Due to the flow limitations at the low Reynolds regime, reliable mixing is essential for a variety of lab-on-chip applications in chemical as well as biomedical analysis. Our acoustic-based mixer consists of a series of alternating embedded microbubbles with wall thickness T = 5 µm arranged along a single microchannel. The channel dimension D has been set to 150 µm based on numerical investigations to ensure strong and local streaming near the microstructures. Two liquids, i.e., de-ionised water and blue ink, are introduced through separated channels while their volume flow is controlled via a high-precision microfluidic pumping system to achieve an average flow velocity v avg . The inlet channels meet at an angle of 90°to minimise diffusion-based mixing while avoiding possible acoustic streaming near sharp-edge features. Figure 4 b) shows the PDMS device with the two laminar flows prior to acoustic excitation, i.e., the piezoelectric transducer is off, as well as during mixing of two fluids using an input voltage of 20 V PP (see Supporting Information SV-3). The average flow velocity inside the microchannel is v avg = 2.13 mm s -1 , which, despite requiring significantly lower input power and not relying on surface treatments, is comparable to results presented for solid-structure-based acoustic mixers. Additionally, as our design allows to prevent geometrical constrictions, unintended trapping of microbubbles inside the mixing channel can be avoided. While bubble-based acoustic mixers allow for increased handling of fluid volumes, our approach circumvents their limitations in temporal stability and re-usability. The graph in Figure ) demonstrates the experimentally determined relationship between the applied input power and the acoustic manipulation capabilities of our device. To allow for the evaluation of device performance, we calculated the mixing indices at different positions of the microchannel, starting with position 1 in front of the mixer (see red labels in Figure ) ). For each position, a mixing index has been derived as the standard deviation of the normalised grey-scale image (area highlighted with yellow lines). A threshold of 10 % has been defined as sufficient mixing based on previous literature. The graph demonstrates that, for our design with 20 alternating embedded microbubbles and for average flow velocities v avg = 2.13 mm s -1 , successful mixing can be achieved for excitation voltages as low as 16 V PP (blue squares) while, for 20 V PP (orange triangle), the threshold is already reached after 8 features.