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Magnetic microdevices

Creation of magnetic field driven microdevices for the targeted transport, mixing in microfluidics has been the subject of the investigation for a couple of years. Physical models are based on the extension of the Kirchhoff model of an elastic rod by adding the energy terms, which depend on the magnetic properties of the rod. It predicts buckling instabilities of superparamagnetic and ferromagnetic rods, which lead to the formation of hairpins in the case of superparamagnetic filaments and loops in the case of ferromagnetic filaments. Accounting for the anisotropy of the hydrodynamic drag the self-propulsion of the hairpin in an AC magnetic field is predicted. The self-propelling motion of the ferromagnetic filaments reminds the motion of Chlamydomonos cells consisting in forward motion with subsequent backward steps. The efficient numerical algorithm based on the projection operator for the numerical simulation of the filaments is developed.It allows us to simulate the loop formation by the ferromagnetic filament at the magnetic field inversion and its relaxation by overturning the loop through third dimension. The thermal fluctuations of the magnetic filaments are analyzed and the dispersion of the magnetic susceptibility of the suspension of magnetic filaments calculated. Interesting feature of the behavior of magnetic filaments in the high-frequency magnetic field consists in the orientation of the magnetic rod perpendicularly to the field, which is confirmed experimentally. Twisting of magnetic rods is considered in a couple of papers. The self-propulsion of the filament induced by periodic twist under the action of the AC magnetic field is analyzed in order to explain the experimental results. The motion of the magnetic cilia under the action of rotating field as prototipe of mixer in microfluidics is described. A model of the magnetic swimmer which consists of magnetic dipole with attached non-magnetic flexible tail is considered. Its self-propulsion occurs due to the wave propagating along the tail caused by orientation oscillations of the dipole in AC magnetic field. Finite magnetic relaxation time of the magnetic rod and its role in the behavior of the magnetic filaments in the rotating field is considered. In several situation the dynamics of flexible rods may be described in terms of their intrinsic parameters.
  1. A.Cebers. Dynamics of a chain of magnetic particles connected with elastic linkers. Journal of Physics: Condensed Matter – 2003, v.15 – P.S1335–S1344
  2. A.Cebers. Flexible magnetic filaments. Current Opinion in Colloid&Interface Science – 2005 ,v.10, - P.167-175.
  3. M.Belovs, A.Cebers. Nonlinear dynamics of semiflexible magnetic filaments in an ac magnetic field. Physical Review E- 2006, v.73- 051503
  4. K.Ērglis,D.Zhulenkovs,A.Sharipo, and A.Cēbers. Elastic properties of DNA linked flexible magnetic filaments. J.Phys.:Condens.Matter – 2008, v.20, 204107
  5. K.Ērglis, R.Livanovičs, A.Cēbers. Three dimensional instability of the flexible ferromagnetic loop. Magnetohydrodynamics -2010, v.46, 245-256
  6. A.Cebers. Flexible magnetic swimmer. Magnetohydrodynamics -2005,v.41 –P.63-71.
  7.  M.Belovs, and A.Cēbers. Ferromagnetic microswimmer. Phys.Rev.E – 2009, v.79, 051503;Erratum:Ferromagnetic microswimmer [Phys.Rev.E 79,051503 (2009)]. Phys.Rev.E – 2009, v.79, 069906(E).
  8. M.Belovs, and A.Cebers. Dynamic fluctuations of dipolar semiflexible filaments. Physical Review E -2006,v.73 – 021507
  9. K.Ērglis, M.Belovs, A.Cēbers. Flexible ferromagnetic filaments and the interface with biology. Journal of Magnetism and Magnetic Materials – 2009, v.321, P.650-654.
  10. M.Belovs, A.Cēbers. Properties of twisted ferromagnetic filaments. Journal of Physics:Conf.Ser. -2009, v.149, 012103.
  11. M.Belovs, T.Cīrulis, and A.Cēbers. Equilibrium shapes of twisted magnetic filaments. J.Phys.A:Math.Theor. – 2009,v.42, 235206
  12. G.Oukhaled, A.Cebers, J.-C.Bacri, J.-M. Di Meglio, Ch.Py. Twisting and buckling: A new undulation mechanism for artificial swimmers. European Physical Journal E – 2012,v.35,121.
  13. M.Belovs, and A.Cēbers. Parametric excitation of bending deformations of a rod by periodic twist. Phys.Rev.E, - 2013, v.87, 023202
  14. A.Cēbers, R.Livanovičs. Flexible ferromagnetic filaments as artificial cilia. International Journal of Modern Physics B – 2011, v.25, 935-941
  15. R.Livanovics, and A.Cēbers. Magnetic dipole with a flexible tail as a self-propelling microdevice. Phys.Rev.E - 2012, v.85,041502
  16. A.Cēbers, H.Kalis. Dynamics of superparamagnetic filaments with finite magnetic relaxation time. European Physical Journal E - 2011,v.34,30.
  17. A.Cebers, and H.Kalis. Intrinsic curve dynamics of magnetic filaments. Magnetohydrodynamics - 2011,v.47, 223-236.