Assembly and dynamic manipulations of 3D Chladni figures in a cylindrical cavity using standing bulk acoustic waves

A method based on standing bulk acoustic waves (BAWs) is introduced for the three-dimensional (3D) arrangement and manipulation of microparticles in a fluid. Specifically, the study demonstrates the simultaneous assembly of both Chladni and inverse Chladni figures by generating controllable 3D standing BAWs in a cylindrical cavity using a single piezoelectric transducer. An aluminum alloy chip-based acoustofluidic device is developed for ultrasonic microparticle manipulations. When exposed to harmonic ultrasonic excitations, standing BAWs are generated in the cylindrical cavity, causing the suspended particles to spontaneously arrange into Chladni patterns, ranging from one-dimensional to 3D spatial structures. Dynamic switching between different Chladni figures can be achieved by adjusting the driving frequencies. 3D finite element simulations were performed to analyze the microparticle acoustophoresis in the cylindrical cavity, which coincides with the experimental observations. Furthermore, we demonstrate that various dynamic manipulations of particle clusters can be achieved by dexterously adjusting the amplitude of the ultrasonic fields. These manipulations allow for transitions between Chaldni and inverse Chladni figures. This BAW tweezer can therefore easily achieve dexterous 3D particle patterning, offering a convenient and effective solution in the development of tissue engineering or additive manufacturing.