- Email: [email protected]
A low-cost, large volume, easy-access design for a portable NMR magnet
Abstracts / Magnetic Resonance Imaging 25 (2007) 544 – 591 may offer a unique pathway to understanding the local interactions of heavy metals with sediment pore walls. [1] Nestle N, Wunderlich A, Niessner R, Baumann T. Environmental Science Technology 2003;37:3972–7.
577
The magnet design has been evaluated in FEM simulations (using CST Studio, CST, Darmstadt) of the magnetic field and a first prototype of the magnet has been built using eight 50.850.825.4-mm magnet bricks and applied in experiments on food and construction materials. doi:10.1016/j.mri.2007.01.083
doi:10.1016/j.mri.2007.01.082 A low-cost, large volume, easy-access design for a portable NMR magnet H. Storka, N. Nestlea,b a TU Darmstadt, Institute of Condensed Matter Physics, Germany, bZentrale Forschung BASF AG Ludwigshafen, Germany During the last few years, FeNdB permanent magnets have become more and more easily available. Building NMR magnet systems on the basis of off-the-shelf magnets in brick, disc or ring shape which are cheaply available via the Internet provides new opportunities for low-cost NMR systems. In recent years, several Halbach-type designs based on small brick magnets, single-sided magnets and other designs based on specially designed magnet geometries have been realized. Specially designed magnets come at much higher cost than off-the-shelf geometries, and the construction of Halbach geometries is mechanically quite demanding due to the need to put the magnet bricks in place despite strong repulsive forces. Furthermore, typical Halbach systems come in tube shape and are accessible only from two sides. Here, we present a more open magnet system based on a Helmholtz-like assembly based on two two-by-two arrays of square permanent magnet bricks (see magnet design and simulation of magnetic field homogeneity in the figure). When choosing the appropriate combination of the distance d between the magnet arrays and the spacing b between the magnet bricks, it is possible to obtain a very good homogeneity in the center of this magnet system. At the same time, the space between the magnet arrays is quite easily accessible from at least three sides (taking into account the need for a spacer between the two plates). The large air gap allows the accommodation of bulky samples (or sample environments) and also space for insulating the magnets in order to improve the field stability. Due to the relatively far distance between the magnet bricks and the target volume, variations in the magnetization of the bricks (which are a major problem in surface magnet systems) play only a minor role in the homogeneity of the field in the target volume in this setup. The good accessibility of the target volume allows using this type of magnet for bsemi-single-sidedQ applications with cylindrical samples in construction, food, geoscience and medical applications.
Time-dependent diffusion of water in clay gel-saturated porous media T. Ohkuboa, M. Yamaguchib a Japan Atomic Energy Agency, Japan, bInstitute of Research and Innovation, Japan PFG NMR diffusion experiments were applied to clay gel-saturated glass beads pack in order to study diffusing water in pore space. The well-known equation [1] between time-dependent diffusion coefficient and pore geometry was applied, the surface–volume ratio (S/V p) and diffusion coefficient of pore fluid (D 0) were estimated for water and clay gelsaturated glass bead pack. The purified montmorillonite from Tsukinuno in Japan was used. It contains small amount of paramagnetic Fe3+ as framework cation. The clay gel was prepared by mixing 5 wt.% of montmorillonite with 95 wt.% of deionized water. The water- and clay gel-saturated glass bead beds were prepared by using 50- and 150-Am-diameter glass beads with 10% error (catalog values).The measurements were performed with a Maran-Ultra (Resonance Instruments, UK) at a Larmor frequency of 23 MHz, which can produce a maximum gradient strength of 237 G/cm. The used pulse sequence was 17-interval bipolar gradient pulse [2]. All NMR measurements were carried out at 308C. Fig. 1 shows the results for time-dependent diffusion measurement of water- and clay gel-saturated glass bead beds. D 0 and S/V p of watersaturated samples were calculated by fitting the data for short time region. Specific surface areas of 50 and 150 Am glass bead beds were 1700 and 630 cm1, respectively. Assuming close-packed structure, bead diameters were estimated to be 57 and 155 Am, indicating very good agreement with the nominal values of the glass beads. D 0 values determined from the fittings were 2.53109 and 2.50109 m2/s, which are very close to the value of bulk water. While diffusion of water in water-saturated glass bead beds is in the fast diffusion limit, D(t) of water in clay gel-saturated glass bead beds in short diffusion time is much smaller than the D(t) of water in glass bead beds without clay gels. However, it is interesting to note that D(t) of clay gelsaturated samples is dependent on the size of glass beads. The fitting values for clay gel-saturated for glass beads with 50 and 150 Am were 1.94109 and 1.53109 m2 /s for D 0 and 2481 and 645 cm1 for S/V p , respectively. The result of D 0 for glass beads with 50 Am was different from 1.58109 m2/s for bulk clay gel, showing incomprehensible
Fig. 1 Diffusion coefficient as a function of the square root of diffusion time for water and clay gel-saturated glass bead.
577
The magnet design has been evaluated in FEM simulations (using CST Studio, CST, Darmstadt) of the magnetic field and a first prototype of the magnet has been built using eight 50.850.825.4-mm magnet bricks and applied in experiments on food and construction materials. doi:10.1016/j.mri.2007.01.083
doi:10.1016/j.mri.2007.01.082 A low-cost, large volume, easy-access design for a portable NMR magnet H. Storka, N. Nestlea,b a TU Darmstadt, Institute of Condensed Matter Physics, Germany, bZentrale Forschung BASF AG Ludwigshafen, Germany During the last few years, FeNdB permanent magnets have become more and more easily available. Building NMR magnet systems on the basis of off-the-shelf magnets in brick, disc or ring shape which are cheaply available via the Internet provides new opportunities for low-cost NMR systems. In recent years, several Halbach-type designs based on small brick magnets, single-sided magnets and other designs based on specially designed magnet geometries have been realized. Specially designed magnets come at much higher cost than off-the-shelf geometries, and the construction of Halbach geometries is mechanically quite demanding due to the need to put the magnet bricks in place despite strong repulsive forces. Furthermore, typical Halbach systems come in tube shape and are accessible only from two sides. Here, we present a more open magnet system based on a Helmholtz-like assembly based on two two-by-two arrays of square permanent magnet bricks (see magnet design and simulation of magnetic field homogeneity in the figure). When choosing the appropriate combination of the distance d between the magnet arrays and the spacing b between the magnet bricks, it is possible to obtain a very good homogeneity in the center of this magnet system. At the same time, the space between the magnet arrays is quite easily accessible from at least three sides (taking into account the need for a spacer between the two plates). The large air gap allows the accommodation of bulky samples (or sample environments) and also space for insulating the magnets in order to improve the field stability. Due to the relatively far distance between the magnet bricks and the target volume, variations in the magnetization of the bricks (which are a major problem in surface magnet systems) play only a minor role in the homogeneity of the field in the target volume in this setup. The good accessibility of the target volume allows using this type of magnet for bsemi-single-sidedQ applications with cylindrical samples in construction, food, geoscience and medical applications.
Time-dependent diffusion of water in clay gel-saturated porous media T. Ohkuboa, M. Yamaguchib a Japan Atomic Energy Agency, Japan, bInstitute of Research and Innovation, Japan PFG NMR diffusion experiments were applied to clay gel-saturated glass beads pack in order to study diffusing water in pore space. The well-known equation [1] between time-dependent diffusion coefficient and pore geometry was applied, the surface–volume ratio (S/V p) and diffusion coefficient of pore fluid (D 0) were estimated for water and clay gelsaturated glass bead pack. The purified montmorillonite from Tsukinuno in Japan was used. It contains small amount of paramagnetic Fe3+ as framework cation. The clay gel was prepared by mixing 5 wt.% of montmorillonite with 95 wt.% of deionized water. The water- and clay gel-saturated glass bead beds were prepared by using 50- and 150-Am-diameter glass beads with 10% error (catalog values).The measurements were performed with a Maran-Ultra (Resonance Instruments, UK) at a Larmor frequency of 23 MHz, which can produce a maximum gradient strength of 237 G/cm. The used pulse sequence was 17-interval bipolar gradient pulse [2]. All NMR measurements were carried out at 308C. Fig. 1 shows the results for time-dependent diffusion measurement of water- and clay gel-saturated glass bead beds. D 0 and S/V p of watersaturated samples were calculated by fitting the data for short time region. Specific surface areas of 50 and 150 Am glass bead beds were 1700 and 630 cm1, respectively. Assuming close-packed structure, bead diameters were estimated to be 57 and 155 Am, indicating very good agreement with the nominal values of the glass beads. D 0 values determined from the fittings were 2.53109 and 2.50109 m2/s, which are very close to the value of bulk water. While diffusion of water in water-saturated glass bead beds is in the fast diffusion limit, D(t) of water in clay gel-saturated glass bead beds in short diffusion time is much smaller than the D(t) of water in glass bead beds without clay gels. However, it is interesting to note that D(t) of clay gelsaturated samples is dependent on the size of glass beads. The fitting values for clay gel-saturated for glass beads with 50 and 150 Am were 1.94109 and 1.53109 m2 /s for D 0 and 2481 and 645 cm1 for S/V p , respectively. The result of D 0 for glass beads with 50 Am was different from 1.58109 m2/s for bulk clay gel, showing incomprehensible
Fig. 1 Diffusion coefficient as a function of the square root of diffusion time for water and clay gel-saturated glass bead.