calculating energy from FFT in different frequency bins

Question

Athira Surendran 2017-6-14

0
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https://ww2.mathworks.cn/matlabcentral/answers/344700-calculating-energy-from-fft-in-different-frequency-bins

回答： Michael Dombrowski 2017-6-29

amplitude_deflection.mat

Hi all,

I've generated FFTs for a set of signals in time domain at different deflections. I want to find in which frequency range the signal is more sensitive. Can someone help me do the following since I'm new to programming and signal processing??

Here's my problem:

So I want to select a frequency range in which all the dominant peaks are coming .

( In this case, by looking at the figure, the frequency range to be considered would be somewhere between 35000Hz-125000Hz (Is there a way to automatically find this ?) Also I don't know where to fix the threshold.)

Divide it into a number of bins (not more than 10) in such a way that each peak should fall completely within one of these bins. (bins need not be of equal length and should be same for all signals)
Then, calculate the energy for each bin in each signal.
Then plot curves for each bin showing the variation of energy in each bin with respect to deflection. (ie. deflection on x-axis and area under curve on y axis.)

Following is the code I'm using for getting FFT (also attached the set of time domain signals and deflection data):

[m, n]= size(amp); % amp- amplitude data
t=linspace(0,5000,n); % time
Fs=2000000;
for i=1:m
  L = n;
  NFFT = 2^nextpow2(L);
  UT = fft(amp(i,:),NFFT)/L;
  f = Fs/2*linspace(0,1,NFFT/2);
  ft(i,:) = zeros(1,NFFT/2);
  ft(i,:) = UT(1:NFFT/2);
  mag(i,:) = 2*abs(ft(i,:));
end;
figure
for i=1:m
  plot(f,mag(i,:))
  hold on;
end;
  xlabel('Frequency (Hz)','fontsize',12)
  ylabel('Magnitude','fontsize',12)
  title('Frequency Spectrum of recieved signals','fontsize',14)
  axis([0,150000,0,4])
  legend(arrayfun(@(deflection) ['Deflection = ',num2str(deflection),'\mum'],deflection,'Uni',0));
  set(gcf, 'Color', 'w');