New ceramic EPR resonators with high dielectric permittivity

Dielectric Ceramic EPR Resonators for Low Temperature Spectroscopy at X-band Frequencies

“…Some DRs were coupled via antennae [9] while others have integrated them into cavity resonators, such as Mattar and Emwas [10] who report signal-to-noise ratio (SNR) gains of stacked DRs of 24 and Jaworski et al [1] with SNR gains of more than 30 at room temperature depending on the sample. DR materials that support low temperature measurements were reported to give SNR gains of up to 170 at 77 K in the work of Golovina et al [11]. Also, ferroelectric materials were proposed due to their high permittivities with SNR enhancements up to 100 [12,13].…”

“…Higher frequencies yield lower signal enhancements, while the lower frequencies are the preferred ones with even higher SNR gains. The low frequency parallel mode was experimentally excited for DRs with lower e r % 35 [11] whereas the high frequency antiparallel mode is reported to be the dominating one for DRs with higher e r . Mett et al [19] state that with an iris coupling of electrically coupled cavity-DR systems only one of such modes can be excited at the same time and the coupled resonance frequencies with f antiparallel [ f empty cav: [ f parallel never cross.…”

“…Furthermore, it features substantial temperature dependencies of the stability of e r ; s e and of tan d between 6 and 300 K [15]. A discussion of the DR materials sapphire and rutile as well as perovskite-based ceramics is presented in the work of Golovina et al [11], where the authors express the need of high dielectric permittivity materials for low cost employability of DRs in existing cryogenic systems. Our goal was to show that DRs provide an easy-to-use setup for commercial spectrometers, where the DR is placed in a typical EPR sample tube together with the studied sample as shown in Fig.…”

“…To obtain this mode a certain geometry and proper values of e r and tan d of the DR material at the given temperature are needed. The dielectric properties need to have a sufficiently low temperature dependence to ensure usage in the temperature range 6 K T 300 K. The frequency f free that is usually considered as optimal when employed in cavity resonating systems is close to the frequency of that very metal cavity resonator [11]. In the work of D. Kajfez [17] an approximate equation of the frequency of the TE 01d -mode is given as…”

“…Here, a thin capillary (ø = 200 lm) is positioned with grease inside the hole of K80 (ø = 1 mm). c Superposition of TE 01d -mode of a DR (thin, red) and TE 102 mode of the cavity resonator (dashed, blue) in the notation of [16] (color online) simulations and CMT of DRs coupled to cavity resonators found the TE 01d mode being able to couple in a parallel (symmetric, in phase) and antiparallel (antisymmetric, out of phase) configuration with respect to the TE 102 or TM 110 modes of the rectangular or cylindrical cavities, respectively [7,11,[19][20][21]. The parallel field superposition results in lower resonance frequencies and the antiparallel fields shows the opposite behavior with higher coupled microwave (mw) resonance frequencies.…”