# Using formulas in BEAMER Modules

## Motivation:

Variables are a convenient way of changing the parameter values in BEAMER modules. Variables can be entered as formulas which, in combination with LOOPS make BEAMER very powerful. As a demonstration we apply a formula to a TRANSFORM module within a LOOP to produce Fresnel Zone Plate structures.

## Solution:

A 1 µm circle is input to a flow comprising a Loop containing a Transform module, and finally a P-XOR module. In the Loop module, the number of rings for the Zone Plate structure is defined while the form as given by a standard Zone Plate formula is entered in the Transform module. This formulas is:

**2*(%index%*0.0139*300+0.0139*0.0139*%index%*%index%/4)^0.5**

and is applied as a scaling factor both in X and Y dimensions. Finally the P-XOR module is used to remove every second ring, thus creating the Zone Plate structure.

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