7. Moiré II - Geometric moiré (out-of-plane) Flashcards
Moiré II - Geometric moiré (out-of-plane)
What is out-of plane moiré used for?
mapping slopes, contours and out-of plane displacement
What are the 3 main techniques of out-of plane moiré?
- shadow moiré
- reflection moiré
- projection moiré
Shadow moiré
What is this technique – describe in 3 stages:
- Superimposition of master grating and its own shadow
- Master grating illuminated by collimated beam
- Gives resulting fringes
What do the resulting fringes of shadow moiré tell you?
- Contours of out-of-plane elevation
- Contour maps of object
- Out-of plane displacement
Draw a quick sketch of shadow moiré
What does ‘w’ represent?
What does ‘δ’ represent?
w = out of plane displacement
δ = apparent shift
When do you get one fringe cycle ?
when m shadow lines are spread over m+1 grating lines
Projection Moiré
This is a similar principle to shadow moiré
Reference grating is projected onto specimen
What are 2 Advantages ?
small reference grating
initially curved objects using one double exposure
Projection Moiré
What are do the resulting fringes give ? (3 things)
out-of-plane displacement
change in shape
difference in shape of two objects
Projection Moiré
Draw a quick sketch of projection moiré with Surface 1 , Surface 2, axial displacement w and point of iinterest P
How do you get the interference pattern
superimpose of the two images with different grating positions,
when superimposed, the surface is moving relative the the grating
Projection Moiré
Point … undergoes …….. movement ,.., and moves across the grating by:
….. = wsin….
As before , N=δ /p
the simple equation is equal to w= … …. /sin..
P, axial , w
δ = wsinα
w= Np/sinα
Projection Moiré for shape change
draw a quick sketch of projection moiré
Projection Moiré for topography
Draw a quick sketch of projection moiré for topography
what is one advantageof this method?
removes need for double exposure by using reference grating in camera
