Magnetic Resonance (MR) is a form of radio frequency (RF) spectroscopy that can be used for quantitative measurement of target elements in crystalline compounds. In the MR technique, the “resonance”, or response, at a particular radio frequency for the element is highly discriminating for that compound, as it is extremely rare for one resonance to overlap another.

Pulses of radio frequency fields are applied using non-contact sensors where the frequency of the field is set to a particular compound’s resonance. The process of excitation and detection is typically completed in milliseconds. However, it is usual to average a number of individual measurements such that the detected signal (“echo”) has an improved signal to noise ratio. The magnitude of the echo is proportional to the number of crystalline unit cells of the target mineral.

In the detection of explosives and drugs, MR measurements are usually detecting the presence of elements such as N, K and Cl where the resonance frequency is highly specific to the particular drug or explosive being targeted.