Acoustic wave-based manipulation of cells and particles in microfluidic channels has gained wide popularity in the past decade since it provides label-free and contact-less manipulation of them in a microfluidic environment using a very simple microfluidic structure and experimental setup. In bulk acoustofluidics, an acoustic resonance field that generates an acoustic standing wave within a microfluidic channel creates acoustic pressure nodes and anti-nodes, to which particles migrate to or migrate away from. However, in a given straight microfluidic channel, the position of the acoustic pressure nodes and anti-nodes are fixed and cannot be changed along the channel, limiting more diverse capabilities in moving particles and cells to a desired location within a microfluidic channel. Here, an acoustic echo-channel where its width changes along the flow direction was created right next to the main flow channel separated by a thin wall that minimizes the disturbance of the acoustic wave. This allows the location of the acoustic pressure nodes and anti-nodes to be controlled in the main flow channel depending on the width of the echo-channel, hence providing more flexibility in manipulating particles and cells to a certain position within a given microfluidic channel. The capability to more freely manipulate particles and cells within a microfluidic channel further expands the application areas of bulk acoustofluidics.

在过去的十年中，基于声波的细胞和粒子在微流体通道中的操纵已获得广泛的普及，因为它使用非常简单的微流体结构和实验装置就可以在微流体环境中对它们进行无标签和无接触的操纵。在体声流体中，在微流体通道内产生声驻波的声共振场会产生声压节点和波腹，粒子迁移到该声波节点或从其扩散出去。然而，在给定的笔直的微流体通道中，声压节点和波腹的位置是固定的，并且不能沿着该通道改变，这限制了将颗粒和细胞移动到微流体通道内所需位置的更多能力。这里，在紧靠薄壁分隔的主流动通道旁边创建了一个沿宽度方向沿宽度方向变化的声学回声通道，该通道将声波的干扰降至最低。这允许根据回声通道的宽度来控制声压节点和波腹在主流通道中的位置，从而在将粒子和细胞操纵到给定微流体通道内的特定位置时提供更大的灵活性。在微流体通道内更自由地操纵颗粒和细胞的能力进一步扩大了大体积声流体技术的应用领域。这允许根据回声通道的宽度来控制声压节点和波腹在主流通道中的位置，从而在将粒子和细胞操纵到给定微流体通道内的特定位置时提供更大的灵活性。在微流体通道内更自由地操纵颗粒和细胞的能力进一步扩大了大体积声流体技术的应用领域。这允许根据回声通道的宽度来控制声压节点和波腹在主流通道中的位置，从而在将粒子和细胞操纵到给定微流体通道内的特定位置时提供更大的灵活性。在微流体通道内更自由地操纵颗粒和细胞的能力进一步扩大了大体积声流体技术的应用领域。