An X-Band Crossed-Loop EPR Resonator

Abstract

A copper X-band (9.22 GHz) cross loop resonator has been constructed for use with 4 mm sample tubes. The Q for the two resonators are 380 and 350, respectively. The resonator efficiency is about 1 G per square root of watt. Operation has been demonstrated with measurement of T₁ by saturation recovery for samples of coal and an immobilized nitroxide radical.

Fig. 1

One-half of driven resonator

Fig. 2

One-half of detector resonator

Fig. 3

Cross-section of driven resonator

Fig. 4

Internal parts of CLR

Fig 5

Assembled CLR enclosed in RF shield. A) Design drawing. B) photograph of completed CLR.

Fig. 6

One implementation of a tuning switching arrangement for a CLR. The pathways for tuning each resonator, and the isolation between them, are sketched in this portion of the spectrometer schematic. The transfer switch between the two resonators of the CLR and the double-throw switches select the appropriate signal paths for tuning each resonator in reflection mode, observing while adjusting isolation between the two resonators, and measuring the EPR signal during LGR or CLR operating modes.

Fig. 7

Saturation Recovery of (A) coal sample with T₁ = 26.4 μs and (B) an immobilized nitroxide radical in polyvinyl alcohol borate glass, with T₁ = 10.6 μs.