Over-moded resonant cavity for magnetic resonance based on a photonic band gap stucture

The present invention relates to a probe for multiple irradiation magnetic resonance techniques like, for instance, dynamic nuclear polarization (DNP) or ENDOR. The probe comprises an overmoded resonant cavity based on a Photonic Band Gap (PBG) structure for the excitation and/or detection of electron paramagnetic resonance in the millimeter or sub-millimeter wave region and an NMR coil for the excitation and/or detection of nuclear magnetic resonance at RF frequencies. The sample, the sample holder and the NMR coil may form part of the PBG resonant structure, possibly contributing to the defects that give rise to the trapping of electromagnetic modes with millimeter or sub-millimeter wavelengths.