FFT of a damping signal

Hello, I have got a damping time dependent signal(attached data) and I wish to get the FFT of the signal. Unfortunately right now I am not able to get the peak frequency. Can someone help me in finding the FFT please.

[dpb]

What have you tried?

[DebiPrasad]

if true
  % code
end
f = (1./tvec);
nfft=length(y);
nfft2=2^nextpow2(nfft);
ff=fft(y,nfft2);
Mx_fft=ff(1:nfft2/2);
xfft=(length(f))*(0:nfft2/2-1)/nfft2;
%fff=ff(1:nfft2/2);
%Mxfft=(1./tvec)'*(0:nfft2/2-1)/nfft2;
figure(4)
plot(xfft,abs(Mx_fft))

        f = (1./tvec);
nfft=length(Mx);
 nfft2=2^nextpow2(nfft);

ff=fft(Mx,nfft2); Mx_fft=ff(1:nfft2/2); xfft=(length(f))*(0:nfft2/2-1)/nfft2; %fff=ff(1:nfft2/2); %Mxfft=(1./tvec)'*(0:nfft2/2-1)/nfft2; figure(4) plot(xfft,abs(Mx_fft))

Answer 1

[Star Strider]

Try this:

D = load('FFT.txt');
t = D(:,1);
s = D(:,2);

Ts = mean(diff(t));                                                 % Sampling Time
Fs = 1/Ts;                                                          % Sampling Frequency
Fn = Fs/2;                                                          % Nyquist Frequency
L = length(t);
FTs = fft(s)/L;
Fv = linspace(0, 1, fix(L/2)+1)*Fn;                                 % Frequency Vector
Iv = 1:length(Fv);                                                  % Index Vector

[pks,locs] = findpeaks(abs(FTs(Iv))*2, 'MinPeakHeight',1E-3);

figure(1)
loglog(Fv, abs(FTs(Iv))*2)
hold on
plot(Fv(locs), pks, '^r')
grid
text(Fv(locs)*1.1, pks, sprintf('\\leftarrow Peak = %.5f at %.3E Hz', pks, Fv(locs)), 'HorizontalAlignment','left')

[DebiPrasad]

Thanks Star Strider. It is helpful

[Star Strider]

My pleasure.

[DebiPrasad]

Hello Star Strider, Cheers for the answer. Just had a follow up question to it, do you know how can I find the peak location from the FFT output?

[Star Strider]

Thank you.

In the frequency domain, this line will do it:

[pks,locs] = findpeaks(abs(FTs(Iv))*2, 'MinPeakHeight',1E-3);

The ‘locs’ variable has the index of the peaks. To get the frequency:

PeakFreq = Fv(locs);

I just now re-ran that code, and the text call will tell you exactly how to do it:

text(Fv(locs)*1.1, pks, sprintf('\\leftarrow Peak = %.5f at %.3E Hz', pks, Fv(locs)), 'HorizontalAlignment','left')

If you want to find the peaks in the time domain, this works:

[TimePeaks, Times] = findpeaks(s, t);

figure(2)
plot(t, s)
hold on
plot(Times, TimePeaks, '^r', 'MarkerFaceColor','r')
hold off
grid

[DebiPrasad]

Thanks very much. Star Strider. This is very helpful

[Star Strider]

As always, my pleasure.