Woven Structure for Flexible Capacitive Pressure Sensors
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.136
Woven Structure for Flexible Capacitive Pressure Sensors Saki Tamura1,4, Justin K. M. Wyss2,3, Mirza Saquib Sarwar2, Addie Bahi1, John D. W. Madden2,3, Frank K. Ko1 1
Department of Materials Engineering
2
Department of Electrical and Computer Engineering
3
School of Biomedical Engineering, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
4
Department of Advanced Fibro-Science, Kyoto Institute of technology Kyoto, 606 8585, Japan
Abstract Flexible and stretchable capacitive pressure sensors have been developed in recent years due to their potential applications in health monitoring, robot skins, body activity measurements and so on. In order to enhance sensor sensitivity, researchers have changed structure of the dielectric of parallel plate capacitive sensor . Here we enhance the sensor sensitivities by changing electrode composition and explore the use of a woven electrode structure sensor with silver coated nylon yarn and EcoflexTM. The woven structure enhanced sensitivity 2.3 times relative to a simple cross-grid geometry (sensitivity was 0.003 kPa-1). Furthermore, it is also observed that the sensor with the woven electrode also had better repeatability and showed less creep than a device using carbon black electrodes. The woven structure of the electrodes enabled the device to be compliant, despite the presence of the stiff nylon fibres – thereby enabling good sensitivity without the creep seen in softer electrodes.
INTRODUCTION Capacitive pressure sensors have long been recognized to be an effective component for interaction with electronic devices. The growing interest in the development of flexible wearable electronics has prompted the interest in flexible sensors. Flexible and wearable capacitive pressure sensors can be used for robotics skins, patient diagnostics, body activity measurements and health monitoring [1-3].
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Capacitive sensors are composed of two electrodes separated by a dielectric. In the simplest parallel plate case, the capacitance is given by C = A/d, where the parameters are dielectric permittivity (ε), electrode area (A), and dielectric thickness (d). When a capacitive pressure sensor is compressed, e.g. by touch, electrodes are pushed closer together. The reduction in dielectric thickness increases the capacitance. The area is also increased during compression, also increasing capacitance.
Figure 1. Capacitive sensor working principle
Application of a compressive stress lead to a thinner and wider structure of higher capacitance. In figure 1, electrodes are in dark grey, while the dielectric is light grey. The electrode materials used in the literature include conducting polymers (e.g. PEDOT), hydrogel, Ag nanowire, carbon nanotube and carbon black based composites
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