Research On Air Relative Humidity Sensor Based On 2D Material Composite Microfiber

It is important to measure the relative humidity(RH) of the air in applications related to agriculture,biology,food industry,and precision instrument working environment.With the development of science and technology,people have higher requirements for the performance parameters of humidity sensors.People need to seek new materials and new solutions to develop high-performance humidity sensors.Two-dimensional materials provide new opportunities for the development of humidity sensors due to their unique physical and chemical properties.As a two-dimensional material,molybdenum disulfide(MoS₂) exhibits strong adsorption characteristics for water molecules.The effective refractive index of MoS₂ changes when water molecules are adsorbed on MoS₂.Based on this characteristic and fiber sensing technology,the humidity sensor based on two-dimensional material composite micro-fiber is proposed.We customized two different microfiber structures and analyzed their light transmission characteristics.Combining with MoS₂ material,we analyzed the humidity sensing characteristics of the sensor through theory and experiments.A series of high-sensitivity temperature/humidity dual parameter sensors and acetaminophen concentration sensors were achieved.The main content of this thesis includes:1.The fabrication methods and transmission characteristics of micronano fiber are introduced.First,the steps of manufacturing the microfiber coupler by the hydrogen-oxygen flame heating taper are introduced in detail.Microfibers with different parameters can be manufactured by controlling the hydrogen flow,taper length,and taper speed of the flame.Secondly,the transmission characteristics of micronano fiber are analyzed.As the diameter of the fiber decreases and the refractive index of the external environment increases,the effective refractive index of the micronano fiber gradually decreases,the energy contained in the core decreases,the degree of evanescent field increases,and the micronano fiber's ability to restrain light is weakened.2.A temperature/humidity dual-parameter sensor based on MoS₂ composite microfiber coupler and an acetaminophen concentration sensor based on the microfiber coupler are proposed.The microfiber coupler is manufactured by a hydrogen-oxygen flame heating taper system.The microfiber coupler is integrated with MoS₂ to achieve high sensitivity measurement of humidity and temperature.We analyze the humidity sensing mechanism of the sensor and experimentally analyze the interaction mechanism between MoS₂ and water molecules and the effect of temperature on the fiber.Microfiber couplers are suitable for high sensitivity measurement in a small refractive index range,and it is used to measure the concentration of acetaminophen in pharmaceuticals.3.A temperature/humidity dual-parameter optical fiber sensor based on microfiber Sagnac loop composite MoS₂ is proposed.The microfiber Sagnac loop acts as a reflector,and the light passes through the sensing area twice,which enhances the degree of interaction between the light and the external environment.We have theoretically and experimentally investigated the response characteristics of relative humidity and temperature to the sensor.As the RH increases,the real part of the effective refractive index of MoS₂ increases,which results in the wavelength shift and intensity change in resonance peak.