How can I convert deformation data into FRF using FFT?

I have deformation data. (unit: mm) (Time domain)

Then, I want to obtain FRF data using FFT.

As follow.

How can I convert deformation data into FRF using FFT?

Answer 1

[Bjorn Gustavsson]

Simply use fft? That will give you the complex discrete Fourier-transform. If you do:

fS = fft(S); % fS will have "DC"-component in the first element
semilogy(2*abs(fS(1:end/2)))

You'll have to determine the frequencies and whether you want abs(fS) or abs(fS).^2.

HTH