In this presentation, we will unveil some cutting-edge recent advancements in acoustic micro-actuators. First, we will demonstrate that GHz actuators not only uniquely enable the synthesis of microjets at speeds of up to meters per second, but also that these speeds could be reached in microseconds, leading to phenomenal accelerations in the mega-g range. Second, we will reveal our latest developments in IDT-based selective manipulation, including 3D trapping and displacement, precise rotation control, and high-resolution patterning. These advancements herald a new era of versatility and control in micro-actuation technology, opening doors to a myriad of transformative applications in micro-robotics, biomedicine, and beyond.

Optical and acoustic forces are both utilized for contact-free manipulation of biological samples in micro-fluidic chambers. While holographic optical tweezers provide fine control of µm-size objects such as cells, acoustic forces are strong enough to handle mm-size samples such as organoids, cancer spheroids or early stage developing organisms. Acoustofluidic actuation, for example, enables the tomographic 3D reconstruction of a zebrafish embryo by OCT, which is otherwise impeded by severe attenuation artifacts. A significant challenge here, however, lies in the fact that the exact orientations of the sample are not known a priori, which requires a more sophisticated reconstruction algorithm.

When considering small particles with respect to the wavelength, the equilibrium positions in radiation traps depend on the properties of the particle and the medium, while the potential energy landscape is entirely determined by the incident wave field. In contrast, large particles add a significant scattered field and the potential becomes particle-dependent, implying that two particles of identical properties find different equilibrium positions depending on their size. This is a general feature of radiation traps, as we show in optics and acoustics.