Influence of structural parameters on the performance of braided core-sheath triboelectric sensing yarns
Respiration is an uninterrupted and important biomechanical behavior that occurs throughout human's whole life,and is used as a diagnostic signal for a variety of diseases.With the development of wearable flexible sensors,new ideas are provided for the design of respiratory sensors that real-timely,non-invasively and comfortably monitor human respiratory motion.Compared to other types of sensors,triboelectric sensors have been widely adopted for self-powered respiration monitoring owing to their compelling features,such as decent biocompatibility,wearing comfort,low cost,and high sensitivity to respiration activities in the aspect of low frequency and slight amplitude motion.Specifically,yarn-based triboelectric sensors have attracted attention for their comfort and high flexible integration.However,most of the studies on triboelectric sensing yarns for respiration monitoring focus on structural design.How structural parameters affect their performance remains unclear,hindering the industrial production of triboelectric sensing yarns.In order to meet the needs of daily long-term monitoring of human respiratory motion and large-scale production,a braided core-sheath triboelectric sensing yarn based on a single-electrode working mode was designed.According to its structure and process characteristics,the effects of the stretchable electrode twist and the braiding parameters of the outer braided layer on the performance of the sensing yarn were discussed.Firstly,six stretchable electrodes with different twists were prepared with the same structural parameters of the outer braided layer,and their tensile and electrical properties were tested.On this basis,the stretchable electrodes with the best performance were selected,and the sensing yarns with different braiding parameters were prepared by changing the number of braided yarns and the braiding angle.In order to satisfy the application in daily garments,the first step was to select the braiding parameters that have stable structure and meet the requirements of tensile properties.Then,the effects of braiding parameters on the electrical property of the sensing yarns were investigated.In this paper,the effects of stretchable electrode yarn twist and braided layer parameters on the dielectric layer thickness,surface morphology and compression deformation of the braided core-sheath triboelectric sensing yarn were investigated.Moreover,correlation analysis was used to investigate the relationship between these factors and the electrical property of the sensing yarns.The results show that the elastic elongation of the sensing yarn gradually increases,while the elastic recovery rate and short-circuit current decrease with the increase of stretchable electrode yarn twist.For the braiding parameters,the elastic recovery rate of the sensing yarn is mainly affected by the braiding angle,and the electrical property by the multiple effects of the braiding parameters.The maximum short-circuit current is obtained when the number of braided yarns is 10 and the braiding angle is 45°.In the contact-separation frequency range of 0.15-1.2 Hz,the short-circuit current of this sensing yarn increases with frequency and has good output stability during 2,000 cycles of motion.The sensing yarn can respond to different respiratory states when it is worn on the human abdomen.The results show that the braided sensing yarn based on the braiding/twisting process can be used for human respiratory status monitoring,which is of great significance for the production of triboelectric respiratory monitoring sensors.To sum up,the effects of braided core-sheath yarn structural parameters on the performance of triboelectric sensing yarns are determined,and the application potential of this sensing yarn for human respiratory status monitoring is tested.The research results provide guidance for the subsequent production of triboelectric respiratory monitoring sensors.
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