Moiré Patterns

Walk past this glowing sculpture and watch as patterns move across the surface, forming pulsating spots through Moiré interference.

Explanation

The patterns on the sculpture are called moiré patterns (pronounced ‘mwar-ay’). These form whenever repeating patterns overlap but are not completely aligned.

The sculpture is made of two overlapping sheets of metal with small holes in them. The holes allow light to shine through, making a repetitive light and dark pattern.

Sometimes the dark areas on the top metal sheet line up so they are beside the dark areas on the lower metal sheet. This creates a larger dark spot. The light areas also match up to create the larger light spots.

As you move along, the top and bottom layers keep matching or unmatching to create the different patterns that you see.

You can find moiré patterns if you look for repeating patterns that are overlapped, but not perfectly. Try looking for them in the wrinkles on shade clothes and lace curtains.

You may also find moiré patterns on overlapping bird feathers—the main portion of the feather is made of small repeating barbs that form a pattern. Overlaying the feathers creates moiré patterns.

Extras for Experts

Moiré patterns highlight small differences in the alignment of two repeating patterns. This makes them useful for measuring whether objects really are aligned.

The moiré fringe method is used in strain measurements to find out how much objects deform under strain.

One of the moiré patterns is on the object that is to be tested for strain, while the other moiré pattern is placed across it. When the object is strained, its pattern is deformed slightly.

The small changes will cause moiré fringes (the banded areas of dark or light) to appear. This shows where the deformations take place.

Questions to Ask

Have you seen unusual patterns appearing whenever you look through a piece of wrinkled cloth? How about when you look through the front and back grills on an electric fan? Where else can you find interesting patterns?

Further Reading

• Moiré pattern
  http://en.wikipedia.org/wiki/Moiré
• Moiré deflectometry
  http://www.ph.ed.ac.uk/~rcd/Dougmoire.html
• Sirohi R S & Krishna H C R, 1993, Mechanical Measurements, New Age Publishers, p95

Moiré Patterns
Two overlapping sheets of metal move across one another to create patterns of interference.

Explore More

Multi-Mirror
What shapes can you make using a few rods and three mirrors? Try making a cube, a pointy pyramid or even a soccer ball.

See more exhibits...

Beauty & science in your world
Share amazing scientific phenomena
that you’ve seen.