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‘);