Transcript ppt - University Of Oregon

Sarah Newton
University of Oregon
Applied Physics
Background

 Many applications in Chemistry and Medicine
 1940's- First Signs of NMR
 Bloch, Purcell, and others noticed the H nuclei had
magnetic properties. It could absorb RF energy when
placed in a field of a strength specific to the identity of the
nuclei.
 When absorption occurs, the nucleus is described as being
in resonance.
Objectives

 Simulate different circuits to give the best resonance
 Develop a detector
Built within constraints: Resonance no higher than 13MHz.
 See CW
 See Pulsed
 Compare and analyze their similarities and differences
Connection to Optics

 NMR and Optical Pumping have the same basic concept
 Optical Pumping
It is a two level system that electronically excites the
constituents of a medium into another energy state. i.e. Laser
What is NMR?

 Type of Spectroscopy that manipulated the magnetic
properties of nuclei within a sample
 That manipulation leads to finding the chemical
properties and environment contained within the
sample.
CW/Pulsed NMR

 CW(Continuous Wave) NMR
 Experiments have a varying frequency of radiation at
constant magnetic field and measuring the absorption of
radiation by the different nuclei.
 Pulsed(Fourier Transform) NMR
 Resonances are not measured one after another but all
nuclei are excited at the same time by a radio frequency
pulse.
 Excited spins emit the absorbed radiation after the pulse.
Intensities of several frequencies are calculated and framed
into spectrum.
Circuit Sim

Sims Graph

Circuit

Methodology

 Magnet is powered up
 Sample lowered into quartz vial (connected to the
circuit.)
 RF gain(from radio receiver) increased to max
 Capacitor dials on bridge circuit turned to minimize
RF gain
 Amps of DC power supply adjusted until a signal
becomes visible on the oscilloscope.
 The small function generator provides a “wobble” on
the coils while the older generator is the driving unit
Intrumentation

Results

(What Should have happened)
 In the CW
-fixed frequency and varying current
-Able to observe the resonant signal (“wiggle”)
individual frequencies in succession
 In pulsed
-A short pulse containing a range of frequencies
-All nuclei spins are excited( with a range of
frequencies)
-Induces a current creating an electrical signal response
at
Conclusion/Summary

 Success!!!
Circuit works and is fully functional
But..
Due to the strange disappearance and reappearance of
resonance at different frequencies we will go back to
the drawing board.
Future Work

 Simulations
 Build a better circuit
 Run both CW and Pulse NMR
Acknowledgements

 Material Science Institute
 Stephen Gregory and Brian Boggs