磁性粒子串於旋轉磁場下交互作用之運動

Interaction of Magnetic Micro-Chains in a Rotating Magnetic Field

林志儒(Chih-Ru Lin)

指導教授 ： 陳慶耀

國立交通大學/工學院/機械工程系所/碩士(2019年)

摘要

由於透過外加磁場可以有效的控制磁性流體中的磁性微粒子，這方面的研究一直是我們非常感興趣的主題。此篇研究主要專注於透過外加旋轉磁場觀察流體中磁性微粒子串的運動現象，在這樣的條件下，磁性粒子串主要會有兩種運動現象，其一為自體受到磁場影響之自轉運動，另一則為受磁性粒子串間磁力影響之公轉運動。由於磁性粒子串之自轉是因為在粒子串與外加磁場之相位角差導致的磁性力矩，粒子串之自轉運動會以與外加磁場之相同頻率旋轉。另外，粒子串彼此之間的吸引力或排斥力使得粒子串在切線方向上產生類似於星球公轉之運動。為了瞭解兩磁性粒子串受到彼此間磁力以及外加磁場影響之運動，我們利用直徑為4.5μm之磁性微粒子進行實驗。在實驗中我們可以發現在粒子串間存在兩種可能之運動，其一為串接運動(Chaining motion)，另外則是互旋運動(Locking motion)。通常的情況下，兩粒子串受到彼此間磁力影響會逐漸靠近最後串接形成一較長串之粒子串。然而，在實驗中我們可以發現另一有趣之運動現象，也就是兩串粒子串可能彼此接近達到平衡後進行互旋運動。在此運動下，兩粒子串以近乎平行的角度相對於某一點進行公轉運動，此現象與雙星互繞之運動極為相似。為了瞭解區別這兩種運動現象，我們對於粒子串之受力進行分析，其中項是受磁場產生之磁力，流體於粒子間摩擦造成之流體阻力。透過這兩種力之間的平衡來分析互旋運動之現象。

關鍵字

超順磁性微米粒子 ； 旋轉磁場 ； 互旋運動

並列摘要

Magneto-microfluidics have been popular research subjects because of their effective manipulability by an external magnetic field. One particular branch of these studies focuses on microchains consisted of magnetic particles and driven by a rotating field. Under such a condition, the microchains are induced to perform two distinct modes of rotational motion: individual rotation and global revolution. Because of the magnetic torque induced by the phase lag between the external field and the individual microchain, the microchain rotates synchronously with the field. On the other hand, the magnetic attraction/repulsion between the microchains drives the microchains undergoing tangential motion similar to planetary revolution. To elucidate the dual rotational motion, experiments of two microchains, consisted of several 5-micrometer magnetic beads, are conducted. Two possible modes of the magnetic interactions between the chains are identified, referred to as chaining and lock-on, respectively. In more common situations, the two chains, subjected an overall magnetic attraction to each other while undergoing global revolution, would approach to connect, and form a longer rotating chain. Nevertheless, an interesting mode of lock-on may occur, in which the two chain appear nearly parallel, and revolute along a certain origin, whose orbits mimic the system of binary stars. To understand the dynamics of these two distinct modes, the forces involves in the system, such as magnetic forces and hydrodynamic drags, are evaluated. The criterion forming the lock-on mode is analyzed based on the balance of these two forces.

並列關鍵字

Superparamagnetic micro particle ； Rotational magnetic field ； Locking motion

參考文獻

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[3] https://en.wikipedia.org/wiki/Ferrofluid

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