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How does a magnetic resonance spectrometer detect absorbed energy?

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magnetic resonance Figure 1: Precession of a magnetic dipole moment μ in the presence of a constant field H and a rotating field H′ (see text)

In a magnetic resonance spectrometer, the detection of absorbed energy relies on the principle of electromagnetic detection.1

The device operates by superimposing a weak oscillating field onto a strong, constant external magnetic field. As the frequency of this oscillating field is slowly varied, the spectrometer continuously measures and records the amount of energy extracted from the field by the sample.1

When the frequency of the oscillating field synchronizes with the Larmor frequency of the precessing particles—a state known as resonance—the particles transition to a higher energy state, absorbing energy from the field. This absorption is recorded as a peak on a spectrum, which appears as a line perpendicular to the baseline of the trace. By identifying these resonance frequencies, scientists can analyze the atomic and nuclear properties of the matter being studied.12