Using nutation-frequency-selective pulses to reduce radio-frequency field inhomogeneity in solid-state NMR

Abstract. Radio-frequency (rf) field inhomogeneity is a common problem in NMR which leads to non-ideal rotations of spins in parts of the sample. Often, a physical volume restriction of the sample is used to reduce the effects of rf-field inhomogeneity especially in solid-state NMR where spacers are inserted to reduce the sample volume to the centre of the coil. We show that band-selective pulses in the spin-lock frame can be used to apply B1-field selective inversions to spins that experience selected parts of the rf-field distribution. Any frequency band-selective pulse can be used for this purpose but we chose the family of I-BURP pulses (H. Geen, R. Freeman, Band-Selective Radiofrequency Pulses, J. Magn. Reson. 93 (1991) 93–141) for the measurements demonstrated here. As an example, we show that the implementation of such pulses improves homonuclear frequency-switched Lee-Goldburg decoupling in solid-state NMR.

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Using nutation-frequency-selective pulses to reduce radio-frequency field inhomogeneity in solid-state NMR

Magnetic Resonance ◽

10.5194/mr-1-187-2020 ◽

2020 ◽

Vol 1 (2) ◽

pp. 187-195

Author(s):

Kathrin Aebischer ◽

Nino Wili ◽

Zdeněk Tošner ◽

Matthias Ernst

Keyword(s):

Solid State ◽

Radio Frequency ◽

Solid State Nmr ◽

Sample Volume ◽

Field Inhomogeneity ◽

Spin Lock ◽

Selective Pulses ◽

Physical Volume ◽

The Family ◽

B1 Field

Abstract. Radio-frequency (rf) field inhomogeneity is a common problem in NMR which leads to non-ideal rotations of spins in parts of the sample. Often, a physical volume restriction of the sample is used to reduce the effects of rf-field inhomogeneity, especially in solid-state NMR where spacers are inserted to reduce the sample volume to the centre of the coil. We show that band-selective pulses in the spin-lock frame can be used to apply B1-field selective inversions to spins that experience selected parts of the rf-field distribution. Any frequency band-selective pulse can be used for this purpose, but we chose the family of I-BURP pulses (Geen and Freeman, 1991) for the measurements demonstrated here. As an example, we show that the implementation of such pulses improves homonuclear frequency-switched Lee–Goldburg decoupling in solid-state NMR.

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Supplementary material to "Using nutation-frequency-selective pulses to reduce radio-frequency field inhomogeneity in solid-state NMR"

10.5194/mr-2020-18-supplement ◽

2020 ◽

Author(s):

Kathrin Aebischer ◽

Nino Wili ◽

Zdeněk Tošner ◽

Matthias Ernst

Keyword(s):

Solid State ◽

Radio Frequency ◽

Solid State Nmr ◽

Field Inhomogeneity ◽

Radio Frequency Field ◽

Selective Pulses ◽

Frequency Field ◽

Nutation Frequency ◽

Supplementary Material ◽

Frequency Selective

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Effects of radial radio-frequency field inhomogeneity on MAS solid-state NMR experiments

Magnetic Resonance ◽

10.5194/mr-2-523-2021 ◽

2021 ◽

Vol 2 (1) ◽

pp. 523-543

Author(s):

Kathrin Aebischer ◽

Zdeněk Tošner ◽

Matthias Ernst

Keyword(s):

Solid State ◽

Radio Frequency ◽

Solid State Nmr ◽

Building Blocks ◽

Magic Angle Spinning ◽

Time Dependent ◽

Magic Angle ◽

Field Inhomogeneity ◽

Radio Frequency Field ◽

Frequency Field

Abstract. Radio-frequency field inhomogeneity is one of the most common imperfections in NMR experiments. They can lead to imperfect flip angles of applied radio-frequency (rf) pulses or to a mismatch of resonance conditions, resulting in artefacts or degraded performance of experiments. In solid-state NMR under magic angle spinning (MAS), the radial component becomes time-dependent because the rf irradiation amplitude and phase is modulated with integer multiples of the spinning frequency. We analyse the influence of such time-dependent MAS-modulated rf fields on the performance of some commonly used building blocks of solid-state NMR experiments. This analysis is based on analytical Floquet calculations and numerical simulations, taking into account the time dependence of the rf field. We find that, compared to the static part of the rf field inhomogeneity, such time-dependent modulations play a very minor role in the performance degradation of the investigated typical solid-state NMR experiments.

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Effects of radial radio-frequency field inhomogeneity on MAS solid-state NMR experiments

10.5194/mr-2021-43 ◽

2021 ◽

Author(s):

Kathrin Aebischer ◽

Zdeněk Tošner ◽

Matthias Ernst

Keyword(s):

Solid State ◽

Radio Frequency ◽

Solid State Nmr ◽

Building Blocks ◽

Magic Angle Spinning ◽

Time Dependent ◽

Magic Angle ◽

Field Inhomogeneity ◽

Radio Frequency Field ◽

Frequency Field

Abstract. Radio-frequency field inhomogeneity is one of the most common imperfections in NMR experiments. They can lead to imperfect flip angles of applied radio-frequency (rf) pulses or to a mismatch of resonance conditions resulting in artifacts or degraded performance of experiments. In solid-state NMR under magic-angle spinning, the radial component becomes time-dependent because the rf-irradiation amplitude and phase is modulated with integer multiples of the spinning frequency. We analyze the influence of such time-dependent MAS-modulated rf fields on the performance of some commonly used building blocks of solid-state NMR experiments. This analysis is based on analytical Floquet calculations as well as numerical simulations taking into account the time dependence of the rf field. We find that compared to the static part of the rf-field inhomogeneity, such time-dependent modulations play a very minor role in the performance degradation of the investigated typical solid-state NMR experiments.

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