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Author: Böse, Holger × Has files: false ×

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Now showing 1 - 10 of 46
  • Publication
    Dielectric Elastomer Sensors with Advanced Designs and their Applications
    ( 2023-03)
    Böse, Holger
    ;
    Ehrlich, Johannes
    Dielectric elastomer sensors (DESs) have been known as highly stretchable strain sensors for about two decades. They are composite films consisting of alternating dielectric and electrode layers. Their electrical capacitance between the electrodes is enhanced upon stretching. In this paper, a variety of advanced designs of DESs is introduced. An explanation of how these sensors work and how they perform in terms of capacitance versus deformation or load force is provided. Moreover, the paper describes how the sensor design affects the sensor characteristics in order to achieve a high measuring sensitivity. The most relevant quantities to be measured are distance variations or elongations, forces and pressure loads. It is demonstrated that the sensor design can be supported by Finite Element Method (FEM) simulations. In the second part of the paper, possible applications of the advanced DESs are outlined. Pure sensor applications to detect or monitor pressure or deformation are distinguished from other applications, where sensors form a part of a human-machine interface (HMI). DESs are predestined to be used in contact with the human body due to their softness and flexibility. In the case of an HMI, a dosed load on a sensor by the user’s hand enables the remote control of arbitrary technical functions. This can preferably be realized with an operating glove, which exhibits different categories of DESs. Possible applications of DESs are described with the support of functional demonstrators.
  • Publication
    Modeling of the actuation performance of dielectric elastomer unimorph bending actuators consisting of different materials
    ( 2023)
    Böse, Holger
    ;
    Ehrlich, Johannes
    ;
    Löschke, Peter
    ;
    Gerlach, Thomas
    Unimorph bending actuators based on dielectric elastomers (DE) are promising components for soft robotic grippers in analogy to the capabilities of the human hand. In a simple manufacturing process of the unimorph actuator, a bendable, but not stretchable passive carrier film is laminated with an active DE film, which expands in the electric field and generates a large bending deformation of the laminated composite film along its length dimension. The actuation performance in terms of the bending angle, actuator tip displacement and blocking force depends not only on the geometrical design of the unimorph actuator, but also on the properties of the used materials such as the Young’s moduli of the passive film and the elastomer film as well as the elastomer’s permittivity. To evaluate the influence of all relevant geometrical and material parameters on the actuation performance, a simple mathematical model was developed. Additionally, DE unimorph actuators were manufactured with silicone elastomer and their performance was experimentally investigated. The results of calculations are compared with those of the corresponding measurements and exhibit a high degree of quantitative agreement. Furthermore, the dependence of the actuator performance on various geometrical and material parameters (thickness of the dielectric and of the carrier film, permittivity and Young’s modulus of the dielectric) is predicted with the mathematical model. These calculations pave the way to a unimorph actuator with strongly improved performance. The key for this high performance is the simultaneous enhancement of the permittivity and the Young’s modulus of the dielectric. Thermoplastic polyurethane (TPU) fulfills these requirements and unimorph actuators based on TPU actually confirm the predicted high performance experimentally. By this way, the simple mathematical model offers a powerful and efficient tool for the optimization of unimorph actuators.
  • Publication
    High-performance dielectric elastomer unimorph bending actuators without pre-stretch
    ( 2023)
    Ehrlich, Johannes
    ;
    Löschke, Peter
    ;
    Böse, Holger
    Dielectric elastomer (DE) single films for bending actuators are normally used with pre-stretch to increase the performance of the actuation. However, pre-stretch requires a high effort in the production of the actuators. In this work, a simple DE bending actuator in a unimorph configuration with high actuation performance is presented. For the manufacturing of the actuator, a silicone film is coated with conductive carbon nanoparticles in a silicone matrix as electrodes on both sides and laminated with a non-stretchable, but highly bendable and light weight polymer film, which acts as a strain limiting layer. Stiffening bars on the strain limiting layer impede an uncontrolled actuator deformation. The bending angle and the displacement of the actuator tip were measured at variable field strength up to 80 kV/mm. In a single DE layer configuration with an electrode area of 50 mm x 30 mm, a bending angle of 15° and a tip displacement of 7 mm were reached. A mathematical model for the bending actuator was applied to compare experimental and theoretical results and to optimize the relevant parameters. By using thermoplastic polyurethane (TPU) as an alternative elastomer material, a bending angle of 40° and a tip displacement of 18 mm could be achieved with the same actuator dimensions and optimized parameters. The simple unimorph bending actuators are promising tools for sensitive grippers on soft robots.
  • Publication
    Dielectric elastomer sensors adapted for monitoring compression load of clamped battery cells
    ( 2023)
    Ziegler, Johannes
    ;
    Uhl, Detlev
    ;
    Böse, Holger
    Condition monitoring of Li-ion cells in battery packs for electric vehicles is becoming increasingly important, not only in terms of safety, but also with respect to predictive maintenance and recycling applications of the battery. Parameters already monitored by the battery management system are the pack temperature and electrical properties such as cell voltage and current flow. The compression load in a stacked battery pack, which changes not only during charging and discharging but also during aging, would provide valuable information about the health condition of the cell. This work shows the development of a dielectric elastomer sensor (DES) system especially adapted for monitoring the compression load of clamped Li-ion cells. By attaching special elastomer-based structures on both sides of an elastomer film, a thin and soft compression load sensor is realized. Various sensor configurations were investigated in order to increase the sensor performance in the required pressure range of the battery cell. The sensor design was varied by using different structures or by modifying the elastomer material or the electrodes of the intermediate elastomer film. The sensor characterization was performed by applying a controlled compression load and simultaneously recording the capacitance signals of the sensor. First cycling experiments using a sensor array in a clamped setup with the battery cell showed that the sensor capacitance depends on the compression load as the cell is charged and discharged. This result demonstrates the great potential in the field of condition monitoring of Li-ion battery cells.
  • Publication
    Dielectric elastomer strain sensors with enhanced measuring sensitivity
    ( 2022)
    Böse, Holger
    ;
    Ehrlich, Johannes
    ;
    Gerlach, Thomas
    ;
    Shinkar, Tatjana
    ;
    Uhl, Detlev
    With the known dielectric elastomer strain sensors, large elongations over long distances with strains up to more than 100 % can be measured with high accuracy, but the sensitivity is limited, when extremely small strains below 1 % have to be monitored. To enhance the accuracy of the strain sensor, an advanced sensor design for low strain measurements was developed. The new sensor consists of two zones, which are connected in series along the sensor length. The active short zone is a stretchable dielectric elastomer strain sensor strip, whereas the passive long zone exhibits non-stretchable, but flexible polymer films. When the whole sensor is stretched, the strain is concentrated only in the stretchable shorter zone. Such sensors with enhanced measuring sensitivity were manufactured with silicone elastomer and investigated with a self-constructed electro-mechanical stretch testing device. The results of the measurements of capacitance, electrode resistance and stretch force vs. elongation were compared with those of corresponding conventional dielectric elastomer strain sensors. Furthermore, the dependence of the capacitance on the strain was calculated with finite element method (FEM) simulations for both sensor types. The advanced sensor design, the results of the experimental characterization and the comparison with the simulation are described in the paper.
  • Publication
    Magnetorheological Elastomers - Material Properties and Actuation Capabilities
    ( 2022)
    Böse, Holger
    ;
    Ehrlich, Johannes
    ;
    Gerlach, Thomas
    Magnetorheological elastomers (MRE) are composite materials, which consist of a soft elastomer matrix filled with soft-magnetic particles. Mechanical and magnetic properties of silicone-based MRE with iron particles in different concentrations as well as their alteration in a magnetic field with variable strength are described in this paper. By applying a magnetic field already during the preparation of MRE bodies, magnetic elastomer materials with anisotropic properties are generated. The mechanical, magnetic and electric properties of such anisotropic MRE materials were studied as well. Beside the exploitation of MRE for applications of vibration reduction, these materials can also be utilized for actuation purposes. The working principles of linear and radial MRE actuators are described. Moreover, some possible applications of linear MRE actuators for haptic feedback and precisely controllable pumps as well as the possible use of radial MRE actuators for proportional valves and for locking devices are outlined in the paper as well.
  • Patent
    Elektromechanischer Wandler und dessen Verwendung
    ( 2021)
    Böse, Holger
    ;
    Liu, Jinchao
    Die vorliegende Erfindung betrifft einen elektromechanischen Wandler mit mindestens einer dielektrischen Elastomerfolie, die mindestens eine elektrisch nicht-leitfähige Elastomerschicht und mindestens zwei elektrisch leitfähige Elektrodenschichten aufweist. Weiterhin enthält der Wandler eine flächige Struktur mit Erhöhungen, Vertiefungen oder Öffnungen, sodass der elektromechanische Wandler senkrecht zur Fläche der dielektrischen Elastomerfolie kompressibel ist. Verwendung findet der elektromechanische Wandler insbesondere in Sensoren. Ebenso ist aber auch die Verwendung als Aktor oder als Generator möglich.
  • Publication
    Actuation with Magnetoactive polymers
    ( 2021)
    Böse, Holger
    ;
    Ehrlich, Johannes
    ;
    Gerlach, Thomas
    Magnetoactive polymers (MAP) are a relatively new class of smart composite materials, which change their mechanical properties in a magnetic field. They consist of magnetisable particles dispersed in a soft elastomer matrix. Besides possible applications in vibration reduction, they exhibit also excellent actuation capabilities, which is demonstrated with various examples in this paper. MAP actuators with linear deformation are predestined for human-machine interfaces with haptic feedback and for pumping devices with sensitive control of the transport of liquid media as well. However, especially interesting are MAP actuators, which perform a radial expansion of a ring-shaped MAP body as an outstanding actuation mode. Such radial MAP actuators can be beneficially exploited for valves with rotational symmetry as well as for seals under rotational loads, which offer a solution for the existing trade-off between the objectives of high tightness and low friction. Furthermore, another useful application of radial MAP actuators are new locking devices, which smoothly block a rotational motion by the radial expansion of an MAP ring in the magnetic field.
  • Publication
    Magnetorheological elastomers - An underestimated class of soft actuator materials
    ( 2021)
    Böse, Holger
    ;
    Gerlach, Thomas
    ;
    Ehrlich, Johannes
    In this paper, the results of various investigations on the viscoelastic and magnetic properties of magnetorheological elastomers (MRE) in magnetic fields of variable strength, are reported. These characteristics have a strong influence on the behavior of MRE in various applications such as vibration damping and tunable vibration absorbers. Moreover, the actuation capabilities of MRE with different kinds of deformation in a magnetic field are considered. The degree of deformation depends on the magnetic field strength and its gradient and can reach about 10%. When removing the magnetic field, the MRE body relaxes back to its initial shape. MRE materials can be used for linear actuators, where the MRE body is deformed due to the attraction by a magnetic circuit acting from one side. Such linear actuators may be applied for haptic feedback and pumps. However, ring-shaped MRE bodies can also deform radially around their cylindrical axis, if the magnetic field is oriented correspondingly. This unusual type of deformation allows the realization of a proportional valve, whose opening is controlled by the magnetic field strength. Similar configurations can be used for controllable seals, for locking devices and even for inchworm drives. Various versions of this actuation principle are discussed in the paper.
  • Publication
    Novel dielectric elastomer sensors for the measurement of elevated pressure loads
    ( 2021)
    Böse, Holger
    ;
    Liu, Jinchao
    ;
    Gerlach, Thomas
    A novel design for dielectric elastomer pressure sensors based on a capacitive measurement principle is introduced. Compared with easily compressible and highly sensitive dielectric elastomer sensors containing internal voids, the new sensors are compact and suitable for an elevated pressure range up to about 2 MPa. In these sensors, a dielectric elastomer film with several dielectric and electrode layers is covered on both surfaces by plates, which exhibit a pattern of openings. When the sensor film is compressed, the elastomer material can expand into these openings, which reduces the film thickness and increases the capacitance. The dielectric elastomer film consists of a soft silicone with carbon black particles in the electrode layers. With this design, the sensitivity of the pressure sensors in terms of the capacitance increase is enhanced in comparison with reference sensors without openings in the plates and the disturbing hysteresis of the capacitance vs. pressure curves is reduced. With FEM Multiphysics simulations, the capacitance enhancement upon pressure increase and the sensor deformation were calculated and compared with experimental data. In a systematic study, different parameters of the sensor design were varied, in order to evaluate their influence on the sensor performance. The results of this study are presented in the paper.