1. PULSED NMRAcquire F.I.D. Free Induction Decay NMR detection soon after a strong pulse: precessing nuclear magnetization induces a signal in coil when it is free of the perturbing EM radiation F.I.D. DIGITIZE Analogue to Digital Converter A.D.C. AddressContents 1 0000 15 1111 2 0001 14 1110 3 0010 13 1101 4 0011 11 1011 5 0100 8 1000 6 0101 4 0100 7 0110 1 0001 8 0111 0 0000 --------- Computer memory Time domain 15 0 11 FFT from FID Computer input Frequency Domain Spectrum Computer output This one- dimensional FT NMR spectrum is the same information as the C.W. NMR spectrum Acquisition is automatically in the digitized form Next Slide

2. dimension A(50),B(50),Y(50),X(50) K=32 open (unit=1, file="output") Print 10,K DO 11 N=1,K X(N)=(N-1)*3.5/K X(N)=EXP(-1.0*X(N)) Y(N)=X(N)*(COS(2*3.14*(N-1)*10.0/K)+ 1 COS(2*3.14*(N-1)*4.0/K)) 11 write (1,20) N,Y(N) DO 12 M=1,K A(M)=0 B(M)=0 DO 13 N=1,K-1 A(M)=A(M)+Y(N)*COS(2*3.14*(M-1)*(N-1)/K) 13 B(M)=B(M)+Y(N)*SIN(2*3.14*(M-1)*(N-1)/K) A(M)=A(M)/K B(M)=B(M)/K M2=M/2 12 write (1,30) M2,A(M2),B(M2) 10 FORMAT(1x,I2) 20 FORMAT(1x,I2,2x,F10.5) 30 FORMAT(1x,I2,2x,F10.5,2x,F10.5) close (unit=1) STOP END A program in Fortran for “Fast Fourier Transform” Digitized FID Signal Digital Computer ----------------------- ----------------------- ----------------------- - ---------------------- ------------ - FFT Program run OUTPUT

3. Time domain FID data: 32 points Real Imaginary 16 data 16data points points Frequency domain spectrum

4. COS Real Imaginary F.T Real Imaginary F.T SIN RealImaginary F.T Arbitrary Phase Provision is made in the data processing system, for routinely applying phase corrections t=0 +1 0 Value between +1 & 0 f c cos(2πνt) + f s sin (2πνt) with f c 2 +f s 2 =1