Publications Search Results

Now showing 1 - 10 of 20
  • Publication
    Inkjet Printing and Characterization of Applied Electrodes for Dielectric Elastomer Transducer
    ( 2020)
    Cabuk, Ozan
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    ; ; ;
    Maas, Jürgen
    Dielectric elastomer (DE) transducers consist of a dielectric elastomer layer coated with flexible electrodes on both surfaces. Apart from the dielectric film, the properties of the electrodes affect the electromechanical behavior of the DE transducers as well. Electrodes must be able to sustain conductivity at large deformations, must exhibit a low stiffness and provide sufficient adhesion to the DE-layer. Different processing technologies exist for application of electrodes suitable for DE-transducer. Among them, the inkjet printing technique gained attention in recent years as a very precise and purely non-contact deposition method to fabricate thin electrode layers. In contrast to other methods, e. g. using a shadow mask in case of spraying, the inkjet technique is very versatile and allows a fast adjustment of the processed electrode geometry. In order to describe the requirements of the inkjet printing process and ink adaptation itself, we present a theoretical description of those processes accompanied with the definition of parameters, which need to be considered during experimental processing. Furthermore, we present first results of our adaptation of an ink formulation and an inkjet printing procedure. For this purpose a commercial electrode paste, Elastosil® LR 3162, made of carbon black-silicone composite, was adapted to the inkjet printing process. In first experimental studies, the adapted ink was inkjet printed onto dielectric elastomer layers by varying the inkjet printing parameters. Different measurements were performed in order to characterize separate dots as well as continuous lines and areas of the inkjet printed electrodes. The electrode thicknesses and its shapes were recorded by surface-profile measurements. The electrical properties of the printed electrodes as well as their mechanical influence on the elastic properties of the elastomer layers were measured under continuous and cyclic mechanical stretching.
  • Publication
    Deep surface relief grating in azobenzene-containing materials using a low-intensity 532 nm laser
    The inscription of deep surface relief grating (SRG) in glassy monomeric azobenzene materials using a low intensity diode pumped solid state (DPSS) laser operating at 532 nm is demonstrated. Previously developed epoxy-based star-like azobenzene-containing material was applied. Both deep SRG and multi-dimensional structures can be fabricated using this cheap, effective material in combination with a low cost laser source. The dependencies of the SRG performance (amplitude, inscription rate, stability) on exposure conditions (time, intensity) and layer thickness are presented. The replication of the inscribed gratings using polydimethylsiloxane is demonstrated. The results show that effective all-optical fabrication of surface relief master-gratings can be realized using low cost chemistry and widely used low-intensity coherent light source operating at 532 nm.
  • Publication
    Low voltage driven dielectric membrane actuators integrated into fast switching electronic circuit boards
    ( 2019)
    Pointner, Tobias
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    In high-tech companies operating worldwide innovation is the key driver for long-term market success. Hence, innovative engineering technologies not only provide technological challenges but also investment risks for decision makers who want to tread new paths in product development. As an important example, the typically required high operating voltage and the need for high voltage power supplies constitute physical, economic and psychological restrictions for the application of dielectric elastomer actuators (DEA). Therefore, based on the view of product integration we aimed to limit the applied voltage below 600 V. To achieve this goal, we developed membrane actuators made of dielectric elastomers, which can be driven by lower voltages provided by low-cost power supplies. In detail, a particular device was developed with specially designed compression fittings clamping the DEA-film which enabling a simple electric contact between the actuator and the circuit board. The prefabricated actuator module was integrated in a fast switching, low-cost electronic circuit board. The power supply generates up to 550 V with a slew rate of a few microseconds, whereas the whole circuit has the geometrical dimension of a credit card. A plunger connected to the DEA-film moves out of plane when the actuator is activated. With the use of permanent magnets, interacting with the plunger, the system can be enhanced to meet industrial requirements in force and stroke. The resulting 'embedded' system offers a platform for further applications in different industrial segments and applications for instance in automation with valves, grippers or micro pumps in process automation and life sciences.
  • Publication
    Bragg polarization gratings used as switchable elements in AR/VR holographic displays
    ( 2018) ;
    Gritsai, Yuri
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    Sahm, Hagen
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    Stumpe, Joachim
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    The high coherence of laser light sources is a key to the application of diffractive optics usable in holographic AR/VR displays. This can be combined with switchable diffractive elements, which are advantageous for several optical functions used in immersive holographic displays such as shutters, polarization filters, for rapid beam deflection and selection. We demonstrate a compact, effective and robust diffraction wide-angle switchable beam-deflecting device based on circular polarization gratings possessing Bragg-performances (Bragg-PG) and a polarization switch. Such grating/polarization switch pair may, for instance, be a discrete switchable deflection element or as a switching element for pre-deflection with field lenses for application in holographic AR/VR displays. Micrometer-thick circular polarization gratings characterized by high diffraction efficiency (DE > 95%), large diffraction angles (< 30°) and wide angular and wavelength acceptance were developed. In the presented embodiment, the output signal is controlled between the zero- and first-diffraction orders by the handedness of circular polarization of the incident light. Forming a stack of two such oppositely aligned gratings can double the deflection angle. These gratings are the result of a two-step photochemichal/thermal processing procedure of a photocrosslinkable liquid crystalline polymer (LCP). The holographic patterning provides a high spatial resolution (period < 700 nm) and the arbitrary orientation of the LC director as well as high optical quality and thermal and chemical stability of the final gratings. Highly efficient (diffraction efficiency, DE > 95% in the vis spectral range) and stable symmetric and slanted circular Bragg polarization gratings were fabricated using the developed material and processing technique. The high usable diffraction angles combined with high DE make the Bragg-PG attractive for HMD AR/VR applications because of the system inherent short focus lengths and large numerical apertures needed to meet the low space budget in HMD and other optical systems.
  • Publication
  • Publication
    Processing line for stacked DE-actuator modules
    ( 2016) ;
    Biedermann, Miriam
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    ;
    Krüger, Hartmut
    Dielectric elastomer actuators (DEAs) are widely studied due to their extraordinary properties. Research and development on DEAs is conducted in order to generate and optimize the elastomeric materials, flexible electrodes, preparation processes of films and layers as well as to build up film, roll and stacked actuators. A broad variety of applications is developed for different kind of actuators. Recently, huge developments were performed in stacked actuators. Such actuators consist of several tens or hundreds of single elastomer layers with flexible electrodes which are processed or aligned on top of each other. Actuator modules with heights of e. g. some millimeters to centimeters are fabricated which provide a deflection in transversal direction in the range of some hundred micrometers to e. g. some millimeters. Here, we present the manufacturing of stacked actuator modules which is performed in a semi-automatic processing line. The elastomeric layers are processed from the liquid phase by doctor-blading which allows the deposition of a homogeneous layer on a substrate with the size of 20 cm x 20 cm. In the next step the elastomer is cured by thermal or UV treatment. Carbon-particle electrodes are deposited by an air-brush technique. This procedure is repeated in order to process stacked actuator modules with e. g. 10 layers which can be combined to larger stacked actuators. Finally, stacked actuators were characterized regarding their geometrical and electrical properties.
  • Publication
    PDMS-based DEA materials incorporating covalently attached softening agents
    ( 2015)
    Biedermann, Miriam
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    Blümke, Martin
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    Krüger, Hartmut
    The use of polydimethylsiloxane (PDMS) materials for the processing of dielectric elastomer actuators (DEAs) is a field of research that gained much in interest particularly in recent years. Up to now a significant limitation to the application of DEAs is their high operation voltage in the range of several thousand volts. There are various approaches to face the challenge of lowering the required voltage and, thus, making these materials even more attractive for versatile applications. Promising concepts to overcome this restriction are the reduction of the film thickness, the increase of the permittivity or the lowering of the mechanical stiffness. The object of this work is to improve the actuation properties of PDMS-based DEA materials by decreasing their Youngs modulus. Therefore a symmetric low-molecular PDMS chains are incorporated covalently into the PDMS network. They form loose chain ends during the network formation and act as a kind of softener within the PDMS network. PDMS materials featuring a broad range of Youngs moduli Y were manufactured by varying the amount of the low-molecular PDMS additive between 0 wt% and 50 wt%. Our concept allows for the precise adjustment of the elastomers stiffness from about Y = 1.7 MPa (0 wt% softener) down to circa Y = 190 kPa (50 wt% softener) starting from one and the same set of basic components. The chemical, mechanical, electrical, and electromechanical properties of these novel materials are presented in detail.
  • Publication
    Silicone films by crosslinking of polymethylhydrosiloxanes with N,N-diallyl-4-nitroaniline
    ( 2015)
    Blümke, Martin
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    Krüger, Hartmut
    Dielectric elastomer actuators (DEAs) enable a wide range of interesting applications since they are soft, lightweight, low-cost and have direct voltage control. However, one of the main obstacles to their wide-spread implementation is their high operating voltage, which tends to be several thousand volts. The operating voltage can be lowered by reducing the thickness, increasing the permittivity or lowering the stiffness of the elastomer. Recently, we offered a method to increase the permittivity of silicones from 3 to 6 via dipole-grafting simultaneously accompanied by significant stiffness reduction. During network formation the used dipole N-allyl-N-methyl-4-nitroaniline and divinyl-terminated polydimethylsiloxane compete to bind covalently to the polymethylhydrosiloxane crosslinker. Therefore, the dipole is connected only as a side-group to the crosslinker. Here we present a new approach using the difunctional dipole N,N-diallyl-4-nitroaniline as crosslinker for polymethylhydrosiloxanes. The Pt-catalyzed crosslinking reaction is optimized to obtain qualified silicone films with different dipole concentrations varying from 0.5 wt% to 1 wt%. The mechanical properties, the permittivity and the electromechanical properties of the films were characterized for varying nitroaniline content. For these novel elastomer materials an actuation strain of 13 % was measured at 40 V/micrometers.