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 Computer memory Time domain 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

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

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

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= Value between +1 & 0 f c cos(2πνt) + f s sin (2πνt) with f c 2 +f s 2 =1