Samuel Rosset

Large-Stroke Dielectric Elastomer Actuators With Ion-Implanted Electrodes

In this paper, we present miniaturized polydimethylsiloxane (PDMS)-based diaphragm dielectric elastomer actuators capable of out-of-plane displacement up to 25% of their diameter. This very large percentage displacement is made possible by the use of compliant electrodes fabricated by low-energy gold ion implantation. This technique forms nanometer-scale metallic clusters up to 50 nm below the PDMS surface, creating an electrode that can sustain up to 175% strain while remaining conductive yet having only a minimal impact on the elastomers mechanical properties. We present a vastly improved chip-scale process flow for fabricating suspended-membrane actuators with low-resistance contacts to implanted electrodes on both sides of the membrane. This process leads to a factor of two increase in breakdown voltage and to RC time constant shorter than mechanical time constants. For circular diaphragm actuator of 1.5-3-mm diameter, voltage-controlled static out-of-plane deflections of up to 25% of their diameter is observed, which is a factor of four higher than our previous published results. Dynamic characterization shows a mechanically limited behavior, with a resonance frequency near 1 kHz and a quality factor of 7.5 in air. Lifetime tests have shown no degradation after more than 4 million cycles at 1.5 kV. Conductive stretchable electrodes photolithographically defined on PDMS were demonstrated as a key step to further miniaturization, enabling large arrays of independent diaphragm actuators on a chip, for instance for tunable microlens arrays or arrays of micropumps and microvalves.

Voltage Control of the Resonance Frequency of Dielectric Electroactive Polymer (DEAP) Membranes

We report on the characterization, active tuning, and modeling of the first mode resonance frequency of dielectric electroactive polymer (DEAP) membranes. Unlike other resonance frequency tuning techniques, the tuning procedure presented here requires no external actuators or variable elements. Compliant electrodes were sputtered or implanted on both sides of 20-35-mum-thick and 2-4-mm-diameter polydimethylsiloxane membranes. The electrostatic force from an applied voltage adds compressive stress to the membrane, effectively softening the device and reducing its resonance frequency, in principle to zero at the buckling threshold. A reduction in resonance frequency up to 77% (limited by dielectric breakdown) from the initial value of 1620 Hz was observed at 1800 V for ion-implanted membranes. Excellent agreement was found between our measurements and an analytical model we developed based on the Rayleigh-Ritz theory. This model is more accurate in the tensile domain than the existing model for thick plates applied to DEAPs. By varying the resonance frequency of the membranes (and, hence, their compliance), they can be used as frequency-tunable attenuators. The same technology could also allow the fine-tuning of the resonance frequencies in the megahertz range of devices made from much stiffer polymers.

Tunable millimeter-wave phase shifter based on dielectric elastomer actuation

A very low-loss tunable millimeter-wave phase shifter driven by dielectric elastomer actuators (DEAs) is presented. The device consists of a fixed coplanar waveguide (CPW) and two metallic loading strips suspended on an elastomer membrane. The horizontal offset between the CPW and the strips is dynamically controlled by integrated DEAs. The variable interaction between the CPW and the loading strips results in a change in the effective permittivity, thereby providing analog-controlled true-time-delay. The design, fabrication, and measurements of this phase shifter based on DEAs are presented, demonstrating state-of-the-art phase shift to loss performance, achieving 235°/dB at 35u2009GHz.

Performance characterization of miniaturized dielectric elastomer actuators fabricated using metal ion implantation

We report measurements of displacement and mechanical work for miniaturized dielectric elastomer actuators (DEAs) whose compliant electrodes were fabricated using metal ion implantation. 20 to 30 mum thick polydimethylsiloxane (PDMS) membranes were bonded to silicon chips with through holes of diameter 2 to 3 mm and were implanted on both sides with gold ions. Out-of-plane deflection recorded as a function of voltage and applied mechanical distributed load was in very good agreement with an analytical model. Unloaded vertical displacements up to 7% of the membranes diameter were recorded and mechanical work up to 0.3 muJ was obtained with an applied pressure of 1 kPa. This performance data and associated model allow such miniaturized polymer actuators to be efficiently dimensioned for different applications, for instance in micropumps and active optical devices.

An ultra-fast mechanically active cell culture substrate

We present a mechanically active cell culture substrate that produces complex strain patterns and generates extremely high strain rates. The transparent miniaturized cell stretcher is compatible with live cell microscopy and provides a very compact and portable alternative to other systems. A cell monolayer is cultured on a dielectric elastomer actuator (DEA) made of a 30u2009μm thick silicone membrane sandwiched between stretchable electrodes. A potential difference of several kV’s is applied across the electrodes to generate electrostatic forces and induce mechanical deformation of the silicone membrane. The DEA cell stretcher we present here applies up to 38% tensile and 12% compressive strain, while allowing real-time live cell imaging. It reaches the set strain in well under 1u2009ms and generates strain rates as high as 870u2009s−1, or 87%/ms. With the unique capability to stretch and compress cells, our ultra-fast device can reproduce the rich mechanical environment experienced by cells in normal physiological conditions, as well as in extreme conditions such as blunt force trauma. This new tool will help solving lingering questions in the field of mechanobiology, including the strain-rate dependence of axonal injury and the role of mechanics in actin stress fiber kinetics.

Multi-touch capacitive sensor with new sensor arrangement

Multi touch sensors are widely used for screen interfaces, but are at an early stage of development for soft wearable technology and humanoid devices. We demonstrated a soft, flexible and stretchable tactile dielectric elastomer (DE) capacitive sensor array which is designed for multi-touch applications. The touch input is measured by the capacitance variation resulting from the deformation of the sensor modelled as a variable parallel plate capacitor. The flexibility and soft nature of capacitive DE sensor makes them comfortable to wear and versatile. This sensor module is composed of a 2-D capacitive sensor array composed of a grid of DE sensors. The sensor arrangement enables the measurement of touch capacitance on and between sensor centerlines. This technology has fewer connections with fewer wires and enables continuous location identification; convenient for emerging wearable technology as well as humanoid devices. It is possibility solution for wearable technology that needs to measure the reaction of forces in the human body; and can also be applicable to measure/control in humanoid devices to determine grasp ability to pick up an object.

The NERD setup: assessing the life time of electrodes for dielectric elastomer transducers

DEAs used in applications such as tunable lenses, soft robotics, etc. are expected to survive many thousands to millions of stretching cycles without degradation of their performance. Here, we present a measurement technique to characterise the evolution of the resistance of compliant electrodes submitted to cyclic biaxial strain, which represents the stretching configuration to which DEAs are usually submitted. We apply the novel electrode resistance degradation (NERD) method to the characterisation of compliant electrodes obtained by inkjet printing a carbon black suspension. We show that although the electrodes can sustain 1 million cycles of stretching at 5%, a 10% cyclic strain causes a much faster degradation, leading to a reduced actuation strain over time. We show that increasing the thickness of the electrodes leads to cracking and accelerated degradation; two layer electrodes degrade more rapidly than single layer electrodes. The NERD setup represents an efficient tool to quickly evaluate the suitability of different electrode formulations for use as compliant electrodes for DEAs.

Capacitive coupling as a new form of signal transmission in underwater dielectric elastomer sensing

Accurately capturing human motion underwater has potential applications in diver health monitoring, human- machine interaction and performance sport coaching. Unfortunately the human body has approximately 200 bones and 600 skeletal muscles giving rise to a broad range of degrees of freedom. To effectively capture this movement with dielectric elastomer sensors a substantial network is required. One often overlooked challenge is the connection between the dielectric elastomer sensor and central electronics. On land this is as simple as wires connecting the two. Underwater however, especially when considering a network of sensors, this becomes a more complicated task. In the proposed method parallel plate capacitors are used to transfer power across the encapsulation layer to the sensor, removing any need for protruding wires or cable glands. With one electrode placed within the encapsulation and the second connected to the sensor, sensors are replaceable even underwater. To maintain sensor performance however, a relatively high capacitance is required. For example if the coupling capacitance is 20x greater than sensor capacitance, sensitivity is reduce by approximately 20%. Whereas if the coupling capacitance is only 10x greater, sensitivity is reduced by 40%. Due to these high capacitance requirements combined with the area and weight restrictions of wearable applications, we have investigated the practicality of implementing capacitive coupling. A capacitive coupling interface has been developed and tested with dielectric elastomer sensors underwater. Analysis of the interfaces impact on sensor sensitivity, measurement electronics and overall coupling capacitor size is presented.