利用形状多样性进行磁性微螺旋桨的新结构-功能设计
Using Shape Diversity on the way to new Structure-Function Designs for Magnetic Micropropellers
摘要：
近年来，在微尺度上模仿生物运动的合成微游泳者已经被开发出来。利用均匀旋转磁场致动螺旋磁性材料是微尺度推进的最广泛的技术之一，部分原因是致动策略围绕致动场频率和螺旋桨速度之间的简单线性关系。然而，完全控制游泳运动员的运动仍然是一个挑战。提高微螺旋桨的可控性对于实现复杂的致动方案至关重要，而复杂的致动方案又与许多应用直接相关。然而，线性关系的简单性限制了群体控制的可能性和灵活性。使用一个池的随机形状的磁性microswimmer，我们表明，形状的复杂性可以有利地转化为增强控制。特别地，通过致动场的频率来控制分选的微螺旋桨的方向反转。这种方向性变化与磁力和流体动力之间的平衡有关。我们进一步展示了一个例子，这种行为可以实验导致简单而有效的排序的个人游泳者从一组。这些螺旋桨仅通过频率来反转游泳方向的能力增加了控制可能性，并且是螺旋桨设计的示例，其中许多应用所需的复杂性直接嵌入螺旋桨几何形状中，而不是诸如致动序列的外部因素。
英文摘要：
Synthetic microswimmers mimicking biological movements at the microscale have been developed in recent years. Actuating helical magnetic materials with a homogeneous rotating magnetic field is one of the most widespread techniques for propulsion at the microscale, partly because the actuation strategy revolves around a simple linear relationship between the actuating field frequency and the propeller velocity. However, the full control of the swimmers' motion has remained a challenge. Increasing the controllability of micropropellers is crucial to achieve complex actuation schemes that in turn are directly relevant for numerous applications. The simplicity of the linear relationship though limits the possibilities and flexibilities of swarm control. Using a pool of randomly-shaped magnetic microswimmers, we show that the complexity of shape can advantageously be translated into enhanced control. In particular, directional reversal of sorted micropropellers is controlled by the frequency of the actuating field. This directionality change is linked to the balance between magnetic and hydrodynamic forces. We further show an example how this behavior can experimentally lead to simple and effective sorting of individual swimmers from a group. The ability of these propellers to reverse swimming direction solely by frequency increases the control possibilities and is an example for propeller designs, where the complexity needed for many applications is embedded directly in the propeller geometry rather than external factors such as actuation sequences.
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