Moiré pattern

About: Moiré pattern is a research topic. Over the lifetime, 1917 publications have been published within this topic receiving 27176 citations. The topic is also known as: moiré fringes & moire pattern.

Digital moiré by a diffractive optical element for deformation analysis of ancient paintings

Abstract: In this paper we propose a digital projection moire system for full-field measurement of out-of-plane deformation of cultural heritage objects. The method is based on a new fringe generator realized by a diffractive optical element illuminated by a spherical wave phase. Two grating patterns on an object before and after deformation are captured by a CCD camera and stored in a computer. With the aid of fast Fourier transform, signal demodulating techniques and a robust and fast phase-unwrapping algorithm, a 3D mapping of deformation can be visualized. The simplicity of the system and the fact that only readily available and unsophisticated equipment is required characterize the proposed method. The theoretical basis of the device is presented. Furthermore, experimental results made with a test object and a real ancient wooden panel painting are presented to demonstrate the validity of the technique.

Projection moiré: using tensor calculus for general geometries of optical setups

Abstract: The projection moire technique enables quantitative measurements of the shape of an opaque curved object surface in space. In contrast to the actual literature, where the interpretation of moire fringes is mostly limited to particular geometrical configurations, we present a strong mathematical tool that makes it possible to accurately analyze more general and complicated geometrical cases. We therefore introduce a mathematical model based on the calculation with projectors and use tensor calculus to deduce the general equations of projection moire. Emphasis is put on relative moire, which is used in most experiments, and on difference moire, which is generally used to calibrate optical systems. The concept of a sensitivity vector, which comes essentially from holographic interferometry, is also introduced. Using a computer-based image processing system, a numerical experimental verification of the obtained theoretical tensor equations is performed. Simultaneously, we describe how to calibrate an optical setup and gain evidence of a few nonlinear effects. This shows which parameters of the setup are of importance and should be carefully controlled. Moreover, we treat some well-known special cases to demonstrate the agreement with the existing literature.

Two-Frequency Moiré Topography

Abstract: Moire topography visualizes the contour lines of an object, but it requires the absolute order of the fringe to be analyzed, and cannot distinguish the concavity and convexity of a portion of an object showing closed moire fringes. The two-frequency moire topography technique proposed here readily gives the absolute order of a fringe, and gives oblique intersection lines which help in identifying the concavity and convexity of local curvature. The technique is especially suitable for collecting data on unknown shapes such as a deformed human body.

The Interrelations between Moiré Patterns, Contour Fringes, Optical Surfaces and Their Sum and Difference Effects

Abstract: A general relationship between potential functions and moire patterns can be realized in a number of forms. The potential function can be worked as an optical surface and combined with other potential functions similarly worked to give the solution to a complex potential problem. Contour fringes can be produced from the optical surfaces or generated on a computer graph plotter directly. When superimposed these contour lines generate moire fringes which are also solutions to potential function problems but with an essential ambiguity of sign. Two circularly symmetrical potential wells have been contoured and moire fringe solutions to simple problems are given.

High-resolution computer-aided moire

Abstract: This paper presents a high resolution computer assisted moire technique for the measurement of displacements and strains at the microscopic level. The detection of micro-displacements using a moire grid and the problem associated with the recovery of displacement field from the sampled values of the grid intensity are discussed. A two dimensional Fourier transform method for the extraction of displacements from the image of the moire grid is outlined. An example of application of the technique to the measurement of strains and stresses in the vicinity of the crack tip in a compact tension specimen is given.