ABSTRACT
When two periodic patterns are superposed, a moiré pattern is formed. This is in fact a very common phenomenon. Moiré patterns are formed by periodic structures of lines or stripes. In general, the superposed patterns should have opaque and transparent regions. Although moiré patterns can be observed with superposition of periodic objects of nearly the same periodicity, the most commonly used objects are linear gratings with equal opaque and transparent regions, often called Ronchi gratings. Sometimes, circular gratings with equal opaque and transparent regions are used. The moiré phenomenon is a mechanical effect, and the formation of moiré fringes is best explained by mechanical superposition of the gratings. However, when the period of these periodic structures is very fine, diffraction effects play a very significant role.
