Calculate energy from FFT

Hi all,

I've generated FFTs for a set of signals at different deflections. I want to calculate total energy for some frequency ranges.

• So first I want to select the frequency ranges in which the dominant peaks of FFT are coming (each peak in each frequency range).
• Then calculate total energy in these frequency ranges.

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');