Publications Search Results

Now showing 1 - 10 of 42
  • Publication
    Dielectric elastomer strain sensors with enhanced measuring sensitivity
    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
    Electroplating and Ablative Laser Structuring of Elastomer Composites for Stretchable Multi-Layer and Multi-Material Electronic and Sensor Systems
    ( 2021)
    Stier, Simon P.
    ;
    In this work we present the concept of electroplated conductive elastomers and ablative multi-layer and multi-material laser-assisted manufacturing to enable a largely automated, computer-aided manufacturing process of stretchable electronics and sensors. Therefore, the layers (conductive and non-conductive elastomers as well as metal layers for contacting) are first coated over the entire surface (doctor blade coating and electroplating) and then selectively removed with a CO2 or a fiber laser. These steps are repeated several times to achieve a multi-layer-structured design. Is it not only possible to adjust and improve the work previously carried out manually, but also completely new concepts such as fine through-plating between the layers to enable much more compact structures become possible. In addition, metallized areas allow the direct soldering of electronic components and thus a direct connection between conventional and stretchable electronics. As an exemplary application, we have used the process for manufacturing a thin and surface solderable pressure sensor with a silicone foam dielectric and a stretchable circuit board.
  • Patent
    Elektromechanischer Wandler und dessen Verwendung
    ( 2021) ;
    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
    Novel dielectric elastomer sensors for the measurement of elevated pressure loads
    ( 2021) ;
    Liu, Jinchao
    ;
    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.
  • Publication
    Magnetorheological elastomers - An underestimated class of soft actuator materials
    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
    Actuation with Magnetoactive polymers
    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
    Dynamic electro‐mechanical analysis of highly conductive particle‐elastomer composites
    The availability of stretchable conductive materials is a key requirement for the development of soft and wearable electronics. Although there are many promising materials, the characterization of these materials under realistic conditions is complex and a standardized and reliable procedure has not been etablished yet. We therefore introduce a comprehensive protocol for the practice-oriented dynamic electro-mechanical analysis of elastomer-particle composites. In addition to strain dependence (0-100% strain) and fatigue strength (10,000 cycles), this protocol aims in particular to clarify the influence of strain rate (0-100% s−1) on conductivity. Samples with the commonly used filler representatives carbon black and silver flakes with 20 vol% each were prepared and investigated. Silicone elastomers of different stiffness were used as matrix in order to determine its influence. We found that while the conductivity of the carbon black composites of about 1 × 102 S m−1 proved to be fatigue resistant and largely independent of the strain rate, the silver flake composites lost their initially higher conductivity of 1 × 104 S m−1 at high strain rates and increasing numbers of cycles. In addition, the use of a softer silicone matrix improved the performance of both particle composites, which was also demonstrated on an exemplary wearable electronic device.
  • Publication
    Magnetorheological Elastomers - Material Properties and Actuation Capabilities
    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
    Kapazitives Sensorsystem und Verfahren zur multimodalen und/oder ortsselektiven Messung von Kräften, Verformungen und/oder Objekt-Näherung
    Die vorliegende Erfindung betrifft ein kapazitives Sensorsystem zur multimodalen und/oder ortsselektiven Messung von Kräften, Verformungen und/oder Objekt-Näherung sowie ein entsprechendes Messverfahren. Verwendung findet das erfindungsgemäße kapazitive Sensorsystem in den Bereichen der Industrie, Automobil, Medizin sowie Sport und Freizeit.
  • Publication
    Glove with versatile operation tools based on dielectric elastomer sensors
    ( 2019) ; ;
    Muth, Stefan
    A wearable glove equipped with various types of dielectric elastomer sensors is described. The capacitive flexible sensors serve for different technical operation functions controlled by defined finger actions. A first type is a pressure sensor located at the thumb of the glove. The applied pressure of the thumb on another finger can tune a technical function. By operating a contact sensor, the adjusted value can be frozen. Contact sensors detect the touch between different fingers. In contrast to other proximity sensors, the electrodes are distributed on two fingers. The approach of one finger to another one increases the capacitance between the electrodes. This sensor type can be used for switches to trigger a technical function such as activation or deactivation. A third sensor type consists of three electrodes where two electrodes are located on one finger and the third electrode is located on another finger. Sliding the second finger on the first finger causes an increase or decrease of two capacitances depending on the relative position of the third electrode in relation to the first two electrodes. This sensor can be used as a slider for tuning a technical function such as brightness or loudness. An advanced version of this sensor is a combination of four electrodes on one finger and a fifth electrode on a second finger. Here, the sliding of the fifth electrode on the other four electrodes changes four capacitances. This configuration works as a two-dimensional slider similar to a computer mouse to control a cursor on a screen. All capacitive sensors are manufactured with silicone elastomer components, where the electrodes contain carbon black particles to become conductive. The sensors are integrated in the fabric of a glove. In addition, the glove is equipped with an electronic compartment containing a microprocessor to measure and process the sensor capacitances. The data is transmitted wirelessly to a personal computer, where the status of the sensors can be demonstrated graphically. The paper shows some examples of finger actions and the corresponding reactions of the sensors.