250 MHz Rapid Scan Cross Loop Resonator

Abstract

A 25 mm diameter 250 MHz crossed-loop resonator was designed for rapid scan electron paramagnetic resonance imaging. It has a saddle coil for the driven resonator and a fine wire, loop gap resonator for the sample resonator. There is good separation of E and B fields and high isolation between the two resonators, permitting a wide range of sample types to be measured. Applications to imaging of nitroxide, trityl, and LiPc samples illustrate the utility of the resonator. Using this resonator and a trityl sample the signal-to-noise of a rapid scan absorption spectrum is about 20 times higher than for a first-derivative CW spectrum.

EPR Everywhere

“…Manufacturers are now developing purpose-built EPR components at low frequencies for low-field EPR applications. For example, several high-quality RF amplifiers in the 100-900 MHz range are offered by Tomco RF and power supplies which allow magnetic field reversal for low-field RS experiments are offered by CAEN [63].…”

“…An even more recent development regarding the rapid-scan background is to remove its influence based on how the experiment is carried out, rather than modifying the rapid-scan resonator. Specifically, for lowfield applications, the Eaton laboratory has developed a field reversal method that largely minimizes the RS background [63]. This field reversal method is currently not accessible at high fields and exemplifies a strategy which is accessible to lowfield applications exclusively.…”

“…The assumption is made that transition metal species have relaxation rates which are too fast at room temperature to be acquired with current in situ pulse EPR spectrometers such as the unilateral EPR system used for OxyChip measurements, described later; however, this is likely not the case for in situ CW and RS spectrometers. As an illustration of the spectral narrowing expected as field and frequency decrease, a general Cu(II) complex with a natural abundance mixture of 63 Cu and 65 Cu was simulated in MATLAB using EasySpin at four frequencies from 34 GHz to 500 MHz (Fig. 1) [89].…”