Development and characterization of ceramic inserts Used in metallic resonators of EPR spectrometers to increase their sensitivity - S. V. Lemishko; I. P. Vorona; I. S. Golovina; V. O. Yukhymchuk; S. M. Okulov; V. V. Nosenko; S. O. Solopan; A. G. Belous (Ukrainian journal of physics, 2021)