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.

For magnetic bearing manufacturers, the installation situations in systems in the field are often unknown and not accessible. Hence, the final system vibration spectrum with respect to excitations by operating the system and therefore mechanical resonances are unknown as well. But to avoid failure, they need to be known before the speed is initially ramped-up in a magnetic bearing suspended system. Therefore, there is a need for an experimental method to predict and prevent already at rotor standstill risks due to plant mechanical resonances. This article shows theoretically and experimentally that conventional magnetic bearing rotor displacement measurement is insensitive on mechanical system resonances. As a solution, two new acoustic response methods are proposed, which can completely detect the system mechanical resonances that will occur during operation already in the standstill levitating state. Furthermore, it is shown with application case studies that these methods can be used for condition monitoring to detect deteriorating changes in the system before rotor speed ramp-up.

In many separation processes, filtration performance degrades over time due to retained particles blocking the flow through the filter membrane. A novel bearingless spinfilter extends the long-term performance by self-cleaning effects. The filter rotor is magnetically levitated and actuated by two self-bearing motors inside a hermetically sealed housing, which eliminates the need for bearings and rotary sealings, that both lead to process fluid contamination. Both bearingless motors have integrated electronics and independently control the levitation of the spinfilter rotor. A first prototype is designed and the concept is validated by the separation of a yeast cell culture. Special focus is placed on the internal rotary seal between the feed and filtrate regions, that is inevitably created when the filter membrane is in motion. Any leakage flow through the seal leads to filtrate impurities, which is minimized in this article with an embedded impeller as a pressure compensation method. A constant filtrate flux of $1750 \,\mathrm{L}\mathrm{h}^{-1}\text{m}^{-2}$ and a filtrate purity of $75 \%$ was achieved in a first series of tests.

This study conducted a comparative evaluation of two bearingless cross-flow fan designs for applications in deep ultraviolet lithography excimer lasers, where maximizing the speed and power of the fan has a direct influence on the throughput and scanning speed of these devices. Using bearingless motor technology enables a combined generation of bearing force and drive torque and leads to a compact, hermetically sealed, and conveniently maintainable drive system. With identical bearingless motors on both rotor sides, it is possible to drive the cross-flow fan symmetrically to high rotational speeds at low torsional loads. The rotor prototypes were optimised, analysed, and pushed to high-speed operation and evaluated with respect to their rotor dynamic and fluid dynamic performance using finite element methods and experimental measurements. For both prototypes, successful numerical studies were performed, where a modal analysis enabled theoretical predictions of expected resonance frequencies, and a CFD analysis visualised local flow effects and provided cross-flow fan design comparisons. A stable operation of up to 12,000 rpm and 5500 rpm was accomplished for the two elaborated designs.

This paper presents a decoupled bearingless cross-flow fan (CFF) that operates at a supercritical speed, thereby increasing the maximum achievable rotational speed and fluid dynamic power. In magnetically levitated CFF rotors, the rotational speed and fan performance are limited by the bending resonance frequency. This is primarily defined by the low mechanical bending stiffness of the CFF blades, which are optimised for fluid dynamic performance, and the heavy rotor magnets on both rotor sides, which add significant mass but a minimal contribution to the overall rotor stiffness. This results in detrimental deformations of the CFF blades in the vicinity of the rotor bending resonance frequency; hence, the CFF is speed-limited to subcritical rotational speeds. The novel CFF rotor presented in this study features additional mechanical decoupling elements with low bending stiffness between the fan blades and the rotor magnets. Thus, the unbalance forces primarily deform the soft decoupling elements, which enables them to pass resonances without CFF blade damage and allows rotor operation in the supercritical speed region due to the self-centring effect of the rotor. The effects of the novel rotor design on the rotor dynamic behaviour are investigated by means of a mass-spring-damper model. The influence of different decoupling elements on the magnetic bearing is experimentally tested and evaluated, from which an optimised decoupled CFF rotor is derived. The final prototype enables a stable operation at 7000 rpm in the supercritical speed region. This corresponds to a rotational speed increase of 40%, resulting in a $28\%$ higher, validated fluid flow and a $100\%$ higher static pressure compared to the previously presented bearingless CFF without decoupling elements.

A novel magnetically double self-bearing drive system for ultracentrifugation in pharmaceutical and chemical industry is presented, built as a prototype and operated. The prototype successfully reached its operating speed of $100^{\prime }000\,\text{rpm}$ . It features an opening stator functionality allowing for fast removal of the ultracentrifuge rotor while enabling future centrifugal acceleration levels of $200^{\prime }000\,\mathrm{g}$ . The openable stators require a stator encapsulation, provoking unavoidable stator yoke air-gaps. Parasitic induced phase-currents were identified, a current-control strategy proposed to diminish them and successfully implemented and operated on the prototype.