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 , for producing a magnetic field in a field of view in front of the at least one pole piece or between the pole pieces , wherein said magnetic field is generated along a pole axis (PA), and wherein the pole piece or the pole pieces are end parts of the magnet system , - a probe head , comprising a microwave resonator and at least one modulation coil or rapid scan coil for producing an additional, time-varying magnetic field aligned along the pole axis (PA), wherein the probe head is arranged in the field of view , and wherein a respective modulation coil or rapid scan coil is arranged between the microwave resonator and a respective pole piece ; wherein the EPR spectrometer is configured to generate with the at least one modulation coil 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 having a modulation coil or rapid scan coil arranged between said pole piece and the microwave resonator , at least a part of said pole piece facing said modulation coil 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 (PA) between a respective pole piece and a modulation coil 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 , for producing a magnetic field in a field of view in front of the at least one pole piece or between the pole pieces , wherein said magnetic field is generated along a pole axis (PA), and wherein the pole piece or the pole pieces are end parts of the magnet system , wherein said magnetic field is generated along a pole axis (PA), and wherein the pole piece or the pole pieces are end parts of the magnet system , - a probe head , comprising a microwave resonator and at least one modulation coil or rapid scan coil for producing an additional, time-varying magnetic field aligned along the pole axis (PA), wherein the probe head is arranged in the field of view , and wherein a respective modulation coil or rapid scan coil is arranged between the microwave resonator and a respective pole piece ; wherein the probe head is arranged in the field of view , and wherein a respective modulation coil or rapid scan coil is arranged between the microwave resonator and a respective pole piece ; wherein the EPR spectrometer is configured to generate with the at least one modulation coil 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 having a modulation coil or rapid scan coil arranged between said pole piece and the microwave resonator , at least a part of said pole piece facing said modulation coil 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 (PA) between a respective pole piece and a modulation coil or rapid scan coil it faces, the following applies: 0 ≤ DPC ≤ 2.0 mm. <EOS>