# Cost function of Fourier transform of the components of the magnetic induction field

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How can one construct a cost function, in Maxwell, that evaluates the Fourier transform of the components of the magnetic induction field (Bx, By) along a circular path? The model is magnetostatic.

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• Concord, MAPosts: 51Member

Hi @vmassana , you can create a polyline as the circular path first -> use field calculator to create two named expressions Bx and By -> add a field report of Bx ( or By) along the circular polyline -> do FFT of those two reports.

In field calculator, Input: Quantity->B

Vector: Scalar?->ScalarX

Repeat the same thing to create By

Create a field report-> select the circle in geometry ->add Bx from Calculator Expressions->New report

Right mouse click on Result->Perform FFT on report...

The Fourier transform plot of the components of the magnetic induction field (Bx) along a circular path, repeat the samiliar step for By.

• Many Thanks Deli, I already have the circular path created on of the model (quadrupole electromagnet), and I know how to evaluate the FFT on a report, the question that I ask is how to construct a cost function in the optimizer (sorry, I omitted this in my question) in order to optimize, for example, some component of the FFT on Bx/By: dipol component, quadrupole component, etc... The number of points over the circular path must be 32 or 64 or 128, ... then the cost function should be able to calculate the FFT on this fields and the goal would be to minimize or maximize some explicit component of the FFT. Some help houw to get it? many thanks in advance.

Valentí