Conference Programme

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R-05: Stretchable Devices
Tuesday, 20/Jun/2017:
4:00pm - 6:15pm

Session Chair: Christoph M. Keplinger, University of Colorado Boulder
Session Chair: Qibing Pei, University of California, Los Angeles
Location: Rm 303

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4:00pm - 4:30pm

Intrinsically Stretchable Electronics Based on Silver Nanowires, Carbon Nanotubes, Conjugated Polymers, and Rubbery Dielectric Polymers

Qibing PEI

University of California, Los Angeles, United States

We are developing intrinsically stretchable conductors, semiconductors, dielectric polymers, integrated stretchable electronic devices. This presentation will describe our latest results in the materials effort and device fabrication. Specific examples include a polymer composite comprising surface-embedded silver nanowires with high transparency, high surface conductivity, and low surface roughness. The mechanical properties of the transparent composite electrode are determined by the polymer matrix employed, and demonstrated properties include flexibility, shape memory, self-healing, and rubbery deformation. Conjugated polymers and semiconductive single wall carbon nanotubes are rendered stretchable by blend morphological control or by embedding in rubbery matrix. Results on stretchable OLEDs, OPVs, and thin film transistors that can be stretched by large strains will also be presented.

4:30pm - 4:45pm

In-situ Electromechanical Testing of Stretchable Metal/polymer Interconnects.


Politecnico di Milano, Italy

The development of wearable sensing medical devices requires to move traditional electronic or electrochemical systems from rigid substrates to flexible, wearable, polymeric materials and tissue. This is a possible thanks to the development of deformable electronics, which can realize wearable electronic devices by means new fabrication techniques and design strategies. Flexible and stretchable electronics refers to electronic devices that can be bent and stretched to large deformation without losing the functionality, opening a new perspective in many engineering fields. These techniques generally rely on polymeric substrates which are typically Polyethylene terephthalate (PET), Polyimide (PI) and Polydimethylsiloxane (PDMS). The deformability of these materials opened new application perspectives, starting from paper-like displays and then extending to the general paradigm of electronic devices, which can establish conformal contact with curvilinear surfaces. The two important parameters that must be regarded are high deformability and low and constant electrical resistance upon deformation.

In this work different designs of metal interconnects on a PI substrate are investigated in terms of mechanical performance and electrical conductivity. To this purpose mechanical tests with in-situ laser confocal scanning and electro-mechanical measures are performed on the samples. Different meander geometries of a 1micron thick aluminum coating on the PI substrates are taken into consideration. The in-situ testing with confocal laser scanning has the purpose to identify the role of the meander geometry on the adhesion of the metal layer on the substrate; while the electromechanical tests aimed at identifying the role of the geometrical feature of the meanders with the evolution of electrical resistance during the uniaxial deformation process.

The in-situ tests have clearly indicated that one specific design parameter plays a relevant role in promoting delamination of the meanders from the substrates; the electromechanical tests allowed to identify the geometry featuring the most stable resistance-strain experimental relationship.

4:45pm - 5:15pm

Electronic Fabric Enabled Wearable Monitoring System for Muscle Contraction in Sports of Elbow Flexions

Xiaoming TAO1, Fei WANG1, Xi WANG1, Raymond SO2, Bao YANG1, Ying LI1

1The Hong Kong Polytechnic University, Hong Kong S.A.R. (China); 2Hong Kong Sports Institute, Hong Kong S.A.R. (China)

Skeletal muscle contractions are important activities for sports and normally monitored by electromyography (EMG), which assesses the conditions of the muscles and the nerve cells that control them. At present, most of EMG systems are complex, affected by sweating and interfere with normal activities, thus are confined in clinic or lab usage. Alternatively, anthropometric measurements have been explored because a range of electronic-fabric based technologies have been developed by our group with satisfactory accuracy and reliability, which thus renders them in this kind of applications. This paper presents an electronic fabric based wearable monitoring system for muscle activities in elbow flexion sports. Printed fabric strain sensors, flexible goniometers and fabric circuit board are integrated with data acquisition and wireless communication module as well as power supply. A fully verified bio-mechanical model, developed by our group earlier, is used to predict the torque generated in elbow flexions in isometric, isokinetic and isotonic modes. The torque generated and activation levels of the related skeletal muscles in the bio-mechanical system can be simply determined by the measured circumferential strain and the elbow angle, which renders a new alternative technology, other than EMG, of wearable physiological monitoring systems for muscle contractions during sports and normal activities.

5:15pm - 5:30pm

Self-powered Accelerometer for Human Motion Detection

Tianyiyi HE1,2,3, Qiongfeng SHI1,2,3, Rahul Kumar GUPTA1,2,3, Hao WANG1,2,3, Srilakshmi SUBRAMANIAN PERIYAL1,2,3, Han WU1,2,3, Chengkuo LEE1,2,4

1Department of Electrical and Computer Engineering, National University of Singapore, Singapore; 2Center for Sensors and MEMS, National University of Singapore, Singapore; 3National University of Singapore Suzhou Research Institute (NUSRI), China; 4NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore

Over the years, several approaches have been devised to widen the operating bandwidth, but most of them can only be triggered at high accelerations. Besides, lots of the vibration energy harvesters (VBH) are still bulky and complex, and these drawbacks have overshadowed their broadband behaviors. Considering the above problems, we propose a flexible, broadband, and hybrid energy harvester (B-HEH) which overcomes current challenges for VBH with its distinctive design with a PDMS based framework. In this work, we will investigate a broadband energy harvester based on the combination of non-linear stiffening effect and multimodal energy harvesting to obtain high bandwidth over the wide range of accelerations. In order to achieve broadband behavior, a polymer based spring exhibiting multimodal energy harvesting is used. Besides, non-linear stiffening effect is introduced by using mechanical stoppers. At low accelerations, the nearby mode frequencies of polymer spring contribute to broadening characteristics, while proof mass engages with mechanical stoppers to introduce broadening by non-linear stiffening at higher accelerations. The electromagnetic mechanism is employed in this design to enhance its output at low accelerations when triboelectric output is negligible. Further, we will demonstrate the triboelectric output measured as acceleration sensing signals in terms of voltage and current sensitivity.

5:30pm - 6:00pm

High Performance, Electrically Powered, Soft Actuators that Self‐Heal

Christoph M. KEPLINGER

University of Colorado Boulder, United States

Traditional electronic devices and machines predominantly rely on rigid materials and metallic conductors. In contrast, stretchable electronic devices and soft machines, which enable a wide range of advanced technological applications, require a new class of materials and structures that have to be stretchable, conductive, transparent, biocompatible or self-healing. Soft actuators are of particular interest for stretchable electronic devices that actively interact with their environment. Currently, soft structures predominantly rely on pneumatic or fluidic actuators, which limit speed and efficiency. Electrically powered muscle‐like actuators, such as dielectric elastomer actuators (DEAs) offer high performance actuation, but they come with their own challenges. Being driven by high electric fields, they are prone to failure by dielectric breakdown and electrical ageing. DEAs are also hard to scale up to deliver high forces, as large areas of dielectric are required (e.g. in stack actuators), which are much more likely to experience premature electrical failure, following the Weibull distribution for dielectric breakdown.
Here a series of advances is presented, that promise to overcome important limitations of electrically powered soft actuators, including I) a new class of versatile, reliable, self‐healing muscle‐like soft actuators, that use an electro‐hydraulic mechanism to combine the strength of fluidic and electrostatic actuators, and II) a new type of soft electrostatic actuator that linearly contracts upon activation with voltage.

6:00pm - 6:15pm

Self-Powered Wearable Microfluidic Sensor for Finger Motion Monitoring

Han WU1,2,3, Qiongfeng SHI1,2,3, Hao WANG1,2,3, Srilakshmi SUBRAMANIAN PERIYAL1,2,3, Tianyiyi HE1,2,3, Chengkuo LEE1,2,4

1Department of Electrical and Computer Engineering, National University of Singapore, Singapore; 2Center for Sensors and MEMS, National University of Singapore, Singapore; 3National University of Singapore Suzhou Research Institute (NUSRI), China; 4NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore

In healthcare monitoring system, such as electronic skin, blood pressure monitoring and pulse waveform monitoring, the flexible and wearable pressure sensors are playing the critical role. Currently, most mechanisms of the pressure sensors are based on resistance and capacitance change induced by force, which need external power to measure the change. Although the traditional triboelectric pressure sensor is self-powered, it requires a macro-scale air gap and its output is also effected by the separation distances. Different from kinds of the mentioned pressure sensors, we presented a microfluidic self-powered pressure sensor in this paper, which is wearable and flexible. This sensor works in triboelectric mechanism and can be applied for dynamic and static pressure sensing. The sensitivity of the pressure sensor is 46 Pa with a linear range of 0-28.3kPa. Moreover, it is conformally attached on human fingers for finger bending rate and bending angle detection. The bending ending angle of fingers with a bending angle of 0o-90o. Besides, this sensor can also be used in the capacitive mechanism as a complementary sensing mechanism for pressure and liquid flow rate sensing. The proposed microfluidic pressure sensor offers more usage flexibility for flow rate, finger motion monitoring and the potentials for more complex human motion monitoring applications.

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