Dielectric microwave resonators in TE011 cavities for electron paramagnetic resonance spectroscopy

Abstract

The coupled system of the microwave cylindrical TE 011 cavity and the TE 01␦ dielectric modes has been analyzed in order to determine the maximum achievable resonator efficiency parameter of a dielectric inserted into a cavity, and whether this value can exceed that of a dedicated TE 01␦ mode dielectric resonator. The frequency, Q value, and resonator efficiency parameter ⌳ for each mode of the coupled system were calculated as the size of the dielectric was varied. Other output parameters include the relative field magnitudes and phases. Two modes are found: one with fields in the dielectric parallel to the fields in the cavity center and the other with antiparallel fields. Results closely match those from a computer program that solves Maxwell's equations by finite element methods. Depending on the relative natural resonance frequencies of the cavity and dielectric, one mode has a higher Q value and correspondingly lower ⌳ than the other. The mode with the higher Q value is preferentially excited by a coupling iris or loop in or near the cavity wall. However, depending on the frequency separation between modes, either can be excited in this way. A relatively narrow optimum is found for the size of the insert that produces maximum signal for both modes simultaneously. It occurs when the self-resonance frequencies of the two resonators are nearly equal. The maximum signal is almost the same as that of the dedicated TE 01␦ mode dielectric resonator alone, ⌳ Х 40 G / W 1/2 at X-band for a KTaO 3 crystal. The cavity is analogous to the second stage of a two-stage coupler. In general, there is no electron paramagnetic resonance ͑EPR͒ signal benefit by use of a second stage. However, there is a benefit of convenience. A properly designed sample-mounted resonator inserted into a cavity can give EPR signals as large as what one would expect from the dielectric resonator alone.

Meta-metallic coils and resonators: Methods for high Q-value resonant geometries

“…This is consistent with the lowest frequency parallel mode described in a dielectriccavity coupled system. 22 We call the dielectric cylinder an "equalization" element for the meta-metallic SRS or FGL component. Because the rf magnetic fields of the dielectric and meta-metallic are in-phase, the rf magnetic fields from each element add constructively, which increases the inductance of both components and lowers the resonance frequency of the combined structure compared to each individually.…”

“…IV B are found to be needed to couple the foil to the dielectric TE 01δ mode. 22 The foil and dielectric are spaced apart by 0.5 mm and placed inside a conducting shield. The rf magnetic field profile is shown in Fig.…”

A dual-mode microwave resonator for double electron–electron spin resonance spectroscopy at W-band microwave frequencies

“…Dual-mode microwave resonators are already known in EPR spectroscopy [6,[16][17][18][19]. However, these resonators were adapted for X-band frequencies only (e.g.…”

“…The resonance configurations with the nearly collinear polarizations of the modes, which were presented in Refs. [18,19] using dielectric rings, cannot be used at high frequencies due to the miniature dimensions of the dielectric inserts. An application of a multimode Fabry-Pérot resonator in combination with a W-band high-power system was reported in Ref.…”

MRI surface-coil pair with strong inductive coupling

“…19 The real parts of the complex eigenfrequencies are different than these by order Q −2 , as for the second-order system. When the circuit is excited at resonance with a real frequency ω = ω 0 , which can be either of the resonance frequencies given by Eqs.…”