Spin Resonance Demonstrator

Case Study


An apparatus demonstrating nuclear-magnetic resonance was required for the educational market. Here, cost is a dominanting factor, with the target being schools and universities at undergraduate level. It was to be used alongside an electron spin-resonance demonstrator that was already in development. Commonality of modules was hoped to help the cost issue.


Nuclear-magnetic resonance (also known magnetic or proton resonance) occurs in a sample in a magnetic field when it is excited with rf energy. Typically, the magnetic field is strong and very homogenous, whilst the rf energy has a defined frequency. The rf energy can flip the spin-state of the (say) hydrogen nuclei, which will then naturally relax back to normal at a later time.

For a given sample, the ratio of frequency to field strength is a very precise value. By slightly shifting either the field or the frequency, the condition at which energy absorption occurs can be controlled.


A literature review and supporting calculations indicated that a possible approach was to utilise a strong permanent magnet and a relatively simple detection system. By applying about 1% modulation of the magnetic field, continuous-wave rf energy at a certain frequency, the point of proton resonance would be “scanned” through. At this point, a small amount of energy is absorbed by the sample as the spins flip. Using a marginal oscillator to generate the rf energy, the depletion of the energy field would result in a drop in the oscillator’s output level. If the output level was being displayed on an oscilloscope, any “dip” in level would be indicatory of nuclear-spin resonance in the sample. With measurement of the magnetic field strength and rf frequency at the point of resonance, their ratio would verify the physical phenomenon.

Key to the project’s success was achieving a homogenous magnetic field, and oscillator stability. The sharpness of resonance is heavily dependent on homogeneity; at very low cost, quality factors (Q) of over 1000 were obtained.


The system has been on sale for several years.