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Xu D.,Auckland Bioengineering Institute | Michel S.,Empa - Swiss Federal Laboratories for Materials Science and Technology | McKay T.,Auckland Bioengineering Institute | O'Brien B.,StretchSense Ltd | And 4 more authors.
Sensors and Actuators, A: Physical | Year: 2015

Abstract Dielectric elastomers, also known as artificial muscles have produced many biomimetic robots. One advantage is their ability to provide feedback through capacitance. However when the sensing frequency is too high, the measured capacitance can underestimate the true value. In this paper, the measured capacitance of dielectric elastomer stacked and rolled configurations were shown to reduce with increasing sensing frequency. A transmission line electrical model linked this to the result of high interconnect and sheet resistances of the electrodes. A design methodology to help determine the working limits of sensing frequency is presented. © 2015 Elsevier B.V.

McKay T.G.,University of Auckland | Gisby T.A.,University of Auckland | Gisby T.A.,StretchSense Ltd | Anderson I.A.,University of Auckland
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Dielectric elastomer Generator(s) (DEG) are highly suited to harvesting from environmental sources because they are light weight, low cost, and can be coupled directly to rectilinear motions and harvest energy efficiently over a wide frequency range. Because of these benefits, simple and low cost generators could be enabled using DEG. Electrical energy is produced on relaxation of a stretched, charged DEG: like-charges are compressed together and opposite-charges are pushed apart, resulting in an increased voltage. The manner in which the DEG charge state is controlled greatly influences the amount of energy that is produced. For instance, the highest energy density ever demonstrated for DEG is 550 mJ/g, whereas the theoretical energy density of DEG has been reported as high as 1700 mJ/g if driven close to their failure limits. The discrepancy between realised and theoretical energy production highlights that large performance gains can be achieved through smarter charge control that drives the generator close to its failure limits. To do so safely, we need to be able to monitor the real-time electromechanical state of the DEG. This paper discusses the potential of self-sensing for providing feedback on the generator's electromechanical state. Then we discuss our capacitive self-sensing method which we have demonstrated to track the displacement of a Danfoss Polypower generator as it was cyclically stretched and harvested energy. © 2014 SPIE.

Carpi F.,Queen Mary, University of London | Anderson I.,University of Auckland | Bauer S.,Johannes Kepler University | Frediani G.,Queen Mary, University of London | And 18 more authors.
Smart Materials and Structures | Year: 2015

Dielectric elastomer transducers consist of thin electrically insulating elastomeric membranes coated on both sides with compliant electrodes. They are a promising electromechanically active polymer technology that may be used for actuators, strain sensors, and electrical generators that harvest mechanical energy. The rapid development of this field calls for the first standards, collecting guidelines on how to assess and compare the performance of materials and devices. This paper addresses this need, presenting standardized methods for material characterisation, device testing and performance measurement. These proposed standards are intended to have a general scope and a broad applicability to different material types and device configurations. Nevertheless, they also intentionally exclude some aspects where knowledge and/or consensus in the literature were deemed to be insufficient. This is a sign of a young and vital field, whose research development is expected to benefit from this effort towards standardisation. © 2015 IOP Publishing Ltd.

Xu D.,University of Auckland | Tairych A.,University of Auckland | Tairych A.,StretchSense Ltd | Anderson I.A.,University of Auckland | Anderson I.A.,StretchSense Ltd
Smart Materials and Structures | Year: 2015

Stretchability is a property that brings versatility and design freedom to human interface devices. We present a soft, flexible and stretchable keyboard made from a dielectric elastomer sensor sheet. Using a multi-frequency capacitance sensing technique based on a transmission line model, we demonstrate how this keyboard can detect touch in two dimensions, programmable to increase the number of keys and into different layouts, all without adding any new wires, connections or modifying the hardware. The method is efficient and scalable for large sensing systems with multiple degrees of freedom. © 2016 IOP Publishing Ltd.

Chau N.,University of Auckland | Slipher G.A.,U.S. Army | O'Brien B.M.,StretchSense Ltd | Mrozek R.A.,U.S. Army | And 2 more authors.
Applied Physics Letters | Year: 2016

In this paper, we describe a stretchable solid-state electronic switching material that operates at high voltage potentials, as well as a switch material benchmarking technique that utilizes a modular dielectric elastomer (artificial muscle) ring oscillator. The solid-state switching material was integrated into our oscillator, which self-started after 16 s and performed 5 oscillations at a frequency of 1.05 Hz with 3.25 kV DC input. Our materials-by-design approach for the nickel filled polydimethylsiloxane based switch has resulted in significant improvements over previous carbon grease-based switches in four key areas, namely, sharpness of switching behavior upon applied stretch, magnitude of electrical resistance change, ease of manufacture, and production rate. Switch lifetime was demonstrated to be in the range of tens to hundreds of cycles with the current process. An interesting and potentially useful strain-based switching hysteresis behavior is also presented. © 2016 Author(s).

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