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@ARTICLE{Zhang:912060,
      author       = {Zhang, Zhiyuan and Sukhov, Alexander and Harting, Jens and
                      Malgaretti, Paolo and Ahmed, Daniel},
      title        = {{R}olling {M}icroswarms along {A}coustic {V}irtual {W}alls},
      journal      = {nature communications},
      volume       = {13},
      reportid     = {FZJ-2022-05287},
      pages        = {7347},
      year         = {2022},
      abstract     = {Rolling is a ubiquitous mode of transport utilized by both
                      living organisms and engineeredsystems. Rolling, on the
                      microscale, has become particularly interesting for the
                      manipulationof microswarms, since enacting such motion does
                      not require special prefabrication techniques.However,
                      rolling motion has to date been restricted by the need for a
                      physical boundary to breakthe spatial homogeneity of
                      surrounding mediums, which limits its prospects for
                      microswarmnavigation and cargo delivery to locations with no
                      boundaries. Here, in the absence of realphysical boundaries,
                      we show that chain-shaped microswarms can undergo rolling
                      motion alongvirtual walls in the aqueous medium, impelled by
                      a combination of magnetic and acousticfields. A rotational
                      magnetic field causes individual particles to self-assemble
                      and rotate, whilethe pressure nodes generated by an acoustic
                      standing wave field serve as virtual walls. Theacoustic
                      radiation force pushes the rotating microswarms towards a
                      virtual wall and providesthe reaction force needed to break
                      their fore-aft motion symmetry and induce rolling. Wedevelop
                      an experiment-supported theoretical model to quantify the
                      net displacement generatedby rolling. Finally, we
                      demonstrate that rolling can be achieved along arbitrary
                      trajectoriesby dynamically switching the orientation of the
                      virtual walls and the rotational directions ofthe magnetic
                      field. Consequently, the concept of reconfigurable virtual
                      walls developed hereovercomes the fundamental limitation of
                      a physical boundary being required for universalrolling
                      movements.},
      cin          = {IEK-11},
      cid          = {I:(DE-Juel1)IEK-11-20140314},
      pnm          = {1215 - Simulations, Theory, Optics, and Analytics (STOA)
                      (POF4-121)},
      pid          = {G:(DE-HGF)POF4-1215},
      typ          = {PUB:(DE-HGF)25},
      doi          = {10.21203/rs.3.rs-1505456/v1},
      url          = {https://juser.fz-juelich.de/record/912060},
}