Performance of dielectric elastomer transducers (DEST) depends on mechanical and electrical parameters. For designing DEST it is therefore necessary to know the influences of these parameters on the overall performance. We show an electrical equivalent circuit valid for a transducer consisting of multiple layers and derive the electrical parameters of the circuit depending on transducers geometry and surface resistivity of the electrodes. This allows describing the DESTs dynamic behavior as a function of fabrication (layout, sheet and interconnection resistance), material (breakdown strength, permittivity) and driving (voltage) parameters. Using this electrical model transfer function and cut-off frequency are calculated, describing the influence of transducer capacitance, resistance and driving frequency on the achievable actuation deflection. Furthermore non ideal boundary effects influencing the capacitance value of the transducer are investigated by an electrostatic simulation and limits for presuming a simple plate capacitor model for calculating the transducer capacitance are derived. Results provide the plate capacitor model is a valid assumption for typical transducer configurations but for certain aspect ratios of electrode dimensions to dielectric thickness -- arising e.g. in the application of tactile interfaces -- the influence of boundary effects is to be considered.
Dielectric elastomer stack actuators (DESA) are well suited for the use in mobile devices, fluidic applications
and small electromechanical systems. Despite many improvements during the last years the long term behavior
of dielectric elastomer actuators in general is not known or has not been published.
The first goal of the study is to characterize the overall lifetime under laboratory conditions and to identify
potential factors influencing lifetime. For this we have designed a test setup to examine 16 actuators at once.
The actuators are subdivided into 4 groups each with a separate power supply and driving signal. To monitor
the performance of the actuators driving voltage and current are measured continuously and additionally, the
amplitude of the deformations of each actuator is measured sequentially.
From our first results we conclude that lifetime of these actuators is mainly influenced by the contact material
between feeding line and multilayer electrodes. So far, actuators themselves are not affected by long term
actuation. With the best contact material actuators can be driven for more than 2700 h at 200 Hz with an
electrical field strength of 20 V/μm. This results in more than 3 billion cycles. Actually, there are further
actuators driven at 10 Hz for more than 4000 hours and still working.
Dielectric elastomer stack actuators (DESA) promise breakthrough functionality in user interfaces by enabling freely
programmable surfaces with various shapes. Besides the fundamental advantages of this technology, like comparatively
low energy consumption, it is well known that these actuators can be used as sensors simultaneously.
The work we present in this paper is focused on the implementation of a DEA-based tactile display into a mobile device.
The generation of the driving voltage of up to 1.1 kV out of a common rechargeable battery and the implementation of
the sensor functionality are the most challenging tasks.
To realize a large range of tactile experiences, both static and dynamic driving voltages are required. We present a
structure combining different step-up topologies to realize the driving unit. The final circuitry complies with typical
requirements for mobile devices, like small size, low weight, high efficiency and low costs.
The sensing functionality has to be realized for different actuator elements regardless of their actual state. An additional
sensing layer on top or within the actuators would cause a higher fabrication effort and additional interconnections.
Therefore, we developed a high voltage compatible sensing system. The circuitry allows sensing of user input at every
Both circuits are implemented into a handheld-like device.
In this paper we discuss the electrical and mechanical modeling of dielectric elastomer stack actuators. The model is
used to extract internal electrical parameters out of measurable values of the whole actuator system. Further parameters
like the uniaxial Young's modulus, the assembly of the stack and the number of connected layers have to be considered.
Using this data the static actuator performance for several driving conditions can be predicted. The final comparison of
model based predicted deformation and real stack deformation show good accordance. Hence, the proven correlation of
actuator layout parameters, fabrication parameters and driving conditions allow application dependent actuator design.
Dielectric elastomer stack actuators (DESA) offer the possibility to build actuator arrays at very high density. The
driving voltage can be defined by the film thickness, ranging from 80 μm down to 5 μm and driving field strength of
30 V/μm. In this paper we present the development of a vibrotactile display based on multilayer technology. The display
is used to present several operating conditions of a machine in form of haptic information to a human finger. As an
example the design of a mp3-player interface is introduced. To build up an intuitive and user friendly interface several
aspects of human haptic perception have to be considered. Using the results of preliminary user tests the interface is
designed and an appropriate actuator layout is derived. Controlling these actuators is important because there are many
possibilities to present different information, e.g. by varying the driving parameters.
A built demonstrator is used to verify the concept: a high recognition rate of more than 90% validates the concept. A
characterization of mechanical and electrical parameters proofs the suitability of dielectric elastomer stack actuators for
the use in mobile applications.
Using dielectric elastomer stack actuators the electrical contact to each conducting layer is a major concern. In order to
integrate these actuators inside micro systems e.g. microfluidic systems compatibility to micro fabrication processes is
required. The contact resistance and number of connected layers influence the overall actuator performance directly.
Lower number of active electrodes decreases the generated deformation of the actuator. High contact resistance has a
negative impact on the dynamic actuator behavior.
For conventional interconnection processes with copper wires, the contact ratio is in the range of 60% to 80%, depending
on the film thickness of the dielectric layer. Furthermore, this process is not compatible to standard micro fabrication
technologies. In this paper we evaluate a process based on electroplating for connecting dielectric elastomer stack
actuators and present a measurement system to characterize the number of connected layers.
The performance of an electroplated contact is defined by the number of connected layers and the contact resistance
between electroplated copper studs and graphite electrodes. It depends on different parameters like the cross sectional
area of the electrode layers for connection and therefore on the layer thickness. Using multiple contacts instead of a
single one the performance of the contact can also be positively influenced.
In this paper we are presenting a concept of a dielectric elastomer actuator (DEA) driven gas valve array for use in a
micro burner unit. Such a unit consists of a spatial array of gas nozzles. Every valve controls the gas flow through a
single nozzle. With individual control of each valve the burner can be activated partially in controlled spatial patterns.
Therefore, the heat dissipation can be controlled and adjusted according to the current needs. For the individual valves a
simple control valve rather than a proportional valve can be used.
Using dielectric elastomer actuators to control the gas flow an additional demand for thermal decoupling between firing
chamber and dielectric elastomer actuator must be met. Therefore, the valve seat is made of a heat-resistant material.
With a polymer based ceramic the thermal decoupling can be achieved. Additionally, this material permits the
fabrication of arbitrary three dimensional structures.
To control the gas flow different configurations of actuator and valve seat are possible. They are compared according to
the complexity of the assembly and the possibility of a monolithic fabrication. The different configurations contain
different actuation modes (thickness variation versus lateral deformation), direct or indirect control of gas flow and
different valve movements relative to gas flow.
Tactile perception is the human sensation of surface textures through the vibrations generated by stroking a finger over
the surface. The skin responds to several distributed physical quantities. Perhaps the most important are high-frequency
vibrations, pressure distributions (static shape) and thermal properties. The integration of tactile displays in man-machine
interfaces promises a more intuitive handling. For this reason many tactile displays are developed using different
We present several state-of-the-art tactile displays based on different types of dielectric elastomer actuators to clarify the
advantages of our matrix display based on multilayer technology. Using this technology perpendicular and hexagonal
arrays of actuator elements (tactile stimulators) can be integrated into a PDMS substrate. Element diameters down to
1 mm allow stimuli at the range of the human two-point-discrimination threshold. Driving the elements by column and
row addressing enables various stimulation patterns with a reduced number of feeding lines.
The transient analysis determines charging times of the capacitive actuators depending on actuator geometry and
material parameters. This is very important to ensure an adequate dynamic characteristic of the actuators to stimulate the
human skin by vibrations. The suitability of multilayer dielectric elastomer actuators for actuation in tactile displays has
been determined. Beside the realization of a static tactile display - where multilayer DEA are integrated as drives for
movable contact pins - we focus on the direct use of DEA as a vibrotactile display.
Finally, we present the scenario and achieved results of a recognition threshold test. Even relative low voltages in the
range of 800 V generate vibrations with 100% recognition ratio within the group of participants. Furthermore, the
frequency dependent characteristic of the determined recognition threshold confirms with established literature.
The functional principle of peristaltic motion is inspired by the pattern in which hollow organs move. The technology of
dielectric elastomer actuators provides the possibility to design a very compact peristaltic pump. The geometries of the
whole pump and the actuator elements have been determined by numerical simulations of the mechanical behaviour and
the fluid dynamics. With eight independent actuators the pumping channel is self-sealing and there is no need for any
valves. The first generation of this pump is able to generate flow rates up to 0.36 μl/min.
Stacked dielectric elastomer actuators (DEA) act as solid state actuators. Modeling such an electromechanical system
demands the knowledge about the mechanical and electrical parameters of the used materials as well as the real static
and dynamic behavior.
In elastomer actuators the electrical properties of the materials might change with applied mechanical stress or applied
voltage as it is known from some materials (e. g. polyacryl). Therefore, we examined the PDMS used in stacked
dielectric elastomer actuators regarding such dependencies. We present results from testing the permittivity of two
different silicones (Elastosil P7670, Wacker Silicones; RTV410, Bayer) versus mechanical stress, frequency of the
driving voltage, film thickness and curing temperature.
The resulting movement of a stacked actuator is not a single displacement of the elements but a rather complex bulk
deformation. Therefore, a planar displacement measurement system is necessary. Laser displacement sensors offer the
possibility of a two-sided measurement. This allows to determine the actual thickness variation even if the actuator array
moves out of plane. The setup includes a prestretching device to clamp the actuators symmetrically and to simulate an
uniaxial load. The realized measurement setup has an effective vertical measurement range of 10 mm, a resolution of
100 nm at a sample rate of 20 kHz. This allows the static and dynamic displacement measurement of planar actuators.
Stacked dielectric elastomer actuators are fabricated by an automated process using spin coating of uncured elastomers.
To improve the performance of these multilayer actuators we present two different ways. To reduce the driving voltage it
is desirable to fabricate dielectric films with a thickness below 20 μm. This can be achieved by high speed spin coating
of an uncured elastomer. Analyzing the automated process reveals nine principal process parameters. An adequate design
of experiment reduces the number of necessary tests to an acceptable value. With these results we are able to spin thin
films with a thickness of less than 5 μm and a thickness variation of about 3%.
Secondly, we examine the influence of nanosized particles of metal oxide powder on the permittivity of the elastomer
film. Three different materials, namely aluminiumoxide, titaniumdioxide and bariumtitanate with a bulk permittivity of
about 10, 100, 1000, respectively, are used to increase the overall permittivity of the composite. To predict the resulting
performance of an elastomer actuator the figure of merit Κ is introduced.
Solid state actuators provide deformation and actuation forces mainly excited by electric fields. Piezoelectric actuators are well established providing high forces at low strain due to their material characteristic. Electrostatic solid-state actuators consist of elastic dielectric layers between compliant electrodes. Applying electric fields of up to 100 V/μm at the electrodes the dielectric contracts due to electrostatic forces and expands in orthogonal direction. We use high elastic silicone elastomers with thin graphite powder electrodes. In order to increase the absolute strain values at limited voltage, we have developed a novel multilayer process technology to fabricate elastomer stack actuators with up to 100 layers. The electromechanical properties of the actuators have been evaluated theoretically and characterised experimentally. Maximum strain values up to 20% for prestressed multilayer films have been achieved. The novel multilayer fabrication technology provides multilayer stack actuators with various electrode patterns like universal linear actuators or matrix arrays for a wide range of applications as tactile displays for telemanipulation or Braille displays. The strain in vertical direction versus driving voltage shows a hysteresis due to viscous friction in the elastomer layers. These measurements correspond to a viscoelastic theoretical model. The mechanical stress versus strain characteristic shows a strong nonlinearity for strains > 30%. The dynamic characteristic has been evaluated by measuring the mechanical impedance in the frequency range of 2 to 1000 Hz.