We present a method for size-independent manipulation of elastic polystyrene (PS), poly(methyl methacrylate) (PMMA), and fused silica (FS) microspheres that uses travelling surface acoustic waves (TSAWs). Normally incident TSAWs originating from an interdigitated transducer (IDT) were used to separate similar-sized pairs of PS and PMMA or PS and FS elastic particles by producing distinct lateral deflections across laminar streamlines in a continuous flow microfluidic channel. Elastic particles with similar diameters but different acoustic impedances exhibit significantly different deflection characteristics when exposed to TSAW-based acoustic radiation forces (ARFs). For instance, exposing a mixture of PS and PMMA particles with similar diameters (～5 μm) to TSAWs with frequencies of 140 MHz and 185 MHz produces larger deflections of the PS and PMMA particles, respectively. This difference arises because of the resonance of the elastic particles with the incoming acoustic waves at certain frequencies. Similar particle deflection characteristics were observed for mixtures of PS and FS particles with comparable diameters (3/3, 4.8/5, 10/10 μm). This difference in deflection distances was used to experimentally characterize the non-linear behavior of the ARFs acting on particles (3–10 μm) exposed to a range of TSAW frequencies (120–205 MHz). Our experimental results can be explained by plotting the acoustic radiation force factor (FF) against the TSAW frequency (fTSAW) and the dimensionless Helmholtz number (1 < κ < 4), which is calculated by using a theoretical model of an elastic microsphere suspended in a fluid.
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机译：我们提出了一种使用行波表面声波（TSAWs）的弹性聚苯乙烯（PS），聚甲基丙烯酸甲酯（PMMA）和熔融石英（FS）微球尺寸无关的操纵方法。源自叉指换能器（IDT）的法向入射TSAW通过在连续流微流体通道中跨层流线产生明显的侧向偏转，从而分离出类似尺寸的PS和PMMA或PS和FS弹性颗粒对。当暴露于基于TSAW的声辐射力（ARF）时，具有相似直径但声阻抗不同的弹性颗粒表现出明显不同的偏转特性。例如，将直径相似（约5μm）的PS和PMMA颗粒的混合物暴露于140 MHz和185 MHz频率的TSAW时，分别会产生更大的PS和PMMA颗粒挠度。之所以会出现这种差异，是因为弹性粒子在某些频率下会与传入的声波发生共振。对于具有可比较的直径（3 / 3、4.8 / 5、10 / 10μm）的PS和FS颗粒的混合物，观察到了相似的颗粒偏转特性。偏转距离的这种差异用于实验表征ARF的非线性行为，该ARF作用于暴露于一定范围TSAW频率（120-205 MHz）的粒子（3-10μm）。通过将声辐射力因子（ F F ）相对于TSAW频率（ f TSAW ）和无因次亥姆霍兹数（1 em>κ <4），这是通过使用悬浮的弹性微球理论模型计算得出的在流体中。
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