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. 2024 Aug 27;24(17):5537.
doi: 10.3390/s24175537.

Development of an Earth-Field Nuclear Magnetic Resonance Spectrometer: Paving the Way for AI-Enhanced Low-Field Nuclear Magnetic Resonance Technology

Eduardo Viciana  1 , Juan Antonio Martínez-Lao  1 , Emilio López-Lao  1 , Ignacio Fernández  2 , Francisco Manuel Arrabal-Campos  1   2
Affiliations

Development of an Earth-Field Nuclear Magnetic Resonance Spectrometer: Paving the Way for AI-Enhanced Low-Field Nuclear Magnetic Resonance Technology

Eduardo Viciana et al. Sensors (Basel). .

Abstract

Today, it is difficult to have a high-field nuclear magnetic resonance (NMR) device due to the high cost of its acquisition and maintenance. These high-end machines require significant space and specialist personnel for operation and offer exceptional quality in the acquisition, processing, and other advanced functions associated with detected signals. However, alternative devices are low-field nuclear magnetic resonance devices. They benefit from the elimination of high-tech components that generate static magnetic fields and advanced instruments. Instead, they used magnetic fields induced by ordinary conductors. Another category of spectrometers uses the Earth's magnetic field, which is simple and economical but limited in use. These devices are called Earth-Field Nuclear Magnetic Resonance (EFNMR) devices. This device is ideal for educational purposes, especially for engineers and those who study nuclear magnetic resonance, such as chemistry or other experimental sciences. Students can observe their internal workings and conduct experiments that complement their education without worrying about damaging equipment. This article provides a detailed explanation of the design and construction of electrical technology devices for the excitation of atomic spin resonance using Earth's magnetic fields. It covers all necessary stages, from research to analysis, including simulation, assembly, construction of each component, and the development of comprehensive software for spectrometer control.

Keywords: EFNMR; Earth’s field NMR; NMR spectrometer.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 18
Figure 18
The main window of the computer software is divided into two parts. On the left side, there is a control panel with textboxes and buttons for managing the acquisition process. On the right side, there is a primary plot window that displays either the detected signal or its Fast Fourier Transform (FFT) analysis.
Figure 1
Figure 1
Energy levels considered before an external magnetic field B0. Populations are generated that are quantized with two energy levels.
Figure 2
Figure 2
(a) Spin population distribution before the application of an RF pulse or polarizing coil in an external magnetic field Bo. Not all spins are aligned with Bo, leading to net magnetization. (b) Spin population distribution after the application of the RF pulse or polarizing coil. The pulse causes some spins to transition to a higher energy state, partially inverting the spin population, but not all spins are fully inverted. This diagram reflects the Zeeman energy levels and the alignment of nuclear spins with the external magnetic field. A radiofrequency (RF) pulse perturbs the nuclear spins from their equilibrium state, which are “on resonance”.
Figure 3
Figure 3
Block diagram of the electrotechnical device for nuclear spin excitation in the Earth’s magnetic field. Bp and Be represent the polarization magnetic field and the Earth’s magnetic field, respectively.
Figure 4
Figure 4
CAD design of the polarizing and receiving coil cylinders.
Figure 5
Figure 5
CAD design of the bases that support the coils and assembled model.
Figure 6
Figure 6
The 3D-printed parts with PETG and Nylon M10 threads.
Figure 7
Figure 7
Wounded polarizing coil.
Figure 8
Figure 8
Winding diagram of the receiver coils.
Figure 9
Figure 9
Wounded receiver coil and test tube.
Figure 10
Figure 10
Testing of receiver coils in the electrotechnical laboratory.
Figure 11
Figure 11
Test results give a good response of the avoiding signal between both coils. Only a little 180° dephased signal was measured, which ensures the cancelation of the signals.
Figure 12
Figure 12
Circuit schematic of excitation coil control.
Figure 13
Figure 13
Block diagram of the amplification and filtering circuit.
Figure 14
Figure 14
Switching amplification and filtering input stages circuit.
Figure 15
Figure 15
Filter stage frequency response. Blue band shadow includes components’ tolerances.
Figure 16
Figure 16
Sequence of pulses followed by the device as a function of time.
Figure 17
Figure 17
Microcontroller schematic and auxiliary components.
Figure 19
Figure 19
The final device was successfully assembled, integrating all components into a cohesive and fully functional EFNMR spectrometer.
Figure 20
Figure 20
1H MR spectrum test was successfully conducted. The magnetometer detected a magnetic field strength of 37.10 μT, resulting in a resonance frequency of 1579 Hz for the 1H nuclei.
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