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Exploring the Rotating Reference Frame in Off-Resonance Pulsed NMR
written by David B. Pengra
Understanding the physics of pulsed nuclear magnetic resonance (NMR) is eased by a transformation to a rotating reference frame. Within such a frame, coincident with the applied RF H1 field that rotates about the static H0 field, the net effective magnetic field is static, and the dynamics of spin precession yield to simple geometric analysis. In most treatments of NMR the resonant frame, defined by the Larmor frequency ω0 = γH0, is used. In this frame the effective field reduces to H1 only, and one can immediately derive the pulse widths needed to optimize the free induction decay (FID) signals--the so-called π/2 and 3π/2 pulses. But what happens in a frame that is off resonance? The same geometrical analysis shows that as the frequency of H1 is detuned from resonance, (1) the pulse width needed to maximize the FID signal increases for "π/2" pulses and decreases for "3π/2" pulses, (2) at a critical value of detuning, the widths of both pulses converge to p2 times the width of the on-resonance π/2 pulse, (3) this critical detuning is equal to the Larmor frequency of H1, and (4) the maximum amplitude the FID signal is unchanged as long as the detuning is less than the critical value. Detuning further causes the optimum pulse width to decrease and the magnitude of the FID signal to drop. This experiment helps students explore a wider range of predictions inherent in the classical model of NMR, and it can be performed on the popular TeachSpin PS1 apparatus with no extra equipment.
2015 Conference on Laboratory Instruction Beyond the First Year of College
Part of the BFY Conference series
College Park, MD: July 22-24, 2015
Pages 80-83
Subjects Levels Resource Types
Education Practices
- Curriculum Development
= Laboratory
Modern Physics
- Nuclear Physics
= NMR
Quantum Physics
- Quantum Experiments
- Spin and Finite Dimensional Systems
- Upper Undergraduate
- Instructional Material
= Laboratory
- Reference Material
= Article
Material Category Formats Ratings
- Articles and Supplements
- application/pdf
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Format:
application/pdf
Mirror:
http://dx.doi.org/10.1119/bfy.201…
Access Rights:
Free access
License:
This material is released under a Creative Commons Attribution 3.0 license. Further distribution of this work must maintain attribution to the published article's author(s), title, proceedings citation, and DOI.
Rights Holder:
American Association of Physics Teachers
DOI:
10.1119/bfy.2015.pr.020
PACS:
76.60.-k
Keywords:
BFY 2015, Free induction decay, Off-resonance NMR, Pulsed NMR
Record Cloner:
Metadata instance created November 17, 2015 by Lyle Barbato
Record Updated:
November 19, 2015 by Bruce Mason
Last Update
when Cataloged:
November 17, 2015
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Record Link
AIP Format
D. Pengra, presented at the 2015 Conference on Laboratory Instruction Beyond the First Year of College, College Park, MD, 2015, WWW Document, (http://www.compadre.org/Repository/document/ServeFile.cfm?ID=13812&DocID=4233).
AJP/PRST-PER
D. Pengra, Exploring the Rotating Reference Frame in Off-Resonance Pulsed NMR, presented at the 2015 Conference on Laboratory Instruction Beyond the First Year of College, College Park, MD, 2015, <http://www.compadre.org/Repository/document/ServeFile.cfm?ID=13812&DocID=4233>.
APA Format
Pengra, D. (2015, July 22-24). Exploring the Rotating Reference Frame in Off-Resonance Pulsed NMR. Paper presented at 2015 Conference on Laboratory Instruction Beyond the First Year of College, College Park, MD. Retrieved May 29, 2017, from http://www.compadre.org/Repository/document/ServeFile.cfm?ID=13812&DocID=4233
Chicago Format
Pengra, David B.. "Exploring the Rotating Reference Frame in Off-Resonance Pulsed NMR." Paper presented at the 2015 Conference on Laboratory Instruction Beyond the First Year of College, College Park, MD, July 22-24, 2015. http://www.compadre.org/Repository/document/ServeFile.cfm?ID=13812&DocID=4233 (accessed 29 May 2017).
MLA Format
Pengra, David B.. "Exploring the Rotating Reference Frame in Off-Resonance Pulsed NMR." 2015 Conference on Laboratory Instruction Beyond the First Year of College. College Park, MD: 2015. 80-83 of BFY Conference. 29 May 2017 <http://www.compadre.org/Repository/document/ServeFile.cfm?ID=13812&DocID=4233>.
BibTeX Export Format
@inproceedings{ Author = "David B. Pengra", Title = {Exploring the Rotating Reference Frame in Off-Resonance Pulsed NMR}, BookTitle = {2015 Conference on Laboratory Instruction Beyond the First Year of College}, Pages = {80-83}, Address = {College Park, MD}, Series = {BFY Conference}, Month = {July 22-24}, Year = {2015} }
Refer Export Format

%A David B. Pengra
%T Exploring the Rotating Reference Frame in Off-Resonance Pulsed NMR
%S BFY Conference
%D July 22-24 2015
%P 80-83
%C College Park, MD
%U http://www.compadre.org/Repository/document/ServeFile.cfm?ID=13812&DocID=4233
%O 2015 Conference on Laboratory Instruction Beyond the First Year of College
%O July 22-24
%O application/pdf

EndNote Export Format

%0 Conference Proceedings
%A Pengra, David B.
%D July 22-24 2015
%T Exploring the Rotating Reference Frame in Off-Resonance Pulsed NMR
%B 2015 Conference on Laboratory Instruction Beyond the First Year of College
%C College Park, MD
%P 80-83
%S BFY Conference
%8 July 22-24
%U http://www.compadre.org/Repository/document/ServeFile.cfm?ID=13812&DocID=4233


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