Acoustic radiation force is a net force experienced by an object under the action of an acoustic wave. Most theoretical models require the acoustic wave to be periodic, if not purely monofrequency, and are therefore irrelevant for the study of acoustic radiation force due to acoustic pulses. Here, we introduce the concept of finite-duration pulses, which is the most general condition to derive the acoustic radiation force. In the case of small spheres, we extend the Gor’kov formula to unsteady acoustic fields such as traveling pulses and interfering wave packets. In the latter case, our study suggests that the concept of acoustic contrast is also relevant to express the acoustic radiation force. For negative acoustic contrast particles, the acoustic trapping region narrows with shorter pulses, whereas positive contrast particles (such as biological cells) can fall in secondary traps when the pulse width deviates from an optimal value. This theoretical insight may help to improve the selectivity of pulsed acoustic tweezers.

中文翻译：

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瞬态声场对小球体的声辐射力

声辐射力是物体在声波作用下承受的净力。大多数理论模型都要求声波是周期性的，即使不是纯单频的也是如此，因此与研究声脉冲引起的声辐射力无关。在这里，我们介绍了有限持续时间脉冲的概念，这是得出声辐射力的最一般条件。对于小球体，我们将Gor'kov公式扩展到不稳定的声场，例如行进脉冲和干扰波包。在后一种情况下，我们的研究表明，声学对比的概念也与表达声辐射力有关。对于负的声学对比粒子，声捕获区域会随着较短的脉冲而变窄，反之，当脉冲宽度偏离最佳值时，正反差粒子（例如生物细胞）会掉入次级陷阱。这种理论上的见识可能有助于提高脉冲声镊的选择性。