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Dr. Manfred Kohl
Karlsruhe Institute of Technology

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0 Microtechnology
0 Piezoelectrics
0 Smart Materials
0 Magnetic Materials
0 Shape memory materials

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Journal article
Published: 03 August 2021 in Actuators
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We present the design, fabrication, and characterization of single and antagonistic SMA microactuators allowing for uni- and bi-directional self-folding of origami-inspired devices, respectively. Test devices consist of two triangular tiles that are interconnected by double-beam-shaped SMA microactuators fabricated from thin SMA foils of 20 µm thickness with memory shapes set to a 180° folding angle. Bi-directional self-folding is achieved by combining two counteracting SMA microactuators. We present a macromodel to describe the engineering stress–strain characteristics of the SMA foil and to perform FEM simulations on the characteristics of self-folding and the corresponding local evolution of phase transformation. Experiments on single-SMA microactuators demonstrate the uni-directional self-folding and tunability of bending angles up to 180°. The finite element simulations qualitatively describe the main features of the observed torque-folding angle characteristics and provide further insights into the angular dependence of the local profiles of the stress and martensite phase fraction. The first antagonistic SMA microactuators reveal bi-directional self-folding in the range of −44° to +40°, which remains well below the predicted limit of ±100°.

ACS Style

Lena Seigner; Georgino Tshikwand; Frank Wendler; Manfred Kohl. Bi-Directional Origami-Inspired SMA Folding Microactuator. Actuators 2021, 10, 181 .

AMA Style

Lena Seigner, Georgino Tshikwand, Frank Wendler, Manfred Kohl. Bi-Directional Origami-Inspired SMA Folding Microactuator. Actuators. 2021; 10 (8):181.

Chicago/Turabian Style

Lena Seigner; Georgino Tshikwand; Frank Wendler; Manfred Kohl. 2021. "Bi-Directional Origami-Inspired SMA Folding Microactuator." Actuators 10, no. 8: 181.

Journal article
Published: 05 March 2021 in Materials
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This paper presents a lumped element model (LEM) to describe the coupled dynamic properties of thermomagnetic generators (TMGs) based on magnetic shape memory alloy (MSMA) films. The TMG generators make use of the concept of resonant self-actuation of a freely movable cantilever, caused by a large abrupt temperature-dependent change of magnetization and rapid heat transfer inherent to the MSMA films. The LEM is validated for the case of a Ni-Mn-Ga film with Curie temperature TC of 375 K. For a heat source temperature of 443 K, the maximum power generated is 3.1 µW corresponding to a power density with respect to the active material’s volume of 80 mW/cm3. Corresponding LEM simulations allow for a detailed study of the time-resolved temperature change of the MSMA film, the change of magnetic field at the position of the film and of the corresponding film magnetization. Resonant self-actuation is observed at 114 Hz, while rapid temperature changes of about 10 K occur within 1 ms during mechanical contact between heat source and Ni-Mn-Ga film. The LEM is used to estimate the effect of decreasing TC on the lower limit of heat source temperature in order to predict possible routes towards waste heat recovery near room temperature.

ACS Style

Joel Joseph; Makoto Ohtsuka; Hiroyuki Miki; Manfred Kohl. Lumped Element Model for Thermomagnetic Generators Based on Magnetic SMA Films. Materials 2021, 14, 1234 .

AMA Style

Joel Joseph, Makoto Ohtsuka, Hiroyuki Miki, Manfred Kohl. Lumped Element Model for Thermomagnetic Generators Based on Magnetic SMA Films. Materials. 2021; 14 (5):1234.

Chicago/Turabian Style

Joel Joseph; Makoto Ohtsuka; Hiroyuki Miki; Manfred Kohl. 2021. "Lumped Element Model for Thermomagnetic Generators Based on Magnetic SMA Films." Materials 14, no. 5: 1234.

Journal article
Published: 17 February 2021 in Applied Energy
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As an alternative to thermoelectric generators, heat engines show great interest thanks to their ability to convert temperature spatial gradient into time-domain temperature variations or vibrations. To this end, MultiPhysic Memory Alloys (MPMAs), combining shape memory characteristics with ferromagnetic properties, provide significant attractive characteristics such as sharp transition with reduced hysteresis as well as magnetic properties enabled by heating, thus allowing easier device development and implementation. In this study, we report the development of a heat engine for small-scale energy harvesting where the MPMA transfers its heat to a pyroelectric element that provides thermal to electrical energy conversion, yielding a more direct energy conversion path compared to conventional electromechanical heat engines. Furthermore, thermally decoupling the pyroelectric element from the MPMA allows a faster cooling of the latter, accounting for higher variation frequency. Compared to the use of electromagnetic transduction through a coil attached to the moving MPMA, this approach is shown to provide 3 to 9 times more power density (according to considered volume), with theoretical potential gains from 8 to 25 with the use of nonlinear electrical interfaces.

ACS Style

Mickaël Lallart; Linjuan Yan; Hiroyuki Miki; Gaël Sebald; Gildas Diguet; Makoto Ohtsuka; Manfred Kohl. Heusler alloy-based heat engine using pyroelectric conversion for small-scale thermal energy harvesting. Applied Energy 2021, 288, 116617 .

AMA Style

Mickaël Lallart, Linjuan Yan, Hiroyuki Miki, Gaël Sebald, Gildas Diguet, Makoto Ohtsuka, Manfred Kohl. Heusler alloy-based heat engine using pyroelectric conversion for small-scale thermal energy harvesting. Applied Energy. 2021; 288 ():116617.

Chicago/Turabian Style

Mickaël Lallart; Linjuan Yan; Hiroyuki Miki; Gaël Sebald; Gildas Diguet; Makoto Ohtsuka; Manfred Kohl. 2021. "Heusler alloy-based heat engine using pyroelectric conversion for small-scale thermal energy harvesting." Applied Energy 288, no. : 116617.

Conference paper
Published: 20 November 2020 in Proceedings of 1st International Electronic Conference on Actuator Technology: Materials, Devices and Applications
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This paper presents the design, fabrication and performance of origami-based folding microactuators based on NiTi films showing the one-way shape memory effect. Freestanding NiTi films are micromachined by laser cutting or photolithography to achieve double-beam structures allowing for direct Joule heating with an electrical current. The NiTi microactuators are interconnected to rigid sections (tiles) forming an initial planar system that self-folds into a predetermined 3D shape upon heating. A thermo-mechanical treatment is used for shape setting of as-received specimens to approach a maximum folding angle of 180°. The bending moments, bending radii and load-dependent folding angles upon Joule heating are evaluated. The shape setting process is particularly effective for small bending radii, which, however, generates residual plastic strain. After shape setting, unloaded beam structures show recoverable bending deflection between 0° and 140° for a maximum heating power of 900 mW. By introducing additional loads to account for the effect of the tiles, the smooth folding characteristic evolves into a sharp transition, whereby full deflection up to 180° is reached.

ACS Style

Lena Seigner; Olha Bezsmertna; Sebastian Fähler; Georgino Kaleng Tshikwand; Frank Wendler; Manfred Kohl. Origami-Inspired Shape Memory Folding Microactuator. Proceedings of 1st International Electronic Conference on Actuator Technology: Materials, Devices and Applications 2020, 64, 6 .

AMA Style

Lena Seigner, Olha Bezsmertna, Sebastian Fähler, Georgino Kaleng Tshikwand, Frank Wendler, Manfred Kohl. Origami-Inspired Shape Memory Folding Microactuator. Proceedings of 1st International Electronic Conference on Actuator Technology: Materials, Devices and Applications. 2020; 64 (1):6.

Chicago/Turabian Style

Lena Seigner; Olha Bezsmertna; Sebastian Fähler; Georgino Kaleng Tshikwand; Frank Wendler; Manfred Kohl. 2020. "Origami-Inspired Shape Memory Folding Microactuator." Proceedings of 1st International Electronic Conference on Actuator Technology: Materials, Devices and Applications 64, no. 1: 6.

Conference paper
Published: 20 November 2020 in Proceedings of 1st International Electronic Conference on Actuator Technology: Materials, Devices and Applications
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The high work density and beneficial downscaling of shape memory alloy (SMA) actuation performance provide a basis for the development of actuators and systems at microscales. Here, we report a novel monolithic fabrication approach for the co-integration of SMA and Si microstructures to enable SMA-Si bimorph microactuation. Double-beam cantilevers are chosen for the actuator layout to enable electrothermal actuation by Joule heating. The SMA materials under investigation are NiMnGa and NiTi(Hf) films with tunable phase transformation temperatures. We show that Joule heating of the cantilevers generates increasing temperature gradients for decreasing cantilever size, which hampers actuation performance. In order to cope with this problem, a new method for design optimization is presented based on finite element modeling (FEM) simulations. We demonstrate that temperature homogenization can be achieved by the design of additional folded beams in the perpendicular direction to the active beam cantilevers. Thereby, power consumption can be reduced by more than 35 % and maximum deflection can be increased up to a factor of 2 depending on the cantilever geometry.

ACS Style

Gowtham Arivanandhan; Zixiong Li; Sabrina Curtis; Prasanth Velvaluri; Eckhard Quandt; Manfred Kohl. Temperature Homogenization of Co-Integrated Shape Memory—Silicon Bimorph Actuators. Proceedings of 1st International Electronic Conference on Actuator Technology: Materials, Devices and Applications 2020, 64, 8 .

AMA Style

Gowtham Arivanandhan, Zixiong Li, Sabrina Curtis, Prasanth Velvaluri, Eckhard Quandt, Manfred Kohl. Temperature Homogenization of Co-Integrated Shape Memory—Silicon Bimorph Actuators. Proceedings of 1st International Electronic Conference on Actuator Technology: Materials, Devices and Applications. 2020; 64 (1):8.

Chicago/Turabian Style

Gowtham Arivanandhan; Zixiong Li; Sabrina Curtis; Prasanth Velvaluri; Eckhard Quandt; Manfred Kohl. 2020. "Temperature Homogenization of Co-Integrated Shape Memory—Silicon Bimorph Actuators." Proceedings of 1st International Electronic Conference on Actuator Technology: Materials, Devices and Applications 64, no. 1: 8.

Journal article
Published: 20 November 2020 in Joule
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Summary Thermomagnetic (TM) generators based on Heusler alloy films have the potential to recover waste heat below 200°C at small temperature differences . Progress in the development of materials that exhibit large abrupt changes in ferromagnetic ordering and in film engineering enable efficient thermomagnetic generation via resonant self-actuation of freely movable film-based devices. Yet, power levels of individual devices are low, and upscaling becomes a key issue of material development and engineering. Here, we address the key question of how film thickness and device footprint affect power and efficiency. We investigate the scaling performance of heat intake, heat dissipation, and resulting local temperature changes. Based on this understanding, the electrical power per footprint could be increased by a factor of 3.4. Maximum values of electrical power per footprint are 50 μW/cm2 at a temperature change of only 3°C, which marks an important milestone in the upscaling of Heusler alloy film-based TM generators.

ACS Style

Joel Joseph; Makoto Ohtsuka; Hiroyuki Miki; Manfred Kohl. Upscaling of Thermomagnetic Generators Based on Heusler Alloy Films. Joule 2020, 4, 2718 -2732.

AMA Style

Joel Joseph, Makoto Ohtsuka, Hiroyuki Miki, Manfred Kohl. Upscaling of Thermomagnetic Generators Based on Heusler Alloy Films. Joule. 2020; 4 (12):2718-2732.

Chicago/Turabian Style

Joel Joseph; Makoto Ohtsuka; Hiroyuki Miki; Manfred Kohl. 2020. "Upscaling of Thermomagnetic Generators Based on Heusler Alloy Films." Joule 4, no. 12: 2718-2732.

Proceedings
Published: 20 November 2020 in Proceedings
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A control circuit for inductive levitation micro-actuators was developed in this research, the circuit’s performance and its electrical parameters are discussed. The developed control circuit was fabricated on a four-layer printed circuit board (PCB) board with a size of 60 × 60 × 25 mm. It consisted of a generator based on high-speed Flip-Flop components and a current amplifier build on a H-bridge configuration. The circuit was able to generate an AC current with a squared waveform in a frequency range from 8 to 43 MHz and with a peak-to-peak amplitude of up to 420 mA. To demonstrate the efficiency of developed circuit and its compatibility with a micro-actuation system, an inductive levitation micro-actuator was fabricated by using 3D micro-coil technology. The device was composed of two solenoidal coil designs, a levitation and a stabilization coil, with outer diameters of 2 and 3.8 mm, respectively. A 25 μm diameter gold wire was used to fabricate the coils, with the levitation coil having 20 turns and the stabilization coil having 12 turns, similar to the micro-structure presented previously by our group. Using the developed control circuit, the micro-actuator was successfully excited and it demonstrated the actuation of aluminum disc-shaped micro-objects with diameters of 2.8 and 3.2 mm and, for the first time, an aluminum square-shaped object with a side length of 2.8 mm at a frequency of 10 MHz. To characterize the actuation, the levitation height and the current amplitude were measured. In particular, we demonstrated that the square-shaped micro-object could be lifted up to a height of 84 μm with a current of 160 mA. The characterization was supported by a simulation using a 3D model based on the quasi-finite element model (FEM) approach.

ACS Style

Vitor Vlnieska; Achim Voigt; Sagar Wadhwa; Jan Korvink; Manfred Kohl; Kirill Poletkin. Development of Control Circuit for Inductive Levitation Micro-Actuators . Proceedings 2020, 64, 39 .

AMA Style

Vitor Vlnieska, Achim Voigt, Sagar Wadhwa, Jan Korvink, Manfred Kohl, Kirill Poletkin. Development of Control Circuit for Inductive Levitation Micro-Actuators . Proceedings. 2020; 64 (1):39.

Chicago/Turabian Style

Vitor Vlnieska; Achim Voigt; Sagar Wadhwa; Jan Korvink; Manfred Kohl; Kirill Poletkin. 2020. "Development of Control Circuit for Inductive Levitation Micro-Actuators ." Proceedings 64, no. 1: 39.

Journal article
Published: 01 March 2020 in Microelectronic Engineering
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This paper presents a novel design and fabrication process for co-integration of SMA/Si bimorph nanoactuators with footprint of 10 μm2 into silicon waveguide structures to enable ultra-compact optical waveguide switching. The nanoactuator is directly attached to a free-standing waveguide being part of a directional coupler. The design includes an etch window for local sacrificial layer processing below the nanoactuator and free-standing monomode waveguides. 3D finite element simulations are performed to evaluate actuator deflection-dependent coupling efficiencies. Fabrication comprises three-step e-beam lithography on a SOI wafer, cryo etching of the Si device layer and magnetron sputtering of the SMA layer. First demonstrators reveal actuator deflections up to 1 μm with reproducibility in the order of 4 nm.

ACS Style

Sanaz Rastjoo; Randy Fechner; Lars Bumke; Mirko Kötz; Eckhard Quandt; Manfred Kohl. Development and co-integration of a SMA/Si bimorph nanoactuator for Si photonic circuits. Microelectronic Engineering 2020, 225, 111257 .

AMA Style

Sanaz Rastjoo, Randy Fechner, Lars Bumke, Mirko Kötz, Eckhard Quandt, Manfred Kohl. Development and co-integration of a SMA/Si bimorph nanoactuator for Si photonic circuits. Microelectronic Engineering. 2020; 225 ():111257.

Chicago/Turabian Style

Sanaz Rastjoo; Randy Fechner; Lars Bumke; Mirko Kötz; Eckhard Quandt; Manfred Kohl. 2020. "Development and co-integration of a SMA/Si bimorph nanoactuator for Si photonic circuits." Microelectronic Engineering 225, no. : 111257.

Journal article
Published: 11 June 2019 in Journal of Applied Physics
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The fabrication of nanostructures of vanadium dioxide ( VO 2)-based films with critical dimensions down to 100 nm and the characterization of their phase transformation properties are presented. Starting materials are VO 2 and V 0.99 Mo 0.01 O 2 films that are deposited by magnetron sputtering. For nanofabrication, two top-down processes are investigated, in which the substrate is nanomachined either before or after film deposition. Electrical resistance measurements on V 0.99 Mo 0.01 O 2 bridge nanostructures exhibit a semiconductor–metal transition similar to reference films. A detailed analysis of phase transition temperatures does not reveal any significant width-dependence as it may be expected when approaching the grain size of 100 nm. The absolute electrical resistance in the semiconducting state scales inversely proportional to the width reflecting homogeneous material characteristics. Yet, the resistance change at the semiconductor–metal transition tends to increase for decreasing width indicating reduced carrier scattering as the absolute number of grain boundaries decreases.The fabrication of nanostructures of vanadium dioxide ( VO 2)-based films with critical dimensions down to 100 nm and the characterization of their phase transformation properties are presented. Starting materials are VO 2 and V 0.99 Mo 0.01 O 2 films that are deposited by magnetron sputtering. For nanofabrication, two top-down processes are investigated, in which the substrate is nanomachined either before or after film deposition. Electrical resistance measurements on V 0.99 Mo 0.01 O 2 bridge nanostructures exhibit a semiconductor–metal transition similar to reference films. A detailed analysis of phase transition temperatures does not reveal any significant width-dependence as it may be expected when approaching the grain size of 100 nm. The absolute electrical resistance in the semiconducting state scales inversely proportional to the width reflecting homogeneous material characteristics. Yet, the resistance change at the semiconductor–metal transition tends to increase for...

ACS Style

S. Rastjoo; X. Wang; A. Ludwig; M. Kohl. Top-down fabrication and transformation properties of vanadium dioxide nanostructures. Journal of Applied Physics 2019, 125, 225104 .

AMA Style

S. Rastjoo, X. Wang, A. Ludwig, M. Kohl. Top-down fabrication and transformation properties of vanadium dioxide nanostructures. Journal of Applied Physics. 2019; 125 (22):225104.

Chicago/Turabian Style

S. Rastjoo; X. Wang; A. Ludwig; M. Kohl. 2019. "Top-down fabrication and transformation properties of vanadium dioxide nanostructures." Journal of Applied Physics 125, no. 22: 225104.

Journal article
Published: 21 March 2019 in International Journal of Applied Electromagnetics and Mechanics
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ACS Style

Lukas Liedtke; Marcel Gueltig; Manfred Kohl. Miniature-scale energy harvesting based on the inverse magnetic shape memory effect. International Journal of Applied Electromagnetics and Mechanics 2019, 59, 377 -383.

AMA Style

Lukas Liedtke, Marcel Gueltig, Manfred Kohl. Miniature-scale energy harvesting based on the inverse magnetic shape memory effect. International Journal of Applied Electromagnetics and Mechanics. 2019; 59 (1):377-383.

Chicago/Turabian Style

Lukas Liedtke; Marcel Gueltig; Manfred Kohl. 2019. "Miniature-scale energy harvesting based on the inverse magnetic shape memory effect." International Journal of Applied Electromagnetics and Mechanics 59, no. 1: 377-383.

Review
Published: 13 August 2018 in Energy Technology
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This review covers fundamentals on the operation and scaling of elastocaloric cooling devices as well as current developments of elastocaloric SMA films and the engineering of SMA film‐based cooling devices. Sputter‐deposited TiNiCuCo alloys showing ultra‐low fatigue enable unique functional properties like tailored transformation temperature gradients. Two substantially different concepts for the development of elastocaloric cooling demonstrators are discussed. One concept relies on the heat transfer by mechanical contact between elastocaloric SMA film and solid heat sink and source elements. The second concept makes use of the heat transfer between elastocaloric SMA film and a heat transfer fluid including the advanced technology of active regeneration. Demonstrators based on a single SMA film reach device temperature spans of 14 K and a high specific cooling power of up to 18 Wg‐1. The performance characteristics are compared with other solid‐state caloric cooling technologies.

ACS Style

Florian Bruederlin; Lars Bumke; Christoph Chluba; Hinnerk Ossmer; Eckhard Quandt; Manfred Kohl. Elastocaloric Cooling on the Miniature Scale: A Review on Materials and Device Engineering. Energy Technology 2018, 6, 1588 -1604.

AMA Style

Florian Bruederlin, Lars Bumke, Christoph Chluba, Hinnerk Ossmer, Eckhard Quandt, Manfred Kohl. Elastocaloric Cooling on the Miniature Scale: A Review on Materials and Device Engineering. Energy Technology. 2018; 6 (8):1588-1604.

Chicago/Turabian Style

Florian Bruederlin; Lars Bumke; Christoph Chluba; Hinnerk Ossmer; Eckhard Quandt; Manfred Kohl. 2018. "Elastocaloric Cooling on the Miniature Scale: A Review on Materials and Device Engineering." Energy Technology 6, no. 8: 1588-1604.

Review
Published: 10 August 2018 in Energy Technology
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Cool Review: Innovative elastocaloric cooling systems have the potential to meet the rising demand for efficient cooling and temperature control on the miniature scale, such as in microelectronic devices and lab‐on‐a‐chip systems. This Review covers fundamentals on the operation and scaling of elastocaloric cooling devices as well as current developments of elastocaloric films and engineering of corresponding devices. This cover artwork reflects this field as a whole, including fundamentals of caloric cooling, material science, and device engineering. More details can be found in the Review by Florian Bruederlin et al. (10.1002/ente.201800137).

ACS Style

Florian Bruederlin; Lars Bumke; Christoph Chluba; Hinnerk Ossmer; Dr. Eckhard Quandt; Dr. Manfred Kohl. Cover Feature: Elastocaloric Cooling on the Miniature Scale: A Review on Materials and Device Engineering (Energy Technol. 8/2018). Energy Technology 2018, 6, 1393 -1393.

AMA Style

Florian Bruederlin, Lars Bumke, Christoph Chluba, Hinnerk Ossmer, Dr. Eckhard Quandt, Dr. Manfred Kohl. Cover Feature: Elastocaloric Cooling on the Miniature Scale: A Review on Materials and Device Engineering (Energy Technol. 8/2018). Energy Technology. 2018; 6 (8):1393-1393.

Chicago/Turabian Style

Florian Bruederlin; Lars Bumke; Christoph Chluba; Hinnerk Ossmer; Dr. Eckhard Quandt; Dr. Manfred Kohl. 2018. "Cover Feature: Elastocaloric Cooling on the Miniature Scale: A Review on Materials and Device Engineering (Energy Technol. 8/2018)." Energy Technology 6, no. 8: 1393-1393.

Invited article
Published: 03 July 2018 in International Journal of Smart and Nano Materials
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This paper presents a dynamic analysis of the free and forced vibration of a free-standing bridge of superelastic shape memory alloy TiNiCuCo film with ultra-low fatigue properties and evaluates its versatility for novel miniature scale damping applications. A thermodynamics-based finite element model is used to simulate the evolution of martensite phase fraction during load-induced martensitic phase transformation. The effects of pre-strain, strain rate and excitation load on the hysteresis of stress-strain characteristics are investigated in order to assess damping energies. The analysis is performed under non-isothermal conditions taking into account heat transfer and rate-dependence of release and absorption of latent heat. We show that damping energy can be maximized by applying an optimum pre-strain. A maximum damping capacity of 0.17 is determined for the case of complete stress-strain hysteresis loop during phase transformation.

ACS Style

Shahabeddin Ahmadi; Kiran Jacob; Frank Wendler; Manfred Kohl. Shape memory alloy film damping for smart miniature systems. International Journal of Smart and Nano Materials 2018, 9, 199 -215.

AMA Style

Shahabeddin Ahmadi, Kiran Jacob, Frank Wendler, Manfred Kohl. Shape memory alloy film damping for smart miniature systems. International Journal of Smart and Nano Materials. 2018; 9 (3):199-215.

Chicago/Turabian Style

Shahabeddin Ahmadi; Kiran Jacob; Frank Wendler; Manfred Kohl. 2018. "Shape memory alloy film damping for smart miniature systems." International Journal of Smart and Nano Materials 9, no. 3: 199-215.

Conference paper
Published: 01 July 2018 in 2018 IEEE 18th International Conference on Nanotechnology (IEEE-NANO)
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This paper presents design, fabrication and characterization of a novel integrated optical waveguide switch that allows for coupling of an input port in either of two output ports. A new fabrication process has been developed to integrate a shape memory alloy (SMA) bimorph nanoactuator with a footprint below 5 μm 2 on a silicon photonic chip. Optical measurements demonstrate a decrease in power transfer by 53 % for a decrease in gap size from 250 nm to 200 nm at a wavelength of 1300 nm, which is in line with FEM-based simulations. The simulations further indicate that a decrease in power transfer by 100% occurs at a gap size of 170 nm.

ACS Style

R. Fechner; C. Chlub; E. Quandt; Manfred Kohl. A Shape Memory Alloy 1×2 Optical Waveguide Switch. 2018 IEEE 18th International Conference on Nanotechnology (IEEE-NANO) 2018, 1 -3.

AMA Style

R. Fechner, C. Chlub, E. Quandt, Manfred Kohl. A Shape Memory Alloy 1×2 Optical Waveguide Switch. 2018 IEEE 18th International Conference on Nanotechnology (IEEE-NANO). 2018; ():1-3.

Chicago/Turabian Style

R. Fechner; C. Chlub; E. Quandt; Manfred Kohl. 2018. "A Shape Memory Alloy 1×2 Optical Waveguide Switch." 2018 IEEE 18th International Conference on Nanotechnology (IEEE-NANO) , no. : 1-3.

Conference paper
Published: 12 April 2018 in Proceedings of the International Conference on Martensitic Transformations: Chicago
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In this contribution, the potential of film and foil-based shape memory alloy (SMA) microactuators for fluid handling applications is explored. SMAs provide a high work density and allow for compact and robust actuator designs based on the one-way shape memory effect. Compared to more commonly used wires, actuators fabricated from thin film or foil material allow for more complex designs having several degrees of freedom and enable shorter switching times in the range of 10 ms. In order to commercialize such actuators, the “memetis GmbH” was founded as a high-tech spin-off of the Karlsruhe Institute of Technology (KIT) in Germany. Memetis is focused on miniature fluid handling products and combines rapid prototyping and rapid manufacturing techniques such as 3D printing, laser cutting and CNC milling of polymer housings for customer-specific device development. A normally open microvalve is presented here as an example, which is actuated by a novel fatigue-free TiNiCu film actuator.

ACS Style

Hinnerk Ossmer; Marcel Gueltig; Christoph Wessendorf; Manfred Kohl; Christof Megnin. Film and Foil-Based Shape Memory Alloy Microactuators for Fluid Handling. Proceedings of the International Conference on Martensitic Transformations: Chicago 2018, 197 -200.

AMA Style

Hinnerk Ossmer, Marcel Gueltig, Christoph Wessendorf, Manfred Kohl, Christof Megnin. Film and Foil-Based Shape Memory Alloy Microactuators for Fluid Handling. Proceedings of the International Conference on Martensitic Transformations: Chicago. 2018; ():197-200.

Chicago/Turabian Style

Hinnerk Ossmer; Marcel Gueltig; Christoph Wessendorf; Manfred Kohl; Christof Megnin. 2018. "Film and Foil-Based Shape Memory Alloy Microactuators for Fluid Handling." Proceedings of the International Conference on Martensitic Transformations: Chicago , no. : 197-200.

Journal article
Published: 11 April 2018 in MRS Bulletin
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Pseudoelastic NiTi-based shape-memory alloys (SMAs) have recently received attention as candidate materials for solid-state refrigeration. The elastocaloric effect in SMAs exploits stress-induced martensitic transformation, which is associated with large latent heat. Most importantly, cyclic mechanical loading/unloading provides large adiabatic temperature drops exceeding 25 K at high process efficiencies. This article summarizes the underlying principles, important material parameters and process requirements, and reviews recent progress in the development of pseudoelastic SMAs with large coefficients of performance, as well as very good functional fatigue resistance. The application potential of SMA film and bulk materials is demonstrated for the case of cyclic tensile loading/unloading in prototypes ranging from miniature-scale devices to large-scale cooling units.

ACS Style

Jan Frenzel; Gunther Eggeler; Eckhard Quandt; Stefan Seelecke; Manfred Kohl. High-performance elastocaloric materials for the engineering of bulk- and micro-cooling devices. MRS Bulletin 2018, 43, 280 -284.

AMA Style

Jan Frenzel, Gunther Eggeler, Eckhard Quandt, Stefan Seelecke, Manfred Kohl. High-performance elastocaloric materials for the engineering of bulk- and micro-cooling devices. MRS Bulletin. 2018; 43 (4):280-284.

Chicago/Turabian Style

Jan Frenzel; Gunther Eggeler; Eckhard Quandt; Stefan Seelecke; Manfred Kohl. 2018. "High-performance elastocaloric materials for the engineering of bulk- and micro-cooling devices." MRS Bulletin 43, no. 4: 280-284.

Journal article
Published: 19 January 2018 in Shape Memory and Superelasticity
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This paper presents a simulation model for the coupled dynamic properties of thermomagnetic generators based on magnetic shape memory alloy (MSMA) films. MSMA thermomagnetic generators exploit the large abrupt temperature-induced change of magnetization at the first- or second-order magnetic transition as well as the short heat transfer times due to the large surface-to-volume ratio of films. These properties allow for resonant self-actuation of freely movable MSMA cantilever devices showing thermomagnetic duty cycles in the order of 10 ms duration, which matches with the period of oscillatory motion. We present a numerical analysis of the energy conversion processes to understand the effect of design parameters on efficiency and power output. A lumped element model is chosen to describe the time dependence of MSMA cantilever deflection and of temperature profiles as well as the magnitude and phase dependency of magnetization change. The simulation model quantitatively describes experimentally observed oscillatory motion and resulting power output in the order of 100 mW cm−3. Furthermore, it predicts a power output of 490 mW cm−3 for advanced film materials with temperature-dependent change of magnetization ∆M/∆T of 4 A m2 (kg K)−1, which challenges state-of-the-art thermoelectric devices.

ACS Style

Manfred Kohl; Marcel Gueltig; Frank Wendler. Coupled Simulation of Thermomagnetic Energy Generation Based on NiMnGa Heusler Alloy Films. Shape Memory and Superelasticity 2018, 4, 242 -255.

AMA Style

Manfred Kohl, Marcel Gueltig, Frank Wendler. Coupled Simulation of Thermomagnetic Energy Generation Based on NiMnGa Heusler Alloy Films. Shape Memory and Superelasticity. 2018; 4 (1):242-255.

Chicago/Turabian Style

Manfred Kohl; Marcel Gueltig; Frank Wendler. 2018. "Coupled Simulation of Thermomagnetic Energy Generation Based on NiMnGa Heusler Alloy Films." Shape Memory and Superelasticity 4, no. 1: 242-255.

Article
Published: 13 November 2017 in physica status solidi (b)
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Elastocaloric cooling demands for temperature changes larger than 30 K to become an alternative to classical vapour compression cooling systems. The principle of active regeneration allows to exceed the materials intrinsic adiabatic temperature change. The resulting temperature gradient of the cooling demonstrator leads to a change in the thermomechanical response along the regenerator bed, according to the Clausius–Clapeyron equation. A lowered efficiency as well as an increased probability of early breakdown of the device due to functional and especially structural fatigue are the result. These changes in the thermomechanical response are especially present in NiTi and NiTiCu-based systems with a coefficient ???T of about 7 and 10 MPa K−1, respectively. To address these issues for future applications a change in the transformation temperature along the shape memory alloy film, adapted to the temperature gradient of the regenerator, is required. Cobalt is well known to reduce the transformation temperatures, while maintaining the functional stability of the TiNiCu-based films. In this study multilayer dc-magnetron sputtering is used to fabricate TiNiCuCo films with a cobalt concentration gradient along the samples, which can be precisely tuned by changing the sputter conditions. Transformation gradients of 0.3 K mm−1 are obtained, showing the same functional stability and adiabatic temperature changes of about −11 K as their counterparts without transformation gradient. Under isothermal conditions, a sloped transformation plateau is observed corresponding to a highly directed martensitic transformation.

ACS Style

Lars Bumke; Christoph Chluba; Hinnerk Ossmer; Christiane Zamponi; Manfred Kohl; Eckhard Quandt. Cobalt Gradient Evolution in Sputtered TiNiCuCo Films for Elastocaloric Cooling. physica status solidi (b) 2017, 255, 1 .

AMA Style

Lars Bumke, Christoph Chluba, Hinnerk Ossmer, Christiane Zamponi, Manfred Kohl, Eckhard Quandt. Cobalt Gradient Evolution in Sputtered TiNiCuCo Films for Elastocaloric Cooling. physica status solidi (b). 2017; 255 (2):1.

Chicago/Turabian Style

Lars Bumke; Christoph Chluba; Hinnerk Ossmer; Christiane Zamponi; Manfred Kohl; Eckhard Quandt. 2017. "Cobalt Gradient Evolution in Sputtered TiNiCuCo Films for Elastocaloric Cooling." physica status solidi (b) 255, no. 2: 1.

Journal article
Published: 22 September 2017 in Journal of Physics D: Applied Physics
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The elastocaloric effect associated with the stress-induced first order phase transformation in pseudoelastic shape memory alloy (SMA) films and foils is of special interest for cooling applications on a miniature scale enabling fast heat transfer and high cycling frequencies as well as tunable transformation temperatures. The focus is on TiNi-based materials having the potential to meet the various challenges associated with elastocaloric cooling including large adiabatic temperature change and ultra-low fatigue. The evolution of strain and temperature bands during tensile load cycling is investigated with respect to strain and strain-rate by in situ digital image correlation and infrared thermography with a spatial resolution in the order of 25 µm. Major design issues and challenges in fabrication of SMA film-based elastocaloric cooling devices are discussed including the efficiency of heat transfer as well as force recovery to enhance the coefficient of performance (COP) on the system level. Advanced demonstrators show a temperature span of 13 °C after 30 s, while the COP of the overall device reaches almost 10% of Carnot efficiency.

ACS Style

F Bruederlin; H Ossmer; F Wendler; S Miyazaki; Manfred Kohl. SMA foil-based elastocaloric cooling: from material behavior to device engineering. Journal of Physics D: Applied Physics 2017, 50, 424003 .

AMA Style

F Bruederlin, H Ossmer, F Wendler, S Miyazaki, Manfred Kohl. SMA foil-based elastocaloric cooling: from material behavior to device engineering. Journal of Physics D: Applied Physics. 2017; 50 (42):424003.

Chicago/Turabian Style

F Bruederlin; H Ossmer; F Wendler; S Miyazaki; Manfred Kohl. 2017. "SMA foil-based elastocaloric cooling: from material behavior to device engineering." Journal of Physics D: Applied Physics 50, no. 42: 424003.

Journal article
Published: 01 September 2017 in Acta Materialia
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ACS Style

Frank Wendler; Hinnerk Ossmer; Christoph Chluba; Eckhard Quandt; Manfred Kohl. Mesoscale simulation of elastocaloric cooling in SMA films. Acta Materialia 2017, 136, 105 -117.

AMA Style

Frank Wendler, Hinnerk Ossmer, Christoph Chluba, Eckhard Quandt, Manfred Kohl. Mesoscale simulation of elastocaloric cooling in SMA films. Acta Materialia. 2017; 136 ():105-117.

Chicago/Turabian Style

Frank Wendler; Hinnerk Ossmer; Christoph Chluba; Eckhard Quandt; Manfred Kohl. 2017. "Mesoscale simulation of elastocaloric cooling in SMA films." Acta Materialia 136, no. : 105-117.