Our world is increasingly powered by electricity, which is largely converted to or from mechanical energy using electric motors. Several applications have driven the miniaturization of these machines, resulting in high rotational speeds. Although speeds of several hundred thousand revolutions per minute have been used industrially, we report the realization of an electrical motor reaching 40 million rpm to explore the underlying physical boundaries. Millimeter-scale steel spheres, which are levitated and accelerated by magnetic fields inside a vacuum, are used as a rotor. Circumferential speeds exceeding 1000 m/s and centrifugal accelerations of more than 4 × 10⁸ times gravity were reached. The results open up new research possibilities, such as the testing of materials under extreme centrifugal load, and provide insights into the development of future electric drive systems.

Objective: This paper presents a comparative study of computational fluid dynamic (CFD) simulations and in vitro hemolysis examinations of a bearingless centrifugal blood pump. The outcomes of the in vitro study are analyzed with the help of CFD hemolysis models. Methods: Several pump prototypes were manufactured and tested. Each model was implemented in a CFD framework and simulated with different Eulerian hemolysis models. The outcomes are compared to experimental data. The model achieving the highest correlation is used to explain the in vitro outcomes in detail. Results: It is shown that a double-stage model achieves the best correlation. The sensitivity of the simulation is considerably lower than that of in vitro tests. The CFD model reveals that most of the cell destruction is caused in the radial gap of the pump. Further critical regions are the bottom volume and the shroud clearance gap. Only 0.5% of the priming volume is subject to overcritical shear stress. Conclusion: Cell compatibility can be improved by increasing the radial gap, lowering the shroud and hub clearance gaps, and increasing the fillet radius of the inlet nozzle. CFD models can be used to examine the cell damage effects and help to further improve the pump design. Significance: This paper compares different Eulerian CFD hemolysis models, parameter sets, and equivalent shear stresses to several in vitro hemolysis tests. The sensitivity of the models is compared to that of in vitro studies. It is shown that CFD simulations have their limitations but can help with interpreting the outcomes of in vitro studies.

In this paper, the design and operating principle of a slotless bearingless slice motor for high rotational speeds is presented. The performance of the proposed concept is evaluated using an experimental prototype. Measurement results demonstrate a stable dynamic behavior during acceleration and an achievable rotational speed of 150 000 rpm, which is, to the knowledge of the authors, the highest rotational speed attained by a bearingless slice motor to date. The system performance is outlined at its maximum speed and power loss measurements are carried out over the entire speed range.

Stabilization of the position and orientation of non-spherical, sub-wavelength particles in mid-air is required for using acoustic levitation forces in applications such as automation of micro manufacturing processes, 3-D scanning, and inspection. Acoustic locking has previously been demonstrated by time-multiplexing of different acoustic traps at the same frequency. In this case, the magnitude of the acoustic levitation forces and the stabilizing torque are coupled by the ratio of the durations during which the different traps are applied and cannot be adjusted independently assuming operation at maximum power. This work presents a compact device that uses a method for independently adjusting the vertical trapping forces and the stabilizing torque using two different ultrasonic frequencies. A 40-kHz vertical standing wave is used to generate levitation forces that counteract the gravitational force. Additionally, a 25-kHz horizontal standing wave is used to generate a tunable stabilizing torque. Using this method, objects made from high-density materials across a wide range of geometries can be locked acoustically with increased stability compared with state-of-the-art methods. This is demonstrated by locking tin cuboids with a density of 7.3 g/cm ³ and plastic cuboids with average side lengths between 0.9 and 3.5 mm. The experimental results demonstrate torsional spring constants of up to 50 nN $\cdot $ m/rad and an orientation stability of <7.5°.

Acoustic levitation forces can be used to manipulate small objects and liquids without mechanical contact or contamination. This work presents analytical models based on which concepts for the controlled insertion of objects into the acoustic field are developed. This is essential for the use of acoustic levitators as contactless robotic grippers. Three prototypes of such grippers are implemented and used to experimentally verify the lifting of objects into an acoustic pressure field. Lifting of high-density objects ($\rho$ > 7 g/cm${}^3$) from acoustically transparent surfaces is demonstrated using a double-sided acoustic gripper that generates standing acoustic waves with dynamically adjustable acoustic power. A combination of multiple acoustic traps is used to lift lower density objects ($\rho \le 0.25g/c{m}^3$) from acoustically reflective surfaces using a single-sided arrangement. Furthermore, a method that uses standing acoustic waves and thin reflectors to lift medium-density objects ($\rho \le 1g/c{m}^3$) from acoustically reflective surfaces is presented. The provided results open up new possibilities for using acoustic levitation in robotic grippers, which has the potential to be applied in a variety of industrial use cases.

Goal: The importance of the main impeller design parameters in bearingless centrifugal pumps with respect to hemolysis for cardiopulmonary bypass (CPB) and extracorporeal membrane oxygenation (ECMO) applications are studied in this work. Methods: Impeller prototypes were designed based on theoretical principles. They were manufactured and their hydraulic and hemolytic performance was analyzed experimentally. The cell compatibility is benchmarked against commercially available centrifugal blood pumps BPX-80 (Medtronic) and FloPump 32 (International Biophysics Corporation). Results: The developed prototypes outperform the BPX-80 and FloPump 32 with regard to hemocompatibility by more than a factor of 4.5. The implemented pump features reduced overall and priming volumes. A significant improvement of the cell compatibility is achieved by increasing the radial gap between the impeller and the pump head. The blade should be sufficiently high and a blade outlet angle of 90° provides favorable performance. No correlation between the hydraulic and hemolytic performance is observed. Conclusions: This work identified the most important geometrical parameters of the impeller for blood pumps with respect to cell compatibility. This provides valuable design guidelines for improving existing pumps.