Performance of silver-plated yarns for knitted structure temperature sensors
With the development of people's active health awareness,fabric temperature sensors have received extensive attention as a smart textile that can monitor human body temperature in real time to obtain physical health status.Among them,the temperature sensor of knitted structure can ensure the stability of the sensor when the fabric is deformed due to its unique coil structure,and is more suitable for measuring human body temperature.The conductive area woven by silver-plated yarns is the core of the knitted structure sensor,and determines the performance of the sensor.However,most of the research on it focuses on the design of structural parameters.There are few studies on the design of silver-plated yarns for sensors,and there is a lack of research on the performance of yarns under the bending state of simulated coil and other external conditions.To ensure the sensing performance of the knitted structure temperature sensor,the resistance values of 10 kinds of typical silver-plated yarns under the bending state of the straight and simulated coils were tested by FLUKE289 digital multimeter and V-2030T microcomputer heating platform.The effects of light oxidation and washing conditions on the electrical conductivity of the yarns were analyzed.The mechanical properties of the yarns were tested and analyzed by a computer servo system tensile tester.The relationship between the linear density,yarn state,temperature,light oxidation time,washing times and resistance was obtained.The experimental results show that the unit resistance of 10 kinds of silver-plated yarns is between 1.245 Ω and 18.788 Ω,and all of them have good electrical conductivity.The higher the linear density and the more multifilaments are,the smaller the unit resistance is;the bending of the yarn will reduce the conductivity to a certain extent.The larger the longitudinal/transverse density is,the greater the resistance of the yarn is affected,and the maximum influence degree is between 0.42％and 6.60％.The fitting R2 of the temperature-resistance relationship of silver-plated yarns in different states is between 0.894 25 and 0.990 40,and the temperature sensing performance is good.The bending state of the yarn does not change the law that the resistance is negatively correlated with the temperature change,but it will slightly reduce its temperature sensitivity linearity.The yarn with a moderate linear density and small linear density has better temperature sensitivity.Specifically,the temperature sensitivity linearity of 155.56 dtex silver-plated yarns is the best,followed by 77.78 dtex and 111.11 dtex silver-plated yarns.Except that 22.22 dtex silver-plated yarns can not meet the requirements of knitted fabric weaving,the other silver-plated yarns with a linear density have good mechanical properties,among which the yarn strength of twist structure is relatively better.Both light oxidation and washing will lead to the deterioration of the conductivity of silver-plated yarns.The yarn with a smaller linear density is more obviously affected by light oxidation,and the yarn resistance is increased to twice the original in only four weeks.The effect of washing on yarn resistance is relatively small.After 10 times of washing,the resistance change of 111.11 dtex silver-plated yarns is the smallest,being 1.92％.Based on the comprehensive analysis of the performance of the yarn,a silver-plated yarn with a medium linear density,a small number of multi-filaments and a twisted yarn structure can be designed to prepare a knitted temperature sensor.The comprehensive analysis and evaluation of the electrical conductivity,temperature sensitivity,mechanical properties and durability of 10 kinds of silver-plated yarns can provide reference for the design of silver-plated yarns for knitted structure temperature sensors with stable performance.
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