A simple version of a nuclear magnetic resonance (NMR) spectrometer consists of the following:
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- A strong magnet to provide a uniform magnetic field B (e.g. 2.35 T) to split the energy levels of nuclides in a sample.
- The sample in a glass tube that is rotated to allow uniform exposure to B.
- A coil (blue lines) connected to a radiofrequency transmitter with a varying AC voltage. The AC voltage is gradually increased during the experiment to generate electromagnetic waves of increasing frequencies.
- A coil wound round the sample tube and connected to a radiofrequency detector. The flipping of nuclear spins, when nuclides are excited at the appropriate electromagnetic frequencies, results in a change in magnetic dipole moment of the nuclides. This change in magnetic dipole moment induces a current in this coil, which is recorded and analysed by a computer.
Such an NMR spectrometer design, where the external magnetic field strength B is fixed while the electromagnetic radiation frequency v is varied, is called a continuous wave NMR (CW-NMR). An alternate design of a CW-NMR has a varying B and a constant v. In this design, a varying-AC coil is wound round the magnet, while a second coil with a fixed AC voltage is wrapped round the sample tube. Measurements are made for the changes in impedance (resistance of an AC circuit) of the second coil when nuclear spin transitions occur. Finally, a more sophisticated NMR spectrometer design exposes the sample to a short and intense burst of radiofrequency radiation called an electromagnetic pulse, and subsequently analyses the data using the mathematical concept of Fourier transform.