Design And Characterization Of Yarn-based Temperature Sensing System And Its Application

Body temperature is one of the important conditions to maintain normal life and health activities of human body,and also reflects human health status.Accurate and real-time monitoring of body temperature plays an important role in the fields of health monitoring and disease prevention.At present,most of the temperature sensors used for human body temperature monitoring in the market are made of hard materials.Although they can realize real-time monitoring,they affect comfort.Therefore,it is necessary to develop flexible temperature sensors.At present,most flexible temperature sensors are made of flexible polymer substrates or fabric substrates by printing,photolithography and other technologies combined with temperature-sensitive materials.However,the polymer-based temperature sensor has poor flexibility.Therefore,some scholars will develop yarns with temperature sensing function or make temperature sensing metal fibers into fabric temperature sensors by weaving or knitting.However,the yarn-based temperature sensor is usually made by wet spinning technology or wrapping the yarn around the outside of the temperature sensing element.Although it has good flexibility,it has poor tensile property,which is difficult to meet the requirements of human skin surface deformation,and its measurement accuracy is low.In this paper,a yarn-based temperature sensing unit with spiral structure is formed by wrapping metal platinum fiber and elastic spandex,and a temperature measuring circuit designed and developed is used to form a sensing system,and the performance characterization and practical application analysis of the system are carried out.The research contents and conclusions are as follows:(1)A yarn-based temperature sensing unit is designed.Platinum fiber with high temperature coefficient of resistance and conductivity is selected as the outer wrapping yarn,and spandex with high tensile property is selected as the core yarn.A yarn-based temperature sensing unit with tensile property was prepared by hollow spindle wrapping spinning machine.The elongation at failure of the sensor unit with twist of 3200T/m can reach 200%.The resistance stability is still maintained after stretching for more than 6000times under the condition of 30%strain.(2)A temperature sensing data acquisition system is designed and manufactured.The prepared yarn-based temperature sensing unit is used as a temperature sensing element,and the measurement accuracy is improved by using three-wire circuit connection and 24-bit AD converter.Kalman filter is used to filter the collected temperature,which improves the stability of the temperature measurement system.(3)The temperature sensing system is used to test the temperature-sensitive performance and service performance.The temperature coefficient and linearity of the sensor resistance measured in the water bath are 3.863×10^-3?^-1 and 0.998,respectively.The temperature coefficient of resistance measured by platform heating method is3.218×10^-3?^-1,the linearity is 0.998,the hysteresis rate is 2.23%,and the resolution and measurement accuracy are all up to 0.1?.The experimental results show that the designed yarn-based temperature sensing system has good temperature stability and measurement accuracy in measuring room temperature and wrist temperature.By combining the sensing unit with the mask,the breathing frequency of the human body can be indirectly measured by measuring the breathing temperature.The measurement results show that the yarn-based temperature sensing system can accurately identify different breathing states such as normal breathing,deep breathing,rapid breathing and breathing while speaking.