Acoustofluidic microdevice for precise control of pressure nodal positions

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.