Browsing by Author "Lin, He-Ching"

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DYNAMICS OF A SUPERPARAMAGNETIC MICROPARTICLE CHAIN IN AN OSCILLATING MAGNETIC FIELD: EFFECTS OF FIELD FREQUENCY
(2017-07-01)
Chen, Ching-Yao
;
Lin, He-Ching
;
Teng, Che-Jui
;
Li, Yan-Hom
;
機械工程學系
Dynamics of an oscillating chain consisting of several magnetic microparticles and driven by oscillating magnetic fields with different frequencies are discussed. Because of a shorter driving time by the external field with a higher field frequency, the oscillating amplitude of the chain reduces. On the other hand, the higher field frequency leads to a faster local angular velocity. These two effects result in inconsistent behavior of the structural stability of the chain, so that the chain ruptures in a field of intermediate frequency. A dimensionless parameter of the reduced frequency is proposed to generally describe the monotonic decrease of the normalized amplitude. The phenomenon of trajectory shift triggered by the higher frequency field is also demonstrated.
Steering of Magnetic Micro-Swimmers
(2013-07-01)
Li, Yan-Hom
;
Lin, He-Ching
;
Chen, Ching-Yao
;
機械工程學系
;
Department of Mechanical Engineering
We experimentally investigate the motion of micro-swimmers consisting of several magnetic particles with different sizes. Swimmers are firstly formed by a static unidirectional field, and then manipulated by an additional dynamical perpendicular field. It is known that such magnetic-particle swimmers (or chains) driven by an external field would oscillate with the orientation of the field but lagging behind by a certain phase angle. In this work, we demonstrate if a swimmer subjected to a strong oscillating field which results in an instantaneous phase lag greater than pi/2, the swimmer can be steered perpendicularly to its original direction. Detailed swimming mechanism and trajectory are presented. By this innovative steering technology, orientation of a micro-swimmer can be effectively manipulated without a physical reconfiguration of the external field arrangement.
Structural instability of an oscillating superparamagnetic micro-bead chain
(2014-07-01)
Lin, He-Ching
;
Li, Yan-Hom
;
Chen, Ching-Yao
;
機械工程學系
;
Department of Mechanical Engineering
Issues concerning the structural instability of an oscillating micro-bead chain are addressed based on systematic experiments. The patterns of rupture are categorized into two distinct regimes, referred to as a weak ductile fracture and a strong ductile fracture. A weak ductile fracture describes a more rigid rupture, which often occurs in a pronounced oscillation driven by strong field strengths. The position of the rupture usually favors toward the two sides of the chain. An interesting phenomenon of a reversed rupture, wherein the ruptured segments oscillate in opposite directions, is observed when there is excessive field strength. An important consequence of the reversed rupture is to cause permanent failure of the chaining structure. On the other hand, a strong ductile fracture, featuring significant deformation before rupture, is favored in a more viscous solvent fluid. The positions of the breakages in this regime favor the central region of the chain. The prominence of rupture instability is enhanced by a weaker directional field or by a longer chain, which is in agreement with quantitative assessments by the normal forces acting between the interfaces of beads. In addition, results of the present experiments provide further validations of the global criterion for rupture instability given by where Mn and N, respectively, represent the dimensionless Mason number and the number of beads in the chain.
Structural instability of an oscillating superparamagnetic micro-bead chain
(2014-07-01)
Lin, He-Ching
;
Li, Yan-Hom
;
Chen, Ching-Yao
;
機械工程學系
;
Department of Mechanical Engineering
Issues concerning the structural instability of an oscillating micro-bead chain are addressed based on systematic experiments. The patterns of rupture are categorized into two distinct regimes, referred to as a weak ductile fracture and a strong ductile fracture. A weak ductile fracture describes a more rigid rupture, which often occurs in a pronounced oscillation driven by strong field strengths. The position of the rupture usually favors toward the two sides of the chain. An interesting phenomenon of a reversed rupture, wherein the ruptured segments oscillate in opposite directions, is observed when there is excessive field strength. An important consequence of the reversed rupture is to cause permanent failure of the chaining structure. On the other hand, a strong ductile fracture, featuring significant deformation before rupture, is favored in a more viscous solvent fluid. The positions of the breakages in this regime favor the central region of the chain. The prominence of rupture instability is enhanced by a weaker directional field or by a longer chain, which is in agreement with quantitative assessments by the normal forces acting between the interfaces of beads. In addition, results of the present experiments provide further validations of the global criterion for rupture instability given by where Mn and N, respectively, represent the dimensionless Mason number and the number of beads in the chain.
Trajectory shift of magnetic microchains in an oscillating field
(2013-05-01)
Li, Yan-Hom
;
Lin, He-Ching
;
Chen, Ching-Yao
;
機械工程學系
;
Department of Mechanical Engineering
We report an interesting phenomenon of "trajectory shift" of magnetic chains in an oscillating field, when the phase angle lags of chains to the external field exceeding 90A degrees. The phenomenon shifts the oscillating trajectory of chain along a new axis, which is perpendicular to its original axis. Applicability of the phenomenon to a stable chain in various conditions is experimented systematically. The trajectory shift provides an effective manipulating mechanism in micro-electro-mechanical-systems, such as steering of micro-swimmers. We successfully demonstrate that the driven direction of a micro-swimmer can be controlled by shifting its oscillating trajectory without a physical re-configuration of the external field.