[i‚lek,trän i¦lek‚tran ‚dəb·əl ′rez·ən·əns] (spectroscopy) A type of electron paramagnetic resonance (EPR) spectroscopy in which a material is irradiated at two different microwave frequencies, and the changes in the EPR spectrum resulting from sweeping either the second frequency or the magnetic field are monitored through detection at the first frequency. Abbreviated ELDOR.