An electron paramagnetic resonance (=EPR) spectrometer, with: - a magnet system, comprising at least one magnet and at least one pole piece, preferably a pair of pole pieces (8a, 8b), for producing a magnetic field in a field of view in front of the at least one pole piece or between the pole pieces (8a, 8b), wherein said magnetic field is generated along a pole axis, and wherein the pole piece or the pole pieces (8a, 8b) are end parts of the magnet system, - a probe head, comprising a microwave resonator and at least one modulation coil (11a, 11b) or rapid scan coil for producing an additional, time-varying magnetic field aligned along the pole axis, wherein the probe head is arranged in the field of view, and wherein a respective modulation coil (11a, 11b) or rapid scan coil is arranged between the microwave resonator and a respective pole piece (8a, 8b); wherein the EPR spectrometer is configured to generate with the at least one modulation coil (11a, 11b) or rapid scan coil said additional, time varying magnetic field with a frequency between 5 kHz and 200 kHz in an EPR measurement, characterized in that for each pole piece (8a, 8b) having a modulation coil (11a, 11b) or rapid scan coil arranged between said pole piece (8a, 8b) and the microwave resonator, at least a part (15a, 15b) of said pole piece (8a, 8b) facing said modulation coil (11a, 11b) or rapid scan coil is made of a function material having an electric conductivity σ f of 10 4 S/m or less, and having a saturation magnetic flux density BS f of 0.2 T or more, and that for a distance DPC along the pole axis between a respective pole piece (8a, 8b) and a modulation coil (11a, 11b) or rapid scan coil it faces, the following applies: 0 ≤ DPC ≤ 2.0 mm. - a magnet system, comprising at least one magnet and at least one pole piece, preferably a pair of pole pieces (8a, 8b), for producing a magnetic field in a field of view in front of the at least one pole piece or between the pole pieces (8a, 8b), wherein said magnetic field is generated along a pole axis, and wherein the pole piece or the pole pieces (8a, 8b) are end parts of the magnet system, wherein said magnetic field is generated along a pole axis, and wherein the pole piece or the pole pieces (8a, 8b) are end parts of the magnet system, - a probe head, comprising a microwave resonator and at least one modulation coil (11a, 11b) or rapid scan coil for producing an additional, time-varying magnetic field aligned along the pole axis, wherein the probe head is arranged in the field of view, and wherein a respective modulation coil (11a, 11b) or rapid scan coil is arranged between the microwave resonator and a respective pole piece (8a, 8b); wherein the probe head is arranged in the field of view, and wherein a respective modulation coil (11a, 11b) or rapid scan coil is arranged between the microwave resonator and a respective pole piece (8a, 8b); wherein the EPR spectrometer is configured to generate with the at least one modulation coil (11a, 11b) or rapid scan coil said additional, time varying magnetic field with a frequency between 5 kHz and 200 kHz in an EPR measurement, characterized in that for each pole piece (8a, 8b) having a modulation coil (11a, 11b) or rapid scan coil arranged between said pole piece (8a, 8b) and the microwave resonator, at least a part (15a, 15b) of said pole piece (8a, 8b) facing said modulation coil (11a, 11b) or rapid scan coil is made of a function material having an electric conductivity σ f of 10 4 S/m or less, and having a saturation magnetic flux density BS f of 0.2 T or more, and that for a distance DPC along the pole axis between a respective pole piece (8a, 8b) and a modulation coil (11a, 11b) or rapid scan coil it faces, the following applies: 0 ≤ DPC ≤ 2.0 mm.