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Abstract

An H-shaped low-field permanent magnet is presented. It has been designed, simulated and optimized using the finite element method. The magnet mainly consists of two poles, each of which consists of 37 hexagonal magnetic blocks that are magnetically connected by an iron yoke. To achieve the magnetic field homogeneity in the ppm range required for NMR applications, mechanical shimming by a vertical adjustment of the hexagonal magnetic blocks has been applied. Here, the displacement of each block from the initial equidistant symmetric design has been optimized by applying a pattern search method. In addition, two pole pieces made of iron have been added to the magnet to further improve the magnetic field homogeneity. The dimensions of these pole pieces have been optimized using a genetic algorithm. The magnetic field homogeneity of 15 ppm (parts per million) measured inside the manufactured prototype verifies the accuracy of the proposed simulation based design approach.

Keywords

Finite element methods genetic algorithms mobile NMR NMR magnet permanent magnet design pattern search algorithms shimming

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References

Keeler

, Understanding NMR Spectroscopy, University of Cambridge, Cambridge, 2002.

Duckett

S.B.

and Mewis

R.E.

, Application of parahydrogen induced polarization techniques in NMR spectroscopy and imaging, Acc. Chem. Res. 45 (2012), 1247–1257.

Richardson

P.M.

, SABRE hyperpolarization enables high-sensitivity 1H and 13C benchtop NMR spectroscopy, Analyst 143 (2018), 3442–3450.

Braun

, NMR hyperpolarization of established PET tracers, ChemistrySelect 3 (2018), 5176–5184.

Casanova

Perlo

and Blümich

, Single-sided NMR, Springer, Berlin, Heidelberg, 2011.

Danieli

, Mobile sensor for high resolution NMR spectroscopy and imaging, J Magn Reson 198 (2009), 80–87.

, Optimal design and test of main magnet in superconducting MRI, Applied Superconductivity 20 (2010), 1810–1813.

You

X.F.

, Biplanar shim coil design for 1.5 T permanent magnet of in vivo animal MRI, Applied Superconductivity 20 (2010), 1045.

Forbes

L.K.

, A target-field method to design circular biplanar coils for asymmetric shim and gradient fields, IEEE Trans Magn 41 (2005), 2134–2144.

10.

Wang

, Development of high-field permanent magnetic circuits for NMRI/MRI and imaging on mice, Biomed Res Int 2016 (2016), 1–11.

11.

Johns

M.L.

Mobile NMR and MRI: Developments and applications, in: Hardware Developments: Halbach Magnet Arrays Blümler

(ed.), Royal Society of Chemistry, 2015, pp. 133–157.

12.

Raich

and Blümler

, Design and construction of a dipolar halbach array with a homogeneous field from identical bar magnets: NMR mandhalas, Concepts in Magnetic Resonance 23B (2004), 16–25.

13.

Baeyens

, A direct search algorithm for global optimization, Algorithms 9 (2016), 1–22.

14.

Jackson

J.D.

, Classical Electrodynamics, Wiley, New York, USA, 1999.

15.

Golay

M.J.E.

, Field homogenizing coils for nuclear spin resonance instrumentation, Rev. Sci. Instrum. 29 (1958), 313–318.

16.

Chmurny

, The ancient and honourable art of shimming, Concepts in Magnetic Resonance 2 (1990), 131–149.

17.

Cooper

R.K.

, Remote (inside-out) NMR. I. Remote production of region of homogeneous magnetic field, Journal of Magnetic Resonance 41 (1969), 400–405.

18.

Mitchell

, Low-field permanent magnets for industrial process and quality control, Prog Nucl Magn Reson Spectrosc 76 (2014), 1–60.

19.

Parker

A.J.

, Shimming Halbach magnets utilizing genetic algorithms to profit from material imperfections, J Magn Reson 265 (2016), 83–89.

20.

Podol’skii

, Design procedure for permanent magnet assemblies with uniform magnetic fields for MRI devices, IEEE Trans Magn 36 (2000), 484–490.

21.

Hafla

, Force computation with the integral equation method, Studies in Applied Electromagnetics and Mechanics 30 (2008), 93–97.

22.

Frei

, Solutions to linear systems of equations: Direct and iterative solvers, COMSOL Blog 9 (2013).

23.

Kirgat

G.S.

, Review of Hooke and Jeeves direct search solution method analysis applicable to mechanical design engineering, IJIERT 1 (2014), 1–13.

24.

Nocedal

and Wright

S.J.

, Numerical Optimization, 2nd edn, Springer, 2006.

25.

Blümich

COMPACT NMR, Walter de Gruyter GmbH, Berlin, Boston, 2014.

An H-shaped low-field magnet for NMR spectroscopy designed using the finite element method

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