Dynamic-field acoustic manipulation techniques benefit numerous applications in microsystem assembly, pattern formation, biological research, tissue engineering, and lab-on-a-chip. These techniques generally rely on a theoretical dynamic model of particle motion in the acoustic field. Accordingly, success of the manipulation task highly depends on the accuracy of the employed dynamic model. However, modelling such dynamic behavior is a great challenge in more advanced acoustic manipulation devices and requires significant simplifications. Here, we introduce a model-free control method based on reinforcement learning for highly-dynamic acoustic manipulation devices. In our method, the controller does not need a prior knowledge of the acoustic field and learns the optimal control policy for each manipulation task by merely interacting with the acoustic field. As a proof-of-concept, we apply our method to a classic acoustic manipulation device, a Chladni plate consisting of a centrally-actuated vibrating plate. By employing the controller, we demonstrate successful manipulation of single and multiple particles towards target locations on the plate surface. The model-free control method is not limited to the Chladni plate and can be potentially applied to a broad range of acoustic manipulation devices as well as other forms of field-based micromanipulation systems, where accurate theoretical modelling of the field is challenging. INDEX TERMS Acoustic manipulation, Chladni plate, dynamic-filed acoustic device, model-free control, real-time control, reinforcement learning.
Acoustic manipulation techniques are becoming increasingly common with a range of applications in the biomedical research, microassembly, and lab-on-a-chip. Recently, a class of devices have attracted considerable attention which utilize dynamic and reconfigurable acoustic fields, known as dynamic-field acoustic devices. A common method of applying dynamic fields is to use mode-switching by rapidly altering the excitation frequency. Such methods generally rely on the switching being performed faster than the time constant associated with the particle motion. Nevertheless, it remains a grand challenge to eliminate or at least reduce the switching time to a minimal value. In this paper, we suggest employing a high-speed controller to minimize the switching time, enabling continuous particle manipulation in a dynamic-field acoustic device. As a proof-of-concept, we apply such idea to a classic acoustic manipulation device, a Chladni plate which consists of a centrally-actuated vibrating plate. By employing a closed-loop real-time controller, we show successful manipulation of particles on the plate on predefined trajectories. The high-speed switching methodology can also be applied to other dynamic-field acoustic methods, such as surface acoustic wave (SAW) devices, acoustic levitators, and in-fluid acoustic devices. This can result in faster and smoother particle manipulation in such devices.
In nature, simple building units can be assembled into complex shapes through long-term time-varying external stimuli that are often spatially nonlinear. In contrast, most artificial methods of externally directed assembly rely on field-or template-based energy minimization. However, methods directing the assembly process by controlling time-varying external stimuli instead of attaining the lowest-energy state remain largely unexplored. In this study, we introduce a method that applies time-varying and spatially nonlinear vibration fields to assemble particles into a desired two-dimensional shape. Our assembly method predicts, controls, and monitors the vibrationinduced particle motion to iteratively minimize the difference between the desired shape and the actual particle distribution. We applied our method to a centrally actuated vibrating plate, also known as a Chladni plate, and assembled up to a hundred submillimeter particles into complex recognizable shapes. The method allows programmable formation of shapes beyond the intrinsic limits of periodic patterning of the plate.
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