Design and optimization of THz coupling in zirconia MAS rotors for dynamic nuclear polarization NMR
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1-s2.0-S109078072400106X-main.pdf
Description
Published version
Size
4.89 MB
Format
Adobe PDF
Checksum (MD5)
b8e5f0a98379361346013f233a433262
Author(s)
Li, Guangjiang
Dastrup, Blake
Palani, Ravi Shankar
Shapiro, Michael A
Jawla, Sudheer K
Griffin, Robert G
Nelson, Keith A
Temkin, Richard J
Date Issued
July 2024
Journal
Journal of Magnetic Resonance
Publisher
Elsevier BV
Version
Final published version
Abstract
We present 3D electromagnetic simulations of the coupling of a 250 GHz beam to the sample in a 380 MHz DNP NMR spectrometer. To obtain accurate results for magic angle spinning (MAS) geometries, we first measured the complex dielectric constants of zirconia, sapphire, and the sample matrix material (DNP juice) from room temperature down to cryogenic temperatures and from 220 to 325 GHz with a VNA and up to 1 THz with a THz TDS system. Simulations of the coupling to the sample were carried out with the ANSYS HFSS code as a function of the rotor wall material (zirconia or sapphire), the rotor wall thickness, and the THz beam focusing (lens or no lens). For a zirconia rotor, the B1 field in the sample was found to be strongly dependent on the rotor wall thickness, which is attributed to the high refractive index of zirconia. The optimum thickness of the wall is likely due to a transmission maximum but is offset from the thickness predicted by a simple calculation for a flat slab of the wall material. The B1 value was found to be larger for a sapphire rotor than for a zirconia rotor for all cases studied. The results found in this work provide new insights into the coupling of THz radiation to the sample and should lead to improved designs of future DNP NMR instrumentation.
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DOI of Published Version
https://doi.org/10.1016/j.jmr.2024.107722
