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@ARTICLE{Chen:189337,
      author       = {Chen, La and Offenhäusser, Andreas and Krause,
                      Hans-Joachim},
      title        = {{M}agnetic tweezers with high permeability electromagnets
                      for fast actuation of magnetic beads},
      journal      = {Review of scientific instruments},
      volume       = {86},
      number       = {4},
      issn         = {1089-7623},
      address      = {[S.l.]},
      publisher    = {American Institute of Physics},
      reportid     = {FZJ-2015-02515},
      pages        = {044701 -},
      year         = {2015},
      abstract     = {As a powerful and versatile scientific instrument, magnetic
                      tweezers have been widely used in biophysical research
                      areas, such as mechanical cell properties and single
                      molecule manipulation. If one wants to steer bead position,
                      the nonlinearity of magnetic properties and the strong
                      position dependence of the magnetic field in most magnetic
                      tweezers lead to quite a challenge in their control. In this
                      article, we report multi-pole electromagnetic tweezers with
                      high permeability cores yielding high force output, good
                      maneuverability, and flexible design. For modeling, we
                      adopted a piece-wise linear dependence of magnetization on
                      field to characterize the magnetic beads. We implemented a
                      bi-linear interpolation of magnetic field in the work space,
                      based on a lookup table obtained from finite element
                      simulation. The electronics and software were custom-made to
                      achieve high performance. In addition, the effects of
                      dimension and defect on structure of magnetic tips also were
                      inspected. In a workspace with size of 0.1 × 0.1 mm2, a
                      force of up to 400 pN can be applied on a 2.8 μm
                      superparamagnetic bead in any direction within the plane.
                      Because the magnetic particle is always pulled towards a
                      tip, the pulling forces from the pole tips have to be well
                      balanced in order to achieve control of the particle’s
                      position. Active video tracking based feedback control is
                      implemented, which is able to work at a speed of up to 1
                      kHz, yielding good maneuverability of the magnetic beads.},
      cin          = {PGI-8 / ICS-8 / JARA-FIT},
      ddc          = {530},
      cid          = {I:(DE-Juel1)PGI-8-20110106 / I:(DE-Juel1)ICS-8-20110106 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {552 - Engineering Cell Function (POF3-552) / 553 - Physical
                      Basis of Diseases (POF3-553) / 523 - Controlling
                      Configuration-Based Phenomena (POF3-523)},
      pid          = {G:(DE-HGF)POF3-552 / G:(DE-HGF)POF3-553 /
                      G:(DE-HGF)POF3-523},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000353837700041},
      pubmed       = {pmid:25933874},
      doi          = {10.1063/1.4916255},
      url          = {https://juser.fz-juelich.de/record/189337},
}