Travelling-wave nuclear magnetic resonance

Nuclear magnetic resonance(1,2) (NMR) is one of the most versatile experimental methods in chemistry, physics and biology(3), providing insight into the structure and dynamics of matter at the molecular scale. Its imaging variant - magnetic resonance imaging(4,5) (MRI) - is widely used to examine the anatomy, physiology and metabolism of the human body. NMRsignal detection is traditionally based on Faraday induction(6) in one or multiple radio- frequency resonators(7-10) that are brought into close proximity with the sample. Alternative principles involving structured-material flux guides(11), superconducting quantum interference devices(12), atomic magnetometers(13), Hall probes(14) or magnetoresistive elements(15) have been explored. However, a common feature of all NMR implementations until now is that they rely on close coupling between the detector and the object under investigation. Here we show that NMR can also be excited and detected by long-range interaction, relying on travelling radio- frequency waves sent and received by an antenna. One benefit of this approach is more uniform coverage of samples that are larger than the wavelength of the NMR signal - an important current issue in MRI of humans at very high magnetic fields. By allowing a significant distance between the probe and the sample, travelling- wave interaction also introduces new possibilities in the design of NMR experiments and systems.