What is a Fourier Transform? A Fourier Transform is a function that changes a signal or waveform from the time domain into the frequency domain. One simple way to look at it is this: Suppose you are at the beach, watching the waves. You could say that a wave hits the shore at specific times (0 second, 2 seconds, 4 seconds, etc.) that would be describing the waveform in the time domain. If, however, you were to say that the waves hit the beach every two seconds, that would be describing it in the frequency domain. So a Fourier transform would take the data given in the time domain and convert that into the frequency domain. The function that does this is: .
The reverse is also possible. You can take the information from the frequency domain, and convert it into the time domain using an Inverse Fourier Transform.
From the Fourier Transform to the Inverse Fourier Transform
Lets start with the basic Fourier Transform:
Suppose that we have some function, say , that is nonperiodic and finite in duration.
This means that for some
Now let's make a periodic function by repeating with a fundamental period . Note that
The Fourier Series representation of is
can now be rewritten as
From our initial identity then, we can write as
Now remember that and
Which means that
Which is just to say that
So we have that
Some Useful Fourier Transform Pairs
Some other usefull pairs can be found here: Fourier Transforms
Another look at Fourier Transforms
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