Dr. Jens Twiefel Profile

Dr. Jens Twiefel

at Leibniz Univ Hannover

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Author

Publications (11)

Proceedings Article | 2 March 2020 Paper

Investigations on the effect of different ultrasonic amplitudes and positions in the vibration distribution on the microstructure of laser beam welded stainless steel

Sarah Nothdurft, Hendrik Ohrdes, Jens Twiefel, Jörg Wallaschek, Jörg Hermsdorf, Ludger Overmeyer, Stefan Kaierle

Proceedings Volume 11273, 112730J (2020) https://doi.org/10.1117/12.2566035

KEYWORDS: Metals, Ultrasonics, Photomicroscopy, Laser welding, Iron, Laser processing

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Proceedings Article | 9 September 2019 Presentation + Paper

Visualization of dynamic stress conditions in elastic solids utilizing high frequency stroboscopic LED arrays

Jian Shi, Hendrik Ohrdes, Michael Weinstein, Jens Twiefel

Proceedings Volume 11105, 1110503 (2019) https://doi.org/10.1117/12.2529955

KEYWORDS: Light emitting diodes, Ultrasonics, Solids, Photoelasticity, Visualization, Field effect transistors, Ultrasonography, Transducers, Light sources, Imaging systems

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Proceedings Article | 10 April 2013 Paper

On ultrasonic squeeze film levitation: modeling and feedback control of ultrasonic bearing systems

Sebastian Mojrzisch, Jens Twiefel

Proceedings Volume 8688, 86881V (2013) https://doi.org/10.1117/12.2010257

KEYWORDS: Transducers, Ultrasonics, Systems modeling, Feedback control, Control systems design, Control systems, Velocity measurements, Sensors, Modeling, Magnetism

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Proceedings Article | 10 April 2013 Paper

Highly-integrated energy harvesting device for rotational applications utilizing quasi-static piezoelectric and electromagnetic generators

Marc Wurz, Gleb Kleyman, Jens Twiefel

Proceedings Volume 8688, 86881L (2013) https://doi.org/10.1117/12.2012256

KEYWORDS: Energy harvesting, Magnetism, Electromagnetism, System integration, Prototyping, Transducers, Ferroelectric materials, Neodymium, Integrated circuits, Toxic industrial chemicals

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Proceedings Article | 10 April 2013 Paper

Vibration shape effects on the power output in piezoelectric vibro-impact energy harvesters

Jens Twiefel

Proceedings Volume 8688, 86880K (2013) https://doi.org/10.1117/12.2012246

KEYWORDS: Computing systems, Systems modeling, Positive feedback, Beam shaping, Energy harvesting, Transducers, Control systems, Feedback loops, MATLAB, Computer simulations

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Vibro-Impcact harvesting devices are one concept to increase the bandwidth of resonant operated piezoelectric vibration generators. The fundamental setup is a piezoelectric bending element, where the deflection is limited by two stoppers. After starting the system in resonance operation the bandwidth increases towards higher frequencies as soon the deflection reach the stopper. If the stoppers are rigid, the frequency response gives constant amplitude for increasing frequencies, as long the system is treated as ideal one-DOF system with symmetric stoppers. In consequence, the bandwidth is theoretically unlimited large. However, such a system also has two major drawbacks, firstly the complicated startup mechanism and secondly the tendency to drop from the high constant branch in the frequency response on the much smaller linear branch if the system is disturbed. Nevertheless, the system has its application wherever the startup problem can be solved. Most modeling approaches utilize modal one-DOF models to describe the systems behavior and do not tread the higher harmonics of the beam. This work investigates the effects of the stoppers on the vibration shape of the piezoelectric beam, wherefore a finite element model is used. The used elements are one-dimensional two node elements based on the Timoshenko-beam theory. The finite element code is implemented in Matlab. The model is calculated utilizing time step integration for simulation, to reduce the computation time an auto-resonant calculation method is implemented. A control loop including positive feedback and saturation is used to create a self-excited system. Therefore, the system is always operated in resonance (on the backbone curve) and the frequency is a direct result of the computation. In this case tip velocity is used as feedback. This technique allows effective parametric studies. Investigated parameters include gap, excitation amplitude, tip mass as well as the stiffness of the stopper. The stress and strain distribution as well as the generated electrical power is analyzed with respect to the proper operation range.

Proceedings Article | 28 March 2012 Paper

Improved pen harvester for powering a pulse rate sensor

Anthony Marin, Patrick Heitzmann, Jens Twiefel, Shashank Priya

Proceedings Volume 8341, 83411D (2012) https://doi.org/10.1117/12.917013

KEYWORDS: Prototyping, Magnetism, Sensors, Composites, Wind energy, Resistance, Energy harvesting, Solar energy, Electromagnetism, Lead

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Proceedings Article | 7 April 2009 Paper

Parameter identification of piezoelectric bimorphs for dynamic applications considering strain and velocity dependent effects

Björn Richter, Jens Twiefel

Proceedings Volume 7288, 72881K (2009) https://doi.org/10.1117/12.815967

KEYWORDS: Systems modeling, Transducers, Energy harvesting, Actuators, Data modeling, Dielectrics, Capacitance, Circuit switching, Mathematical modeling, Motion models

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Proceedings Article | 7 April 2009 Paper

Design and experimental investigations of high power piezoelectric transducers for a novel squeeze film journal bearing

Su Zhao, Jens Twiefel, Joerg Wallaschek

Proceedings Volume 7288, 72881G (2009) https://doi.org/10.1117/12.815724

KEYWORDS: Transducers, Spindles, Ultrasonics, Ceramics, Systems modeling, Finite element methods, Aerodynamics, Acoustics, Electromagnetism, Control systems

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Proceedings Article | 3 April 2008 Paper

Digital signal processing for an adaptive phase-locked loop controller

Jens Twiefel, Martin Klubal, Carlos Paiz, Sebastian Mojrzisch, Holger Krüger

Proceedings Volume 6926, 69260A (2008) https://doi.org/10.1117/12.776091

KEYWORDS: Control systems, Field programmable gate arrays, Signal processing, Digital signal processing, Sensors, Actuators, Signal detection, Phase measurement, Analog electronics, Demodulation

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Proceedings Article | 27 April 2007 Paper

Design method for piezoelectric bending generators in energy harvesting systems

Björn Richter, Jens Twiefel, Thomas Sattel, Jörg Wallaschek

Proceedings Volume 6525, 652504 (2007) https://doi.org/10.1117/12.715788

KEYWORDS: Resistance, Mathematical modeling, Chemical elements, Data modeling, Energy harvesting, Systems modeling, Mechanics, Capacitance, Dielectrics, Transducers

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The increased demand for mobile systems using low-power electronics leads to a need for new power sources. Using batteries as power source may be inapplicable in distributed systems like wireless sensor networks because the batteries have to be exchanged frequently. Energy Harvesting systems are one possible energy source for such systems exploiting environmental energy like mechanical vibrations. One good solution to convert vibration energy is the use of piezoelectric generators usually realised as piezoelectric bending beams. The generators convert mechanical energy to electrical energy due to resulting strain of the element. However, the power output of piezoelectric generators is a challenging task even if low-power applications have to be driven. Due to the low electric power output of piezoelectric generators, it is an important task to obtain a suitable geometric design of the transducer element. Beside the element dimensions the electric power output depends on the input excitation as well as on the electric load to be powered. To analyse the system behaviour, input variables and the generator itself have to be described in a mathematical model. This enables the calculation of optimal elements in principle. A modal electro-mechanical model of the piezoelectric element assuming to be base-excited is used in this paper. Although the modal model is very helpful to analyse the system, it cannot be easy used to determine a proper design of the piezoelectric elements. The problem is that the parameters of the model do not show any apparent relations to geometric dimensions or material data. Therefore, a mathematical method to obtain the parameters from the physical properties of a piezoelectric bending element is briefly described. The knowledge of the link between physical and modal parameters allows the usage of the mathematical model as a qualified design method. The input parameters of the linked model are the material data which can be found on data sheets. Additionally, boundary conditions of the environment like the impedance of the driven load and the vibration excitation has to be specified. The linked model shows the influences on power output to connected electric loads. The given power demands of applications which have to be satisfied yields in a design space of suitable elements. The design method enables the development engineer to select piezoelectric generator elements.

Proceedings Article | 17 March 2006 Paper

Model-based design of piezoelectric energy harvesting systems

Jens Twiefel, Björn Richter, Tobias Hemsel, Jörg Wallaschek

Proceedings Volume 6169, 616909 (2006) https://doi.org/10.1117/12.658623

KEYWORDS: Electroluminescence, Energy harvesting, Systems modeling, Mathematical modeling, Actuators, Chemical elements, Transducers, Resistance, Model-based design, Factor analysis

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Showing 5 of 11 publications

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