free induction decay fourier transform

 1 % A script for display the process of Fourier Transform of FID

 2 % FID stands for Free Induction Decay,which is a signal over time domain.We

 3 % can get the signal over frequency through fourier transform.And FID is

 4 % one of the most important signal form

 5 %function s=s(t,M,T,w)

 6 %s=M*exp(-t/T).*cos(w*t);

 7 %M=10;

 8 %T=1;

 9 %w=200*pi;

10 T=1;

11 N=128;

12 t=linspace(0,T,N);

13 %s=s(t,M,T,w);

14 s=10*exp(-t).*cos(200*pi*t);

15 subplot(2,1,1);

16 plot(t,s);

17 xlabel('t');

18 ylabel('signal intensity');

19 title('FID signal in time domain');

20 dt=t(2)-t(1);

21 f=1/dt;

22 f=f*(0:N-1)/N;

23 S=fft(s);

24 subplot(2,1,2);

25 plot(f,abs(S));

26 xlabel('Frequency');

27 ylabel('Amplitude |S(k)|')

28 title('FID over frequency domain through Fourier Transform');