My structure is periodic and I designed its unit cell in COMSOL. I used Electromagnetic waves,Frequency domain physics and Frequency domain study and swept on different frequencies. I want to integrate product of z-component of E field in two frequency f1,f2 (e.g. emw.Ez(@f1)*emw.Ez(@f2)) on the volume of unit cell.
I used "Volume Integration" in "Derived Values" of "Results", but this part perfoms integration for frequency as separable, not combination of frequencies.