the two ends of a continuous spectrum. The phase moire effect allows the detection of sub-resolution intensity or phase patterns with a transparent screen. When applied to x-ray imaging, it enables a polychromatic far-field interferometer (PFI) without absorption gratings. X-ray interferometry can non-invasively detect refractive index variations inside an object1-10. Current bench-top interferometers operate in the near field with limitations in sensitivity and x-ray dose efficiency2, 5, 7-10. The universal moire effect helps overcome these limitations and obviates the need to make hard x-ray absorption gratings of sub-micron periods.

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

Abstract: This study proposed to generate digital sampling Moire fringes by two-pixel down-sampling as a substitute for microscope scanning Moire fringes, and further reconstruct multiplication Moire fringes for micron/nano-scale deformation measurement. The displacement and strain sensitivities of the proposed reconstructed multiplication Moire 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 Moire technique to deformation measurement.

Projection of phase singularities in moiré fringe onto a light field

Abstract: A moire pattern, which is a kind of spatial interference between two periodic patterns, is regarded as a spatial modulation of a “field.” By defining the displacement field, we reveal that moire patterns can have a topological phase singularity, similar to a disclination in liquid crystal and, more generally, a vector field treated in the singular optics. We propose that topological singularities in the moire displacement field can be projected by passing an electromagnetic field through a metasurface. We designed a metasurface constructed from two layers of a metal disk array operating in the terahertz band; then we numerically estimated the spatial distribution of its transmission properties. The phase singularities in the electromagnetic fields coincided with the singularities appearing in the moire pattern. We found two kinds of singularities, and the phase of the electromagnetic field changed by 2π or 4π around them. These phase changes were independent of the light frequency, implying that the topol...

Numerical evaluation of moiré pattern in touch sensor module with electrode mesh structure in oblique view

Abstract: Capacitive touch sensor screen with the metal materials has recently become qualified for substitution of ITO; however several obstacles still have to be solved. One of the most important issues is moire phenomenon. The visibility problem of the metal-mesh, in touch sensor module (TSM) is numerically considered in this paper. Based on human eye contract sensitivity function (CSF), moire pattern of TSM electrode mesh structure is simulated with MATLAB software for 8 inch screen display in oblique view. Standard deviation of the generated moire by the superposition of electrode mesh and screen image is calculated to find the optimal parameters which provide the minimum moire visibility. To create the screen pixel array and mesh electrode, rectangular function is used. The filtered image, in frequency domain, is obtained by multiplication of Fourier transform of the finite mesh pattern (product of screen pixel and mesh electrode) with the calculated CSF function for three different observer distances (L=200, 300 and 400 mm). It is observed that the discrepancy between analytical and numerical results is less than 0.6% for 400 mm viewer distance. Moreover, in the case of oblique view due to considering the thickness of the finite film between mesh electrodes and screen, different points of minimum standard deviation of moire pattern are predicted compared to normal view.

Precision surface type measuring device

Abstract: The invention discloses a precision surface type measuring device, and the device comprises a light source, a projection grating, a first double telecentric system, a second double telecentric system, a grating detection assembly, a space beam splitting system, a first detector, a second detector and a processing unit, wherein a grating moire fringe is split into two moire fringes with constant phasic differences through a grating assembly detection, the two moire fringes is completely split from space through the space beam splitting system to image to a pair of detectors, and the measured object surface height is obtained according to the first moire fringe light intensity I1 and the second moire fringe light intensity I2. The device is insensitive for measuring the variation of light intensity, and the adaptability of the measured surface material and technology from the measuring system is improved.

3D display device and Moire fringe reducing method and device thereof

Abstract: The invention provides a 3D display device and a Moire fringe reducing method and device thereof. The method comprises an optical device parameter of the 3D display device is determined; according to the optical device parameter, the widths of Moire fringes of a microlens array in different inclination angles, relative to a display screen, are determined; and according to the inclination angle corresponding to the minimal width, a final inclination angle between the display screen and the microlens array is determined. According to the invention, the final inclination angle capable of achieving a Moire fringe reducing effect and between the display screen and the microlens array can be determined rapidly, simply and accurately, the width of Moire fringes is minimal in the inclination angle, and interference of Moire fringes in 3D display effect is reduced.

A digital moiré fringe method for displacement sensors

Abstract: In this study, a displacement measurement method based on digital moire fringe is described and experimentally demonstrated. The method is formed by only one grating with a constant pitch. First, the magnified grating image is received by an imaging array and is sent to a computer. Then, the digital moire fringes are generated by overlaying the grating image with its mirrored one. Finally, a specifically designed algorithm is used to obtain the fringes’ phase difference before and after movement and calculate the displacement. This method has the effects of amplifying displacement and averaging the grating lines error, the same as the traditional moire technique using two pieces of gratings. At the same time, the proposed system is much easier to assemble and the measurement resolution can be set more flexibly. One displacement measuring system based on this method was built up. Experiment results show that its measurement errors are less than 0.3 μm and less than 0.12 μm at the resolutions of 0.1 μm and 0.03 μm, respectively.

Development of a wafer warpage measurement technique using Moiré-based method

Abstract: This paper reports on a novel technique for measuring wafer warpage, using the design concepts of moire shift, digital moire, autocollimator, and the scanning profiling method. The measurement system is divided into two parts: an optical moire system and a phase analysis system. The optical arrangement can be adjusted to control the projection of a linear grating image onto the surface of a wafer to be reflected back into a CCD camera. The grating image acquired by the CCD camera is used for measurement whereas a reference grating image is obtained using the digital moire method. By overlapping the two images of the measurement and the reference gratings, the corresponding moire fringes are formed. The phase of the moire fringes will change proportionally to the degree of warpage in the wafer, which can be measured by detecting variations in the phase shift of the moire fringes in the scanning profile across the surface of the entire wafer. Measurement resolution can be controlled by adjusting the pitch size of the grating or the focal length of the focusing lens, or by adjusting the angle between the images of the measurement and reference gratings. Experiment results demonstrate that the proposed method is able to achieve an angular resolution of 0.2 μrad. As compared to the current warpage measurement techniques, the proposed method has the ability of high measurement resolution, high stability, and high flexibility.

Moiré effect in cylindrical objects

Abstract: The moire effect in single-walled cylindrical objects (gridshells) is investigated. The surface of such an object is a rolled-up periodic grating (mesh). Analytical formulae are obtained for the period of the moire patterns, which depends particularly on the direction of the wavevector of the grating. The experiments confirm the theory. The results can be applied to nanoparticles and to three-dimensional autostereoscopic displays.

Moiré alignment algorithm for an aberration-corrected holographic grating exposure system and error analysis.

Abstract: To meet the required manufacturing accuracy of high-quality aberration-corrected holographic gratings, we propose a moire alignment algorithm for the exposure system of holographic gratings. A model holographic grating exposure system is built with multiple degrees of freedom based on optical path function theory. The whole process algorithm is then derived, including the fourth-order orthogonal polynomial of the holographic gratings, fitted aberration coefficients, and an optimized Levenberg–Marquardt algorithm for the exposure system’s recording parameters. Finally, the simulated alignment and error analysis of a 2400 gr/mm aberration-corrected holographic grating’s exposure system are presented. The proposed moire alignment algorithm for such exposure systems can effectively improve the alignment accuracy, ensuring better holographic grating aberration correction ability.

Opto-mechanical tilt sensor using moiré effect for slope movement remote sensing

Abstract: A novel tilt sensing device using the circular grating moire effect is proposed in this paper. The relationship of the tilt angle and the features extracted from moire patterns was investigated through a controlled experiment. A prototype of the circular moire tilt sensing device was designed and fabricated. Images of the moire patterns were captured using a high-resolution web camera mounted onto the device. The principle of tilt detection using the circular moire was demonstrated using the controlled experiment. The graphs obtained from the experiments show parabolic trends in the relationship between peak-to-valley height of the transformed polar curve and the tilt angle. The mean absolute error for y-z direction and x-z direction tilting is 0.216 and 0.183 respectively.

Fresnel-zone-like moiré patterns: optical generation and plasmonic modulation with proposed surface profilometry application

Abstract: A novel scheme of surface plasmon resonance-assisted Fresnel-zone-like moire pattern generation has been theoretically and experimentally investigated in a dual shearing environment. Lateral shear is followed by radial shear with the help of a Wollaston prism and a birefringent lens, respectively. The superposition of two contrast-reversed Fresnel-zone-like patterns (FZP) with parallel equi-spaced straight lines interestingly generates the displaced replication of the original FZP, particularly when the lateral shear is of a sufficient amount. Modulation due to plasmonic excitation has also been observed on such patterns for two different substrate materials. Binary representation of radially sheared images has been illustrated and further utilized for the proposed non-contact surface profilometry of metal coatings.

Synthesis of superposition shape images by light interacting with superposed layers of lenslet gratings

Abstract: The present invention describes methods and apparatuses for creating superposition shape images by superposed base (102,107) and revealing (101) layers of lenslet gratings. The superposition shape images form a message recognizable by a human observer or by an image acquisition and computing device such as a smartphone. The superposition shape images may be created by different superposition techniques ranging from 1D moire, 2D moire and level-line moire superposition techniques to lenticular image and phase shift superposition techniques. Moire superposition techniques enable creating superposition shape images at different apparent depth levels. Applications comprise the protection of documents and valuable articles against counterfeits, the creation of eye-catching advertisements as well as the decoration of buildings and exhibitions.

Fringe Sensitivity of Projection Moire Topography Due to Position of Light Source and Object Distance According to Grating Periods

Abstract: In projection moire topography, the investigation of fringe sensitivity, which means the change rate of fringe order according to object height, is important and necessary to reduce the measurement error of the shape of an object. Using the fringe sensitivity, the determination of the absolute orders of moire fringes can be performed very easily and rapidly. The important parameters in the determination of absolute orders of fringes are the positions of light source and object, and the grating period in projection moire topography. Among these parameters, the fringe sensitivity due to the transverse motion of the light source and the longitudinal motion of the object according to grating periods are analyzed and compared. As a result, whereas the fringe sensitivity in the transverse-motion method increases linearly and gradually as the distance between light source and imaging sensor increases, the fringe sensitivity due to the longitudinal-motion method decreases dramatically as the distance between imaging lens and object increases. In these methods, the fringe sensitivity and its change increase as the grating period increases. Keywords: Projection Moire Topography, Moire fringe, fringe sensitivityOCIS codes: (120.4120) Moire’ techniques, (120.4640) Optical instruments, (100.3175) Interferometric imaging

Moire interferometry patterns for rotational alignment of structures

Abstract: In some manufacturing applications the alignment of fine structures formed on the surface of a part such as micro-scribed patterns on solar panels can be critical to the panel performance. Variations in pattern uniformity may degrade the efficiency of the solar panel if the pattern deviates significantly from designed parameters. This paper will explore the use of moire patterns to interpret the angular alignment of such structures on 3 dimensional non-planar shapes. The moire interferometry pattern creates a beat between the scribed pattern and a reference pattern that is a function of both the shape of the part as well as the shape of the scribed pattern. Both the part shape variations and the patterns of interest are typically much smaller than can be seen visually. Similar challenges exist when inspecting specular models or testing low quality optics. The moire effect allows small displacements to be measured from patterns that are well below the resolution of the camera systems that are used to view the patterns. Issues such as the separation of the shape of the part from the alignment of the fine structure as well as resolution and robustness of the technique will be explored in this paper.

Photorefractive moiré-like patterns for the multifringe projection method in Fourier transform profilometry.

Abstract: In the present paper, the method of simultaneous moire-like fringe pattern projection for Fourier transform profilometry is described. The photorefractive holographic interferometric process produces controlled moire-like patterns with two or more different variation directions. Each low spatial frequency fringe pattern is experimentally obtained as a result of the superposition of two high spatial frequency sinusoidal gratings, with slightly different pitches, for each fringe variation direction. These dynamic moire-like patterns are induced due to an optical holographic beating of the sinusoidal induced gratings in the volume of the photorefractive Bi₁₂TiO₂₀ (BTO) crystal sample used as dynamic holographic medium. Two or more moire-like fringe patterns, with at least two different variation directions, simultaneously (or not), are projected onto the object surface. Thus, this is the 2D fringe projection stage of our proposed Fourier transform procedure to determine the profile of a simple object.

Projection moire fringe method-based out-of plane displacement measurement system and method

Abstract: The invention relates to a projection moire fringe method-based out-of plane displacement measurement system and method. Light emitted by a light source is projected onto the surface of a measured object through a projection grating and a projection lens, so that grid lines can be formed on the surface of the measured object; the grid lines are subjected to out-of plane displacement modulation of the surface, and as a result, the grid lines are distorted; the distorted grid lines are imaged on a reference grating through an imaging lens, so that moire fringes can be formed; the moire fringes are recorded by a CCD camera; and out-of plane displacement can be calculated through analyzing the phase variation of a moire fringe image. According to the measurement system and method of the invention, the measurement area, resolution and measurement range of the system can be flexibly adjusted according to test requirements; and even a large-area object is tested, high resolution and high precision can be still realized. The automation degree of the measurement system of the invention is high, after acquired images are subjected to later-stage processing of a computer, quick batched measurement can be realized; and the whole system has high anti-external environmental interference performance and is suitable for on-site testing.

Electrically conductive film, display device with the same, and method of evaluating electrically conductive film

Abstract: PROBLEM TO BE SOLVED: To provide an electrically conductive film having a mesh pattern which can suppress a moire pattern from being generated according to intensity of a display and improve visibility even in a case of superposition on a pixel array pattern of a display unit differing in light emission intensity, a display device, and a method of evaluating a pattern of the electrically conductive film.SOLUTION: There is provided an electrically conductive film given irregularity by constituting, in wave lines, a plurality of metal thin wires such that evaluation indexes of moire patterns of respective colors by making human visual response characteristics operate on intensities of moire equal to or larger an intensity threshold among intensities of moire patterns at frequencies of respective moire patterns equal to or less than a frequency threshold according to an observation distance, wherein a frequency and an intensity of a moire pattern are calculated for each color from first and second peak frequencies and first and second peak intensities of a 2DFFT spectrum of transmissivity image data of a polygonal wiring pattern with regularity and lightness image data of a pixel array pattern of each color in monochromatic light illumination.SELECTED DRAWING: Figure 16

Electron beam moiré fringes imaging by image converter tube with a magnetic lens

Abstract: An image converter tube with a magnetic lens was used to obtain static images of moire fringes formed by electron beam. These moire fringes are formed due to the interference between the anode mesh and the photocathode containing slits of various spatial frequencies. Moire fringes are observed at an accelerating voltage of 3.5 kV requiring the magnetic excitation condition of ∼550 ampere-turns. Not only the features of the fringes are analyzed but also the change of fringe spacing as a function of the rotation angle is investigated. The experimental results are found well in agreement with the theoretical analysis. By changing the rotation angle or adjusting the excitation condition of the magnetic lens, we were able to record parallel moire and secondary moire fringes too. The secondary moire fringes can be observed in the rotation angle range of −39.5° to −50.6°. The theoretical analysis indicates that the secondary moire is formed by the interference between the photocathode slits and the 2-D periodic structure of the anode mesh. Combining our proposed moire method with the pulse-dilation technique may potentially open the door for future applications, in various fields including, but not limited to, ultrafast electrical pulse diagnostics.

Investigation of phase object trace duplication in moiré deflectometry.

Abstract: In a deflectometry experiment for finding the temperature distribution around a hot wire as a phase object, the trace of the wire in a moire pattern is duplicated, and it is observed that the separation of the wire traces varies when the distance between two gratings of a moire deflectometry setup is changed. By investigation of moire deflectometry, it is found that the object trace duplication cannot be interpreted by ray deflection theory, which is based on geometric optics. By using diffraction theory, the effect of a phase object on a moire pattern is studied, and some generalized formulations are presented. It is demonstrated that the deformation of moire fringes does not originate from the wavefront derivative, but superposition of two separated wavefronts causes fringe deformation. By this approach, the accuracy of ray deflection analysis is improved. Finally, the results of this model are simulated, and the simulation has good agreement with the experimental model.

Deformation measurement method not affected by microscope scan distortion due to secondary moire fringe

Abstract: PROBLEM TO BE SOLVED: To solve the problem that a distortion of scan line of a scan type microscope causes distortion of moire fringes to bring about an error in deformation measurement that uses moire, and in a phase shift method that removes distortion, an analysis range becomes narrower because a grid itself must be photographed, and further, in a case where a device itself is shifted for phase shifting, a device is required and is expensive.SOLUTION: A technique that utilizes secondary moire fringe (Secondary Moire) in which two images having been photographed before and after deformation of a sample are synthesized so that scan moire fringes are superposed each other so that an effect of scan distortion is eliminated for measurement of sample deformation, has been developed.SELECTED DRAWING: Figure 3

In-plane motion measurement by using digital sampling moiré method

Abstract: Digital sampling moire (DSM) method is a newly developed vision-based technique that uses the phase information of moire fringes to measure movement of an object. The moire fringes are generated from a sequence of digital images, containing a cosinusoidal grating pattern attached to the object, through down-sampling and interpolation. As the moire fringes can magnify the pattern’s movement, this technique is expected to provide more accurate displacement measurement than the other vision based approaches. In this study, a method combining DSM with monocular videogrammetric technique is proposed to measure in-plane rotation and translation of structures. In this method, images of a two-dimensional (2D) grating pattern attached to a moving structure are acquired and decomposed into two perpendicular gratings through Fourier transform. The DSM method is used to obtain 2D phase distributions of the gratings which provide an estimation of physical coordinates for those points on the grating pattern. A previously developed monocular videogrammetric technique can then be used to obtain the rotation angle and the translation of the grating pattern. The proposed method is validated using both numerical simulation and laboratory tests.

Structured illumination induced moiré fringes for resolution enhancement in digital holographic microscopy

Abstract: This work describes resolution enhancement of digital holographic microscopy based on structured illumination, in which low-frequency moire fringes are induced and recorded for hologram reconstruction. Higher resolution can be performed with the known structured patterns.

Conductive film, display device equipped with the same and conductive film evaluation method

Abstract: PROBLEM TO BE SOLVED: To provide a conductive film having a mesh pattern which can inhibit creation of moire to vastly improve visibility; and provide an evaluation method of the pattern.SOLUTION: A conductive film which is composed of a parallelogram wiring pattern to which irregularities are provided to have a rectangular wiring pattern in which irregularity within a predetermined range is provided to an angle of each diamond shape of a diamond wiring pattern where a moire rating index calculated from an evaluation value of a moire of each color obtained by providing the action of human visual responsivity depending on a monitoring distance to each moire intensity of equal to or more than an intensity threshold value out of moire intensities in a frequency of each moire equal to or less than a frequency threshold value in the frequency and the intensity of the moire, which are calculated with respect to each color from first and second peak frequencies and first and second peak intensities of 2DFFT spectrum of transmissivity image data of the diamond wiring pattern before the irregularities are provided and brightness image data of a pixel arrangement pattern of each color at monochromatic light lighting becomes equal to or less than an evaluation threshold value.

X-ray photographing system

Abstract: PROBLEM TO BE SOLVED: To reduce image degradation caused by influence of body motion, in an X-ray photographing system using a Talbot interferometer or Talbot-Lau interferometer.SOLUTION: An X-ray photographing system includes: an X-ray photographing apparatus 1 including a control unit 181 for making an X-ray detector 16 acquire a plurality of original moire fringe images at the same lattice position by making the X-ray detector acquire moire fringe images a plurality of times in storage time shorter than charge accumulation time necessary for acquiring one reconstruction moire fringe image used for creating one reconstruction image; and a controller 5 including a control unit 51 for creating a reconstruction moire fringe image by adding the plurality of original moire fringe images acquired by the X-ray detector 16 to create a reconstruction image for a subject on the basis of the created reconstruction moire fringe image.SELECTED DRAWING: Figure 8