Research On The Design And Performance Of Flexible Strain Sensor Based On Iron Nanowire Sensitive Composites

With the rapid development of the flexible electronic industry,especially in the fields of artificial intelligence,electronic skin,human-machine interface,medical health and so forth,high-performance flexible sensors have become a popular research topic.However,it is still challenging to simultaneously achieve high sensitivity,large stretch and linear response for flexible tensile strain sensors.Among them,iron nanowires（Fe NWs）have high aspect ratio,saturation magnetization,and appropriate conductivity.It is expected to build a flexible tensile strain sensor with high sensitivity and large linear range.Therefore,this thesis proposes to optimize the easily oxidized Fe NWs,and introduce the structure to complete the construction of two kinds of composite flexible tensile strain sensors.The performance of the sensors is studied by using the experimental platform,and the sensing mechanism is analyzed combined with micro characterization.Finally,a flexible strain sensor with high sensitivity,large tensile and linear response is successfully developed.The specific research contents and conclusions of this thesis are as follows:1.This thesis expounds the research significance,current situation and challenges of flexible strain sensor,and points out the direction to solve this difficulty,which leads to the research content of this paper.2.The performance parameters of the flexible strain sensor developed in this thesis are defined,the construction scheme of the flexible strain sensor is drawn up,and the experimental platform,characterization equipment and corresponding test scheme used in this paper are introduced.3.In view of the poor oxidation resistance of Fe NWs,Ag with excellent conductivity and stability was selected to prepare Fe@Ag NWs with high aspect ratio by liquid phase reduction and ayered island growth method.PMMA fiber prepared by electrospinning was used as sensitive unit structure and prepared by spraying method Fe@Ag NWs fiber.It is assembled into a flexible strain sensor with sandwich structure.The results show that the flexible strain sensor,which is made of two layers Fe@Ag NWs fiber by sprayed for four times as a sensitive unit,has the best electrical performance.The sensor has high gauge factor（GF=3.16）and excellent linear response（R²=0.9974）in the tensile range of 0-55%.In addition,the response time of the sensor under 10%strain is less than 210 ms and it has experienced more than 1000cycles at 10%strain.4.Carbon materials（carbon nanotubes（CNTs）,reduced graphene oxide（r GO））with high elasticity were selected to coat Fe NWS by immersion method,and polyurethane sponge（PUS）was introduced to form a strain sensor with rigid flexible coupling three-dimensional interconnected conductive network.The results show that the sensor soaked in Fe NWS for three times and then soaked in carbon material has relatively excellent conductivity and C-V curve.Among them,CNTs@Fe₃ PUS sensor has high conductivity（24.37 S/cm）for CNTs have better coating effect.The strain curves of sensors coated with different carbon materials are further compared and analyzed.CNTs@Fe₃ PUS sensor exhibits a good linear response（R²=0.981）and a high strain factor（GF,～7.404）in a large strain range of 110%,and under 50%strain（～1000 cycles）it has good reproducibility.In addition,the response time of the sensor under 10%strain is 130 ms,which shows that it has fast response characteristics and can be widely used in various fields.5.According to the micro characterization and performance analysis results of this thesis,combined with the sensing mechanism theories such as tunneling induction,crack conduction effect,stack separation,etc.,the sensing mechanism analysis of the sensor prepared in this thesis is completed.Fe@Ag NWs fiber-based sensor with the help of flexible fiber and rough Fe@Ag NWs,a stable dislocation laminated conductive network is constructed,which has excellent linear response curve.With the advantages of sponge,Fe NWs and carbon material,a rigid flexible coupling conductive network is constructed in the sponge porous flexible strain sensor based on Fe NWs/carbon material.Finally,CNTs@Fe₃ PUS sensor with high sensitivity and linear response under large strain is prepared.The CNTs@Fe₃ PUS sensor is attached to some parts of the human body.It is found that the sensor is suitable for the detection of various human movements,such as grasping objects,joint bending,micro expression,and so on.