A multilayered element resonator for CW-ESR and longitudinally detected ESR at radio frequency

Abstract

The design and evaluation of a multilayered element resonator (MLR), which consists of multiple layers of half-loop conductor plates and insulator sheets, are presented. An MLR and a bridge shielded loop-gap resonator (BLGR), which have similar sizes and resonant frequencies, were fabricated to compare their performances. Using the MLR and the BLGR, the modulation field width and signal intensity of a phantom containing a nitroxide radical were measured by employing a continuous-wave electron spin resonance (CW-ESR) technique at a radio frequency of 300 MHz. Using the same resonators, the longitudinally detected ESR (LODESR) signal intensities of the phantom were also compared. The loaded Q values of the resonators were almost the same. The modulation widths in the MLR were significantly wider than those in the BLGR when the modulation coils were driven at the same voltage. The signal intensities of CW-ESR and LODESR from the phantom in the MLR were significantly greater than those from the BLGR. Since eddy currents disturb the penetration of the modulation field in CW-ESR or detection of changes in magnetization in LODESR observations, these results show that, in the MLR, the eddy currents were suppressed to a greater degree than in the BLGR.

Resonance-Field Dependence in Electrically Detected Magnetic Resonance: Effects of Exchange Interaction

“…This indeed applies well to their experimental results, which show an increase of the linewidth with the increase of the resonance field (3). On the contrary, this theoretical result does not accord with our experimental results, which show no evidence of such broadening (or splitting) (18). This discrepancy is most likely due to the fact that their theory does not explicitly include the exchange interaction that must be present in the transient spinspin pair.…”

“…Barabanov et al (17), on the other hand, examined much lower frequencies of 2-10 MHz and obtained different type of field dependence, i.e., the EDMR signal intensity is approximately proportional to the square of the microwave frequency. We have recently performed an EDMR study with microwave frequencies in an intermediate range of 300-900 MHz (18). Our results reveal a saturation-type field dependence, where, although the EDMR signal intensity increases with the increase of the resonance field, the increasing rate decreases gradually.…”

“…It should be noted that we do not need to distinguish the spin state of the pair because this effect is already included in k rec in the above subsection. Equations [18] can be solved with the steady-state approximation as n e = G/( f k rec ). [19] Since the conductivity is proportional to n e and we have neglected the intrinsic carrier concentrations, we obtain…”

Noninvasive in vivo determination of intracerebral oxygen concentration in rats by a longitudinally detected ESR (LODESR) technique

“…If a conventional bridged loop-gap resonator (BLGR) is used as an RF resonator, eddy currents in the loop and bridged shield counterbalance signal currents of the pickup coil caused by M z changes. However, the eddy currents in the MLR can be suppressed to a greater degree than in the BLGR (19).…”

“…2. A multilayered element resonator (MLR; resonant frequency ϭ 280 MHz, inner diameter ϭ 40 mm, axial length ϭ 19 mm) was used as an RF resonator (19). The on/off-modulated RF was applied to the sample in the RF resonator by using an RF oscillator (MG3633A; Anritsu Corporation, Japan; frequency range, 10 kHz to 2700 MHz), a pin switch (mini circuit; ZYSWA, New York; frequency range ϭ DC to 5 GHz; switching time ϭ 5 ns), and a power amplifier (A1000-1050; R&K Company Ltd., Japan; gain ϭ 46 dB, output impedance ϭ 50 ohms, frequency range ϭ 200 -1000 MHz, maximum average power ϭ 50 W; noise figure ϭ 10 dB).…”