Update: The version described below will not be released and is no longer available, but the mentioned features may enter the new CompassMR implementation that works on much more devices than the original version (try it! It does not rely on Java).

Old info: The educational applet above was made for introducing Compass Magnetic Resonance relevant for NMR and MRI (requires Oracle Java browser plug-in). It is a prototype of a new version of the Java Compass with an added focus on the effects of interaction between magnetic dipoles during magnetic resonance experiments. In this new implementation by Daniel Mark Gittings, a talented British student, the oscillating B1-field currently affects both needles equally, whereas the added finger can be used to push the left optional dipole. We want to develop the software a bit further before it replaces the current official release. Stay tuned.

The relevance to nuclear J-coupling is described in slide 33 in an MMCE presentation on the foundations of NMR. Please note, however, that J-coupling is not a dipolar coupling: In the simulation, dipolar coupling is introduced as an example of interactions between two oscillators. Nuclear J-coupling between neighboring nuclei is another example, but it is mediated by electrons and is not a direct dipolar interaction. The effect of sufficiently weak/strong couplings is energy shifts of oscillation eigenmodes in both cases, and corresponding peak-splitting in spectra.

The following math goes into the simulation: Bloch equations modified to acount for the needles not having intrinsic angular momentum, and dipole-dipole interactions. The math of classical coupled harmonic oscillators is here.