2. Experimental Detection of the Magnetic Resonance signal requires setting up a non-equilibrium state What is the thermal equilibrium available to start with? The spin system, the ensemble, has a time independent Net Magnetization along the z-direction (the direction of the magnetic field) Z X Y Magnetic field Non-equilibrium Tilt the magnetization away from the z-direction Detect the xy component

3. CW RF Oscillator mw power RF Crystal Detector Display/Record Pulsed RF Transmitter Probe with sample coil and sample in Magnetic Field High gain RF receiver/detector Time domain signal to computer for FFT Display monitor/Plotter Signal generation Signal receiving and detection CW Mode of detection Pulsed Mode of Detection

4. Oscillator Oscillation Level Detector Current Source Oscillation Level at fixed frequency ‘ν’ When No ESR Oscillation Level reduced when there is ESR absorption Detected DC Level No ESR Reduced DC On ESR Absorption hν=gβH No oscillations 0 1 2 If the Current is increased from 0 to beyond resonance field, then, the field [ H t ] increases with time and causes resonance at resonance field value 2 1 hν=gβ H The role of a phase Φ shifter in the diagram would be explained in the succeeding slides CLICK to transit to next slide Φ Shifter HtHt

5. Z - Magnetization along the Field RF Pulse : π/2 pulse to flips the magnetization into xy plane Defocusing and signal decay Output from receiver coil - FID XY - Magnetization induces RF signal in the receiver coil CW Oscillator GATE DC Pulse generator Probe In Magnet RF Pulse Receiver- detector Display Monitor Recorder Z X Y