The use of ultrasound for trapping and patterning particles or cells in microfluidic systems is usually confined to particles which are considerably smaller than the acoustic wavelength. In this regime, the primary forces result in particle clustering at certain locations in the sound field, whilst secondary forces, those arising due to particle–particle interaction forces, assist this clustering process. Using a wavelength closer to the size of the particles allows one particle to be held at each primary force minimum. However, to achieve this, the influence of secondary forces needs to be carefully studied, as inter-particle attraction is highly undesirable. Here, we study the effect of particle size and material properties on both the primary and secondary acoustic forces as the particle diameter is increased towards the wavelength of the 1-dimensional axisymmetric ultrasonic field. We show that the resonance frequencies of the solid sphere have an important role in the resulting secondary forces which leads to a narrow band of frequencies that allow the patterning of large particles in a 1-D array. Knowledge regarding the naturally existent secondary forces would allow for system designs enabling single cell studies to be conducted in a biologically safe manner.

中文翻译：

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在一维超声驻波中捕获和构图大颗粒和细胞

超声波用于在微流体系统中捕获和图案化颗粒或细胞的方法通常仅限于远小于声波波长的颗粒。在这种情况下，主要作用力导致声场中某些位置处的粒子聚集，而次要作用力（由于粒子间的相互作用而产生的力）则有助于该聚集过程。使用更接近颗粒尺寸的波长可将一个颗粒保持在每个主力最小值处。然而，为了实现这一点，必须非常仔细地研究次级力的影响，因为粒子间的吸引是非常不希望的。这里，我们研究了随着粒径朝向一维轴对称超声场的波长增加，粒径和材料性质对一次和二次声力的影响。我们表明，实心球体的共振频率在产生的次级力中起着重要作用，次级力导致窄的频率带，从而允许在1-D阵列中对大颗粒进行构图。关于自然存在的次级力的知识将允许进行系统设计，从而能够以生物学上安全的方式进行单细胞研究。我们表明，实心球体的共振频率在产生的次级力中起着重要作用，次级力导致窄的频率带，从而允许在1-D阵列中对大颗粒进行构图。关于自然存在的次级力的知识将允许进行系统设计，从而能够以生物学上安全的方式进行单细胞研究。我们表明，实心球体的共振频率在产生的次级力中起着重要作用，次级力导致窄的频率带，从而允许在1-D阵列中对大颗粒进行构图。关于自然存在的次级力的知识将允许进行系统设计，从而能够以生物学上安全的方式进行单细胞研究。