1. AC2T research GmbH, Wiener Neustadt 2700, Austria e-mail:
2. Institute of Fluid Mechanics and Heat Transfer, Vienna University of Technology, Vienna 1060, Austria;
3. AC2T research GmbH, Wiener Neustadt 2700, Austria
4. AC2T research GmbH, Wiener Neustadt 2700, Austria;
5. Institute for Sensor and Actuator Systems, Vienna University of Technology, Vienna 1040, Austria
6. ebm-papst St. Georgen GmbH & Co.KG, St. Georgen 78112, Germany