Permanent magnet is the key component of nuclear magnetic resonance (NMR) instrument. Based on the principle of Halbach array, this study designs and optimizes a multilayer Halbach permanent magnet for human finger NMR detection. The quality factor (QF) is introduced to represent the performance of magnetic field, firstly. The impact on magnetic performance, caused by various magnet heights, is analyzed using Finite Element Method(FEM). In order to compensate the end effect, the radial adjustment method is proposed, combining the adjustments of the radial size and the radial position of the magnet blocks. Comparing the effect on magnetic field of three different plans, the results show that combining the adjustments of inner radius and outer radius shims the field dramatically. Finally the designed construction is stacked by 11 layers of magic rings and each layer is composed of 8 trapezoid-shaped magnets. The magnetic field of the center cylindrical region (ϕ20 × 20 mm) of the structure is calculated, whose final strength achieves up to 447 mT and homogeneity is within 500 ppm. The designed magnet structure is manufactured and the measurement is finished in the end. The proposed construction has the advantages of small size and high uniformity, which has an extensive application prospect in portable NMR system.

Nuclear magnetic resonance (NMR) relaxometry techniques have been widely used for evaluating hydrated cement paste as non-destructive and quantitative measurements. The important crystalline solid phases, such as Portlandite and Ettringite, are formed in the hydration of cement paste. However, it is challenging to quantify these crystalline solid phases by conventional NMR relaxation methods, due to their short-lived NMR signal lifetimes. A novel method for 2-D NMR $T_{1}$ – $T_{\mathrm {2S}}$ measurement of hydrated cement paste is proposed in this article. Combining a homebuilt NMR probe with short deadtime and high sensitivity, the $T_{1}$ – $T_{\mathrm {2S}}$ method can provide a more complete assessment of hydrogen-bearing crystalline solid phases (i.e., Portlandite and Ettringite) in hydrated cement paste. Experimental results demonstrated that the proposed method produced two additional distinct peaks in the $T_{1}$ – $T_{2}$ correlation map, compared with conventional methodologies. The attribution of the two peaks to Portlandite and Ettringite in hydrated cement paste was confirmed by heating experiments and partial least-square regression (PLSR) method. This technique has enabled detection and quantification of Portlandite and Ettringite in hydrated cement paste.

The conventional Halbach permanent magnet usually has a high length-to-interdiameter ratio (LDIR) to gain a higher magnetic field homogeneity but can cause an increase in volume and weight, limiting the application in miniaturization. This article proposes a novel design and shimming method for the Halbach magnet to have not only a lower LDIR but also a better homogeneity. In this article, a multilayer magnetic ring structure was first designed through theoretical calculation and simulation optimization, which compensated for the magnetic field inhomogeneity. Then, a passive shimming method was applied which simulated the first-order and second-order terms of magnetic field inhomogeneity using small magnetic blocks whose magnetization direction was consistent with the main magnetic field. This method has high shimming efficiency and can avoid the demagnetization of the magnetic blocks caused by their magnetization directions against the direction of the main magnetic field, especially when the intensity of the magnetic field is close to or beyond the remanence of the magnetic blocks. The magnetic field intensity of the proposed magnet is 1.08 T and the homogeneity reaches close to the sub-ppm. The performance of the magnet was verified in the portable magnetic resonance imaging (MRI) system combined with a set of homemade low-power gradient coils. MRI images of phantoms and okra reached a resolution of 156 $\mu \text{m}$ [pixel size 156 $\mu \text{m}$ , matrix 128 $\times128$ , and field-of-view (FOV) $20\times20$ mm ² ], which shows the potential for wide application of the proposed design and shimming method.

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A low-field nuclear magnetic resonance spectrometer for non-invasive monitoring of human finger blood glucose fluctuations was developed. Saline solution and blood serum samples with different glucose concentrations were first detected by the spectrometer and it has been found that there was a high-linear correlation between the glucose concentration and the transverse relaxation time. Then, the spectrometer was employed to noninvasively measure a finger from each of the several volunteers. The experiment results showed that the transverse relaxation time of the human finger increases with human blood glucose concentration. In conclusion, the human finger nuclear magnetic resonance spectrometer could be a potential tool to noninvasive monitoring of human body’s blood glucose fluctuations in the future.