Elastomeric Electrodes Research Articles

Flexible yet Durable Microneedle Electrodes Based on Nanowire-Embedded Polyimide for Precise Wearable Electrophysiological Monitoring.

A precise recording of electrophysiological signals requires high-performance flexible bioelectrodes to build a robust skin interface. The past decade has witnessed encouraging progress in the development of elastomeric electrodes for wearable electrophysiological monitoring; however, it remains challenging to achieve excellent flexibility, conformal contact, and high durability simultaneously. Herein, we report on an effective method to fabricate flexible yet durable microneedle electrodes (MEs) based on vertically aligned gold nanowires (Au NWs) embedded polyimide (PI), which meet the above three design requirements. The Au NWs embedded PI MEs could build conformal contact with human skin and maintain electrical stability with minimal contact impedance by effectively penetrating the stratum corneum of the skin. In comparison studies, we found our MEs outperformed conventional gel or elastomeric soft electrodes. We further integrated the vertical Au-NW MEs into a wearable healthcare system and achieved wireless real-time recordings of electromyography (EMG) and electrocardiography (ECG) with high signal-to-noise ratios (SNRs) and low motion artifacts. Our fabrication strategy opens a new route to improve the durability and reliability of emerging nanomaterial-based soft bioelectrodes for long-term wearable healthcare applications.

Design of hybrid Ag–Au nanostructure based fully elastomeric nanocomposite electrodes for soft integrated electronics

Recent advancements in stretchable devices have opened new avenues for constructing soft electronics for use in applications such as health-monitoring wearables, advanced integrated circuits, and soft robotics. Meeting the increasing demand for enhanced functionality in soft electronics requires the development of soft conductors with high electrical conductivity, mechanical durability, and cost-effectiveness. Researchers have addressed this challenge by creating percolated networks within the elastomer as a nanocomposite using low-dimensional conducting nanomaterials to endow non-stretchable metallic materials with mechanical stretchability. For example, silver nanowires (AgNWs) have found wide application as essential fillers in soft conductor nanocomposites owing to their remarkable aspect ratio and cost-efficiency. However, their application is limited by their susceptibility to environmental degradation and poor compatibility with semiconducting materials. In this work, the hybrid Ag–Au based nanomaterials as a filler nanomaterial within an elastomer in a nanocomposite format was generated, as it exploits the strengths of each material while mitigating their respective weaknesses. Specifically, the work introduces the merit of the hybrid elastomeric electrodes that consist of AgNWs decorated with Au nanoparticles (AANWs), and Au nanosheets (AuNSs) embedded in a polydimethylsiloxane (PDMS) elastomer. These electrodes exhibit remarkable mechanical resilience and electrical conductivity, making them suitable for application in transistors, logic gates, integrated electronics, and soft displays. The work explores the synthesis and properties of hybrid materials comprising AgNWs and AuNSs, highlighting the promising potential of these materials for future research and development.

Novel Polyurethane Based, Fully Flexible, High-Performance Piezoresistive Sensor for Real-Time Pressure Monitoring.

Flexible piezoresistive pressure sensors are garnering substantial attention, in line with advancements in biointegrated and wearable electronics. However, a significant portion of piezoresistive pressure sensors suffer from the trade-off between sensitivity and pressure range. Moreover, the current piezoresistive sensors generally rely on a rigid metallic electrode, severely deteriorating their long-term durability. Herein, a fully flexible piezoresistive sensor coupling polyurethane (PU) based electrode and active sensing element is proposed to circumvent the aforementioned problems. By rationally regulating the double-permeable conductive networks within the PU matrix, an elastomeric electrode and sensing element are implemented, respectively. The assembled heterostructured configurations enable impressive sensitivity up to 7.023 kPa-1, broad pressure detection (up to 420 kPa), an ultralow pressure sensing limit (0.1 Pa), and extraordinary operation stability over 80000 cyclic pressings along with fast response/relaxation times (60 ms/80 ms). Additionally, the fully flexible sensor is capable of both real-time detection of physiological signals and mimicking keyboards, implying its viability as a high-performance pressure sensor.

Novel IP2C sensors with flexible electrodes based on plasma-treated conductive elastomeric nanocomposites

Ionic polymer-metal composites (IPMC) are devices composed of metallic electrodes and an ionomeric polymer membrane in a ‘sandwich’ architecture and. Their main property is electromechanical actuation or sensing based on the movement of ions. Metallic electrodes are commonly used for their high electrical conductivity, malleability, and chemical resistance. However, the high cost of noble metals, such as platinum, long manufacturing time, and fatigue failure limit their application. Therefore, the replacement of metallic electrodes with conductive elastomeric nanocomposites (CENs) was evaluated to reduce the costs and complexity of manufacturing the device and increase its working life. In this work, carbon nanotubes were used as the conductive fillers. The dispersion to achieve high electrical conductivity was carried out directly in the synthetic or natural polyisoprene rubber latex assisted by surfactant and high-power sonication. To improve the adhesion between the elastomeric electrode and the ionic membrane (Nafion), plasma treatment with atmospheric air was applied as a surface modifier. This treatment improved the hydrophilicity and adhesion of the rubbers by forming oxygenated groups and increasing the surface nanoroughness. In this way, ionomeric polymer–polymer composite (IP2C) devices were fabricated using Nafion and plasma-modified CENs, this type of electrode is unprecedented in the literature for this application. These devices showed displacement and strain sensing capacity at levels close to the conventional IPMC in all tested frequency ranges and applied accelerations. Notably, the IP2C obtained better resolution at low frequencies than the control.

Electrostatic-hydraulic coupled soft actuator for micropump application

The development of a soft actuator with high displacement is crucial for the effective operation of micropumps, ensuring a high fluid pump rate. This study introduces an innovative approach by presenting the design and fabrication of a novel electrostatic-hydraulic coupled soft actuator for a micropump within a microfluidic system. This pioneering soft actuator, leveraging electrostatic-hydraulic coupling, showcases a unique solution to enhance the performance of micropumps. The versatility of such a soft actuator makes it particularly promising for biomedical applications. The actuator comprises dielectric fluid in an elastomeric shell and electrodes to form the out-of-plane fluid-amplified displacement. This displacement amplification was used to generate a pumping actuation in the micropump. The actuator was characterized in terms of dielectric fluid volume, electrode size, temporal response, and amplification displacement. The soft actuator showed a maximum amplified displacement of 0.51 mm at 10 kV of the applied voltage, but a higher voltage caused a dielectric breakdown. Moreover, the actuator demonstrated the ability to operate at frequencies of 0.25 Hz and 0.1 Hz. The results of the study indicate that the fabricated electrostatic-hydraulic coupled soft actuator is a dependable and effective method of actuation for a micropump in a microfluidic system. The experimental characterization of the micropump revealed a maximum flow rate of 2304 μl min−1.

Controlled electroactive release from solid-state conductive elastomer electrodes

This work highlights the development of a conductive elastomer (CE) based electrophoretic platform that enables the transfer of charged molecules from a solid-state CE electrode directly to targeted tissues. Using an elastomer-based electrode containing poly (3,4-ethylenedioxythiophene) nanowires, controlled electrophoretic delivery of methylene blue (MB) and fluorescein (FLSC) was achieved with applied voltage. Electroactive release of positively charged MB and negatively charged FLSC achieved 33.19 ± 6.47 μg release of MB and 22.36 ± 3.05 μg release of FLSC, a 24 and 20-fold increase in comparison to inhibitory voltages over 1 h. Additionally, selective, and sequential release of the two oppositely charged molecules from a single CE device was demonstrated, showing the potential of this device to be used in multi-drug treatments.

Excellent Miniature Thin Film Dielectric Elastomer Sensors for Robot Fingers Used in Human-Robot Interaction

Traditional sensors used to measure properties such as deformation and pressure often use materials such as metals, ceramics, piezos and polymers. However, since many of these materials are hard, it can be difficult to measure them with a single sensor when the pressure or elongation applied to the object changes. In this experiment, a dielectric elastomer thin-film pressure sensor (0.2 mm) was fabricated using hydrogenated nitrile rubber with significantly improved hardness and elongation. This single sensor can accurately measure pressure from 1gf to 20kgf. Also, the response speed was 50ms, which was sufficiently fast. A dielectric elastomer stretch sensor was also developed. This sensor uses elastic and flexible single-walled carbon nanotubes as dielectric elastomer electrodes for the hydrogenated nitrile rubber. This greatly improved the mechanical flexibility and stretchability of the stretch sensor, making it possible to operate it as a sensor even at 400% elongation. By attaching this stretch sensor to the robot's finger closely, it is possible to detect the dynamic movement of the robot's finger and to detect the force (pressure) when the fingertip touches the target object with the above pressure sensor. In addition, by using the small diaphragm-type dielectric elastomer actuator, it was confirmed that the sensation of the robot's touching an object could be fed back to the human finger. As a result, it is thought that the feeling of the robot’s finger touching an object could be driven more realistically and accurately. In addition, both a dielectric elastomer stretch sensor and a dielectric elastomer pressure sensor were attached to the finger of the robot, and the movement of the human’s finger was sensed and the force (pressure) when the finger touched the object was also able to be detected.

Surface electromyography using dry polymeric electrodes.

Conventional wet Ag/AgCl electrodes are widely used in electrocardiography, electromyography (EMG), and electroencephalography (EEG) and are considered the gold standard for biopotential measurements. However, these electrodes require substantial skin preparation, are single use, and cannot be used for continuous monitoring (>24 h). For these reasons, dry electrodes are preferable during surface electromyography (sEMG) due to their convenience, durability, and longevity. Dry conductive elastomers (CEs) combine conductivity, flexibility, and stretchability. In this study, CEs combining poly(3,4-ehtylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) in polyurethane are explored as dry, skin contacting EMG electrodes. This study compares these CE electrodes to commercial wet Ag/AgCl electrodes in five subjects, classifying four movements: open hand, fist, wrist extension, and wrist flexion. Classification accuracy is tested using a backpropagation artificial neural network. The control Ag/AgCl electrodes have a 98.7% classification accuracy, while the dry conductive elastomer electrodes have a classification accuracy of 99.5%. As a conclusion, PEDOT based dry CEs were shown to successfully function as on-skin electrodes for EMG recording, matching the performance of Ag/AgCl electrodes, while addressing the need for minimal skin prep, no gel, and wearable technology.

A cerebral cortex-like structured metallized elastomer for high-performance triboelectric nanogenerator

The advancement of wearable electronics, particularly triboelectric nanogenerators (TENGs), relies on the development of flexible, stretchable, and compressible electrodes that possess a large active surface area, high electrical conductivity, and excellent mechanical stability and deformability. However, existing elastomeric electrodes face challenges in meeting all of these requirements. Herein, we present a novel approach to address these limitations and create electrodes with elastomeric properties, stable metal-like electrical conductivity, and an expanded active surface area. For this goal, we perform an assembly of metal nanoparticles (NPs) in toluene and amine-functionalized organic linkers in alcohol onto the thiol-functionalized, embossed-structured elastomer. Particularly, the assembly process involves ligand exchange reaction-mediated metal NPs and subjecting them to solvent-swelling/deswelling of the embossed PDMS. This process induces the formation of cerebral cortex-like structured elastomer electrode, which is subsequently electroplated with Ni. The resulting electrodes exhibit metal-like electrical conductivity, elastomer-like flexibility, and cerebral cortex-like structure with substantially large surface area and high stress relieving properties. When combined with an intaglio-structured dielectric PDMS electrode, the device exhibits impressive TENG performance, surpassing the performance of conventional TENGs. This approach provides a basis for developing and designing a variety of high-performance flexible electronics, including TENGs.

Nonlinear dynamics of an artificial muscle with elastomer–electrode inertia: Modelling and analysis

Artificial muscles are dielectric elastomeric system that mimic the response of the natural muscle and are helpful in many bio-mimicking applications. The existing literature is based on the assumption that electrodes are compliant and are focused on materials with greater extensibility than biological matter. The present work deals with the modelling and nonlinear dynamic analysis of dielectric elastomers considering the elastomer–electrode inertia and damping effect for bio-mimicking. The distinguishing point of the proposed work is the appearance of terms related to the elastomer–electrode inertia effect in the governing equation. Further, the biological muscle’s nonlinear elastic behaviour is incorporated using the Fung material model. Equilibrium stretch variation with parameter exhibits cusp catastrophe. The effect of electrode inertia on the equilibria is examined. Single-well and double-well potential energy characteristics are obtained for constant voltage. The basin of attraction illustrates the sensitiveness of system dynamics on the initial state and damping. The system response, when subjected to time-varying voltage, is explored. Multi-frequency response exists due to harmonic, sub-harmonic, and super-harmonic resonance condition. The resonant frequency variation with geometry and inertia is presented. Time-varying voltage may lead to chaotic behaviour illustrated through the bifurcation diagram. The presence of a strange attractor and positive Lyapunov exponent in the chaotic region further justify the existence of chaos. Additionally, chaotic behaviour is obtained in the case of single-well and double-well potential. Also, the existence of similar attractors with same fractal dimension is shown. The inertia effect significantly changes the dynamic characteristic from chaotic to non-chaotic or vice-versa. The mechanical and electrical load may lead to chaotic or non-chaotic behaviour depending on the geometry of the elastomer. The chaotic region’s dependence on the damping value is also obtained. Our results show that electrode inertia significantly impacts the elastomer under quasi-static and dynamic conditions. The proposed work gives a foundation for precisely designing artificial muscle for practical applications like soft robotics, artificial arms, and different prosthetic implants.

Micro/nano‐wrinkled elastomeric electrodes enabling high energy storage performance and various form factors

AbstractStretchable elastomer‐based electrodes are considered promising energy storage electrodes for next‐generation wearable/flexible electronics requiring various shape designs. However, these elastomeric electrodes suffer from the limited electrical conductivity of current collectors, low charge storage capacities, poor interfacial interactions between elastomers and conductive/active materials, and lack of shape controllability. In this study, we report hierarchically micro/nano‐wrinkle‐structured elastomeric electrodes with notably high energy storage performance and good mechanical/electrochemical stabilities, simultaneously allowing various form factors. For this study, a swelling/deswelling‐involved metal nanoparticle (NP) assembly is first performed on thiol‐functionalized polydimethylsiloxane (PDMS) elastomers, generating a micro‐wrinkled structure and a conductive seed layer for subsequent electrodeposition. After the assembly of metal NPs, the conformal electrodeposition of Ni and NiCo layered double hydroxides layers with a homogeneous nanostructure on the micro‐wrinkled PDMS induces the formation of a micro/nano‐wrinkled surface morphology with a large active surface area and high electrical conductivity. Based on this unique approach, the formed elastomeric electrodes show higher areal capacity and superior rate capability than conventional elastomeric electrodes while maintaining their electrical/electrochemical properties under external mechanical deformation. This notable mechanical/electrochemical performance can be further enhanced by using spiral‐structured PDMS (stretchability of ~500%) and porous‐structured PDMS (areal capacity of ~280 μAh cm−2).

Pre-strain accommodation enabled multi-dimensionally and hierarchically elastomeric MoSe2/MXene and AC/MXene electrodes for stretchable sodium ion capacitors

Stretchable supercapacitors with simultaneously high energy/power densities and long life can enrich integrated power options for ever-increasing wearable electronics. However, supercapacitors with high electrochemical performances while maintaining high stretchability are still challenging. Herein, we report stretchable sodium ion capacitors (S-SICs) based on multi-dimensionally and hierarchically elastomeric composite electrodes, and stretchable high voltage gel polymer electrolyte (3.0 V). The elastomeric composite electrode is constructed by stretchable 3D electrospun polyurethane (PU) fibrous mat and conductive 1D Ag nanowire network. 2D MoSe2/MXene and 3D AC/MXene as anodic and cathodic materials are embedded in this conductive and stretchable mat. This hierarchical structure enables multi-dimensional conductive connections under tensile condition. The pre-strain treatment on PU fibrous mat further increases the relatively stretching distance before losing conductive connection among hierarchical components. The electrodes exhibit superior sodium ion storage performances (420 mAh g−1 at 5 A g−1), as well as good stretchability and stability (95% after 1000 cycles at 2 A g−1). Based on this, the S-SICs with high operating voltage demonstrate high energy/power densities (max. 5.44 mWh cm−3, 493.55 mW cm−3) and good stretchability. This prototypical exhibition of S-SICs indicates a promising design direction of stretchable supercapacitors with high electrochemical performances and tolerance of stretchability.

Mechanically Tissue‐Like and Highly Conductive Au Nanoparticles Embedded Elastomeric Fiber Electrodes of Brain–Machine Interfaces for Chronic In Vivo Brain Neural Recording

AbstractImplantable neural probes are a crucial part of brain–machine interfaces that serve as direct interacting routes between neural tissues and machines. The neural probes require both mechanical and electrical properties to acquire high‐quality signals from individual neurons with minimal tissue damage. However, overcoming the trade‐off between flexibility and electrical property is still challenging. Herein, a fiber neural probe, composed of core polymer and Au nanoparticles (AuNPs) on the outer shell, is fabricated by absorbing Au precursor following in situ chemical reduction with a variation of percolating and leaching time. The proposed fiber exhibits excellent electrical properties, with an electrical conductivity of 7.68 × 104 S m−1 and an impedance of 2.88 × 103 Ω at 1 kHz, as well as a Young's modulus of 170 kPa, which is comparable to that of brain tissue (≈100 kPa). Additionally, the AuNPs fiber neural probe demonstrates extremely stable in vivo electrophysiological signal recordings for four months with reduced foreign body responses at the tissue–probe interface. Furthermore, this innovative approach encourages a new paradigm of long‐term recording in the fields of neuroscience and engineering to better understand brain circuits, develop bioelectronic devices, and treat chronic disorders.

Stretchable Sponge Electrodes for Long-Term and Motion-Artifact-Tolerant Recording of High-Quality Electrophysiologic Signals.

Soft electronic devices and sensors have shown great potential for wearable and ambulatory electrophysiologic signal monitoring applications due to their light weight, ability to conform to human skin, and improved wearing comfort, and they may replace the conventional rigid electrodes and bulky recording devices widely used nowadays in clinical settings. Herein, we report an elastomeric sponge electrode that offers greatly reduced electrode–skin contact impedance, an improved signal-to-noise ratio (SNR), and is ideally suited for long-term and motion-artifact-tolerant recording of high-quality biopotential signals. The sponge electrode utilizes a porous polydimethylsiloxane sponge made from a sacrificial template of sugar cubes, and it is subsequently coated with a poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) conductive polymer using a simple dip-coating process. The sponge electrode contains numerous micropores that greatly increase the skin–electrode contact area and help lower the contact impedance by a factor of 5.25 or 6.7 compared to planar PEDOT:PSS electrodes or gold-standard Ag/AgCl electrodes, respectively. The lowering of contact impedance resulted in high-quality electrocardiogram (ECG) and electromyogram (EMG) recordings with improved SNR. Furthermore, the porous structure also allows the sponge electrode to hold significantly more conductive gel compared to conventional planar electrodes, thereby allowing them to be used for long recording sessions with minimal signal degradation. The conductive gel absorbed into the micropores also serves as a buffer layer to help mitigate motion artifacts, which is crucial for recording on ambulatory patients. Lastly, to demonstrate its feasibility and potential for clinical usage, we have shown that the sponge electrode can be used to monitor uterine contraction activities from a patient in labor. With its low-cost fabrication, softness, and ability to record high SNR biopotential signals, the sponge electrode is a promising platform for long-term wearable health monitoring applications.

Preparation of Rat Sciatic Nerve for Ex Vivo Neurophysiology.

Ex vivo preparations enable the study of many neurophysiological processes in isolation from the rest of the body while preserving local tissue structure. This work describes the preparation of rat sciatic nerves for ex vivo neurophysiology, including buffer preparation, animal procedures, equipment setup and neurophysiological recording. This work provides an overview of the different types of experiments possible with this method. The outlined method aims to provide 6 h of stimulation and recording on extracted peripheral nerve tissue in tightly controlled conditions for optimal consistency in results. Results obtained using this method are A-fibre compound action potentials (CAP) with peak-to-peak amplitudes in the millivolt range over the entire duration of the experiment. CAP amplitudes and shapes are consistent and reliable, making them useful to test and compare new electrodes to existing models, or the effects of interventions on the tissue, such as the use of chemicals, surgical alterations, or neuromodulatory stimulation techniques. Both conventional commercially available cuff electrodes with platinum-iridium contacts and custom-made conductive elastomer electrodes were tested and gave similar results in terms of nerve stimulus strength-duration response.

Mechanically resilient integrated electronics realized using interconnected 2D gold-nanosheet elastomeric electrodes

With the growing interest in wearable devices in recent decades, considerable effort has been devoted to developing mechanical elastomeric devices such as sensors, transistors, logic circuits, and integrated circuits. To successfully implement elastomeric devices subjected to large mechanical deformations or stretching, all the components, including conductors, semiconductors, and dielectrics, must have high stability and mechanical sustainability. Elastomeric conductors, which exhibit excellent electrical performances under mechanical deformations, are key components of elastomeric devices. Herein, we prepared fully elastomeric electrodes based on interconnected 2D gold nanosheets (AuNSs) to develop mechanically resilient integrated electronics. The AuNS elastomeric electrodes exhibited a sheet resistance of less than 2 Ω/sq under 50% stretching and sustained 100,000 stretching–releasing cycles. These electrodes with a dedicated design were used in combination with elastomeric semiconductors of P3HT nanofibrils in the PDMS elastomer (P3NF/PDMS) and an ion gel as a dielectric to realize elastomeric transistors, inverters, and NOR and NAND logic gates. Additionally, an elastomeric 8 × 8 transistor array that can sustain various types of mechanical stimuli was successfully demonstrated. Furthermore, the elastomeric electronic devices implemented on a soft robot showed no interfering performances during robot gripping motion. The proposed framework is expected to aid in the rapid development and broaden the application scope of soft electronics.

Monolithic Stacked Dielectric Elastomer Actuators.

Dielectric elastomer actuators (DEAs) are a promising actuator technology for soft robotics. As a configuration of this technology, stacked DEAs afford a muscle-like contraction that is useful to build soft robotic systems. In stacked DEAs, dielectric and electrode layers are alternately stacked. Thus, often a dedicated setup with complicated processes or sometimes laborious manual stacking of the layers is required to fabricate stacked actuators. In this study, we propose a method to monolithically fabricate stacked DEAs without alternately stacking the dielectric and electrode layers. In this method, the actuators are fabricated mainly through two steps: 1) molding of an elastomeric matrix containing free-form microfluidic channels and 2) injection of a liquid conductive material that acts as an electrode. The feasibility of our method is investigated via the fabrication and characterization of simple monolithic DEAs with multiple electrodes (2, 4, and 10). The fabricated actuators are characterized in terms of actuation stroke, output force, and frequency response. In the actuators, polydimethylsiloxane (PDMS) and eutectic gallium–indium (EGaIn) are used for the elastomeric matrix and electrode material, respectively. Microfluidic channels are realized by dissolving a three-dimensional printed part suspended in the elastomeric structure. The experimental results show the successful implementation of the proposed method and the good agreement between the measured data and theoretical predication, validating the feasibility of the proposed method.

Printable elastomeric electrodes with sweat-enhanced conductivity for wearables.

We rationally synthesized the thermoplastic and hydrophilic poly(urethane-acrylate) (HPUA) binder for a type of printable and stretchable Ag flakes-HPUA (Ag-HPUA) electrodes in which the conductivity can be enhanced by human sweat. In the presence of human sweat, the synergistic effect of Cl- and lactic acid enables the partial removal of insulating surfactant on silver flakes and facilitates sintering of the exposed silver flakes, thus the resistance of Ag-HPUA electrodes can be notably reduced in both relaxed and stretched state. The on-body data show that the resistance of one electrode has been decreased from 3.02 to 0.62 ohm during the subject's 27-min sweating activity. A stretchable textile sweat-activated battery using Ag-HPUA electrodes as current collectors and human sweat as the electrolyte was constructed for wearable electronics. The enhanced conductivity of the wearable wiring electrode from the reaction with sweat would provide meritorious insight into the design of wearable devices.

Graphene Elastomer Electrodes for Medical Sensing Applications: Combining High Sensitivity, Low Noise and Excellent Skin Compatibility to Enable Continuous Medical Monitoring

Continuous monitoring of vital bio-signals is crucial to track the well-being of patients and to allow for timelymedical intervention in cases of emergency. This paper presents a compact and wearable electrocardiogram (ECG) sensor using graphene-elastomer electrodes, which were characterised, first using an electronic patient simulator, then on a human subject. We demonstrate that the proposed electrodes are highly conductive, flexible and ultralight (weighing less than 10 mg). Their skin-impedance values are significantly lower than existing electrodes including other graphene-based sensors. In addition, we demonstrate that they can be applied on the skin in dry form without needing an intermediate gel layer, or excessivemechanical pressures, overcoming an important challenge for long term monitoring applications. The proposed configuration enables the design ofwearable devices that can outperformwell-refined commercial sensors, providing great potential for electronic/mobile health applications.

Geometric optimization of dielectric elastomer electrodes for dynamic applications

Dielectric elastomers are soft actuators, made of an elastomer membrane sandwiched by compliant electrodes. Because of their high energy density and quick response, they are well suited for dynamic applications such as loudspeakers. Thanks to progress in the manufacturing process of dielectric elastomer actuators, the electrode shape can be patterned to very diverse shapes. In this study, we focus on the relation between the electrode shape and the dynamical and acoustical behavior of a dielectric elastomer loudspeaker. By using a finite element model of the loudspeaker, an optimization algorithm is set up to compute optimal electrode shapes according to chosen objectives, such as maximizing or minimizing the contribution of an eigenmode to the radiated sound. The optimal designs are then tested experimentally, and the efficiency of the optimization procedure is assessed. It is shown that the frequency response of dielectric elastomer loudspeakers can be tuned by optimizing the shape of the electrodes, and simulations suggest that the directivity can also be controlled. Finally, perspectives of the proposed optimization method are briefly discussed.