This study designs a closed-loop magnetic circuit using permeable materials to increase the uniformity and intensity of the magnetic field based on an internal conductive square Magnetohydrodynamics ...(MHD) thruster that consists of a pair of NdFeB magnets. To reduce the magnetic leakage from the thruster, magnetic shields made of various permeable metals are used to encase the MHD thruster. The experimental results show that a stainless steel shell lighter than a black iron shield and moderately increases the magnetic field strength is more suitable for applications in seawater. For a single shield, the field intensity inside the thruster increases linearly with the thickness of the shell. The field strength increases further when a second shell is used. However, the field intensity decreases when the distance between the two shells is increased. An MHD thruster that is 100 mm long, 5mm wide, and 50mm high is hung on a sliding track with negligible friction and is fully submerged in the saline water for the verification of its performance. Increasing the thickness of the stainless steel shell from 2mm to 4mm results in the increase of the propulsive force from 0.064 N to 0.265 N, and the speed of the thruster from 0.075m/s to 0.098 m/s, respectively. The experimental results are used to propose a modified design for a magnetic circuit that increases the uniformity and strength of the magnetic field in the central region of a square MHD thruster that consists of permanent magnets.
Behaviors of a magnetic microchain which is an oscillating motion of micrometer-size magnetic particles’ cluster caused by an external magnetic field were investigated numerically. The hybrid ...simulation code which was based on the lattice Boltzmann method, the immersed boundary method and the discrete particle method was developed. The behaviors of a magnetic microchain depends on the number of magnetic particles in the magnetic microchain, frequency of external alternating magnetic field and the strength of applied magnetic field. Three types of behaviors, i.e., rigid rotational oscillation, rotational oscillation with deforming into S shape and splitting into several chains, depends on the number of magnetic particles.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Superparamagnetic
micro-bead chains and microswimmers under the influence of an oscillating magnetic field are studied
experimentally and numerically. The numerical scheme composed of the lattice ...Boltzmann method,
immersed boundary method, and discrete particle method based on the simplified Stokesian
dynamics is
applied to thoroughly understand the interaction between the micro-bead chain (or
swimmer), the oscillating magnetic
field, and the hydrodynamics drag. The systematic experiments and
simulations demonstrated the behaviors of the microchains and microswimmers as well as the
propulsive efficiencies of the swimmers. The effects of key parameters, such as field
strengths, frequency, and the lengths of swimmer, are thoroughly analyzed. The numerical
results are compared with the experiments and show good qualitative agreements. Our
results proposed an efficient method to predict the motions of the reversible magnetic
microdevices which may have extremely valuable applications in biotechnology.
Microfluidic devices constitute the key technology enabling the development of more functional lab-on-a-chip systems for medical applications. This study presents an alternative method for precisely ...fabricating microfluidic pillar array channels by using irradiation by an ultrashort pulse from an ultrafast laser. Unlike conventional photolithography, which requires complex procedures and techniques, the ultrafast laser process is a straightforward approach for fabricating a functional microfluidic device with multiple pulses of an ultraviolet (UV) wavelength. To satisfy the requirements of the industrial process for mass production of microfluidic devices, a picosecond (PS) laser is used as a light source. Under the optimal energy fluence of 15.28J/cm2 with a pulse overlap of 95%, the scanning curve process can be executed in the clockwise direction for forming microfluidic pillar array structures. Simultaneously, the experimental evidence shows that the ultrafast laser process produces ablated soda-lime glass channels with hydrophilic surfaces on their inner walls. Based on the processing parameters of pillar structure with the number of pulses, the value of ablation rate can be 0.04μm/pulse. This work provides a direct patterning process through which a pillar array with functional structures can be constructed within the microfluidic device.
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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 90°. 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.
Steering of Magnetic Micro-Swimmers Li, Yan-Hom; Lin, He-Ching; Chen, Ching-Yao
IEEE transactions on magnetics,
07/2013, Letnik:
49, Številka:
7
Journal Article, Conference Proceeding
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 π/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.
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
M
n
1
/
2
∗
N
>
1.7
,
where
Mn
and
N
, respectively, represent the dimensionless Mason number and the number of beads in the chain.
The dynamics of microchains containing superparamagnetic particles in an oscillating field are studied experimentally. The chains are first formed by a static directional field, and then manipulated ...by an additional dynamical perpendicular field. The present methodology represents a simple reversible chaining process, whose particles can be re-dispersed after removal of the field. The motion of superparamagnetic chains is dominated by magnetic torque and induced hydrodynamic drag. The effects of key parameters, such as field strengths and the lengths of particle chains, are thoroughly analyzed. Distinct behaviors, from rigid body oscillations and bending distortions to rupture failures, are observed by increasing the amplitudes of oscillating fields or chains’ lengths. Because of lower induced drag, a shorter chain follows the field trajectory closely and oscillates more synchronically with the external field. On the other hand, the influences of field strengths are not consistent. Even the overall oscillating phase trajectory in a stronger external field deviates less significantly from the corresponding field trajectory, a stronger dynamical component of the external field results in larger phase angle lags at certain points. The experimental results confirm the criterion of ruptures can be effectively determined by the value of (
N
*
Mn
1/2
), where
Mn
is the Mason number defined as the ratio of induced drag to dipolar attraction, and
N
represents the number of particles contained in a chain.
In this study, we investigated the dynamics of microchains containing superparamagnetic microbeads under the influence of oscillating magnetic fields in a confined space. The behavior of constrained ...microchains was investigated experimentally. Chains in confined spaces were first formed using a static directional field or a permanent magnet and then manipulated using an additional dynamical perpendicular field. An oscillating chain in a confined space can be designed to mimic magnetosome chains synthesized by magnetotactic bacteria, which have been exploited recently for various applications in biological and medical sciences. The effects of crucial parameters, such as the lengths of particle chains and sizes of confined spaces, were thoroughly analyzed to observe the distinct behavior and investigate the dynamics of the constrained chains.
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•Magnetosome-like chains were produced by superparamagnetic micro-beads.•Dynamical chains in confined space sustain stronger induced drags than in free one.•Confined spaces lead to significant phase lag angle but hardly impact oscillating amplitude.•Magnetic particle chain is more unstable while being manipulated in confined space.
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