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Hi all,
I'm designing an electro-optic device and want to calculate the overlap integral between the optical (waveguide) and the electric (electrode) fields.

I'm designing the 2D cross section. For that I'm using two physics: Electromagnetic waves (to calculate the Optical Field distribution) and Electrostatic (to calculate Electric field distribution).

I'm trying to calculate the overlap integral, namely : surf_int(E_opt^2*E_el dxdy)/surf_int(E_opt^2 dxdy).

What I've done, so far, to calculate this has been defining two surface integration: One for the numerator and one for denominator.
Model Builder->Derived Values-> Surface Integration-> Manually selected the domains-> defined the expression: ewfd.Ex*conj(ewfd.Ex)*es.Ex (numerator) ; ewfd.Ex*conj(ewfd.Ex) (denominator).

And separately calculate the Overlap as numerator/denominator.

I'm now trying to use the Model Couplings Integration.

In the Model Builder-> Definitions, I've defined 2 operators : intop1 and intop2 selecting the domains I want to calculate the integrals.

I've then defined a variable 1a entering in the table:
Onum: intop1(ewfd.Ex*conj(ewfd.Ex)*es.Ex)
Oden: intop2(ewfd.Ex*conj(ewfd.Ex))


When I try to evaluate in Global Evaluation Onum/Oden, I'm getting this error:

Failed to evaluate variable.
-Variable Onum
-Global scope:
Failed to evaluate expression.
-Expression: real((Onum/Oden))
Failed to evaluate expression.
-Expression: real(Onum/Oden)

Any clue? Is it related to units? I guess that the intop1 and 2 integrates over volumes. I do I integrate over surface then?

Thank you for any help.
Best,
Domenico