This PDF file contains the front matter associated with SPIE Proceedings Volume 12482, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Existing smartwatches offer convenient health monitoring and interfaces with mobile devices. However, the interactivity between a user and a smartwatch suffers from the limited size of the screen and buttons. To improve the usability of smartwatches, novel human-computer interaction methods are introduced into the watchband. To this end, we present a modular lightweight watchband consisting of various capacitive sensing modules—TouchBand. It is made with a flexible printed circuit board (PCB) supporting the bottom electrodes, silver-coated conductive fabric as the top electrodes, and Eco-Flex as the dielectric to electrically separate the PCB and fabric. The watchband incorporates three control modules—(i) two shear-sensitive pressure sensing buttons, (ii) two capacitive sliders, and (iii) one proximity sensing array for hand gesture recognition. Shear forces are captured by analyzing the asymmetric changes in multiple mutual-capacitance readings produced by a shear motion between the top and bottom layers, where overlapped electrodes reside. Sliders pick up changes in proximity as fingers are moved across the sensor surfaces. Hand gestures could be recognized by monitoring the capacitance-based proximity readings between the watchband electrodes and the user’s skin. Eyes-free input to the watch becomes feasible by providing a shear/sliding touch input to the watchband as well as performing a free-hand gesture on the wearing hand. With a flexible printed circuit (FPC) connection to the compact custom electronics, all modules of the watchband were sampled at 50 Hz while consuming 30 mW of power. Meanwhile, the measurement data was wirelessly transmitted through Bluetooth Low-Energy 5.0 (BLE) to a nearby mobile device for real-time data analysis and visualization.

Physicalization helps the user understand complex data intuitively. Especially when confronted with complex, multidimensional datasets as in the smart home environment, classic graphical user interfaces struggle to visualize data in a way compatible with the paradigm of Calm Technology and new means of displaying data need to be explored, to decrease the cognitive burden on the user. Shape changing interfaces (SCI) using smart materials can change their appearance under electrical stimuli and provide the means to physicalize the data found in the smart home from sensors, appliances or others. Within the scope of this work, a smart display using dielectric elastomer unimorph actuators (UDEA) is developed, which can be used to explore how dielectric elastomers (DE) can be used for an SCI. A dynamic model of previous work has been adapted to the updated geometry. Reproducible production of the actuators is one focus of the current work. A novel sheet-to-sheet process for manufacturing multilayer DE-laminates is presented. Manual processing of the laminates to actuators is described and effects of human error on actuator performance in this process is assessed and found to be low to ensure reproducible fabrication. Finally the system design is presented and discussed. The developed display allows controlling 15 independent shape changing devices and will allow to gain more knowledge about physicalization of data using DE actuators.

In recent works, we proved that some dielectric elastomer (DE) actuator topologies, normally used as linear actuators at low frequencies (LFs), can produce sound taking advantage of high-frequency (HF) structural vibrations of the DE membrane surface. Because structural vibrations take place along different deformation directions compared to those involved in LF actuation, these DE actuators (DEAs) can generate sound even when their LF pumping motion is constrained, or while they are driven to produce a concurrent LF pumping motion. This observation can be used to develop acoustic buttons, which produce sound while being deformed by a user, or multi-function audio-tactile interfaces, which provide combined HF acoustic and LF tactile feedbacks through multi-chromatic voltage inputs. In this paper, we propose a self-sensing approach to estimate LF deformations of multi-function DEAs. In contrast with traditional self-sensing approaches, in which an additional sensing signal is superimposed to the main driving signal, here we solely rely on the HF acoustic voltage input, which we also use as the sensing signal. We prove that self-sensing of LF deformations can be achieved even in the presence of complex HF driving signals, such as soundtracks. This allows reconstructing LF deformations induced either by a LF voltage excitation (superimposed to the driving acoustic signal), or by variable external forces (e.g., user touches, such as in user interfaces). In the future, this self-sensing approach might be used to build multi-functional sound interfaces that adapt their output based on a user-driven deformation, or for virtual reality rendering applications.

Fiber dielectric elastomer actuators (DEAs) are potential candidates for the realization of artificial muscles owing to, amongst others, their linear actuation principle. In this work, a polydimethylsiloxane (PDMS) hollow fiber is prepared through a spinning method using the photocurable thiol-ene reaction between a thiol (R-SH) group and a double bond (C=C). The developed PDMS hollow fiber has an external diameter of 463 μm and uniform wall thickness of 78 μm, and presents tensile properties of ~600 % strain at break and 0.22 MPa strength, compared to these of the planar film of 86 % strain at break and 0.14 MPa tensile strength. Fiber DEAs are prepared by using ionic liquid as an inner electrode and ionogel as an electrical outer sheath. Due to the highly transparent PDMS elastomer layer and ionic liquid-based electrodes, the fiber DEA presents a transparency of ~91 % in a visible light spectrum. The fiber DEA exhibits a large linear strain of 9 % at 50 V/μm. Furthermore, the fiber DEA can be assembled into bundles for increased forces. The work presented herein provides a pathway for creating active soft matter with complex architectures to enable fast programmable actuation for multiple applications including invisible robots.

The quality of pear fruits is correlated with their firmness, which is assessed by a firmness index derived from the resonance frequency and mass. Postharvest pear fruits ripen during storage, which affects the firmness. A nondestructive measurement technique is necessary to predict fruit firmness without causing any damage. Thus, this study proposes a vibration experiment technique based on dielectric elastomer actuator (DEA) excitation to determine the resonance frequency of pear fruits without any damage. Therefore, DEAs can be attached directly on fruits with curved surfaces because of their stretchability, light weight, and responsiveness and can be used to transfer the excitation force effectively. For our experiments, thin laminated DEAs were fabricated to obtain sufficient vibration excitation force, and resonance frequencies of the pear fruits were confirmed. Subsequently, the firmness indices of each target fruit were calculated and assessed. Finally, the variations in firmness indices of pear fruits during storage were confirmed, and the effectiveness of the proposed technique was validated.

Dielectric Elastomer Actuators (DEAs) are known for their outstanding properties such as low weight, high energy density and self-sensing capability. Compared to conventional magnetic actuators, they are manufactured from generally inexpensive and widely available polymer materials, making the technology particularly attractive for developing actuator systems that are potentially low-cost and serve a wide range of applications. This advantage can be further enhanced by developing scalable and standardized system designs that use identical parts in order to reduce product variation and enable high volumes in a mass production process. Following this approach, this paper introduces a low-profile and compact linear actuator design, which provides a configurable force and stroke transmission in order to serve different load-profiles without changing shape and dimension of the DEA itself. The design is based on rectangular-shaped, in-plane operating DEAs coupled to a unibody linkage mechanism, which is likewise flat and based on compliant joints and rigid links. A negative rate stiffness mechanism enables to increase the performance output of the actuator system in terms of cyclic converted energy in quasi-static operation. By configuring the lever ratios of the input and output sides accordingly, it can either behave stroke-magnifying or force-magnifying. Thus, as an example, a system with negative and one with positive transmission ratio are realized and characterized with respect to their force and their stroke behavior.

Sensor arrays are ubiquitous. They capture images in digital cameras, record the swipes of our fingers on the screens of our phones and tablets, or map pressure distribution over an area. Soft capacitive sensors have long been proposed to make electronic pressure-sensing skins. However, although different designs of entirely soft capacitive sensors have been proposed, large arrays of those sensors are challenging to produce. Indeed, arrays require high-resolution patterning of electrodes, and routing of long and thin electrical connections. These two tasks remain difficult or costly for the high-resistivity compliant electrodes of dielectric elastomer sensors. Instead of relying on the complex patterning of arrays to provide location resolution, we propose to use a plain, unstructured sensor with a single pair of electrodes but rely on computing power to infer pressure location and amplitude from clever sensing signals. Here, we propose a new machine-learning-based approach, which enables us to identify pressure location on a continuous 1D sensor split into 5 sensing zones with an accuracy greater than 98 %. We also demonstrate that we can identify pressure location and qualitative pressure magnitude (soft, medium, hard) on a 3-zone sensor with 99% accuracy.

Human grasp is gentle yet firm, with integrated tactile touch feedback. Current robotic sensing is mainly visual, which is useful up until the point of contact. To understand how an object is being gripped, tactile feedback is needed. Ras Labs makes Synthetic Muscle™, which is a class of electroactive polymer (EAP) based materials and actuators that sense pressure from gentle touch to high impact, controllably contract and expand at low voltage (battery levels), and attenuate force. EAP development towards sensing provided for fingertip-like sensors that were able to detect very light pressures to 0.005 N and with a wide pressure range over 45 N with high linearity. Algorithms, machine learning (ML), and artificial intelligence (AI) were integrated into these sensors for object and grip determination (position, grip force, any slip or wobble) and immediate correction for pick-and-place and other applications. High tack EAPs also have good adhesion to a variety of substances and had self-healing properties. Using these adhesive EAPs and other strategies, sensors and actuators were created where all components stay together. Synthetic Muscle™ was also being retrofitted as actuators into a partial human hand-like biomimetic gripper that focused on the pincer grip. The combination of EAP shape-morphing and sensing promises the potential for robotic grippers with human hand-like control and tactile sensing. This is expected to advance robotics, whether it is for agriculture, medical surgery, therapeutic or personal care, or in hazardous environments where humans cannot enter, as well as for collaborative robotics to allow humans and robots to intuitively work safely and effectively together.

Capacitive dielectric elastomer sensors (DES) are well-known in robotic sensing applications due to their sensitivity and stability under tensile strain. These sensors rely on changes in geometry to detect deformation. Since DES are thin, they are resistant to out-of-plane compression and this is made more difficult if they are bonded to a rigid surface. Here, we present a new type of DES that detects changes in the fringe field between interdigitated electrodes (IDEs). This is made possible using a compression sensitive silicone/carbon black composite that sits atop the electrodes. The IDEs create a fringing field extending into the composite whose relative permittivity can change by 250% when compressed. As a result, there is no longer any design challenges brought on by the incompressibility of elastomers. Additionally, since compliant electrodes are not required in this configuration, and the electrodes are kept in a single plane on a commercial PCB, the fabrication process is simple. This sensor is convenient to be used as a tactile sensor for either conventional rigid or soft robotic grippers, allowing the safe manipulation of soft and delicate objects.

A pressure injury is a complex chronic wound that forms when the delivery of oxygen and nutrients to soft tissue regions is compromised due to prolonged pressure, commonly over bony prominences, which results in local ischemia, cell death and potentially fatal infections. Its early diagnosis and prediction are challenging, despite technological advancements. It remains one of the most burdensome, costly and fatal secondary medical conditions, which affects millions of people annually. Here, we present a soft, flexible and stretchable pressure sensor array made out of silicone elastomer material, carbon black particles and stretchable, conductive, silver-plated fabric. Its working principle is based on capacitive sensing, where electrodes form an array of parallel plate-like capacitors that enable the detection of pressure due to the deformation of the dielectric layer. We explored a variety of different dielectric architectures consisting of pillar structures of various shapes that make it compressible and potentially increase sensitivity. The sensor array is designed to be shape-conformable, scalable in size and resolution, and able to detect and measure pressure within the desired pressure range for pressure injuries (0-200 mmHg) over short (≤15 minutes) and long periods (≥8 hours) with consistent accuracy and low repeatability error.

For long-range swimming fish, low cost of transportation is a critical requirement. This also applies to autonomous fishlike robots (AFR). As with their biological cohorts, AFR require sensory input that characterizes the flow of the water surrounding them. Thus, there is a need for low power hydrodynamic sensors that can be deployed on a fish-like robot, and which can provide flow information from open water conditions. Electroactive polymers offer opportunities for flow sensing on soft and flexible AFR. We developed and evaluated an approach for capacitive electroactive polymer flow sensing. This uses dielectric elastomer sensor membranes mounted on a liquid-filled cavity protruding into the flow. Flow speed and incident angle on a hydrofoil standing in for the fish are registered through electrical capacitance changes resulting from deformation of its 350μm thick membrane. Through its triple-electrode design, measurements are largely shielded against the influence of the surrounding water on the capacitor. Differences in flow speed along the sensor can be detected with high reproducibility for extended durations of time. The developed sensors were assessed regarding accuracy, reliability, and durability. For performance and long-term testing, an automated tabletop water tunnel test rig was created. This setup enables sensor testing for flows up to 1 m/s with automated incident angle control and data logging. We are thus presenting further steps towards robust ocean-faring hydrodynamic sensory systems by demonstrating advances in electroactive sensory technology and testing facilities.

Soft polymer actuators are in increasing demand due to their more fluid like motion and flexibility when actuated than compared with rigid actuators, which makes them valuable in diverse engineering applications. One of the main types of soft polymer actuators is the dielectric elastomer actuator, whose working principle is to apply a voltage potential difference between electrodes to reduce the thickness of the elastomeric material while expanding its area. This paper looks at manufacturing a micro soft polymer dielectric elastomer actuator utilizing two-photon polymerization 3D printing. The actuator contains micro channels that are filled with an electrode by using capillary action. A complex helical geometry is designed, printed, and tested for electrode filling capabilities. Quite a few obstacles are described in this paper including the use of a newly released two-photon polymerization resin which has limited supporting resources, as well as the complex helical geometry having a large compliance that vastly complicates its fabrication, post-processing, handling, electrode filling, electrode integration, and actuation testing. However, these challenges are overcome by using the standard printing recipes currently available for the resins, adding electrode isolation layers, and printing thicker elastomer zones for more structural support. The results found solidify the approach of filling microchannels with electrodes through capillary action and lead to further the focus and creation of multi-functional micro soft actuators.

Polar group-modified polysiloxanes obtained by anionic ring-opening polymerization possess high dielectric permittivity and are of great interest for application in dielectric elastomer actuators (DEAs). A self-healing elastomer can be obtained by in situ polymerization and cross-linking using a cyclic siloxane monomer with polar side groups and a cross-linker consisting of multiple connected siloxane rings. In previous works, a non-polar cross-linker has been used, which requires the addition of a solvent for compatibilization with the polar monomer. In polymerization reactions of siloxanes, the addition of solvent leads to a more pronounced formation of cyclic by-products. These cycles impair the mechanical properties of the elastomer and cannot be removed after the reaction, as the material is already cross-linked. Therefore, in this work, we use a polar cross-linker that can be mixed with the polar monomer without adding solvent. Nitrile groups have been studied extensively for increasing the permittivity of the polysiloxane backbone. For a functionalization of 100%, a dielectric permittivity of ~18 was reached. In most cases, the nitrile group was attached to the siloxane backbone in the form of cyanopropyl groups. Still, the influence of the alkyl spacer on the material's dielectric and mechanical properties has not been studied. In this work, we synthesize cyanoalkyl-functional cyclic siloxanes with different lengths of the alkyl spacer and polymerize them solvent-free to high-permittivity polysiloxanes.

Dielectric elastomer actuator (DEA) based flexible and stretchable electronics have attracted considerable attention over the past decades. The electrode components play an important role in the DEA performance. In this work, we studied how the incorporation of soft matrices in the electrodes affects the DEA actuation. The ultrasonic spraying was used to fabricate multiwall carbon nanotube (MWCNT) based electrodes for DEA. The results indicated that the addition of a water-soluble block polymer and silicone gel (acting as the soft matrices) could improve the actuation of the DEA with neat MWCNT electrodes by ~10% and ~24%, respectively. An inkjet printing ink, consisting of polydimethylsiloxane (PDMS), carbon black (CB) and chlorobenzene, was further developed. The stability, particle size, resistance, and morphology of 1-3 printing layers were characterized. The DEA with the inkjet-printed CB/PDMS electrodes showed 50% area stain at 2500 V, which is higher than the actuation with neat CB powder or CNT electrodes reported previously. Both results of the ultrasonic spraying and inkjet printing confirmed that the incorporation of soft matrices in the electrodes is helpful for DEA actuation.

Filled polymer composites are capable of combining the favourable mechanical properties of polymers with desirable electrical properties of filler particles. Carbon-black elastomer nanocomposites are capable of conducting electricity while maintaining high stretchability. Despite these materials having been studied and utilised for a number of decades, the relationship between their internal structure and their macroscopic properties is still not fully understood. A major feature of their behaviour is significant piezoresistivity, which can be a nuisance in certain applications and a benefit in others. It is known that there is a relationship between the piezoresistivity of the material and the percolation threshold. However, the exact mechanisms underlying this behaviour are not rigorously understood. This work utilises Monte Carlo modelling to propose and examine ways in which the structure of the internal nanoparticle network, and the evolution of said network with strain could help to explain the piezoresistivity of these materials. Hopefully, a more detailed understanding of this mechanism will lead to an improved capability to customise it for various applications.

We have developed a diver-robot empathetic communication system that allows the diver to feel the disturbance around the robot and control the robot remotely using hand gestures. The underwater robot is embedded with soft dielectric elastomer (DE) sensors to sense the direction and amplitude of the disturbance around its surroundings, defined as the physical indentation of the eye sensors. The direction and intensity of the disturbance communicate to the user remotely via an array of vibrotactile actuators in the form of a bracelet. Wears of the glove will feel what the robot is going through, represented by different vibration intensities and patterns. The smart glove employs five dielectric elastomer sensors to capture finger motion and implements a machine-learning classifier in the onboard electronics to recognize gestures. Hence allowing the wearer to send commands in the form of hand gestures for correcting the underwater robot’s posture. The system will be tested in a user study to determine performance improvement over the traditional robotic control interface. Our work has demonstrated the capability of DE sensing for advanced human-machine interaction.

When dielectric elastomer actuators (DEAs) are actuated via high voltage, their electrical capacitance changes according to the geometry. Therefore, displacement of the actuator can be correlated to the change in capacitance, thus opening up the possibility of self-sensing DEA devices. Self-sensing can be exploited to achieve a sensorless closed loop DEA system, which is attractive from size, weight, and cost perspectives. This research work presents an embedded control system, which enables self-sensing closed loop position control of a DEA. The proposed architecture is cost effective, compact in size, easy to integrate as well as to reprogram in comparison to previous self-sensing implementations relying on FPGA systems. In the developed setup, the online self-sensing algorithm is used for estimation of displacement in a spring-biased strip DEA. For this system, understanding and mapping the correlation between estimated capacitance, applied voltage, and resulting displacement is essential for achieving an accurate DEA position reconstruction. An experimental setup is developed, and used to test a spring-biased DEA system. Self-sensing based feedback control is then used to achieve a tight regulation of the actuator displacement. To verify the effectiveness of the sensorless closed loop control system, its performance is finally compared to sensor-based feedback architectures.

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.

Besides their use in separation and filtration processes, ion-exchange membranes have been adopted as electroactive polymer actuators in soft robotics and biomedical engineering, due to their unique coupling between electrochemistry and mechanics. Actuation is generated by the asymmetry in cations and anions transport, as one of the two species is bonded to the membrane backbone, whereas the other can move throughout the membrane. Typically, electrodes are plated on the membrane to enable application of an external electric field. A new, promising contactless actuation configuration for underwater applications consists of immersing a bare membrane in an electrolyte solution, between external electrodes. When an electric field is imposed across the electrodes, a macroscopic bending deformation is observed. Despite major advances in understanding the actuation of cation-exchange membranes (with fixed anions), the actuation of anion-exchange membranes (with fixed cations) is an almost untapped field. In this work, we experimentally investigate the contactless actuation of anion-exchange membranes. In the experiments, we systematically vary the anions in the external solution and inside the membrane, to unravel their effects on membrane actuation. In all tested combinations, the membrane always bends in the opposite direction compared to cation-exchange membranes. Additionally, we find a prominent influence of the external anions on the actuation strength, consistent with previous theories that attribute actuation to solvation effects. Our results help shade light on the chemoelectromechanics of anion-exchange membranes, toward their increase adoption as soft actuators.

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.

As a recently invented soft actuator, hydraulically amplified self-healing electrostatic (HASEL) actuators have exhibited strong potential for employment in soft and biomimetic robots. HASEL actuators rely on the principle of hydraulics and electrostatic forces to generate motion. Many existing HASEL actuator-driven robots only exhibit one degree-of-freedom (DoF) motion. The few existing designs that generate multi-DoF motion are often bulky and use multiple stacks of HASEL pouches. In this paper, a bio-inspired robotic tail powered by HASEL actuators is presented. The tail is a popular structure considered for bioinspiration, due to its ability to exhibit fluidic multi-DOF motion while being compliant. While HASEL actuators-driven tails have been developed in the past, very few of them exhibit multi-DOF complex motion, which is a critical aspect of a tail. The proposed robotic tail utilized compact multi-directional HASEL actuators that used two inputs to achieve motion in three-dimensional space. The transient and steady state voltage–deflection angle correlations of the rightward, leftward, and upward curls of the robotic tail under different loading conditions were experimentally characterized. Furthermore, a lifecycle test was conducted at multiple inputs. Satisfactory performance was obtained. For example, the robotic tail could generate 169.8◦ side-ward deflection and 262.7◦ upward deflection when no loads were applied.

Highly anisotropic, fiber-based structures are a successful concept in nature. Usual dielectric elastomer actuators are entirely soft and rely on the integration of stiff carrier frames for the fragile dielectric membranes. Within this work, a completely soft, fiber-reinforced free-standing tubular actuator concept is presented. The circumferentially running carbon fibers are integrated into the inner electrode of the DEA and stabilize the cross-section, while having negligible impact on the mechanical stiffness in the axial direction. Through the segmentation of the outer electrode of the actuator, active bending in the corresponding directions is achieved. Moreover, if all segments are activated simultaneously, the actuator expands axially. The presented manufacturing approach allows for the adjustment of the dimensions over a wide range of diameters and lengths. Furthermore, the local stiffness of actuators can be tailored by varying the amount of fibers incorporated into the electrode. The electroactive deformation of actuators with different diameter-to-length ratios and fiber densities is investigated.

Dielectric elastomer actuators (DEAs) have advantageous characteristics and, therefore, their application is widespread in the field of soft robotics. Their properties can be specifically adapted by both the selection of materials and the manufacturing process. Previous research has shown that fiber reinforcement of the structure can significantly enhance the unidirectional motion. In the presented work an actuator consisting of a silicone film as the dielectric, a textile carbon-fiber-reinforced electrode and a carbon black electrode are used. The electrode based on the carbon fibers additionally serves as unidirectional stiffener. Due to this highly anisotropic textile electrode, the DEA barely contracts in fiber direction. However, the active force of the DEA during actuation can be further increased through an initial pre-stretching. The aim of this work is to investigate the influence of the pre-stretching in fiber direction on the actuator performance and the long-term stability of the pre-stretch. The active force of different actuators is recorded with uniaxial tensile tests over several deformation cycles. This enables the investigation of effects deriving both from the manufacturing process and the layer structure of the textile DEA. The acquired data are evaluated and compared to results of an analytical model. To explore the ability of the fibers to maintain the initial pre-stretching of the DEA during activation, digital image correlation as an in-situ imaging technique is applied. It could be shown shown that there is no change in width due to the anisotropy. The results of the investigations are used to control and improve the manufacturing process of the textile DEA.

This work addresses inkjet printing and material selection in the fabrication of P(VDF-TrFE-CTFE) actuators. It investigates different substrate (PEN, polyimide and a PET-based) and conductive ink (metal- and carbon-based) combinations to minimize process complexity and need for specialized equipment. Fabrication study indicated that PEN and carbon black combination best meets these objectives, attaining an actuator's electrical bandwidth of 9.36 kHz. The manufactured actuators achieved 206 μm tip deflections upon quasi-static excitation, and up to 3 mm in resonant operation at 115 Hz. Therefore, manufacturing flexible designs of well-performing smart material actuators is viable using widely available and low-budget equipment.

It is widely known that dielectric elastomer (DE) material exhibits a strongly rate-dependent hysteresis in their stress-stretch response. It is experimentally observed, however, that the hysteresis of some DE materials (e.g., silicone) behaves as practically rate-independent when operating in the sub-Hz range. Despite this fact, the investigation and modeling of rate-independent hysteretic effects in DEs has received much less attention in the literature, compared to the rate-dependent ones. In this paper, we propose a new lumped-parameter dynamic model capable of describing a stress-stretch DE hysteresis with both rate-dependent and rate-independent effects. The model is grounded on a physics-based approach, combining classic thermodynamically-consistent modeling of DE large deformations and electro-mechanical coupling with a new energy-based Maxwell-Lion description of the hysteretic process. After presenting the theory, the model is validated by means of experiments conducted on silicone-based rolled DE actuators.

Dielectric elastomer generators (DEGs) can convert mechanical energy into electricity based on variable capacitance. DEGs can potentially harvest energy from renewable energy source such as wind and ocean waves due to their light weight, low cost, and high energy density. To scale up the energy output, multiple single-layer generator units are stacked to form a multilayer DEG. The fabrication of DEGs with reliable multilayer structure having high deformability and long-term stability remains a critical challenge. We report a scalable multilayering technique to produce robust DEG stacks with circular diaphragm configuration. A 4-layer stacked VHB films showed a threefold voltage gain during constant charge operation and an estimated energy density of 100 J/kg. Furthermore, by introducing a dielectric elastomer binder between the VHB films, we demonstrate strong interlayer adhesion in the stacked DEGs, enabling long-term operation stability. As a result, a 4-layer circular diaphragm DEG survived more than 100,000 cycles of mechanical deformation between 0 and 100% area strain. Carbon nanotube (CNT) coating was used as the compliant electrode. Its resistance remains almost constant after 4000 cycles of conditioning.

There is an increasing interest to use novel elastomers with inherent or modified advanced dielectric and mechanical properties, as components of dielectric elastomer actuators (DEA). This requires corresponding techniques to assess their electromechanical performance. One performance criterion is the electrically induced deformation of the active electrode area. In this work, a rectangular DEA is used to investigate the influence of the ratio between the active electrode and the passive area on the actuator deformation. For this purpose, a dielectric silicone film is bonded on one surface to a unidirectional carbon fiber fabric. Thereby, highly anisotropic mechanical properties are implemented. When strains are applied perpendicular to the fiber direction, the composite hardly contracts in the fiber direction due to the superior stiffness of the fibers. In addition, the conductive fiber structure also acts as a highly anisotropic compliant electrode. By application of a second paste-like electrode onto the silicone film a DEA is created that operates in a pure shear configuration. This assembly enables the modification of the active-to-passive area ratio and the investigation of its effect on the actuator deformation. Image-based measurements are used to determine the strain of the active electrode area. The experimental results are compared to a lumped-parameter model that considers the electromechanical properties of the fiber-reinforced DEA. In summary, the ratio of the active-to-passive area has a significant influence on the measured deformation. Especially for novel actuator materials that do not exhibit large strains, an active-to-passive ratio of 50 % proves to be particularly advantageous.

Polyvinyl chloride (PVC) gel actuators, as an electroactive material, have promising features, such as large actuation strokes and fast response, generated with a simple structure at relatively low applied voltage. Hence, the effective exploitation of these features should enable pumps with high output performance and scalability. In this study, we present a peristaltic pump using PVC gel actuators. Specifically, the pump comprises three sets of rigid electrodes sandwiching a PVC gel membrane. Thus, applying a voltage to the electrodes leads to a deformation in the thickness direction. Consequently, this deformation squeezes a liquid below the membrane, resulting in a flow. Further, the sequential actuation of each electrode pair realizes peristaltic motion that generates a continuous flow of a liquid in one direction. In particular, we fabricated a pump using a PVC gel with a micro-patterned surface. More precisely, the surface pattern comprises 300 μm-base square pyramids (height 261 μm). Due to the relatively large surface pattern compared to the previous study, a large displacement in the thickness direction of ~110 μm was observed at a voltage of more than 500 V. Additionally, the maximum flow rate generated from the pump was 195.3 μL/min at 0.5 Hz. This value is comparable to or even higher than the values obtained in previous pumps that utilized PVC gel actuators.

In this paper, a model to describe the electrochemomechanical behavior of conducting polymer (CP) based tri-layer transducer is proposed. This model will be used for simulation, control and estimation purposes. Energetic Macroscopic Representation (EMR) has been investigated in order to provide a displacement estimator and an inversion-based control for position feedback of the CP based actuator (CPBA). This work is illustrated with experimental and simulation results.

In electrolyte solutions, the application of an external voltage elicits a series of complex microscopic phenomena. When there is no charge transfer between solution and electrodes (non-Faradaic processes), an extremely thin electric double layer is formed on each of the electrodes, screening the bulk of the solution from the external electric field. In the simplest double layer models, the volume of ions in the solution is neglected. For relatively small voltage values, one can easily reach values of concentrations in the double layers over the physical packing limit. To address this issue, steric effects associated with the finite volume of ions are introduced, toward limiting the maximum concentration in the double layers. These effects are often introduced at a microscopic scale, through modifications of the entropy of mixing. However, the macroscopic interpretation of these models remains elusive. Here, we propose a purely continuum model of steric effects in electrolyte solutions. We show that including steric effects at a microscopic scale is equivalent to requiring that each constituent of the solution is incompressible at a macroscopic level. Incidentally, the macroscopic model easily extends steric effects to multiple ions of different sizes, a challenging task for microscopic models. We highlight the consequences of our model on electrolyte solutions and ionic membranes. In particular, we show how our model constitutes a simple mathematical formulation for actuators with ionic liquid solvents. Our effort supports the creation of physics-based models of ionic actuators, facilitating their mathematical description.

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.

Nylon-11 nanowires have been fabricated in flexible track-etched polymer templates. Customized fabrication equipment was employed to realize an air-flow and gravity assisted template-wetting synthesis technique. X-ray diffraction analysis suggests that the strength of the piezoelectric phase of the nanowire crystals is directly proportional to the air-flow.

Dielectric elastomer sensors (DES) are compliant systems that, allow the detection of geometric changes caused by external forces. However, a simple DES provides only the amplitude of a deformation. In order to fully describe a tensile force vector, it is necessary to characterize it by its length, direction, and origin. Therefore, there are many approaches to improve the information that can be obtained from the sensor, such as arranging DES patterns or modifying the impact of the applied mechanical force by using external components. To improve and parallelize the information provided by the mechanical deformation of the system, we aim to combine the operation principle of structured resistive strain sensors with the capacitive properties of DES. By structuring the electrodes with different patterns and combining two dissimilar electrodes in one setup, it is possible to detect the length and direction of a force vector with one sensing element. To study the patterning and its effect on resistive and capacitive signals, we use an aerosol jet printing technique that allows selective deposition of a conductive ink. The printed lines show a higher resistance increase when forced perpendicular to the pattern and vice versa, which allows to distinguish the direction and the type of applied force. In this study, the influence of printing parameters and signal interpretation for different forces are investigated. The results show that the combination of resistive and capacitive signals allows discrimination between different motions.

Dielectric Elastomer (DE) transducers are characterized by their geometrical dimensions and in particular by the properties of the elastomer and electrode materials. Therefore, in addition to dimensions, it is advantageous to consider optimization of material properties to fulfill transducer requirements, such as blocking force, free stroke, or response time. A big challenge in describing the properties of DE materials deals with utilizing different but commonly used hyperelastic material models and their parameters, which differ in complexity and corresponding model errors. Thus, determined material parameters are not necessarily consistent. In addition, parameters are depending on the measurement method, its conditions and the samples themselves. All of this leads to heterogeneous datasets making data access more complicated and in certain cases impossible for users. To overcome this, OBDA (ontology-based data access) approaches have been proven to access these heterogeneous datasets individually and efficiently and to gain the relevant information with the help of an ontology. Within a research project funded by the Federal Ministry of Education and Research, an extended OBDA approach is developed: OBDMA (ontology-based data and model access) combines data access with model-based working steps. While the joint project considers four different smart material classes, this paper focuses on dielectric materials and their transducers, in particular the development of methods to handle hyperelastic material models and their parameters. The various possibilities of material models and parameter identification methods are discussed on the basis of a measurement curve. Finally, the working principle and the advantages of the OBDMA system are demonstrated by means of a representative DE use case.