One of the main technical challenges in the development of dielectric elastomer (DE) stack actuators is
the design and realization of suitable electrodes. They must be compliant and be able to undergo large
strains without adding too much stiffness. Metal electrodes are therefore normally out of question due to
their high stiffness, though their electrical properties are excellent. In this work a new design approach is
presented which comprises rigid metal electrodes. Its functionality is proven by means of numerical simulations
and experimental tests. It allows the customized tailoring of transducer elements due to the designable
electrode structure. A functional demonstrator is built and tested concerning its electrical, mechanical and
electromechanical behavior. For this new actuator type a full electromechanical model is developed. It contains
all transfer characterisitcs in a nonlinear description and accounts for various physical effects arising from the
special actuator design. Due to its standardized interface configuration it can well be used in combination
with existing models for mechanical structures and electrical amplifiers to completely model active systems.
It is applicable for the realistic simulation necessary in the development of active solutions with EAP devices.
A first longterm test with 108 load cycles was performed in order to show the durability of the actuator.
Dielectric elastomers (DE) have proved to have high potential for smart actuator applications in many laboratory
setups and also in first commercially available components. Because of their large deformation capability
and the inherent fast response to external stimulation they proffer themselves to applications in the field of
active vibration control, especially for lightweight structures. These structures typically tend to vibrate with
large amplitudes even at low excitation forces. Here, DE actuators seem to be ideal components for setting up
control loops to suppress unwanted vibrations. Due to the underlying physical effect DE actuators are generally
non-linear elements with an approximately quadratic relationship between in- and output. Consequently,
they automatically produce higher-order frequencies. This can cause harmful effects for vibration control on
structures with high modal density. Therefore, a linearization technique is required to minimize parasitic
effects. This paper shows and quantifies the nonlinearity of a commercial DE actuator and demonstrates the
negative effects it can have in technical applications. For this purpose, two linearization methods are developed.
Subsequently, the actuator is used to implement active vibration control for two different mechanical
systems. In the first case a concentrated mass is driven with the controlled actuator resulting in a tunable
oscillator. In the second case a more complex mechanical structure with multiple resonances is used. Different
control approaches are applied likewise and their impact on the whole system is demonstrated. Thus, the
potential of DE actuators for vibration control applications is highlighted.
The focus of this paper is on the modeling of dielectric elastomer actuators and generators. One of the effects
that is rarely considered in modeling of these systems is the influence of the materials' specific resistance on the
performance. The non-ideal electrical properties of both elastomer and electrode material will cause undesired
parasitic effects. Although for most laboratory scale prototypes these effects are hardly recognizable, they
may however play an important role for larger structures and especially for dynamic applications. Therefore,
an analytical model is developed and presented in this paper which can give helpful instructions for the design
and fabrication process of EAP-systems. It is proven to be valid by means of the finite element method and
subsequently extended for more complex systems.
To solve a wide range of vibration problems with the active structures technology, different simulation approaches for several models are needed. The selection of an appropriate modeling strategy is depending, amongst others, on the frequency range, the modal density and the control target. An active system consists of several components: the mechanical structure, at least one sensor and actuator, signal conditioning electronics and the controller. For each individual part of the active system the simulation approaches can be different. To integrate the several modeling approaches into an active system simulation and to ensure a highly efficient and accurate calculation, all sub models must harmonize. For this purpose, structural models considered in this article are modal state-space formulations for the lower frequency range and transfer function based models for the higher frequency range. The modal state-space formulations are derived from finite element models and/or experimental modal analyses. Consequently, the structure models which are based on transfer functions are directly derived from measurements. The transfer functions are identified with the Steiglitz-McBride iteration method. To convert them from the z-domain to the s-domain a least squares solution is implemented. An analytical approach is used to derive models of active interfaces. These models are transferred into impedance formulations. To couple mechanical and electrical sub-systems with the active materials, the concept of impedance modeling was successfully tested. The impedance models are enhanced by adapting them to adequate measurements. The controller design strongly depends on the frequency range and the number of modes to be controlled. To control systems with a small number of modes, techniques such as active damping or independent modal space control may be used, whereas in the case of systems with a large number of modes or with modes that are not well separated, other control concepts (e.g. adaptive controllers) are more convenient. If other elements (e.g. signal amplifiers or filters) in the signal paths have a significant influence on the transfer functions, they must be modeled as well by an adequate transfer function model. All the different models described above are implemented into one typical active system simulation. Afterwards, experiments will be performed to verify the simulations.
Smart materials based on carbon fiber-reinforced plastics with embedded PZT sensors and actuators are expected to be a favorite composite for vibration damping and noise reduction. Due to the wide variety of physical properties of the components various damage mechanisms may reduce or even remove the sensing and actuating capabilities of the piezoceramic material. Comprehensive non-destructive characterization and integral health monitoring help to optimize the structure and its manufacturing and are essential prerequisites to ensure performance and availability of smart components during their life time. The first part of the paper presents high resolution non- destructive imaging methods including microfocus X-rays, ultrasonics and eddy currents. These methods are used to characterize damages resulting from non-optimal manufacturing and external load. The second part is dedicated to newly developed imaging techniques using the active piezoceramics as transmitters of acoustic, electromagnetic and thermal fields. The third part focuses on health monitoring by impedance spectroscopy using the same piezoceramics as for vibration damping. Electromechanical finite-element-modeling and experimental investigations at strip-shaped specimens have shown the close connection between mechanical properties and electrical impedance.