Design and Development of a Flexible Strain Sensor for Textile Structures Based on a Conductive Polymer Composite

Abstract

Abstract:The aim of this work is to develop a smart flexible sensor adapted to textile structures, able to measure their strain deformations. The sensors are "smart" because of their capacity to adapt to the specific mechanical properties of textile structures that are lightweight, highly flexible, stretchable, elastic, etc. Because of these properties, textile structures are continuously in movement and easily deformed, even under very low stresses. It is therefore important that the integration of a sensor does not modify their general behavior. The material used for the sensor is based on a thermoplastic elastomer (Evoprene)/carbon black nanoparticle composite, and presents general mechanical properties strongly compatible with the textile substrate. Two preparation techniques are investigated: the conventional melt-mixing process, and the solvent process which is found to be more adapted for this particular application. The preparation procedure is fully described, namely the optimization of the process in terms of filler concentration in which the percolation theory aspects have to be considered. The sensor is then integrated on a thin, lightweight Nylon fabric, and the electromechanical characterization is performed to demonstrate the adaptability and the correct functioning of the sensor as a strain gauge on the fabric. A normalized relative resistance is defined in order to characterize the electrical response of the sensor. Finally, the influence of environmental factors, such as temperature and atmospheric humidity, on the sensor performance is investigated. The results show that the sensor's electrical resistance is particularly affected by humidity. This behavior is discussed in terms of the sensitivity of the carbon black filler particles to the presence of water.

Recent advances in flexible sensors for wearable and implantable devices

“…2,[12][13][14] Such remarkable advances have been achieved through various solutions through the use of electrical active matrices on flexible rubberlike substrates to obtain various functions, such as high bendability, 15,16 ultrasensitivity, 7,17 transparency, 1,2,18-21 or wellestablished human-device interfaces. 8,9,22,23 In general, to be able to measure multifunctional mechanical and electrical signals, a number of circuit elements involving organic/inorganic matrix arrays, 3,4,17,[24][25][26][27][28][29][30][31] hybrid composites, [32][33][34][35][36][37][38] graphene, 39,40 and nanowires (NWs) or nanotube assemblies [41][42][43][44] need to be integrated on various flexible substrates. 45 About a decade ago, flexible electronic skins (e-skins) for pressure sensing were first introduced with polymer-based switching matrices for future displays, robots, and prosthetics of mechanical communications [ Figure 1(a)].…”

Effect of extensional cyclic strain on the mechanical and physico-mechanical properties of PVC-NBR/graphite composites

“…Conversely, measurement of electrical conductivity under strain can be a probe to understanding microstructural changes. Carbon black-filled conductive rubbers have wide applications, such as pressure sensitive sensors which can be used for shock proof switches [7], sensors for measurement of vehicle weights to collect toll tax on roads [8], and smart flexible sensors adapted to textile structures, able to measure their strain deformations [9], and tactile sensor that is thin and flexible and able to attach to a curved surface and will make the robot operate in unstructured environments [10,11]. For an electronic application of the CPC, the sensor should have a good linear behavior (with the effect of elongation), while the specific electrical resistivity of the system should be in a measurable range (<100 Ω·m) [12].…”

Investigation of Electrical Stability of Nonwovens with Conductive Circuits Using Printed Conductive Inks

“…For the first case, the elongation of the sensor in one direction will cause a shrinking in the other two directions resulting in a decrease in cross-section, and the electrical resistance will increase. In the second case, the intrinsic alteration of the sensor by an external phenomenon may be caused, for example, by a change in the electrical conduction of the conductive particles, or by a modification in the quality of the polymer/filler particle interface [15]. Note that, in our approach, we will limit ourselves to the case where the change in conductivity is mainly due to a geometric change in the resistance section.…”

“…These sensors are used, in fact, for a specific application in the aeronautical field, which consists in measuring the fabric deformations in a parachute canopy manufacture. The study of these materials has shown that the variation of the electrical resistance of these CPC sensors can result from two phenomena [15]. The first one is related to a transformation in the sensor geometry.…”