Fourier transform of logistics (sigmoid) curves in Matlab

I have different shape of sigmoid curves that I can give you all the raw data, and I would like to look into more details if there is any tendency by converting them with Fourier transform. Having the frequency domain with the curves, we can find/detect the peaks (first, second, to at least third or fourth) to compare each curve whether there is some behavior between the curves. The details are attached. Thanks.