Magnetic Lenz lenses increase the limit-of-detection in nuclear magnetic resonance

TL;DR

This paper introduces magnetic Lenz lenses that focus magnetic flux to enhance NMR sensitivity in small samples, offering a new approach to improve detection limits without miniaturizing coils.

Contribution

It is the first experimental demonstration of Lenz lenses in magnetic resonance, providing a mathematical framework and simulation-based optimization methods.

Findings

Lenz lenses can significantly increase NMR sensitivity.

Optimal lens arrangements can be identified through simulations.

Lenz lenses enable focusing magnetic flux without miniaturizing coils.

Abstract

A high NMR detection sensitivity is indispensable when dealing with mass and volume-limited samples, or whenever a high spatial resolution is required. The use of miniaturised RF coils is a proven way to increase sensitivity, but may be impractical and is not applicable to every experimental situation. We present the use of magnetic lenses, denoted as Lenz lenses due to their working principle, to focus the magnetic flux of a macroscopic RF coil into a smaller volume and thereby locally enhance the sensitivity of the NMR experiment - at the expense of the total sensitive volume. Besides focusing, such lenses facilitate re-guiding or re-shaping of magnetic fields much like optical lenses do with light beams. For the first time we experimentally demonstrate the use of Lenz lenses in magnetic resonance and provide a compact mathematical description of the working principle. Through simulations we show that optimal arrangements can be found.