Controlling Acoustic Traps for the Contactless Handling of Objects (CATCH)

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The contactless manipulation of liquid drops and delicate solid objects by acoustic levitation methods has numerous applications in chemistry, pharmacy, biology, and microelectronics. Over the last years, new advances in acoustic levitation enabled the controlled motion of levitated objects in 3D, but undesired oscillations may hinder certain applications that require a high precision in motion. To increase the manipulation speed and reduce undesired oscillations, we will investigate the application of open-loop and closed-loop control systems in the context of acoustic levitation. This investigation will be conducted by combining the German group’s expertise in control engineering with the Brazilian group’s expertise in acoustic levitation systems. In this study, liquid and solid objects will be levitated and manipulated by an acoustic levitation system consisting of a phased array of low power ultrasonic transducers. Control engineering methods, such as feed forward control and H-infinity control, will be applied to both reduce the oscillation and increase the manipulation speed of the levitated object. This investigation will be divided into three parts. We will start our study by designing an appropriate acoustic levitation system and creating a corresponding white-box model, which parameters will be experimentally determined by system identification methods. Subsequently, we employ the created model to develop an open-loop control system to manipulate solids and liquids. These results will be utilized for the development of a camera-based real time closed-loop position control to handle model errors and process disturbances such as acoustic streaming. The improvements of the controlled process will be evaluated using criteria such as absolute position error, maximum speed and oscillation amplitude. Finally, the new levitation system will be installed in a Small-Angle X-ray Scattering (SAXS) equipment in order to manipulate, mix, and analyze levitating substances in mid-air.