High-Bandwidth Q-Band EPR Resonators
- 469 Downloads
The emerging technology of ultra-wide-band spectrometers in electron paramagnetic resonance—enabled by recent technological advances—provides the means for new experimental schemes, a broader range of samples, and huge gains in measurement time. Broadband detection does, however, require that the resonator provides sufficient bandwidth and, despite resonator compensation schemes, excitation bandwidth is ultimately limited by resonator bandwidth. Here, we present the design of three resonators for Q-band frequencies (33–36 GHz) with a larger bandwidth than what was reported so far. The new resonators are of a loop-gap type with 4–6 loops and were designed for 1.6 mm sample tubes to achieve higher field homogeneity than in existing resonators for 3 mm samples, a feature that is beneficial for precise spin control. The loop-gap design provides good separation of the B 1 and E field, enabling robust modes with powder samples as well as with frozen water samples as the resonant behavior is largely independent of the dielectric properties of the samples. Experiments confirm the trends in bandwidth and field strength and the increased B 1 field homogeneity predicted by the simulations. Variation of the position of the coupling rod allows the adjustment of the quality factor Q and thus the bandwidth over a broad range. The increased bandwidth of the loop-gap resonators was exploited in double electron–electron resonance measurements of a Cu(II)-PyMTA ruler to yield significantly higher modulation depth and thus higher sensitivity.
We thank Andrin Doll and Stephan Pribitzer for helpful discussions and resonator tests on other applications. We are grateful to an anonymous reviewer for providing a derivation of Eq. (10) and correcting an error in constants in the original form of this equation. Funding by the Swiss National Science Foundation (grant no. 200020–169057) and by the German Science Foundation (DFG; SPP1601, GO 555/6-2) supported this work.
- 1.C. Poole Jr., Electron Spin Rresonance—A Comprehensive Treatise on Experimental Techniques (Dover Publications Inc., Mineola, New York, 1983)Google Scholar
- 32.A.M. Bowen, C.E. Tait, C.R. Timmel, J.R. Harmer, in Structural Information from Spin-Llabels and Intrinsic Paramagnetic Centres in the Biosciences, vol. 152, ed. by C.R. Timmel, J.R. Harmer (Springer, Berlin, Heidelberg, 2013), pp. 283–327Google Scholar