skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Design and optimization of arrays of neodymium iron boron-based magnets for magnetic tweezers applications

Abstract

We present the design methodology for arrays of neodymium iron boron (NdFeB)-based magnets for use in magnetic tweezers devices. Using finite element analysis (FEA), we optimized the geometry of the NdFeB magnet as well as the geometry of iron yokes designed to focus the magnetic fields toward the sample plane. Together, the magnets and yokes form a magnetic array which is the basis of the magnetic tweezers device. By systematically varying 15 distinct shape parameters, we determined those features that maximize the magnitude of the magnetic field gradient as well as the length scale over which the magnetic force operates. Additionally, we demonstrated that magnetic saturation of the yoke material leads to intrinsic limitations in any geometric design. Using this approach, we generated a compact and light-weight magnetic tweezers device that produces a high field gradient at the image plane in order to apply large forces to magnetic beads. We then fabricated the optimized yoke and validated the FEA by experimentally mapping the magnetic field of the device. The optimization data and iterative FEA approach outlined here will enable the streamlined design and construction of specialized instrumentation for force-sensitive microscopy.

Authors:
;  [1]
  1. Department of Mechanical Engineering and Materials Research Laboratory, University of California, Santa Barbara, California 93106 (United States)
Publication Date:
OSTI Identifier:
22392500
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 86; Journal Issue: 5; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; BORON; DESIGN; FINITE ELEMENT METHOD; GEOMETRY; IRON; ITERATIVE METHODS; LENGTH; MAGNETIC FIELDS; MAGNETS; MICROSCOPY; NEODYMIUM; OPTIMIZATION

Citation Formats

Zacchia, Nicholas A., and Valentine, Megan T. Design and optimization of arrays of neodymium iron boron-based magnets for magnetic tweezers applications. United States: N. p., 2015. Web. doi:10.1063/1.4921553.
Zacchia, Nicholas A., & Valentine, Megan T. Design and optimization of arrays of neodymium iron boron-based magnets for magnetic tweezers applications. United States. doi:10.1063/1.4921553.
Zacchia, Nicholas A., and Valentine, Megan T. 2015. "Design and optimization of arrays of neodymium iron boron-based magnets for magnetic tweezers applications". United States. doi:10.1063/1.4921553.
@article{osti_22392500,
title = {Design and optimization of arrays of neodymium iron boron-based magnets for magnetic tweezers applications},
author = {Zacchia, Nicholas A. and Valentine, Megan T.},
abstractNote = {We present the design methodology for arrays of neodymium iron boron (NdFeB)-based magnets for use in magnetic tweezers devices. Using finite element analysis (FEA), we optimized the geometry of the NdFeB magnet as well as the geometry of iron yokes designed to focus the magnetic fields toward the sample plane. Together, the magnets and yokes form a magnetic array which is the basis of the magnetic tweezers device. By systematically varying 15 distinct shape parameters, we determined those features that maximize the magnitude of the magnetic field gradient as well as the length scale over which the magnetic force operates. Additionally, we demonstrated that magnetic saturation of the yoke material leads to intrinsic limitations in any geometric design. Using this approach, we generated a compact and light-weight magnetic tweezers device that produces a high field gradient at the image plane in order to apply large forces to magnetic beads. We then fabricated the optimized yoke and validated the FEA by experimentally mapping the magnetic field of the device. The optimization data and iterative FEA approach outlined here will enable the streamlined design and construction of specialized instrumentation for force-sensitive microscopy.},
doi = {10.1063/1.4921553},
journal = {Review of Scientific Instruments},
number = 5,
volume = 86,
place = {United States},
year = 2015,
month = 5
}
  • Rare-earth transition-metal magnetic materials consisting of Nd/sub 2/Fe/sub 14/B with small amounts of Si, produced by melt-spinning, have been studied using fluorescence extended x-ray absorption fine structure. A windowless Si(Li) solid-state detector was used to collect the Si fluorescence. These polycrystalline samples are unusual in that they are magnetically isotropic, yet have a very high remanent magnetization. The silicon atom is bonded to a single shell of iron atoms at a distance of 2.46 +- 0.05 A. The results strongly suggest that (1) Si does not segregate at the grain boundaries or cluster with other Si atoms, and that (2)more » Si replaces the iron atom at the ''c'' site of the standard Nd/sub 2/Fe/sub 14/B structural model within the grains.« less
  • The preparation of Nd-Fe-B permanent magnets by rapid solidification processing is described. The initial rapid quench is typically carried out by melt spinning; magnetic hardening can be achieved either by quenching directly from the melt or by annealing an overquenched precursor. In both instances, optimum permanent magnet properties are associated with the formation of a uniform, finely crystalline (<100 nm diam) microstructure consisting primarily of the Nd/sub 2/Fe/sub 14/B phase. Consolidation of the rapidly solidified material into isotropic magnets can be achieved by cold compaction with a resin binder or by hot pressing to full density. Owing to the extremelymore » fine grain size, orientation of the isotropic ribbons by grinding followed by magnetization would be difficult. Crystallographic anisotropy can be achieved, however, by hot deformation. Alignment occurs entirely by thermomechanical means with rotation of the easy crystallographic direction normal to the direction of plastic flow. Energy products to 40 MGOe have been achieved by this technique. Properties of the various types of magnets prepared from this material are presented as is microstructural data at key points in the manufacturing process.« less
  • The fabrication of electromagnetic acoustic transducers (EMATs) is described. Neodymium iron boron permanent magnets allow compact devices to be constructed. Pick-up mechanisms in both magnetic and non-magnetic metals are discussed and demonstrated experimentally EMATS are suitable detectors for broadband laser generated ultrasound such systems, being non-contacting, can operate at high temperature.
  • A new method is described which produces fully dense, well-aligned Nd-Fe-B magnets from rapidly quenched ribbons. Full density is achieved by hot pressing at approximately 15 kpsi in argon at 700 C. A second hot press in a larger die cavity to allow deformation transverse to the press direction (die upsetting) introduces a preferred magnetization direction parallel to the press direction. Energy products of 40 MGOe (Br/Hci = 13.5 kG/11 kOe) have been generated by this method. 7 references.
  • We present the design, calibration, and testing of a magnetic tweezers device that employs two pairs of permanent neodymium iron boron magnets surrounded by low-carbon steel focusing tips to apply large forces to soft materials for microrheology experiments. Our design enables the application of forces in the range of 1-1800 pN to {approx}4.5 {mu}m paramagnetic beads using magnet-bead separations in the range of 0.3-20 mm. This allows the use of standard coverslips and sample geometries. A high speed camera, custom LED-based illumination scheme, and mechanically stabilized measurement platform are employed to enable the measurement of materials with viscoelastic moduli asmore » high as {approx}1 kPa.« less