Velocity distributions remotely measured with a single-sided NMR sensor

Area of Science:

• Nuclear Magnetic Resonance Spectroscopy
• Fluid Dynamics
• Analytical Chemistry

Background:

• Pulsed field gradient nuclear magnetic resonance (PFG NMR) is a key technique for measuring molecular displacement.
• Conventional NMR magnets have restricted geometry, limiting applications for flow measurements.
• Single-sided NMR sensors offer an open geometry, enabling broader NMR applications.

Purpose of the Study:

• To present the first approach for measuring velocity distributions ex situ using PFG NMR on a single-sided NMR sensor.
• To address distortions in displacement encoding caused by inhomogeneous fields in PFG NMR.
• To demonstrate a novel method for remote velocity distribution measurement.

Main Methods:

• Implementation of a pulsed field gradient sequence on a single-sided NMR sensor.
• Numerical simulations to analyze and correct for field distortions (B0 and B1).
• Combination of an alternating stimulated spin-echo PFG sequence with a multi-echo acquisition scheme.

Main Results:

• Demonstration of corrected displacement encoding in the presence of inhomogeneous fields.
• Significant increase in method sensitivity through a multi-echo acquisition scheme.
• Successful measurement of velocity propagator in laminar flow with good agreement to theory.

Conclusions:

• Single-sided NMR sensors can be effectively used for ex situ velocity distribution measurements.
• The proposed PFG NMR sequence and correction methods overcome limitations of conventional NMR.
• This technique expands the applicability of NMR for studying fluid flow in previously inaccessible systems.