High-frequency energy harvesting with mechanical frequency conversion
Mechanics
Final Report Abstract
During this project the Dynamics & Vibrations group gained a lot of experience in the field of piezoelectric generators using mechanical frequency transformation from low to high frequency oscillations. The group succeeded in reaching most of the established goals, concerning the modeling and design of such energy harvesting applications as well as experimental verification of the analytical results. The main focus of the research was the investigation of the generator operation of ultrasonic motors by inverting the direction of actuation. To this end, three different ultrasonic motors were investigated with respect to their capability of being used in the reverse direction as generators. Besides detailed analytical studies, also numerical investigations were performed in order to verify the obtained results. The research was divided into two main parts, namely the analysis of the initiation of self-excited vibrations and the analysis of the steadystate characteristics of the generators. The generators showed that a minimum rotation speed is required to initiate self-excited vibrations of the stator. The resulting vibrations in the steady-state operation are dominated by the modes of the stator oscillating in the corresponding natural frequencies. The property that the generator oscillates in its natural frequencies independently of any excitation parameters, allows broad-band applicability in energy harvesting systems. This concept of ultrasonic generators was proven by extensive experimental investigations. Furthermore, for the case where various modes can occur in the steady-state vibrations, an optimization of the electrical components was discussed in detail. This is for example the case for the Shinsei USR-60, where depending on the excitation different modes become self-excited. Surprisingly, the Shinsei USR-30, which is also a plate-type ultrasonic motor, showed during all experiments a steady-state behavior dominated by only one specific bending mode. In this case, all disadvantages resulting through the consideration of various modes in the electrode optimization are cancelled. This effect can be explained by different domains of attraction of each vibration mode. An ongoing research can focus on a deeper understanding in how these domains of attraction can be estimated, in order to be able to design a piezoelectric generator with desired dynamic properties. Moreover, in future work the proposed ultrasonic generators have to be applied on real life systems, in order to gain more experience about their performance characteristics.
Publications
- Analysis of technical systems using Carleman linearization, International Conference on Structural Nonlinear Dynamics and Diagnosis, Marrakech, Morocco, 30 th April – 2nd March, 2012
Spelsberg-Korspeter, G., Heffel, E.
- Dynamics of a milkshaker - Passage through resonance and frequency transformation, IFAC – Mathematical Modelling, 7(1), 1171-1773
Spelsberg-Korspeter, G., Heffel, E.
(See online at https://dx.doi.org/10.3182/20120215-3-AT-3016.00207) - Liapunov Functions and Carleman Linearization, 83rd annual Meeting of the GAMM, Darmstadt, Germany, 26th-30th March 2012
Heffel, E., Hagedorn, P.
- Friction Induced Vibrations for Energy Harvesting Applications, Energy Harvesting, IWPMA / EHW 2013, Hannover
Heffel, E.; Hagedorn, P.
(See online at https://dx.doi.org/10.2314/IWPMA_14, 2013) - Friction Induced Vibrations for Energy Harvesting Applications, Proceedings of the 10th International Workshop on Piezoelectric Materials and Applications in Actuators and 8th Annual Energy Harvesting Workshop, Hannover, Germany, 14 th-18th July, 2013
Heffel, E., Hagedorn, P.
- Transmission Characteristics of Energy Harvesting Systems Using Self- Excited Vibrations, 3rd International Conference on Vibro-Impact Systems and Systems with Non-Smooth Interactions, Leinsweiler, Germany, 22th-26th July, 2013
Heffel, E., Hagedorn, P.
- Ultrasonic Generators for Energy Harvesting Applications: Self-Excitation and Mechanical Frequency Transformation, Forschungsberichte des Instituts für Mechanik der Technischen Universität Darmstadt, Band 32, ISBN 978-3-935868-32-7
Heffel, E.
